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Thread: To folded dipole or not... that is the question.

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    Default To folded dipole or not... that is the question.

    So, I inherited all this infrastructure with a Hustler G7 and a Hustler G6 for GMRS, along with other ham grade verticals all which claim some hefty dB gains... ahem.

    At this point I have a feeling the system overall performance cannot be improved any further without really taking a hard look at the antennas. I've already replaced everything else in the feedline, replaced all LMR400 garbage with Heliax, all UHF chrome plated trash with silver plated N connectors, all RG58 patches are now made from harbor freight RG400 with silver plated connectors, I added preselectors to all inputs on both the U and V side, etc... range really got good after all this... preselector probably being the most significant upgrade.

    The primary link is the VHF side, antenna is ~40 feet above ground, and we tuned it quite well, at ~50 ohms and -39dB return loss... etc. But it seems that both the G7 and G6 are better as cloud warmers than as an effective antenna: How so? Well, it seems they are sending all those claimed 6dBd up towards the sky... and not towards the horizon, my suspicion is b/c range is absolutely great on receive, the G7 picks up mobiles on 1/4waves, on 25w, from nearly 20 miles away... but the mobiles can't pick the base after the 8 mile mark, no matter what. Looking at the terrain topography there seems to be a large relative altitude change, and it seems the vehicles go down under the antenna main lobe... not sure...

    So, for those of you who have gone from verticals to folded dipoles, what should be my expectations? Did the range improve after switching from a high gain vertical to a folded dipole? Also, did you notice a lower noise threshold? If so, how much?

    What recommendations in terms of number of bays should I get? Just 2? or 4? For UHF I might be able to splurge for a 4 bay stack, but for VHF 2 is probably as big as it can fit on the mast...

    Thanks in advance.

    G.


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    It sounds like this infrastructure is to support repeaters even though its not mentioned. I've owned a couple of G7s on VHF and had a G6 UHF on a GMRS repeater many years ago and will never use them again. Besides one of the G7s self destructing and falling apart, the gain seems to be less than advertised. Going from a Hustler G6-3 to a well used 20+ yr old DB-408 for the GMRS repeater was a noticeable improvement in performance. The advertised gain in dBd between the antennas is only .6 and that would be difficult to notice on air so either the Hustler is lower or the DB Products is higher and I think I we know which one it is.

    This GMRS repeater was about 1,000ft above average terrain and you didn't mention your specifics, which would play into gain and beamwidth and the potential need for downtilt. A 2 bay dipole array might only have about as much gain as what you already have and I would go at least a 4 bay giving a realistic 6dBd gain or go even larger. Most of my other past UHF repeaters had 10dBd sticks by Telewave with factory recommended downtilt for the HAAT and they worked really well with handhelds at a good distance. I'm a believer in as much gain as you can get and if the HAAT is above 1,000ft point that down into your area of operation.

    Otherwise there is nothing magical about an exposed dipole array except they are honest, in that you can see what you get and they have the most gain you can realize for their height or length or number of elements of any type vertical antenna. They generally have no problems with PIM from dissimilar metals or other factory mistakes but can suffer from corrosion over time. At one site we have a Telewave 4-bay dipole and they are black powder coated, which is holding up nicely after roughly 25yrs. The Telewave is also very broad band, like 406-512MHz and they make great master receive antennas feeding preselectors and preamps for both commercial and amateur off a single antenna.

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    Forgive me, but something isn’t adding up. You stated the base/repeater receives very well but the talk out range leaves a lot to be desired. So, no matter what the true gain is for a given antenna, the radiation pattern in the azimuthal and elevation planes remain reciprocal. That is, you can’t physically have greater gain on receiver than you would have on transmit.

    Some things to ponder with the less than desirable talk out ranges might include the general noise floor in the mobile environment verses that at the base/repeater site. I would be advisable to perform a spectrum analysis of the transmit channel to verify that the RF power output as measured on a typical
    wideband wattmeter is actually concentrated in the carrier and sidebands with no significant distribution of RF energy in spurs and harmonics.

    The latter point deserves some merit to check out in that you reported the receiver came to life after adding a preselector. So, either the transmitter to receiver isolation was inadequate to start with or the transmitters power spectrum is questionable and was contributing to desense?

    Of course, I agree that commercial folded dipole designs are far superior for all of the reasons mentioned to include the use of downtilt where the combination of antenna gain and HAAT would so dictate the application of downtilt. Again, the same physic for a single antenna used for both the uplink/downlink will have reciprocal radiation patterns and barring any localized effects on receive due to reflections or diffraction.

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    Hi CARC383, thank you!

    So, yes and no, its not mentioned b/c there are no repeaters. This might change, tho. ATM is all EVX mobiles cobbled together via EVX-links and a WAN to link to another site on another state. I've measured substantial improvements going to heliax, preselectors, N silver, etc... but I feel the antenna is the limiting factor now... and after reading your comments it sounds like it might very well be the actual problem. Time to start folding...

    Based on your post it seems that for UHF a 4-bay folded dipole is the way to go... and I assume this 4-bay is arranged in a 2x2 configuration, correct? (as opposed to a 4x1 vertical arrangement) If the dipole has the same gain and you had better performance it feels like it has a better radiation pattern. Which I think is the problem with those verticals, they radiate upwards, and not towards horizon, so if you have a null in the pattern its pretty much over.

    For VHF I've been leaning towards a DB 2-bay dipole, setup in an omni configuration, trade some gain for much better radiation pattern...

    Thanks.

    G.

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    Quote Originally Posted by MotoBill View Post
    Forgive me, but something isn’t adding up. You stated the base/repeater receives very well but the talk out range leaves a lot to be desired. So, no matter what the true gain is for a given antenna, the radiation pattern in the azimuthal and elevation planes remain reciprocal. That is, you can’t physically have greater gain on receiver than you would have on transmit.

    Some things to ponder with the less than desirable talk out ranges might include the general noise floor in the mobile environment verses that at the base/repeater site. I would be advisable to perform a spectrum analysis of the transmit channel to verify that the RF power output as measured on a typical
    wideband wattmeter is actually concentrated in the carrier and sidebands with no significant distribution of RF energy in spurs and harmonics.

    The latter point deserves some merit to check out in that you reported the receiver came to life after adding a preselector. So, either the transmitter to receiver isolation was inadequate to start with or the transmitters power spectrum is questionable and was contributing to desense?

    Of course, I agree that commercial folded dipole designs are far superior for all of the reasons mentioned to include the use of downtilt where the combination of antenna gain and HAAT would so dictate the application of downtilt. Again, the same physic for a single antenna used for both the uplink/downlink will have reciprocal radiation patterns and barring any localized effects on receive due to reflections or diffraction.
    Well, nothing to forgive, Bill, thanks for the help! So, yes, that is why I am asking... it doesn't make any sense (to me) that the base can hear mobiles from 15+ miles away crystal clear but the mobiles can't hear the base with more power and a much higher gain antenna after mile 8 or so. It goes from perfect copy, to all of the sudden its not there anymore, coincidentally, the RX LED on the car's EVX mobile blinks, but no DMR audio comes through... or sometimes you get a few R2D2 sounds... but nothing intelligible.

    Yes, adding the preselector to the base did make a huge difference, as before adding it the range on receive was 5 miles at best...

    Some of the terrain around here abruptly loses (or gains) elevation... perhaps the vertical base antenna has a poorer radiation pattern, but the base radio is less desensed, vs. the cars, which might have a better radiation pattern due to 1/4 wave NMO, but the mobile radios are more desensed... somehow... and I know desense can be far worse than a poorly tuned antenna... As for noise treshold, RSSI measuring reads less noise than there is at the house, and the cars have preselectors installed too, although these are smaller RFS 4-cavity preselectors, not like the large one used at base. Could be RF noise inside the car? perhaps... not sure how to address that? maybe some loops and ferrite chokes right under the antenna? The duplexer in the cars are RFS 5085-3 units... those are fairly decent duplexers... so I wouldn't expect those to have a problem with insufficient isolation.

    Thanks!

    G.

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    G.

    It could well be RFI in the mobile environment causing the apparent lack of sensitivity or decreased talk out range.
    So it appears your communications mode is DMR that makes it a bit harder to diagnose desense or the apparent lack of sensitivity.

    What I would do if there were mine to diagnose is to use the same procedure normally done to establish the off-air noise floor at a base/repeater site. That is to say, you could insert a directional coupler in-line with the receiver (radio) that’s initially terminated with a dummy load.

    Next connect a signal generator/service monitor to the isolated port of the directional coupler and inject an on-frequency signal. Adjust the output level such as to establish some reference point at either 12 dB SINAD or 20 dB of quieting. Note the RF output level then proceed to remove the termination and replace replace it with the antenna cable.

    Now readjust the signal generator level one again to obtain the identical benchmark obtained before while noting the difference in the signal generator output. An increase in output level will equate directly to degree of receiver desense present.

    This may not be all that easy to accomplish in a mobile installation nor with it be definitive in that the total noise floor will be a composite of RFI generated by the vehicular electrical system, plus extraneous RF pollution present at any given location along and in the service area. But at least this test should help to identify if the vehicular electrical system is an offender, and if so, to what degree.

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    If this were my site and setup, I would do some additional debug, using the ISO-T method that MotoBill calls out above, I also would switch off of DMR into analog mode for testing, its much easier to hear interference, the signal fading out due to coverage, etc. DMR hides almost all of that, its much easier to debug and prove issues using your ear and drive testing in analog mode. Generally, when I am working on a digital repeater, I switch it to analog to set it up and optimize it, then switch to digital.

    All that being said, the antennas you have are not great, the 4 bay folded dipoles are nice, I have many of them from telewave that have lasted many many years, I also have the telewave "blue stick's" fiberglass antennas((like the ANT450F6) that have also lasted many many years at some pretty harsh environment sites.

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    Switch to FM... duh... why didn't I though of that. I've already performed an ISOtee, but with the cars at the base, never while driving, I guess assumptions shouldn't be assumed .... thanks! Looks like I will have to ride in the car to perform some ISOTEEs on the mobile system...

    scoutcamper... looks like Another strike for the antennas... sounds like its time to replace them...

    Thank you!! I'll report back once I have some time to perform the investigation... see what is causing all this..

    G.

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    A couple of things seem unusual at this point like why did you go all silver connectors and cables (low PIM) if they are not in a full duplex repeater path? The only reason to do that would be to avoid creating a higher noise floor or desense in a full duplex repeater system. The upgrade to silver plating over nickel or other crap will have no benefit on a simple two way radio connected to a base antenna. At this point going from LMR cable to Heliax is simply reducing loss and not getting away from potential PIM generating LMR cable.

    The base > mobile range compared to mobile > base range needs explaining and the excellent writeup by MotoBill would answer many questions and going analog as scoutcamper says might expose some things. It might be good to post the make and model of the base and mobile radios and if they are all low budget Chinese and you are in a very high RF environment. That would explain the comment that preselectors made improvements on the base radios and maybe the mobiles are getting blitzed by out of band shit. I've added many DCI type preselectors to 2m and 70cm amateur base setups and have only seen improvements when the radios are one chip wonders with no preselection of their own and pick up more out of band stuff than in band. Usually a quality Icom or other major brand works great on the same antenna with no preselector.

    If your dealing with radios from TYT, Baofeng, Wouxun, etc, that might explain the base station improvement with a preselector and your mobile range problems. If this is the case and you don't have the equipment to run MotoBills tests, temporarily swap out a mobile radio with a high quality one and see if your receive range doesn't improve to match what the base radio with preselector can do. Or if you have a spare preselector, stick that in a mobile and run a range test. If there is any improvement then strong out of band signals from FM/TV/paging/etc. could be blitzing your radios and creating internal IMD, high noise floor and other problems.

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    Just be careful with vertical beamwidth on DB408, etc. IIRC it is 17 degrees. They are very very good antennas, but I typically use them for receive and a Unity for transmit, with plenty of vertical separation. You can't beat a unity for transmit. I personally like the Comtelco unity, and they can be ordered tuned as well.

    Although it sounds like you may be stuck with single antenna.

    It really may be worth trying a unity or 3db, just to see what it does.

    I cannot tell you how many high-gain antennas I've replaced with Comtelco unity and all of the problems went away.

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    Quote Originally Posted by CARC383 View Post
    A couple of things seem unusual at this point like why did you go all silver connectors and cables (low PIM) if they are not in a full duplex repeater path? The only reason to do that would be to avoid creating a higher noise floor or desense in a full duplex repeater system. The upgrade to silver plating over nickel or other crap will have no benefit on a simple two way radio connected to a base antenna. At this point going from LMR cable to Heliax is simply reducing loss and not getting away from potential PIM generating LMR cable.

    The base > mobile range compared to mobile > base range needs explaining and the excellent writeup by MotoBill would answer many questions and going analog as scoutcamper says might expose some things. It might be good to post the make and model of the base and mobile radios and if they are all low budget Chinese and you are in a very high RF environment. That would explain the comment that preselectors made improvements on the base radios and maybe the mobiles are getting blitzed by out of band shit. I've added many DCI type preselectors to 2m and 70cm amateur base setups and have only seen improvements when the radios are one chip wonders with no preselection of their own and pick up more out of band stuff than in band. Usually a quality Icom or other major brand works great on the same antenna with no preselector.

    If your dealing with radios from TYT, Baofeng, Wouxun, etc, that might explain the base station improvement with a preselector and your mobile range problems. If this is the case and you don't have the equipment to run MotoBills tests, temporarily swap out a mobile radio with a high quality one and see if your receive range doesn't improve to match what the base radio with preselector can do. Or if you have a spare preselector, stick that in a mobile and run a range test. If there is any improvement then strong out of band signals from FM/TV/paging/etc. could be blitzing your radios and creating internal IMD, high noise floor and other problems.

    Why I did it you ask? Well, its simple: I am done buying crap many times over: from now on its All silver All trimetal, All Heliax and All N, and no CCRs, no exceptions. Buy once, cry once. I used to be the guy who always had enough money to do it wrong many times over, and never enough to do it right once.... no mas. Hopefully that is a good enough explanation.

    The radios used are EVX-5300 mobiles and XPR5550e, I don't think those qualify as pieces of garbage.

    What I should've prefaced this with is the fact that the Madison WI Candelabra Tower, a 1400 foot wonder, and the other giant massive 1200 footer placed 2 miles away from the 1400 RF firebreathing monster, all have multiple broadcast stations in the tens of kW range. So even the EVX mobiles suffer quite a bit without a preselector, CCRs take a massive 40dBm effective sensitivity loss, as measured by ISO-T tests. So, rest assured I don't have a single piece of garbage CCR radio on the entire fleet: "dead before caught with a Baoturd..."

    It seems that the two antennas are the last thing I need to ditch (obvious now after reading the replies here) before I can proceed with the SLR upgrades next year.

    There are many repeaters currently in use on this setup, just not the traditional timing DMR repeater... Everything uses double slot DMR simplex repeaters using two EVX-5300 connected via digital EVX-links, in U/U, U/V or V/V fashion. It was a heck of a lot cheaper than buying XPR repeaters a few years back...

    G.

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    Quote Originally Posted by PSEhub View Post
    Just be careful with vertical beamwidth on DB408, etc. IIRC it is 17 degrees. They are very very good antennas, but I typically use them for receive and a Unity for transmit, with plenty of vertical separation. You can't beat a unity for transmit. I personally like the Comtelco unity, and they can be ordered tuned as well.

    Although it sounds like you may be stuck with single antenna.

    It really may be worth trying a unity or 3db, just to see what it does.

    I cannot tell you how many high-gain antennas I've replaced with Comtelco unity and all of the problems went away.
    Yes, well technically there are two masts, so two antennas, one on each mast, but not enough vertical separation for two antennas per band on each mast.

    Dang, now I really want to buy some coat hangers, err... folded dipoles, PSEhub... The DB404 4-bay for UHF is probably as far as I'll go. The DB-222 is probably what will get bought for the VHF side.

    I don't think a unity antenna has ever been tried. When you speak of a Comtelco unity, you mean something like the Comtelco BS100U-B? Any particular store where that one could be acquired? Or what model do you recommend?

    Thanks!

    G.

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    Ok on setting high standards for cables and connectors. It just typical to do that as a good baseline for full duplex systems and I thought your were working with repeaters. I hope you can perform some of the tests that were suggested by others to pinpoint the problem but from your info on the RF surroundings I'll place my bet on the mobiles being blitzed by strong out of band stuff and that a band pass filter or preselector similar to what you used on the base radios will get your receive range well past 8mi and similar to the base radios receiving the mobiles.

    I'm also a fan of doing it once and doing it right. I spent the last years of my career moping up after other techs and engineers that didn't know or didn't care and ended up in charge of RF training for those poor souls along with my regular engineering duties.


    Quote Originally Posted by gMan1971 View Post
    Why I did it you ask? Well, its simple: I am done buying crap many times over: from now on its All silver All trimetal, All Heliax and All N, and no CCRs, no exceptions. Buy once, cry once. I used to be the guy who always had enough money to do it wrong many times over, and never enough to do it right once.... no mas. Hopefully that is a good enough explanation.

    The radios used are EVX-5300 mobiles and XPR5550e, I don't think those qualify as pieces of garbage.

    What I should've prefaced this with is the fact that the Madison WI Candelabra Tower, a 1400 foot wonder, and the other giant massive 1200 footer placed 2 miles away from the 1400 RF firebreathing monster, all have multiple broadcast stations in the tens of kW range. So even the EVX mobiles suffer quite a bit without a preselector, CCRs take a massive 40dBm effective sensitivity loss, as measured by ISO-T tests. So, rest assured I don't have a single piece of garbage CCR radio on the entire fleet: "dead before caught with a Baoturd..."

    It seems that the two antennas are the last thing I need to ditch (obvious now after reading the replies here) before I can proceed with the SLR upgrades next year.

    There are many repeaters currently in use on this setup, just not the traditional timing DMR repeater... Everything uses double slot DMR simplex repeaters using two EVX-5300 connected via digital EVX-links, in U/U, U/V or V/V fashion. It was a heck of a lot cheaper than buying XPR repeaters a few years back...

    G.

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    As a side note I have a UHF amateur repeater, an amateur 900 repeater and a GMRS repeater running in my garage as test beds with various and constantly changing antennas. A few months back and as a coincidence I was swapping antennas around to see what affects they have in my mildly hilly terrain around here. I don't have exact gain specs on the antennas as they were no name brand supplied for testing by a vendor and on the UHF amateur machine here I went from a 17ft dual band antenna to a 24ft dual band then to a Sirio 380-470MHz broad band 1/4 wave ground plane. The 17ft could be roughly compared to a Diamond 510X and the 24ft might be compared to a Diamond X700HNA.

    At extreme distance we noticed an improvement going from the 17ft to the 24ft antenna but with an increase in annoying picket fencing in noisy areas. Some difficult areas that are close by but non line of sight on the other side of a hill suffered the worst going from the 17ft to 24ft. Going to the 1/4 wave ground plane smoothed out the picket fencing and improved the close in non line of sight area but extreme distance suffered greatly. In one direction the repeater was reaching past 60 miles with the 17 and 24ft jobs but with the 1/4 wave the range was cut to about 25-30mi in the same direction. There may have been a few spots that worked further but range just sucked on the 1/4 wave. The HAAT for the repeater is about 350ft.

    This recent antenna resting reinforces my opinion that unless you have hills and deep valleys with mobiles running around tucked up under the repeater, go for as much gain as you can afford as long as you can keep the radiation pattern within your area of interest. I think 6dBd gain would be my worst goal and about 10dBd being on the high side for offerings from reputable antenna mfrs.

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    Yeah, doing it right seems to pay in the long run as I've come to find out more and more lately.

    Cars have two VHF radios working in full duplex, just not in the DMR standard timeslot 1 and 2 manner; these work like traditional FM repeaters, both sides are double slot DMR signals... so no timing is required. Eventually this will be converted to ERDM with SLR1000s, single frequency, no need for duplexers, potentially just a preselector... but that is different story for a another day.

    The cars currently have preselectors too, but its a smaller 4 cavity RFS VHF preselector. Between the preselector and the duplexer there is a 2.7 dBm signal loss. 1.6 dBm loss on the preselector and 1.1 dBm loss on the duplexer.

    Yes I have all the tools to perform the tests. I just have to get out and do them...

    Still, seems like new antennas will be needed...

    Big thank you to everyone who posted! Seems I have plenty to do, so time to stop yapping and time to start fixing...

    G.


    Quote Originally Posted by CARC383 View Post
    Ok on setting high standards for cables and connectors. It just typical to do that as a good baseline for full duplex systems and I thought your were working with repeaters. I hope you can perform some of the tests that were suggested by others to pinpoint the problem but from your info on the RF surroundings I'll place my bet on the mobiles being blitzed by strong out of band stuff and that a band pass filter or preselector similar to what you used on the base radios will get your receive range well past 8mi and similar to the base radios receiving the mobiles.

    I'm also a fan of doing it once and doing it right. I spent the last years of my career moping up after other techs and engineers that didn't know or didn't care and ended up in charge of RF training for those poor souls along with my regular engineering duties.

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    I've not encountered your dual radio full duplex DMR two timeslot mobile setups but I would want to make sure that is working properly and not the cause of the mobile range problem. Sounds like a number of things could go wrong in that setup.

    BTW, when speaking of gain or loss as in antenna gain or feedline loss, its simply in dB. dBm references the numbers to a milliwatt and there is no need to use the m suffix if your not actually relating to a power level.


    Quote Originally Posted by gMan1971 View Post
    Yeah, doing it right seems to pay in the long run as I've come to find out more and more lately.

    Cars have two VHF radios working in full duplex, just not in the DMR standard timeslot 1 and 2 manner; these work like traditional FM repeaters, both sides are double slot DMR signals... so no timing is required. Eventually this will be converted to ERDM with SLR1000s, single frequency, no need for duplexers, potentially just a preselector... but that is different story for a another day.

    The cars currently have preselectors too, but its a smaller 4 cavity RFS VHF preselector. Between the preselector and the duplexer there is a 2.7 dBm signal loss. 1.6 dBm loss on the preselector and 1.1 dBm loss on the duplexer.

    Yes I have all the tools to perform the tests. I just have to get out and do them...

    Still, seems like new antennas will be needed...

    Big thank you to everyone who posted! Seems I have plenty to do, so time to stop yapping and time to start fixing...

    G.

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    I am not the biggest RF engineer here, but I find the DB40x to always skip right over users, yet they are fine for receive. I have been told by many that VBW does not matter as much for receive as it does for transmit. I have found the same to be true.

    Real world Example:

    Dealer that doesn't understand VBW installs 4 XPR8400s in a tall building with steal and concrete with 4 DB408s on roof with no vertical separation 15 feet horizontal only apart on roof. SL7550s on first floor can't hear repeater, but repeater can hear them.

    Dealer that doesn't understand VBW instead of putting different antennas puts MTR3000s and cranks power to 100Ws. SL7550s on first floor now work fine.

    They were able to compensate for the 17 degree pancake by doubling TX power.

    This is perfect example of how even with all of the desense due to lack of vertical separation, and 2W SL7550, the 17 degree pancakes do just fine for receive, but require a ton of TX power to compensate on the repeater output.

    We use a ton of the BS450U-C for transmit, and then either BS450XL3-C or DB404 or DB408s for receive. The Comtelco hold up much better to the elements, especially UV, than the Laird counterparts and I find the performance to be slightly better as well.

    For single antenna, almost always FG4500 or BS450U-C.

    You just have to really watch VBW, and whether down tilt is needed.

    With a Unity for TX with good vertical separation you can just crank up power if needed for users far way, but if you have a 17 degree pancake like the DB408 for transmit, you will never be able to make up for the pancake for close-by users with TX power alone.


    This is not all based in science or theory, this is just real world experience. Never discount the power of high-quality unity gain.

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    LMAO... "the SL7550 on first floor now works fine" hahahaha, but it probably works like 40 miles away too... holy smokes... 100W on a DB408... that will yield some absurdly long range, equivalent ERP of like 1kW, not bad... and just to get to the 1st floor... wow. Oh well... talk about efficient usage of airwaves...

    Seems exactly what is happening right now... and throwing more power to the problem will be the absolute last ditch effort resort...

    So, seems LAIRD antennas are more readily available, given my current means, that is... so I am going to pick one unity for U, and one unity for V, and see if it makes any difference. At the end of the day, the "dubious" 3 or 4 dB gain claim on the current G6/7 are not going to make much of a difference if the VBW is going off to the clouds (like the SL7550 on the first floor). I remember reading somewhere that the G7 had like an 11 deg vertical beamwidth... who knows...

    Thank you PSEHub... greatly appreciated.

    G.



    Quote Originally Posted by PSEhub View Post
    I am not the biggest RF engineer here, but I find the DB40x to always skip right over users, yet they are fine for receive. I have been told by many that VBW does not matter as much for receive as it does for transmit. I have found the same to be true.

    Real world Example:

    Dealer that doesn't understand VBW installs 4 XPR8400s in a tall building with steal and concrete with 4 DB408s on roof with no vertical separation 15 feet horizontal only apart on roof. SL7550s on first floor can't hear repeater, but repeater can hear them.

    Dealer that doesn't understand VBW instead of putting different antennas puts MTR3000s and cranks power to 100Ws. SL7550s on first floor now work fine.

    They were able to compensate for the 17 degree pancake by doubling TX power.

    This is perfect example of how even with all of the desense due to lack of vertical separation, and 2W SL7550, the 17 degree pancakes do just fine for receive, but require a ton of TX power to compensate on the repeater output.

    We use a ton of the BS450U-C for transmit, and then either BS450XL3-C or DB404 or DB408s for receive. The Comtelco hold up much better to the elements, especially UV, than the Laird counterparts and I find the performance to be slightly better as well.

    For single antenna, almost always FG4500 or BS450U-C.

    You just have to really watch VBW, and whether down tilt is needed.

    With a Unity for TX with good vertical separation you can just crank up power if needed for users far way, but if you have a 17 degree pancake like the DB408 for transmit, you will never be able to make up for the pancake for close-by users with TX power alone.


    This is not all based in science or theory, this is just real world experience. Never discount the power of high-quality unity gain.

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    UPDATE: Antenna FG4500 has been ordered... ETA probably by Wed next week... eager to see how it works.

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    I completely skipped over this post... I am sorry. Thank you... so the Madison, WI area is hilly, really hilly; that's aside from the angry RF firebreathing 1200+ feet towers, the superdoppler radars, etc. There are some valleys/dips where I suspect the mobiles are going under the main antenna lobes... therefore reception totally goes south in those areas.

    Man, 350 feet is nice... it might all come down to having to rent a place to put the stuff high up... in the end its just a matter of more $$$ ...

    How close where those nearby difficult areas? 5 miles? 10 miles? 3 miles?

    Range requirement is only ~15 miles max, as there is really zero need to go beyond that mark.

    Those antennas you tried sound like ham grade magicalgainers... those are mediocre at best for low altitude placement, and I know b/c the Diamond F23 was tried before on this site (similar to the Diamond 510X), and its collecting dust on a box with all the other "magical db gain" antennas, and results were mediocre at best from what I've been told, it probably was replaced due to water inside the foam, I can see the mold on the inner elements... the G7 seems like it was a better antenna and that's probably why its still on the mast... the other antennas are an X50C2, which is an atrocious piece of garbage... SWR is high across the entire V and U bands, impedance isn't 50ohms no matter where you park the VNA at... might as well use a paperclip... and there is a bunch of TRAM VHF and UHF spare parts and other unbranded antenna remains... the TRAM antennas seem to have developed super high SWR, upon close inspection the coils and threads were all corroded and pitted, probably due to water ingestion...


    G.

    Quote Originally Posted by CARC383 View Post
    As a side note I have a UHF amateur repeater, an amateur 900 repeater and a GMRS repeater running in my garage as test beds with various and constantly changing antennas. A few months back and as a coincidence I was swapping antennas around to see what affects they have in my mildly hilly terrain around here. I don't have exact gain specs on the antennas as they were no name brand supplied for testing by a vendor and on the UHF amateur machine here I went from a 17ft dual band antenna to a 24ft dual band then to a Sirio 380-470MHz broad band 1/4 wave ground plane. The 17ft could be roughly compared to a Diamond 510X and the 24ft might be compared to a Diamond X700HNA.

    At extreme distance we noticed an improvement going from the 17ft to the 24ft antenna but with an increase in annoying picket fencing in noisy areas. Some difficult areas that are close by but non line of sight on the other side of a hill suffered the worst going from the 17ft to 24ft. Going to the 1/4 wave ground plane smoothed out the picket fencing and improved the close in non line of sight area but extreme distance suffered greatly. In one direction the repeater was reaching past 60 miles with the 17 and 24ft jobs but with the 1/4 wave the range was cut to about 25-30mi in the same direction. There may have been a few spots that worked further but range just sucked on the 1/4 wave. The HAAT for the repeater is about 350ft.

    This recent antenna resting reinforces my opinion that unless you have hills and deep valleys with mobiles running around tucked up under the repeater, go for as much gain as you can afford as long as you can keep the radiation pattern within your area of interest. I think 6dBd gain would be my worst goal and about 10dBd being on the high side for offerings from reputable antenna mfrs.

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    Its more of a reflector/range extender, etc, its wasn't meant to repeat back to the radios around the car (as usually there is only one, the driver), although it could, since the VHF portables can hear the other side just fine... double slot saves the issues of the timing, which can be a bit of a pita if your repeater is out of range...

    Yes, you are right its dB only (no m).

    In the cars, the preselector + duplexer + cables incur in a 3 dB IL. The isolation from TX/RX is ~79 dB. Power is 5W and 25W for the two mobiles in a car. Perhaps -79 dB is not enough isolation...

    G.

    Quote Originally Posted by CARC383 View Post
    I've not encountered your dual radio full duplex DMR two timeslot mobile setups but I would want to make sure that is working properly and not the cause of the mobile range problem. Sounds like a number of things could go wrong in that setup.

    BTW, when speaking of gain or loss as in antenna gain or feedline loss, its simply in dB. dBm references the numbers to a milliwatt and there is no need to use the m suffix if your not actually relating to a power level.

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    I consider the repeaters here as a neighborhood system that serves just a few friends, so its mostly used within a few miles or less until a member of the group ventures out into the big city. Then it goes 20-30mi reliably in the direction away from the hill its on and twice that down some freeway corridors. In one direction I can actually hit the Mexican border with a mobile 100+mi away but its mostly line of site over water. The top of this hill is about 1,100ft and I'm at about the 350ft level on one side of the hill. Its impossible to reach the far side of this hill and my home repeaters only see a little more than a 180 degree swath out away from the hill where they work reliably.

    The most common problem area is only a mile to a mile and a half away but its over a hill tucked up against the hill where one of the members goes hiking with a hand held. The area is mapped out very well using different antennas and a Diamond 510X or Comet GP9 type 17ft antenna seems to be the best compromise for overall range. I'm guessing they are in the 7 to 8dBd gain range on UHF and so far they are not creating any detectable IMD or causing any repeater desense as I do perform receive tests injecting RX signals upstream of the duplexer with antenna and load.

    Another thing I noticed is a slight change in antenna height is very noticeable. Most antennas that get swapped use the exact same mast and start at the same height, so going from a 24ft monster to a 1/4 wave is loosing about 23ft of height. If I raise the 1/4 wave up so the tops of both antennas are at the same height the difference is much less but that's because of the terrain around here. If this was the very peak of the hill the 23ft of height would not matter.

    The Laird FG4500 is only a unity gain antenna and if used here my range would be cut in half or less to distant mobiles compared to the 17ft hammy antenna.


    Quote Originally Posted by gMan1971 View Post
    I completely skipped over this post... I am sorry. Thank you... so the Madison, WI area is hilly, really hilly; that's aside from the angry RF firebreathing 1200+ feet towers, the superdoppler radars, etc. There are some valleys/dips where I suspect the mobiles are going under the main antenna lobes... therefore reception totally goes south in those areas.

    Man, 350 feet is nice... it might all come down to having to rent a place to put the stuff high up... in the end its just a matter of more $$$ ...

    How close where those nearby difficult areas? 5 miles? 10 miles? 3 miles?

    Range requirement is only ~15 miles max, as there is really zero need to go beyond that mark.

    Those antennas you tried sound like ham grade magicalgainers... those are mediocre at best for low altitude placement, and I know b/c the Diamond F23 was tried before on this site (similar to the Diamond 510X), and its collecting dust on a box with all the other "magical db gain" antennas, and results were mediocre at best from what I've been told, it probably was replaced due to water inside the foam, I can see the mold on the inner elements... the G7 seems like it was a better antenna and that's probably why its still on the mast... the other antennas are an X50C2, which is an atrocious piece of garbage... SWR is high across the entire V and U bands, impedance isn't 50ohms no matter where you park the VNA at... might as well use a paperclip... and there is a bunch of TRAM VHF and UHF spare parts and other unbranded antenna remains... the TRAM antennas seem to have developed super high SWR, upon close inspection the coils and threads were all corroded and pitted, probably due to water ingestion...


    G.

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    Quote Originally Posted by CARC383 View Post
    I consider the repeaters here as a neighborhood system that serves just a few friends, so its mostly used within a few miles or less until a member of the group ventures out into the big city. Then it goes 20-30mi reliably in the direction away from the hill its on and twice that down some freeway corridors. In one direction I can actually hit the Mexican border with a mobile 100+mi away but its mostly line of site over water. The top of this hill is about 1,100ft and I'm at about the 350ft level on one side of the hill. Its impossible to reach the far side of this hill and my home repeaters only see a little more than a 180 degree swath out away from the hill where they work reliably.

    The most common problem area is only a mile to a mile and a half away but its over a hill tucked up against the hill where one of the members goes hiking with a hand held. The area is mapped out very well using different antennas and a Diamond 510X or Comet GP9 type 17ft antenna seems to be the best compromise for overall range. I'm guessing they are in the 7 to 8dBd gain range on UHF and so far they are not creating any detectable IMD or causing any repeater desense as I do perform receive tests injecting RX signals upstream of the duplexer with antenna and load.

    Another thing I noticed is a slight change in antenna height is very noticeable. Most antennas that get swapped use the exact same mast and start at the same height, so going from a 24ft monster to a 1/4 wave is loosing about 23ft of height. If I raise the 1/4 wave up so the tops of both antennas are at the same height the difference is much less but that's because of the terrain around here. If this was the very peak of the hill the 23ft of height would not matter.

    The Laird FG4500 is only a unity gain antenna and if used here my range would be cut in half or less to distant mobiles compared to the 17ft hammy antenna.
    If you need gain I would suggest the G7... I did measure it against the F23 and the G7 is a better antenna... but then again, given the advice collected from this thread I would just buy an 8-bay VHF folded dipole....

    The FG4500 is meant as a test, and from what I can see is that all the antennas tried prior were all super magical gainer antennas... nothing to lose by trying. In the end, tho, the final antenna will be most likely a 4-bay DB404 dipole... and PSEhub has been quite helpful, to me, and others, so I am going to listen to his advice... although I still prefer Motorola over Kenwood... I know he likes Kenwood NX radios.

    Issue here is very hilly terrain with large altitude changes... whereas if this was atop a hill with nothing but flatlands surrounding it that would be a different story... Range is certainly easier to come by when you have access to a higher ground location...

    Most RF from collinear verticals is picked up by the bottom element... which seems to corroborate what you've just stated... but in this case the mast will be extended to keep the tip of the smaller antenna exactly where the tip of the longer antenna was. Effectively the FG4500 base will be almost 10 feet where the current G6 (UHF) is.

    100 miles reach is excessive for this application... I am sure business using radios within 100 miles won't appreciate their FM radios chirping due to DMR when we talk...

    G.

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    Quote Originally Posted by CARC383 View Post
    This recent antenna resting reinforces my opinion that unless you have hills and deep valleys with mobiles running around tucked up under the repeater, go for as much gain as you can afford as long as you can keep the radiation pattern within your area of interest. I think 6dBd gain would be my worst goal and about 10dBd being on the high side for offerings from reputable antenna mfrs.
    Thought I'd throw in one other example here, this time semi-wide area IN BUILDING portable coverage, where you also really need to watch non-unity tighter VBW TX antennas. Multiple business complexes near an airport, pretty much no HAAT, flat terrain, noisy RF environment.

    4x 3db Laird UHF, SLR5700, 4 duplexers, no vertical separation but maybe 30 ft horizontal (still useless). Most buildings are 3 stories or less, antennas are on top of 3 story building.

    Lots of windows, not an excessive amount of steel or concrete.

    Other end of complex only ~3-4 "blocks" away has dead spots in stairwell first floor on side of building opposite repeaters.

    Swap out with Unity Comtelco, problem solved.

    Now coverage far away is a little bit worse, and still limited by crappy duplexers, no vertical separation, etc etc at main site.

    Repurpose the still fairly new 3db Laird (again this is budget) as a receive only voting site ~10 miles away (4x SLR5700 RX only), turn up SLR5700s at main site to full power. Again, pretty flat metro area.

    Now the system has performed better than ever. The "Percentage reliability" also goes up when you have overlapping receive sites like this.

    Its unfortunate so many dealers overlook the power of a nice, quiet, non-desensitized satellite receiver site.

    You still get to "upsell" the customer more equipment, but its actually doing something good this time, and its an easier install and doesn't require any FCC licensing, hardly any battery backup since its RX only, etc etc.

    In a lot of budget commercial applications, you can't have towers with separate TX and RX, nice combiners and multi-couplers, nice vertical separation.

    So a great way to achieve different RX and TX antenna patterns and more isolation is Digital Voting.

    Use some Unities on your crappy install no-vertical separation, cheapy duplexer main site, then put a super hot satellite voting site without all the IL and desense a few miles away.

    Now you're essentially accomplishing the same thing you would on a tower with vertical separation, different/optimal RX and TX antenna patterns, nice combiner, etc etc only in a budget commercial setting.

    Its extremely satisfying looking at Genesis or Trbonet Watch RSSI coverage map and seeing the satellite receivers doing their thing.


    Mototrbo Digital voting is rock solid, but if you want to take things a step further, you'd have to go full simulcast and diversity receive with Kenwood Kairos

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    PSEhub, thanks!!

    Now I am eagerly awaiting for the FG4500 to arrive now... and I think I can do two separate antennas for RX/TX...

    LOL, it is unfortunate I didn't register in this site sooner...

    G.