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

  1. #26
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    So, updates, updates.

    I ran the system in NFM as suggested here, and it is clear that the signal was fading almost completely away when not heard, in NFM the signal would be almost a perfect copy until it wasn't there, very little picket fencing throughout the 15 mile range test. NFM provided better fringe area performance, in DMR the breakup was unbearable wheras in NFM you could clearly make out the voice... anyhow.

    In order to measure RSSI at different locations I hooked up one of the extra 5550e I have, and the readings ranged from -95dBm to -127dBm, in a very short distance, especially with changes of altitude. Worth mentioning that the 5550e was able to pick signals much better than the EVX mobiles were, even with the preselector on the EVX, the 5550e was noticeable better even without it. Some signals where the EVX mobiles wouldn't produce any audio, the 5550e was nearly full audio recovery in DMR. Especially signals that measured in the -120dBm range for the 5550e... The NFM performance was also better on the 5550e, but not as night and day difference as it was while operating in DMR.

    Also performed ISO-tee tests at a few of the locations where the RX was breaking out on the EVX, but it didn't show much of a change in effective sensitivity from place to place, perhaps a 2dBm improvement with the RFS preselector at best... so not sure if that would've been measurement error, or just situation... etc. The 95 to 127 swings I don't think they can be explained by just a desense on the receiver... I could be wrong tho.

    However, things got rather interesting when operating the EVX mobiles in NFM without the RFS preselector: There was a noticeable decrease in signal quality, signal was clearly there, but it felt like garbled, something barely unnoticeable while on DMR tho... and when the preselector was connected the NFM signal became much cleaner... although you could still hear some "interference" (for the lack of a better word) in the very fringe areas it was a perfectly copyable transmission.

    Perhaps I need to run an even higher isolation preselector than the little RFS one current on the cars... like the one we use at the base. I'll have to tune one of the spare EMR preselectors to verify this theory... I still think this could be related to VBW... the beam is passing above the antenna...

    G.


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  3. #27
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    I run a 16 bay folded dipole antenna on GMRS and it works quite satisfactorily but my HAAT is 32 meters. The installation is certainly not a "cloud-burner" as installed. Hope this helps.

  4. #28
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    Wouldn't it be nice to pull the main breakers on the radio towers and doppler radar in your area and run the tests again? I suspect everything would work fine and without any preselectors.

    As far as the antenna beamwidth being too narrow, in my experience its not a big deal for a hilltop repeater serving a moderately hilly area. In my area we have stuff on 5,000ft mountain tops and when you get tucked up against the base of those there are dead spots, but for a 1,000ft hill and a 6dBd gain antenna on top it should not be a show stopper. With that you will have some weak spots and maybe not full quieting here and there but the beamwidth will be at least +/- 7degrees above and below the horizon at 3dB down (or 3dBd gain) and there is still a lot of signal available at steeper angles downward.

    Getting into a slight fade area of the antenna and having massive out of band interference that rips your radio a new butthole is a completely different problem and that appears to be the problem here. At least to me.

    Quote Originally Posted by gMan1971 View Post
    So, updates, updates.

    I ran the system in NFM as suggested here, and it is clear that the signal was fading almost completely away when not heard, in NFM the signal would be almost a perfect copy until it wasn't there, very little picket fencing throughout the 15 mile range test. NFM provided better fringe area performance, in DMR the breakup was unbearable wheras in NFM you could clearly make out the voice... anyhow.

    In order to measure RSSI at different locations I hooked up one of the extra 5550e I have, and the readings ranged from -95dBm to -127dBm, in a very short distance, especially with changes of altitude. Worth mentioning that the 5550e was able to pick signals much better than the EVX mobiles were, even with the preselector on the EVX, the 5550e was noticeable better even without it. Some signals where the EVX mobiles wouldn't produce any audio, the 5550e was nearly full audio recovery in DMR. Especially signals that measured in the -120dBm range for the 5550e... The NFM performance was also better on the 5550e, but not as night and day difference as it was while operating in DMR.

    Also performed ISO-tee tests at a few of the locations where the RX was breaking out on the EVX, but it didn't show much of a change in effective sensitivity from place to place, perhaps a 2dBm improvement with the RFS preselector at best... so not sure if that would've been measurement error, or just situation... etc. The 95 to 127 swings I don't think they can be explained by just a desense on the receiver... I could be wrong tho.

    However, things got rather interesting when operating the EVX mobiles in NFM without the RFS preselector: There was a noticeable decrease in signal quality, signal was clearly there, but it felt like garbled, something barely unnoticeable while on DMR tho... and when the preselector was connected the NFM signal became much cleaner... although you could still hear some "interference" (for the lack of a better word) in the very fringe areas it was a perfectly copyable transmission.

    Perhaps I need to run an even higher isolation preselector than the little RFS one current on the cars... like the one we use at the base. I'll have to tune one of the spare EMR preselectors to verify this theory... I still think this could be related to VBW... the beam is passing above the antenna...

    G.

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  6. #29
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    Quote Originally Posted by jrlaw View Post
    I run a 16 bay folded dipole antenna on GMRS and it works quite satisfactorily but my HAAT is 32 meters. The installation is certainly not a "cloud-burner" as installed. Hope this helps.
    A 16 bay folded dipole! holy crap!!

    Its clear the folded dipole isn't a "cloud burner" from all the experiences I've collected about those antennas, its the cheap verticals running on this setup that are, however. So, it seems that changing those will be the thing to do.

    G.

  7. #30
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    Quote Originally Posted by CARC383 View Post
    Wouldn't it be nice to pull the main breakers on the radio towers and doppler radar in your area and run the tests again? I suspect everything would work fine and without any preselectors.

    As far as the antenna beamwidth being too narrow, in my experience its not a big deal for a hilltop repeater serving a moderately hilly area. In my area we have stuff on 5,000ft mountain tops and when you get tucked up against the base of those there are dead spots, but for a 1,000ft hill and a 6dBd gain antenna on top it should not be a show stopper. With that you will have some weak spots and maybe not full quieting here and there but the beamwidth will be at least +/- 7degrees above and below the horizon at 3dB down (or 3dBd gain) and there is still a lot of signal available at steeper angles downward.

    Getting into a slight fade area of the antenna and having massive out of band interference that rips your radio a new butthole is a completely different problem and that appears to be the problem here. At least to me.

    Hey CARC383, thank you.

    I would love to pull the main breakers on those angry RF firebreathing towers, and the breaker of the dang "supperdoppler" too... but unfortunately, its not within the realm of possibilities.

    Will be trying the EMR preselector on mobile, which has around -20dBm of additional isolation vs the smaller RFS 4 cavity ones we are using.

    @PSEhub: The FG4550 arrives here on Friday, just hoping the weather holds to do all the work this weekend...

    G.