EMR preselector tuning help/procedure.

gMan1971

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I recently acquired another preselector like the one in the pic. I have a few of those in service but they came pretty well tuned already, so I didn't need to do much to get them tuned to the frequency range I needed. However, this one is so bad, its not even usable. I've inspected it and it is in perfect condition internally, everything is shiny, all bolts move, no rust... and looks exactly the same (except positions don't match to the other ones I have) I've tried setting things similar to how the other ones are but it is still nowhere near as good as the other ones I have... so after a lot of trial and error I figured I'd ask if there are any manuals, or procedures as to how to tune those preselectors. They seem to have the 5 bolts and the 4 plastic knobs which rotate some sort of internal flat metal plates inside... again, I am not claiming to be an expert, hence why some help would be greatly appreciated.

Thanks.

G.
 

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Bill_G

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Well, EMR is lower tier product. If it doesn't tune like you think it should *and* it looks good inside, it's broke. Find another one, or find something better.
 
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gMan1971

gMan1971

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Well, EMR is lower tier product. If it doesn't tune like you think it should *and* it looks good inside, it's broke. Find another one, or find something better.
What would be considered a better preselector? I have a few Quantar preselectors that seem to be quite decent... anything worthy of mention?

Thanks.

G.
 

Bill_G

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EMR is about as good as it gets for $500. And if you need to qualify a Made in America quota, EMR helps.


Sinclair makes VHF presel with 2.5mhz passband that is half the cost of EMR, but it only comes in BNC-F connectors. They are a little squirrely to mount, and squirrely to tune, but they get the job done.


TX RX makes a great product if you need tighter skirts, something that tunes as expected, and lasts forever.

 
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moetorola

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How are you trying to tune it, regular tracking generator? I think a return loss bridge would be the way to go with those for tuning.
 
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gMan1971

gMan1971

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EMR is about as good as it gets for $500. And if you need to qualify a Made in America quota, EMR helps.


Sinclair makes VHF presel with 2.5mhz passband that is half the cost of EMR, but it only comes in BNC-F connectors. They are a little squirrely to mount, and squirrely to tune, but they get the job done.


TX RX makes a great product if you need tighter skirts, something that tunes as expected, and lasts forever.


Made in USA is certainly a plus.

2.5 mhz passband sounds good. The Quantar preselectors are pretty tight too... and small!

I have TX/RX cavities, those are really good... but like you said, <150 bucks you can't beat the EMR preselector.

G.
 
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gMan1971

gMan1971

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How are you trying to tune it, regular tracking generator? I think a return loss bridge would be the way to go with those for tuning.
Return loss bridge? any link as to how to perform such alignment? I use a regular VNA+signal generator... but its just too hard to see the peaks/valleys of the different dials....

G.
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Call EMR, they have great tech support.
I will, hope they support 2nd hand equipment... :) after all, they made it.

G.
 

moetorola

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Return loss bridge? any link as to how to perform such alignment? I use a regular VNA+signal generator... but its just too hard to see the peaks/valleys of the different dials....

G.
Post automatically merged:


I will, hope they support 2nd hand equipment... :) after all, they made it.

G.
I use the Eagle RLB, there is info on the web and maybe video's on uses for an RLB and its advantages.

 
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gMan1971

gMan1971

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I use the Eagle RLB, there is info on the web and maybe video's on uses for an RLB and its advantages.


Well, just ordered an Eagle RLB.

Thank you.

G.

EDIT: After watching a few videos looks like the RBL method can also be used to tune antennas and other devices, so, once again, thank you.
It would appears the RLB is like a directional coupler (ISO-tee).
 
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MotoBill

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From what little I know about the EMR preselector subject of this thread, is that the screws with locknuts tune the helical inductors (the obvious part) but that the adjustments under the caps are the coupling adjustments. I would expect that you'd tune the each stage with an RLB for minimum return loss across the desired passband with the least ripple while carefully tweaking the coupling for the desired skirt selectivity needed for your application.

The coupling adjustments make sense much the same as you'd expect when rotating the coupling loops of a standard cavity filter. That is
to say that the tighter the coupling the lower the passband Q and the lower the insertion loss while the lighter the coupling the greater the passband Q and the higher the insertion loss. It looks like your job is going to be a balancing act between obtaining the desired passband response against insertion loss that I understand is approximately 2 dB when properly aligned.

Have fun!
 
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gMan1971

gMan1971

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From what little I know about the EMR preselector subject of this thread, is that the screws with locknuts tune the helical inductors (the obvious part) but that the adjustments under the caps are the coupling adjustments. I would expect that you'd tune the each stage with an RLB for minimum return loss across the desired passband with the least ripple while carefully tweaking the coupling for the desired skirt selectivity needed for your application.

The coupling adjustments make sense much the same as you'd expect when rotating the coupling loops of a standard cavity filter. That is
to say that the tighter the coupling the lower the passband Q and the lower the insertion loss while the lighter the coupling the greater the passband Q and the higher the insertion loss. It looks like your job is going to be a balancing act between obtaining the desired passband response against insertion loss that I understand is approximately 2 dB when properly aligned.

Have fun!

Thank you, MotoBill, so its the same thing as the angle adjustments on the cavities. Once I get the RLB I I'll be able to tune this thing, especially given how sharp the spikes are with an RLB approach (rather than the S11 --> S21 approach)

Thanks everyone... this thread was really useful.

G.
 
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gMan1971

gMan1971

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Received the Eagle RLB150, and it took about 10 minutes to tune the preselector with it. Nothing like the right tool for the right job. Thank you!
 

MotoBill

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Received the Eagle RLB150, and it took about 10 minutes to tune the preselector with it. Nothing like the right tool for the right job. Thank you!

Just curious, how large of a passband did you tune it for and did you happen to sweep it to measure the out of passband roll off response?
Also, did you end up moving the coupling adjustments at all?
 
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gMan1971

gMan1971

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Just curious, how large of a passband did you tune it for and did you happen to sweep it to measure the out of passband roll off response?
Also, did you end up moving the coupling adjustments at all?

The coupling knobs were so out of alignment that it couldn't be tuned without moving them, otherwise it was un-tunable. I had to reset the screws to a fixed "center" position and then moved the coupling until I got the lowest return loss at the given frequency, then adjusted the rods to the center frequency. The thing the RLB provided was clear spikes to move around, it was easier, all it took was move all spikes on top of each other... vs the S11-->S21 method which displays such a rounded curve that you couldn't tell much, if anything.

The IL now is ~1.0 dBm through most of the +/- 3 Mhz passband, (from 1.49 dBm IL before). While the roll off is not as sharp as the Quantar preselectors I have, I think that after getting used to the RLB I'll probably get better at this.... again, this is my first foray into it and I only spent 10 minutes on it to get the hang of it.... As for rolloff, etc, beyond 10 mhz from center its a -38 dBm attenuation, and after 20 mhz from center and beyond is a solid -80 dBm attenuation all the way from DC to 1 Ghz.. All in all, I think it was money very well spent on the RLB. So, once again, thanks!

G.
 

MotoBill

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The coupling knobs were so out of alignment that it couldn't be tuned without moving them, otherwise it was un-tunable. I had to reset the screws to a fixed "center" position and then moved the coupling until I got the lowest return loss at the given frequency, then adjusted the rods to the center frequency. The thing the RLB provided was clear spikes to move around, it was easier, all it took was move all spikes on top of each other... vs the S11-->S21 method which displays such a rounded curve that you couldn't tell much, if anything.

The IL now is ~1.0 dBm through most of the +/- 3 Mhz passband, (from 1.49 dBm IL before). While the roll off is not as sharp as the Quantar preselectors I have, I think that after getting used to the RLB I'll probably get better at this.... again, this is my first foray into it and I only spent 10 minutes on it to get the hang of it.... As for rolloff, etc, beyond 10 mhz from center its a -38 dBm attenuation, and after 20 mhz from center and beyond is a solid -80 dBm attenuation all the way from DC to 1 Ghz.. All in all, I think it was money very well spent on the RLB. So, once again, thanks!

G.
Thanks, gMan. I was very curious about the coupling (caps I think) adjustments as to how they would interact with the helical tuning. The IL you have achieved is very impressive and is better than the published spec in EMR's catalog. Great work and thanks for sharing your experience with tuning this preselector.
 
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gMan1971

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Well, thanks, but the RLB made it super easy to see where the peaks were (you see the phase angle changing, that is where the peaks usually are), so all you literally need to do is just connect the dots until your return loss is the same as measured with a dummy load, that alone gets you very very close, then, the final numbers after finetuned via the S11 --> S21 method to optimize IL, achieve 50 ohms impedance and as close to 0 degrees phase on the radio side. The number in this preselector came out to be at 1.12 dBm IL loss.

I think I need a better VNA now... :D dang, the money pit knows no bottom...
 

com501

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We have a couple of the RLBs, the high frequency ones work about the same as the 'budget' model An HP VNA would do very well, but the cost is probably slightly less than a new Tesla Model S, but not much.