Jason

Just curious, why do you have an eight way splitter in line to the receiver. The preamp is there to offset the loss in the splitter. Try eliminating both, but not the preselector.

On Thu, Apr 3, 2025 at 12:17 PM, Mike wrote:

I'm curious what the 8-way divider was feeding in addition to the DR-2X??

?

I'm curious what the 8-way divider was feeding in addition to the DR-2X??

?

Also, we found a 30dB notch filter laying around and tuned and added it to the input.? We then flipped the amp back on.... still no dice, but it did clean up the input nicely so we likely won't need a preamp going forward.? 20W will have to do for now.? Will investigate adding a better duplexer.

?

@Chris Boone WB5ITT

?

I'm going to message you directly about that duplexer you mentioned.

?

?

The Yaesu DR-2X has no front end filtering to speak of and relies completely on the duplexer and other front end filtering to survive. I had one on a perfectly tuned 4 can Motorola 1500 series Bp/Br duplexer (85dB isolation) with 85w amp and it was not happy with noticeable desense. I replaced the duplexer with a Celwave PD526 series six cavity 120dB isolation and it finally plays nice. I also found my 5w input amp fed by the DR-2X at 5w had all kinds of spurious crap coming out of the DR-2X transmitter but the DR-2X was fairly clean at 20w so I use the repeater at 20w with a 6dB attenuator into the amp for 85w out and that is working ok.?

?

If you have a certain amount of isolation in the duplexer, adding a preamp with no preselector filter will roughly reduce the amount of duplexer isolation by the amount of gain the preamp has by amplifying transmitter noise. Plus you may be hitting the preamp with enough out of band energy to create IMD which can raise the noise floor or produce ghost signals that may land on your repeater input frequency. I would suggest looking at the output of the existing amplified 8-way divider with a good spectrum analyzer to see what the repeater receiver is seeing when running at 100w. Is the desense due to increased noise floor or is there an actual signal present on the input only when the repeater is transmitting, etc? If so you can start removing things to see what affects the desense like remove the preamp and connect the repeater receiver right to the duplexer and see if the desense is reduced or eliminated. I see you have run the repeater at 20w without the power amp and desense is reduced but you need to know why its better.?

?

I suspect the main problem is the duplexer does not have enough isolation and using a preamp without an adequate cavity filter in front of the preamp is degrading isolation and the power amp is adding to the problem. A better duplexer and an adequate preselector filter ahead of the preamp with amp running at 250w in the future might all work together but maybe not with a DR-2X but might with a commercial quality repeater.

?

When you say the input goes away when it rains or snows are you talking about the receiver input as in it doesn't receive at all during rain or snow? If so to what extent? Just weak distant signals or from a radio transmitting right at the repeater site? How bout a service monitor right into the duplexer or repeater receiver? This sounds like a separate problem needing more info.?

If you need a good quality 6can BpBr, I have a Celwave / EMR 506 that'll work?

UPDATE:? Connecting the feedline directly to an HT and removing the repeater, preamp and duplexer yields a great simplex signal in both directions.?

?

So...... Duplexer, preamp or repeater I'm assuming.

I'll work on getting pictures.?

?

The first time this antenna needs to be replaced, we will spring for a commercial model.?

Just trying to have the output match the sensitivity of the input.? The input makes it miles and miles farther out when just running the repeater barefoot.? About 100 gets it to parity based on a rough guess.

This is great information.? We have a few cavities around that may have been exactly for this at one time or another.? Will look into it.

Hi

I can tell you that a 4 can duplexer does not provide enough rejection for 100 watts. Six cans of BpBr are needed with higher power above 40 watts.?

That's why these small mobile duplexers with six cans of only rejection are only?good for 40-50 watts.

Maybe you can simply add two more BpBr cavities.

I'm sorry, correction.? Input is 447.900.

Hello from Michigan!

?

I'm wondering if some folks have an idea of what might be going on here.

?

Equipment:

Yaesu DR-2X

Glenayre 97 series 250W UHF amp

Glenayre 2728 PSU

Sinclair preamp with a PA8075 chip.? Output split to 8 ports.? ASSY 363750, Board 261022

4 can UHF duplexer.? Unclear make/model.

1/2" Heliax, N Connectors

Polyphaser

Diamond 11dBi fiberglass vert

?

I have an amateur band UHF repeater I've been working with exhibiting the following symptoms:

?

Input desense when output amp is turned on, set to 100W.? ? It's being driven at 100W due to power supply current limitations of a single Glenayre 2728.? We've turned this off for now and are running the repeater barefoot at medium power (~20W).? This resolved this issue.? We'd obviously like our 100W back.

?

Now what we have, again with the amp off and disconnected from RF, is that the input is nearly completely gone after significant rain or snow.? After the roof of the building dries up from evaporation, the input comes back.? There is no water in the antenna, feedline, or connectors after double checking all of this with 24 hours of rainfall.? SWR seems to be the same whether the input is functioning or not.? I'll attach photos of a NanoVNA sweep taken while the input was not working yesterday.

?

I have someone running down to the site today to attach a regular HT to the antenna directly, bypassing the repeater, duplexer, and preamp.? With the input currently down, we'll see whether the HT fares better.

?

Any suggestions would be appreciated.

Pic 1: Base of tower, connection to polyphaser.
Pic 2: After duplexer
Pic 3: After Polyphaser, 60ft of Heliax, but before preamp and duplexer.

Input frequency is 442.900.

?

An attenuator something like this one may be easier....?? use your
existing 5w input amp...

I have no idea who this guy is, I'm just using his auction as an

example.?? But $27 and free shipping?

?

Decades ago I saw an attenuator between an exciter and an amplifier...

?

Mike WA6ILQ