Celwave PD-497 duplexer/ general duplexer jumper cable lengths

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Josh
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Celwave PD-497 duplexer/ general duplexer jumper cable lengths

Post by Josh »

Good evening:

It's been a really long time since I posted here and was active on the forum. I've been around though. My work retired some Celwave PD-497 6-cavity VHF duplexers some years ago and I snagged one. It was tuned for the railroad but could be tuned for ham. Recently I've had the desire to retune it and using an inexpensive NanoVNA, tuned the cavities and notch frequencies on each individual can the best I could for a 600khz VHF, 2-meter split. The repeater seems to be somewhat deaf... but I if it's not a radio receiver issue, my question for the membership here is a about a more abstract topic regarding coaxial cable jumper lengths and their absolute importance to a repeater system.

My duplexer cans had factory jumpers between them, but no 'T' antenna connector cables. In my test setup, I had the cables to the repeater mismatched by both type of cable and lengths... I think one was 8ft, the other maybe 6. I put a 'T' connector on the transmitter side of the duplexer to the antenna and and a 1ft jumper over to the rx side.

So, in my "test" setup, which according to my SWR meter on TX is really good, and field tests show that to be true, the RX side is really lacking. How much of a factor does equal length cables between the transmitter and duplexer, receiver and duplexer, and both legs to the T-connector for the antenna truly play when it comes to performance? I expected it all to be fair. My estimation is poor to marginal. Either the receiver is bad, or the repeater is being desensitized but I can't say which so far.

I plan on testing more tomorrow and have matched the cable lengths to the 'T' connector as well as the transmitter an receiver to the duplexer, but I am not hopeful for a better result.

-Josh
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Re: Celwave PD-497 duplexer/ general duplexer jumper cable lengths

Post by PETNRDX »

Those cable lengths are pretty critical.
Pretty sure they should all be 9 inches.
The manual for it is on Repeater-Builder.
If the "radio" to duplexer cables make a difference, then you have an issue.
They should work with random lengths.
But the intercavity and last cavity to the Tee are critical.
Steve K.
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Re: Celwave PD-497 duplexer/ general duplexer jumper cable lengths

Post by PETNRDX »

By the way that length assumes RG-204, if you use something with a different velocity factor, you will have to re-calculate for that.
Steve K.
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Re: Celwave PD-497 duplexer/ general duplexer jumper cable lengths

Post by PETNRDX »

I can't type today...
RG-214.
Steve K.
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Josh
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Re: Celwave PD-497 duplexer/ general duplexer jumper cable lengths

Post by Josh »

Thanks for the responses. I built a better 'T' cable with RG8, but will source some RG214 and make it right with 9" jumpers, that's no big deal, but an important thing to note and appreciated.

I also found out my NanoVNA needed adjustment to the TXCO frequency as it was off by about 70khz, which resulted in poor duplexer tuning. I compared values from known good factory tuned filters and corrected it. I took it and retuned my duplexer cans and found that the transmitter is now putting out two more watts than it was before, so clearly some affect was made. (It was a 25 watt radio putting out 10.9 or so watts, not it's over 12.).

-Josh
PETNRDX
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Joined: Sun Nov 25, 2001 4:00 pm
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Re: Celwave PD-497 duplexer/ general duplexer jumper cable lengths

Post by PETNRDX »

RG-8 and RG-214 *should* both have a velocity factor around the same, .66 so you should be able to tune up and test with RG-8.
I have not played with those NANO-VNA's much.
I should probably buy one to compare just for the fun of it.
Some folks tell me that some of those things are pretty good for the money.
Steve K.
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Josh
Posts: 1931
Joined: Mon Sep 03, 2001 4:00 pm
What radios do you own?: APX4K, XTL5K, NX5200, NX700HK

Re: Celwave PD-497 duplexer/ general duplexer jumper cable lengths

Post by Josh »

I've been testing tuning and tweaking things for the past week and today my piece of RG214 came in. I very carefully created two 'T' connector cables at the same length the other cables on the duplexer are, but the results were marginally better. It looks like I can't upload a picture to the forum, this is what I can tell you and what I'm thinking.

Each cavity by itself tunes great, I get good wave forms, between 35 and 40bd in the notch and -.54dB loss in the pass.

Put them all together and make pass band adjustments, the best I can get is -40db into the "pass notch" and the actual notch for both the transmit and receive side when checked out separately in their respective sets is not well defined, it dips at the right spot, but is really wide and eventually comes back up almost 500khz away.

The PD-497 Celwave manual from repeater-builder shows two different builds of the duplexer. 144-174 should have 9" jumpers in the system. 132-144Mhz should have 9.5" jumpers. When I stretched out one of the jumpers as a reference for my two newly made jumpers, (and I tested several after) I made the discovery that they are 8.75" from PL259 tip to PL259 tip... now the manual seems to show PL250 sleeve to sleeve should be the reference measurement.

This dupelxer was setup for 160.800 and 161.070 according to the tag, it was retuned at some point before I got it, but given railroad band 160mhz, would it make sense for the jumpers to be the factor preventing good tuning? I'm beginning to think so based off of a video on Youtube from Telewave where they talk about a wall of different length cables they use when building a duplexer for peak performance. But this is Phelps-Dodge/Celwave, and after performing the tuning procedure to the manual and having no luck, then trying a sort-of hybrid attempt to fudge the reading the best I could and still having bad luck, it's either all the cans are bad or there's something else I'm missing.

Thanks for reading and those that have helped me walk through this.
-Josh
PETNRDX
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Joined: Sun Nov 25, 2001 4:00 pm
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Re: Celwave PD-497 duplexer/ general duplexer jumper cable lengths

Post by PETNRDX »

I sent you an Email using this website's Email utility.
Lemme' know if you don't get it.
The topic is maybe we connect via direct email so you can send me a picture of your setup and maybe what the results look like.
I love those duplexers, but the really can be hard to tune.
Steve K.
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Josh
Posts: 1931
Joined: Mon Sep 03, 2001 4:00 pm
What radios do you own?: APX4K, XTL5K, NX5200, NX700HK

Re: Celwave PD-497 duplexer/ general duplexer jumper cable lengths

Post by Josh »

I got an e-mail notification of the PM/DM, I just need to find it through the forum interface. Thanks
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