You should be tuning the bandpass for maximum return loss, not least
insertion loss.
I've found that older Wacom duplexers develop center plunger contact
problems as they age. I trashed quite a few 900 MHz duplexers and combiner
cavities because the insertion loss was intermittantly high; the poor
center plunger contact was very obvious when tuning them - they were
"scratchy" and it was very obvious when the trace on the VNA while adjusting
the tuning rod.
I guess you've checked the obvious - look for a bad connector in the
harness.
--- Jeff WN3A
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of terry dalpoas
> Sent: Saturday, September 19, 2009 8:58 PM
> To: [email protected]
> Subject: Re: [Repeater-Builder] UHF Duplexers
>
>
>
> Eric,
>
> The repeater is 70cm amateur (444.625 TX/449.625 RX). These
> duplexers have been used on this same repeater for I'd say
> 10-13 years. I was given the repeater by the previous owner
> because the site was lost and he did not have time to repair
> the problems that did show up (the PA went out). I had a
> mobile PA that I turned down and used it and ran the repeater
> from my house for a few months (ran fine), then disconnected
> it. It sat in my shop from Oct 2008 until around 1 month
> ago. It was not as before. I wound up basically rebuilding
> the receiver, and I rebuilt the original PA. However, this
> year in Oklahoma, we did get a lot of rain and it did get
> pretty warm in my shop (along with high humidity. I wonder
> if the heat and humidity might have done something to the
> duplexers. I do have another set of these that were on the
> link transciever (the link was set up to run full duplex as
> well), I may retune them to see what I have.
>
> Equipment and tuning method. Here is what I was taught how
> to do it. I use an IFR 1200S service monitor, and the only
> spare radio I have at the moment is an Icom T7H HT. I start
> with RX (449.625) first. I connect the IFR to the antenna
> port, a reciever on the RX port (high pass), and a dummy load
> one the TX (low pass). I adjust RX pass freq for best SINAD.
> I then change the receiver and IFR to the TX freq and adjust
> for the best rejection, or worst SINAD. I do the TX
> (444.625) side the same way, best SINAD TX pass, worst SINAD
> RX reject.
>
>
> I tuned a set of duplexers this way before on a 2m repeater
> using 6 cavity Sinclair BpBr with no problems, this is the
> first I have messed with a set of Wacom's.
>
> Terry KM5UQ
>
> ________________________________
>
> From: Eric Lemmon <[email protected]>
> To: [email protected]
> Sent: Saturday, September 19, 2009 6:30:57 PM
> Subject: RE: [Repeater-Builder] UHF Duplexers
>
>
>
> Terry,
>
> Is your repeater in the 70cm Amateur band? If so, and your
> WP-678 duplexer
> was not originally tuned for that band, that may be where the
> problem lies.
> I have a Remec-Wacom WP-678 duplexer that I bought from the
> factory for GMRS
> service, and its insertion loss at the transmit frequency is 1.14 dB,
> equivalent to 38.5 watts out for 50 watts in. Your duplexer's measured
> insertion loss exceeds 4 dB.
>
> Most Wacom UHF commercial-band duplexers will tune down into
> the Amateur
> band, but not all of them. It appears that your duplexer is tuned
> improperly, or it may be impossible to tune it to your pair.
> What method
> and equipment are you using to tune the duplexer?
>
> 73, Eric Lemmon WB6FLY
>
>
> -----Original Message-----
> From: Repeater-Builder@ yahoogroups. com
> <mailto:Repeater-Builder%40yahoogroups.com>
> [mailto:Repeater-Builder@ yahoogroups. com
> <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of
> terry dalpoas
> Sent: Saturday, September 19, 2009 2:11 PM
> To: Repeater-Builder@ yahoogroups. com
> <mailto:Repeater-Builder%40yahoogroups.com>
> Subject: [Repeater-Builder] UHF Duplexers
>
> Just about finished with the Mastr II UHF repeater. I've run
> into a problem
> with the duplexers. They are a set of WACOM BpBr Model WP678.
> I am putting
> 48W into them, but only 18.5W out. I believe this should be better. RX
> will open squelch at around .2-.3 uV through the cans (this I
> know is OK).
> Could there be a problem with the TX side of the cans?
>
> Terry KM5UQ
>
>
>
>
>
>
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>
>
>
