I think Eric's response covered it pretty well. Lacking the right
equipment, tuning for return loss can't be done with a great deal of accury.
The closest you could get using basic instruments would be to look at
reflected power with a high-quality directional wattmeter (Bird 43) with the
cavity terminated into a very good load (30 dB or better return loss), with
the usual caveat not to tune while transmitting.
In your situation, given that you're not sure whether you don't know if you
have bad hardware or a tuning problem, I'd strongly recommend you find
someone with a VNA to do it. If you can't find anyone locally, if you want
to pay the shipping I'll do it for you.
--- Jeff WN3A
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of terry dalpoas
> Sent: Sunday, September 20, 2009 12:02 PM
> To: [email protected]
> Subject: Re: [Repeater-Builder] UHF Duplexers
>
>
>
> Jeff,
>
> Best I can tell the connecting harness is good. I may try
> the set meant for the link radio and see what they do. How
> do I tune for maximum return loss? If it is better, you can
> contact me off the group, so it does not get tied up.
>
>
> Terry KM5UQ
>
> ________________________________
>
> From: Jeff DePolo <[email protected]>
> To: [email protected]
> Sent: Sunday, September 20, 2009 10:16:59 AM
> Subject: RE: [Repeater-Builder] UHF Duplexers
>
>
>
>
> 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: 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 8:58 PM
> > To: Repeater-Builder@ yahoogroups. com
> <mailto:Repeater-Builder%40yahoogroups.com>
> > 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 <wb6...@verizon. net
> <mailto:wb6fly%40verizon.net> >
> > To: Repeater-Builder@ yahoogroups. com
> <mailto:Repeater-Builder%40yahoogroups.com>
> > 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%40yahoog roups.com>
> > [mailto:Repeater- Builder@ yahoogroups. com
> > <mailto:Repeater- Builder%40yahoog roups.com> ] On Behalf Of
> > terry dalpoas
> > Sent: Saturday, September 19, 2009 2:11 PM
> > To: Repeater-Builder@ yahoogroups. com
> > <mailto:Repeater- Builder%40yahoog roups.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
> >
> >
> >
> >
> >
> >
> > No virus found in this incoming message.
> > Checked by AVG - www.avg.com
> > Version: 8.5.409 / Virus Database: 270.13.78/2347 - Release
> > Date: 09/20/09 06:22:00
> >
> >
> >
>
>
>
>
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 8.5.409 / Virus Database: 270.13.78/2347 - Release
> Date: 09/20/09 06:22:00
>
>
>
