No preamp.
Yes. the receiver was aligned per instructions (poor as they are.) The receiver is the Kendecom MR-4 which is part of the standard Mark 4 Yes. the transmitter was aligned per instructions (which are actually pretty good) and looks very clean on the spectrum analyzer. From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 Sent: Saturday, July 19, 2008 1:28 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Duplexer Tuning / Desense (DB-4060) Preamp on the Receiver? Was the Receiver front-end aligned on the specific new frequency? Specific Receiver Model? Were the transmitter and any power amplifiers properly aligned? [The big questions...] Transmitter Power Output? Insertion loss setting on the duplexer probes? Were the duplexer cable harness lengths changed? What was the default/original factory set duplexer frequency? cheers, s. > The old cans (Decibel DB4060 - 4 cans total) had been in > storage and were apparently used by another ham for > experimentation after they were taken off line. I'd > replaced the notch caps a couple of years ago because > whoever was experimenting with them tightened them > until they cracked. I've also disassembled them and > made sure they were clean and had no signs of arching > or other damage. > They were originally tuned on 146.25/85 (but as I said, > they'd been 'played' with) and I'm moving them to 145.11 > (minus 600 KHz). I first tuned them with a signal generator > per the DB Products instructions and they tuned in very well. > The peaks were good on both sides and the notches were about -85 > db, using my crude measuring system. Losses on the pass-band > were less then 2 db (probably more like 1 db). This pre-tuning > was done with an HP-8640 signal generator, a scope, and other > miscellaneous goodies. > > Tonight I got a service monitor (HP-8920) from a buddy who > works for the FAA. I set it to duplex and checked my peaks. > They were very close to perfect already, but I managed to get > the last little bit of RF through the pass-cavities. Next > I set out to tune the notches. I was able to get decent > notches, but apparently they are not deep enough (despite > having measured -85 with the signal generator) because I still > have about 15 db of desense. I've been through them 4 or 5 > times tonight (until I'm sick of them) but that's the best > I can do. (I did discover that if I tune the receiver notch > enough, I can pull the transmitter down to nothing!) > > I just reviewed (again) Kevin's article on Repeater-Builder > entitled 'Getting the most from your Repeater System', and > the one thing I need to do yet is check for internal desense. > I had to replace the Teflon-type cable which leads from the > Mark IV transmitter to the back panel, and when I replaced > it, all I had was some RG-8X. I'm (sort of) hoping that's > the problem, but I won't know until I check. I can't see > where I've missed anything obvious, although tuning these > types of duplexers is new to me. I spent 17 years in the Air > Force working navigation and comm gear, so I'm pretty well > versed in what I'm doing, but since this is a new venture for > me, I'm certainly open to suggestions. I'll check for > internal desense tomorrow, but in the meantime if anybody has > anything to add, please chime > in. > TIA, > > Mike > WM4B > Kathleen, GA >
<<image001.jpg>>
<<image002.jpg>>
