It's difficult to answer that question without more information about your system. Please answer these questions:
1. What make and model antenna was used before you replaced it with the four-bay antenna? 2. What make and model antenna is now installed? 3. How long is the new 1/2" hardline, and is it Andrew LDF4-50 Heliax? 4. What is the present transmitter power output, measured at the TX output jack? 5. What is the receiver 12dB SINAD sensitivity, measured at the RX input jack? 6. What type of cable is used to connect the end of the hardline to the antenna jack on the duplexer? 7. Do you have the test equipment to verify the tuning of the duplexer? 8. Have you confirmed that the transmitter is not producing spurious signals at the RX frequency? If it turns out that the notch duplexer is not up to par, an economical solution might be to add a bandpass cavity between the existing notch duplexer's RX output jack and the repeater's RX input jack. However, my personal preference would be to replace the notch duplexer with a BpBr cavity duplexer, such as a Telewave TPRD-1584 shown here: <www.telewave.com/pdf/TWDS-6039.pdf> You're looking at an expenditure of $1,500 or so, not including double-shielded jumpers and high-quality connectors. If the cable in Item 6, above, is anything but RG-214/U, RG-400/U, or Heliflex, that may be the cause of your problem. Ideally, that particular jumper should always be made to order, with the correct connectors on each end- no barrels or adapters. RG-213/U, 9913, and LMR-400 are definitely a no-no! 73, Eric Lemmon WB6FLY -----Original Message----- From: Ken Franks [mailto:[email protected]] Sent: Friday, July 10, 2009 8:49 AM To: Eric Lemmon Subject: RE: [Repeater-Builder] Repeater Desense? Thanks! I'll check it out after lunch here. Our IT guy has a little knowledge since we used to run a TV broadcast out of the school here but it has been many, many years. Do you feel that purchasing a BpBr 4-cavity would be a wise investment for us, over the mobile notch? What are the benefits? This is a part of our District's school safety/security radio system so we'd like to make it as solid as possible. Thanks! >>> "Eric Lemmon" <[email protected]> 7/10/2009 11:30 AM >>> Okay, so you definitely have a mobile notch duplexer, which has practically no bandpass effect since it works entirely by notching out the opposite frequency in the split. Since the problem began when you changed the antenna, my suspicion is that the new antenna's pattern allows more TX signal to bathe the repeater than before. Some versions of Yaesu/Vertex VXR repeaters were supplied with single-shield jumpers inside the cabinet, and this allowed some random desense to occur. That happened in my own VXR-5000, and I completely cured it by replacing the factory jumpers with RG-400/U double-shielded coax. The original Vertex jumpers had gray jackets with no identification, so they were replaced with RG-400/U. If you do make new cables, make them with the correct connectors on each end, so that you do not have to use any adapters. I think you're pushing the notch duplexer to the limit of its capability, and you can test this by dropping the TX power to 15 or 20 watts, and checking again for desense. Also, you might try temporarily swapping it for a BpBr four cavity duplexer. 73, Eric Lemmon WB6FLY -----Original Message----- From: Ken Franks [mailto:[email protected] <mailto:Franks%40godwinschools.org> ] Sent: Friday, July 10, 2009 8:04 AM To: Eric Lemmon Subject: RE: [Repeater-Builder] Repeater Desense? it is a commercial VHF (rx 152, tx 159). yes, the duplexer is mounted inside. I went to take a look at the make/model and it was not legible due to a faded sticker. It should be within operating spec's though since it was the one purchased with the unit and been in service for 3 years. Interestingly enough, one of our IT people went to look at it and found that the closer he held the PT to the duplexer, the dropping of rx when tx'ing resolved but was pretty fuzzy sounding yet. Then, when he held the PT even closer and transmitted, it began to operate properly again and no longer sounded fuzzy. >>> "Eric Lemmon" <[email protected] <mailto:wb6fly%40verizon.net> > 7/10/2009 10:32 AM >>> If this is a 2m repeater, and the duplexer is mounted inside the VXR-7000 cabinet, it must be a mobile notch duplexer. I don't believe that such a duplexer can perform with a 600 kHz split. Please elaborate on the make and model of duplexer you have, and the RX and TX frequencies. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:Repeater-Builder%40yahoogroups.com> [mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of kfd29 Sent: Friday, July 10, 2009 6:59 AM To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:Repeater-Builder%40yahoogroups.com> Subject: [Repeater-Builder] Repeater Desense? Just replaced a damaged mast for our VHF repeater. Went with a 4-bay dipole as a replacement, along with switching out the old coax with 1/2" hardline. Everything else stayed the same, VXR-7000 and internal duplexer. All worked well after a final check, until night came along, when it seems to possible to a casulty of desense? In base mode, tx and rx are wonderful, but when switched to repeater mode as soon as it rx's and attempts to transmit, it cuts itself out. About a one second in, out, back in, out, etc. Not sure what happened but around mid-day it started working fine again, then last night started acting up again. Any thoughts? suggestions? Did recheck all connections from antenna down and everything is tight.
