[Repeater-Builder] 440 de-sense
Hi, I have a slight problem with a 444.6 output repeater and looking for the best and low cost approach to fix. We have just moved to the site and the owner has the 440 repeater. The ants are all at the same height and hence we only have a small amount of horiz separation. We can't change this as on cell tower as part of the owners deal for the site. So what it is, is it. We link the the site on 446.7125 and 446.60, and his repeater at 10 watts, is DE-sensing our receivers which are GE MVP's. Guess looking to the experts on best viable solution. I have been able to try anything yet but have considered a mobile duplexer as an option. Thanks Randy
Re: [Repeater-Builder] 440 de-sense
how about trying a 1/4 wave stub tuned to his freq on your rcv line? That is IF it is coming in there. or is it coming in thru the wiring? Chuck K0XM On Thu, Mar 6, 2008 at 7:57 AM, wb8art [EMAIL PROTECTED] wrote: Hi, I have a slight problem with a 444.6 output repeater and looking for the best and low cost approach to fix. We have just moved to the site and the owner has the 440 repeater. The ants are all at the same height and hence we only have a small amount of horiz separation. We can't change this as on cell tower as part of the owners deal for the site. So what it is, is it. We link the the site on 446.7125 and 446.60, and his repeater at 10 watts, is DE-sensing our receivers which are GE MVP's. Guess looking to the experts on best viable solution. I have been able to try anything yet but have considered a mobile duplexer as an option. Thanks Randy Yahoo! Groups Links
RE: [Repeater-Builder] 440 de-sense
A quarter-wave stub of coax won't have enough Q to attenuate the 444.6 signal without also degrading the 446.x signals as well. A high-Q pass/reject cavity is the way to go. The bandpass characteristics of a typical pass/reject cavity should allow both 446.7125 and 446.600 to pass with near-equal attenuation as they are close in frequency, while still being able to knock down the 444.6 signal about 40 dB or more depending on loop settings. Before going out and spending money, measure how strong the 444.6 sig is at your 446.x receivers. That will tell you how much rejection you really need. If your desired signals are strong, you might only need to knock down the 444.6 to maybe -20 dBm. If your 444.6 sigs are marginal, it may need to be down below -30 dBm, but probably not more than -40 dBm for your MVP's. I'm assming you're not using a preamp, for if you are, it's probably only exacerbating the problem. You could try using filter sections from a duplexer to do this, but most UHF duplexers are designed for a 5 MHz split, so you may not be able to get the notch close enough to the pass (about 2 MHz) without incurring high insertion loss at the pass frequencies. But your paths have enough margin, maybe you can get away with it. --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Chuck Kraly Sent: Thursday, March 06, 2008 9:04 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] 440 de-sense how about trying a 1/4 wave stub tuned to his freq on your rcv line? That is IF it is coming in there. or is it coming in thru the wiring? Chuck K0XM On Thu, Mar 6, 2008 at 7:57 AM, wb8art [EMAIL PROTECTED] mailto:[EMAIL PROTECTED] wrote: Hi, I have a slight problem with a 444.6 output repeater and looking for the best and low cost approach to fix. We have just moved to the site and the owner has the 440 repeater. The ants are all at the same height and hence we only have a small amount of horiz separation. We can't change this as on cell tower as part of the owners deal for the site. So what it is, is it. We link the the site on 446.7125 and 446.60, and his repeater at 10 watts, is DE-sensing our receivers which are GE MVP's. Guess looking to the experts on best viable solution. I have been able to try anything yet but have considered a mobile duplexer as an option. Thanks Randy
Re: [Repeater-Builder] 440 de-sense
Randy, There could be 2 problems why you get desense. 1.overload by the other repeater tx, but more likely 2. his wide band tx noise, down maybe 85 db, is getting into your receiver...the wide band noise is actually on your rcvr freq. Solution to 1 is maybe a cavity narrow filter on your receiver. Solution to 2 is a notch cavity on the other repeater TX at your receive freq. Does same as the duplexer on our repeater tx. I am assuming you can put a dummy load on each repeater and there is no desense...nothing interacting between the gear on the ground. 73, ron, n9ee/r From: wb8art [EMAIL PROTECTED] Date: 2008/03/06 Thu AM 07:57:54 CST To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] 440 de-sense Hi, I have a slight problem with a 444.6 output repeater and looking for the best and low cost approach to fix. We have just moved to the site and the owner has the 440 repeater. The ants are all at the same height and hence we only have a small amount of horiz separation. We can't change this as on cell tower as part of the owners deal for the site. So what it is, is it. We link the the site on 446.7125 and 446.60, and his repeater at 10 watts, is DE-sensing our receivers which are GE MVP's. Guess looking to the experts on best viable solution. I have been able to try anything yet but have considered a mobile duplexer as an option. Thanks Randy Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
RE: [Repeater-Builder] 440 de-sense
Randy, There could be 2 problems why you get desense. 1.overload by the other repeater tx, but more likely 2. his wide band tx noise, down maybe 85 db, is getting into your receiver...the wide band noise is actually on your rcvr freq. I thought about that issue (Tx noise from the repeater) when I wrote my original reply but didn't bother to comment on it. The offending transmitter is a repeater, transmitting low (444.6) and receiving high (449.6). Its duplexer, assuming it's pass/reject, and I can't imagine it wouldn't be if it's at a commercial site, should provide a fair amount of noise supression at the vicitim's receive frequencies in the 446.7ish range, though not the full 90 dB or thereabouts that it provides on the repeater's receive channel at 449.6. Maybe it's affording 40 dB or so of attenuation at 446.7 as a WAG. When combined with the spatial isolation between antennas (20 or 30 dB as another WAG), there should be a decent amount of noise attenuation already. In contrast, the victim receivers have no protection from the high-level signal from the repeater transmitter, hence I would expect the lack of carrier supression to be the first evil to combat. But, Tx noise supression via additional filtering on the repeater Tx may ultimately need to be added later if protecting the receivers from overload doesn't cure the problem. Again, without having measurement data to work with, it's hard to say for sure, but starting with filtering on the link Rx's seems like a logical first step. --- Jeff WN3A
