Your problem... a few suggestions 1. Has anything physically changed with your stuff or with others that you can notice?... new equipment in the shack?.... a new installation nearby? Nexrad radar perchance? Now there's a nice squarewavy broadband noise generator... We have a similar such beast here. In other words what's new??
2. Have you looked at the adjacent channels witha mobile using the RX antenna ... up or down...does noise still appear...does it only appear with the repeater TX up and in transmit mode? 3. Spectrum analyser... I'd borrow one. Looking through on the RX antenna.. ( you might need to try to notch out that FM transmitter or it may overload the spectrum analyser).. you may need to go transmitter hunting with it in the mobile too... 4. You got a military base nearby? No kidding! We and just about everyone else suddenly had all kinds of white noise racket on our UHF repeaters... quickly traced it to some military exercises being conducted with the US and the Canadian military (such as it is)... AWACS radar and or whatever other strange RF cloaking devices they were using in those planes were ripping up the entire UHF band... there were some unhappy campers around here for a day or so... If it's the military your probably outa luck.... they march to a different drummer. 5 If you can see it on a mobile RX input... (is it only there when the repeater transmitter is on?) drive around and see if the noise peaks locally....if it is only there with the TX... it may be a new digital (P25?) service that's become an IMD product. 6 Have you checked the SWR on the RX antenna? How long has it been there... corrosion/dioding from a loose swaged joint?... there may be another TX nearby (other than you own) that's creating dioding noise from oxidized joints? Does this appear all the time? Did the problem start slowly then eventually become 24/7? 7. Ok I just went through this yesterday installing yet another VHF/UHF box for a ham group... (I've been poking around with repeaters since the 70's) Cables new... moved? Try moving cabling and coax...Biggy!! bad or improperly installed coax connectors? .... how old is the intercabling coax..RX to filters/duplexer etc? Using some of that 40% braid crap that Tandy/RadioShack used to sell back in the '80s when copper went big money?? Get rid of it!! Get good quality (Amphenol) RG 213/8u, LMR or RG 214 (my preference) Use an RX preamp? Take it out if you use one and try again. If you are using one of those untuned 20db gain broadband preamps with a j-fet.... throw it away!! Get a proper one with a helical front end if you must. 2000' should be adequate antenna separation @600khz ...unless your running big power... 250 watts or more. that's almost half a mile! Desense is probably not the problem. Happy hunting.. witha bit of work you should be able to figure out what that noise is. VA7AA ----- Original Message ----- From: "skipp025" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Friday, May 26, 2006 8:47 AM Subject: [Repeater-Builder] Re: White Noise on Two Meters..... >> I have an interesting thing happening on our two meter >> repeater. We have what appears to be a blanking white >> noise that is present on the input. The repeater is a >> split site system with a 440 link from the two meter >> receiver site over to the transmitter site about 2000ft >> away. There are no duplexers in the system to cause problems. > > Duplexers cause problems..? > >> The link on 440 is clean of any noise, so we are quite >> confident the link is not a problem. > > You could easily test the link for proper operation if not > already done. > >> On two meters, when a signal is anything less than full >> quiteing, we get a white noise that will almost mask the >> audio. We have tried different receivers such as the GE >> MVS and now a GE Master II. We have removed the preamplifier >> with minimal results. > > Have you listened on the receiver frequency with other radios > on different antennas..? even a mobile in front of the > building? Do you have access to another antenna or antenna port > at the same site/location? > >> The receivers have excellent sensitivity and the tuning >> process of the receivers is correct. We have also tried >> putting pass cavities ahead of the receiver with no >> appreciable change. The antenna is a DB-224 mounted on >> a broadcast tower just below the bays of an FM broadcast >> commercial transmitter. We have turned OFF the fm broadcast >> transmitter at times to check if perhaps this was the >> problem but no change was noted. > >> > ANY IDEAS from anyone??? >> > THANKS! >> > Gary - W5GNB > > Sure, hang another antenna at ground level and listen to the > frequency for a problem on-channel signal. If it's something > related to the current antenna system, the test antenna would > be a big hint for removing the repeater antenna from the problem > list. > > If the problem is an on-channel signal, you might hear it on > the test antenna. If you're able to get away from the building on > the same mountain top... you might be able to figure out if any > problem on-channel signals are sourced from the same building. > ... and with a bit of basic DF Homework you could possible source > a problem signal to other locations. > > The quesiton: Is a problem on-channel signal near or far? > > cheers, > skipp . > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.394 / Virus Database: 268.7.2/349 - Release Date: 5/26/2006 > > Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
