If it's mixing in the receiver or transmitter, notching one of the offending signals may help (such as a notch cavity on 152.240 or 152.840 MHz). Of course, it could be mixing in a number of other places, too.
Joe M. Joe Montierth wrote: > > It's not the 600 KHz that is the problem. The problem > is that the paging transmitters are spaced the same as > the TX/RX spacing on 2M, thus creating the possiblity > of a third-order mix. > > Here is what is happening, mathematically: > > 146.94 + 152.24 - 152.84 = 146.34 > > When all the transmitters are on, all three signals > are in the air at high levels around the site. > Anything that can mix could be creating the intermod > problem, from one of the amplifiers themselves, to a > preamp or even a piece of baling wire tied to a fence > post. The mixer doesn't have to be especially > efficient, since it is so close to the affected RX, a > few microwatts of re-rediated power may be sufficient. > That is why this can occur even when everyone has BP > filters and isolators and the transmitters look clean > on a spectrum analyzer. > > So a 600 KHz filter would be of no use. > > Joe > > --- DCFluX <[EMAIL PROTECTED]> wrote: > > > > > I didn't specify it had to be a cavity. > > > > Try shorted stub type, just steal a 1000 ft roll of > > standard issue > > cable guy RG-6 and go to town. > > > > Or use a L/C filter. > > > > It would be an intresting experiment anyway. > > > > > > On Wed, 22 Dec 2004 00:51:36 -0500, Thomas Oliver > > <[EMAIL PROTECTED]> wrote: > > > > > > Do you have any idea how big a 600 khz notch > > cavity would be? > > > > > > About 400 ft > > > > > > We had problems here in the Flint area with two > > paging transmitters that > > > were 600 khz apart also 152.240 and 152.840 one or > > both are off the air now. > > > > > > tom n8ies > > > > > > > [Original Message] > > > > From: DCFluX <[EMAIL PROTECTED]> > > > > To: <[email protected]> > > > > Date: 12/21/2004 11:09:12 PM > > > > Subject: Re: [Repeater-Builder] Digest Number > > 2865 > > > > > > > > > > > > What about building a notch circuit tuned to 600 > > kHz? And then put > > > > one each on both TX and RX? > > > > > > > > > > > > On Tue, 21 Dec 2004 20:06:10 -0800, Neil McKie > > <[EMAIL PROTECTED]> > > > wrote: > > > > > > > > > > > > > > > A new VHF paging system just was installed > > near here in the > > > > > last few weeks. > > > > > > > > > > Rich wrote: > > > > > > > > > > > > 155.820 > > > > > > BEND, CITY OF WNNU934 > > > > > > 100 watts Overturf Butte (Bend) > > > > > > 100 watts Awbrey Butte (Bend) > > > > > > 300 watts Wampus Butte (La Pine) > > > > > > 300 watts Gray Butte (Madras) > > > > > > > > > > VHF paging is apparently here to stay - > > whether we like it or not. > > > > > > > > > > Neil - WA6KLA > > > > > > > > > > > > > > > Dan Hancock wrote: > > > > > > > > > > > > We had exactly the same problem in Ann > > Arbor. The > > > > > > pagers were exactly 600 kz apart and up in > > the 158 Mhz > > > > > > segment. We installed notch filters and > > sharp > > > > > > band-pass filters on the repeater with some > > success. > > > > > > Nothing kept it our entirely. I was about to > > try a > > > > > > crystal filter on the front end when the > > interference > > > > > > just ended. One of the transmitters was > > taken off the > > > > > > air. Note though in our situation, the > > pagers were > > > > > > there first. > > > > > > > > > > > > I can't imagine in this day and age, with > > the death of > > > > > > VHF paging being on the near horizon, why > > anyone would > > > > > > put up a NEW VHF paging transmitter. > > However,if one of > > > > > > these pager transmitters is indeed a new > > installation, > > > > > > it may be possible to force them off the > > air. I can't > > > > > > quote the section, but the FCC told me one > > time in a > > > > > > different interference situation that a new > > or changed > > > > > > transmitter operation it totally responsible > > for > > > > > > solving interference related to their > > transmitter > > > > > > within 5 miles of their transmitter, even if > > their > > > > > > transmitter meets specs. This rule might > > possibly just > > > > > > apply in this situation. They have installed > > a new > > > > > > operation that produces an uncurable mix > > that wipes > > > > > > out your operation. That mix could be > > occurring in > > > > > > your transmitter, your receiver, one of the > > paging > > > > > > transmitters, someone else's transmitter, > > etc, etc, > > > > > > etc. I would suggest that you immediately > > contact your > > > > > > nearest FCC field office and discuss this > > with them. I > > > > > > wish I could give you the section, but the > > engineer > > > > > > who told me about it never actually quoted > > the > > > > > > section. > > > > > > > > > > > > Good luck. > > > > > > > > > > > > Dan Hancock N8DJP > > > > > > President, RADAR Inc. > > > > > > www.qsl.net/wr8dar > > > > > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > > > Yahoo! Groups Links > > > > > > [EMAIL PROTECTED] > > > > > > > > > > > > > > > __________________________________ > Do you Yahoo!? > The all-new My Yahoo! - Get yours free! > http://my.yahoo.com > > > > Yahoo! Groups Links > > > > > > -- > No virus found in this incoming message. > Checked by AVG Anti-Virus. > Version: 7.0.296 / Virus Database: 265.6.2 - Release Date: 12/20/2004 -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.296 / Virus Database: 265.6.2 - Release Date: 12/20/2004 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/
