With yours and Kevins reply, I have decided to go with a set of WP-643's and not use the WP-639's, I belive this would get me going. and if I need the pre amp then i will add it along with the pass cavities.
One more Quick Question, since i have the set of 639's here. what would the affect of two cans from the 639s be if added to the 643's receiver side beside the loss. Brent ----- Original Message ----- From: "Eric Lemmon" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, March 21, 2005 9:01 PM Subject: Re: [Repeater-Builder] Desense, I'm guessing? > > Brent, > > Although there are those who will disagree with me on this, I think your > WP-639 duplexer is simply not capable of sufficiently isolating your receive > and transmit frequencies. While the WP-639 may "get by" on a low-powered > system without a preamp, you may be demanding too much in your installation. > > Since the operating range of a repeater is limited more by its receive > capability than by its power output, it makes sense to maximize the receive > capability and run the minimum output power needed. > > First of all, the phrase "factory tuned" needs to be qualified. I will > readily acknowledge that the majority of big-name duplexer manufacturers have > the equipment (network analyzer) and expertise (highly-trained technicians) > to properly tune a duplexer exactly to your stated operating frequencies. > Very often, a factory-tuned duplexer is accompanied by a rather pompous > statement of the form, "This duplexer has been carefully tuned on > laboratory-grade equipment, and NO FURTHER TUNING IS REQUIRED." Yeah, > right! Unless I drove to the plant and picked up that duplexer myself, I can > guarantee that it will be jostled, dropped, and bounced around during > shipment to the point that it MAY be detuned enough to adversely affect its > operation. I always check duplexers, isolators, and cavity filters on my own > laboratory-grade equipment before installation, and I find perhaps 30% of > them needing realignment. Please understand that the detuning most likely > occurred during shipment, and is not the fault of the manufacturer. > > Whenever you put a preamp in front of a receiver, you really should put a > very narrow bandpass cavity filter in front of it. It always comes as a > surprise to neophyte repeater owners that a "bandpass/bandreject" or "BpBr" > duplexer has almost no bandpass action at all. The notch or reject action is > the major player, and the bandpass effect is minimal if nonexistent. > Moreover, nearby carriers can sail right through the duplexer and cause major > desense to your receiver. When you add a preamp, you are not just opening > the barn door wider, you are amplifying all of the intruders! > > My personal preference is for two 8" bandpass cavities set for a total of 1.0 > dB insertion loss after the receive side of the duplexer, and before the RF > preamplifier. Don't be tempted to use one 10" or one 8" cavity set for 1.0 > dB instead of two set for 0.5 dB each; the out-of-band rejection by two > cavities is much greater than one cavity by itself. This is something I > learned by experience- you can believe me now, or go off and find out for > yourself. Trust me, you WILL settle on a minimum of two cavities. > > In the present climate of terrorist activity and natural disasters, it does > not make any sense to deploy a repeater system that "barely gets by" or is > "good enough" for the majority of users. It makes me very proud to be a > member of an Amateur Radio group that designs and installs repeater systems > that are as good as, and in many cases are better and more reliable than, > commercial systems operated by public safety organizations. I sincerely wish > that all repeater operators felt the same way! > > 73, Eric Lemmon WB6FLY > > Brent wrote: > > > One of my 2m repeaters has a problem. It is a GE Mastr II base/repeater. > > I have a set of Wacom WP-639 on the machine, and an ARR preamp. ..a user > > 2 air miles from the site is wiped out of the > > receiver while the Tx is On, I turn the PA down below 20watts and he ( or > > all users) are clear. I have tried two different antennas before thinking > > about the duplexers, and want to double check other options before the > > cans.. these were factory tuned..cans. > > > > > > > > Yahoo! Groups Links > > > > > > > > --- > [This E-mail scanned for viruses at TNWEB LLC] > > > > > -- > No virus found in this incoming message. > Checked by AVG Anti-Virus. > Version: 7.0.308 / Virus Database: 266.7.4 - Release Date: 3/18/2005 > > -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.308 / Virus Database: 266.7.4 - Release Date: 3/18/2005 --- [This E-mail scanned for viruses at TNWEB LLC] 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/
