[Repeater-Builder] Preamp Info Wanted
Hello to all and thanks for reading. I am in the market for a preamp for my 2 Meter repeater. I am not looking to invite intermod so am asking for suggestions on what to buy. I am only looking to compensate for losses in feedline-cavities so huge gain is not required. As a matter of fact, I am assuming I will have to use an attenuator in front of the preamp. Anyway, any advice on a brand/model of preamp you have used successfully greatly appreciated. 73 de W2AFD Howard
Re: [Repeater-Builder] Preamp Info Wanted
we use a lot of TX RX products John - Original Message - From: Howard To: Repeater-Builder@yahoogroups.com Sent: Friday, May 16, 2008 10:56 AM Subject: [Repeater-Builder] Preamp Info Wanted Hello to all and thanks for reading. I am in the market for a preamp for my 2 Meter repeater. I am not looking to invite intermod so am asking for suggestions on what to buy. I am only looking to compensate for losses in feedline-cavities so huge gain is not required. As a matter of fact, I am assuming I will have to use an attenuator in front of the preamp. Anyway, any advice on a brand/model of preamp you have used successfully greatly appreciated. 73 de W2AFD Howard
Re: [Repeater-Builder] Preamp Info Wanted
Howard, there are a couple of things to keep in mind on installing a preamp: 1. The losses in the duplexer and feedline cannot be made up in a preamp placed at the receiver input. You can increase the receiver gain with a preamp, but those losses are not recoverable. 2. You want to place the preamp at the output of the duplexer and put the attenuator between the preamp and the receiver. If you have a good preamp with a high level intercept point, you can usually gain a few dB if the repeater receiver is not as sensitive as it could be. Sensitivities in the order of .35 uV for 12 dB SINAD are common and they can be improved with a preamp, but if you are already using a receiver with .15 or so sensitivity, you will not be able to see any improvement by adding a preamp. In fact, it is quite possible to decrease the sensitivity due to overload in the preamp. Do a test on the repeater receiver to see what it's sensitivity is at present and compare to the figures given above to see if a preamp can add any useful sensitivity to the system. Often you can gain some sensitivity by using an Iso-Tee at the antenna port of the duplexer to inject the signal generator and tune the receiver front end through the duplexer thus compensating for any reactance in the duplexer. Using a SINAD test and tuning for best quieting will often result in improved sensitivity over using a meter on the first limiter to tune up the receiver. Hope this helps - 73 - Jim W5ZIT Howard [EMAIL PROTECTED] wrote: Hello to all and thanks for reading. I am in the market for a preamp for my 2 Meter repeater. I am not looking to invite intermod so am asking for suggestions on what to buy. I am only looking to compensate for losses in feedline-cavities so huge gain is not required. As a matter of fact, I am assuming I will have to use an attenuator in front of the preamp. Anyway, any advice on a brand/model of preamp you have used successfully greatly appreciated. 73 de W2AFD Howard _
Re: [Repeater-Builder] Preamp Info Wanted
Jim Brown wrote: Sensitivities in the order of .35 uV for 12 dB SINAD are common and they can be improved with a preamp, but if you are already using a receiver with .15 or so sensitivity, you will not be able to see any improvement by adding a preamp. In fact, it is quite possible to decrease the sensitivity due to overload in the preamp. This is a very good, succinct sentence that says it all. Nicely done, Jim. Do a test on the repeater receiver to see what it's sensitivity is at present and compare to the figures given above to see if a preamp can add any useful sensitivity to the system. Agreed here too. As my elmers taught me... If you didn't measure the system before you made the change, how do you know if you made it better or worse? To get maximum performance out of any system, is a process that includes full performance measurements BEFORE adding or changing anything. If you KNOW your usable receiver sensitivity going in, including site noise with the antenna connected, and perhaps some other basic things like the noise-figure of your chosen receiver... You can then choose appropriate pre-amplification and filtering to match the circumstances that match your particular radio, antenna, duplexer... or what I call overall system configuration. What kind of VHF receiver is it? What's the factory spec for 12 dB SINAD? Is it already performing to that level? That's first... then pre-amps. One logical step at a time... is the easiest way to find maximum receiver performance. Nate WY0X
RE: [Repeater-Builder] Preamp Info Wanted
Great info given But something else to consider Where is the Repeater Located , Maybe a Place You cannot get to Easy in the winter on a Mountain Etc , I use the advanced research Preamps on My 440 and 220 Repeaters , They work Great Except when the GasFet goes Bad it is Like a 20 DB Or more of Attenuation, it Has only happened twice in 5 Yrs. I do Not know if they are all like that. Happy Repeater Building Don KA9QJG
