Curt, I've also found some low noise pre-amps that have little tuning and are wide band can be zapped by static and lightning. The transistors used are for low level signals of course and can have problems dealing with sources like lightning.
Lightning energy has the RF properties of pretty flat DC to 1 MHz and then roll off at a 20 db/decade rate. So as you go higher in freq the less energy. Also as with any wide band signal the energy is spread over wide range. I can see you inserting a band pass cavity or filter will remove much of this energy reducing the affect on a pre-amp. 73, ron, n9ee/r >From: Curt Seaton <[EMAIL PROTECTED]> >Date: 2008/04/01 Tue PM 09:51:21 CDT >To: [email protected] >Subject: Re: [Repeater-Builder] Static on grounded feed line system. > >Something else to consider is what we experienced on our two and 440 >repeaters. Our 440 has a stationmaster type of antenna into the >duplexer into a preamp then into the Micor repeater. Most of the >electrical storms we had caused me to go to the site to replace the >preamp transistor. After many trips, I installed a single bandpass type >low insertion loss cavity between the duplexer and the preamp. That was >3 years ago... Then I found out that most all duplexers don't really >offer broadband selectivity, they do their main job of notching out the >appropriate frequencies to allow the repeater to do it's job, but then >several MHz away, the signals start slowly coming back in. Remember >lightning is quite broadband and strong. Our two meter repeater had a >bandpass in it's path also. It is my suggestion that in addition to the >all the appropriate grounding of the feedline that you may consider a >real band pass type of cavity (may be easier than to use a shorted stub >and more broadband) which has two independent loops in the cavity. >Sharpness is NOT needed here, so go for the lowest insertion loss and >let the loops do their static/lightning rejection... > >Good luck > >Curt W1FSM > >wa5luy wrote: >> Our repeaters are located on a 200 foot self supporting tower at the >> top of a 1200 foot mountain. Anytime there is a storm with in 50 miles >> we get a lot of pulsing static on the 2 meter repeater which is a >> Micor. This is not noticeable on the 440 repeater. We hear this when >> the receiver is open from a signal and when the repeater identifies >> with the receiver squelched. >> >> >> >> > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
