[Top] [All Lists]

[TowerTalk] Do Log-Periodics Stress the Selectivity of theReceiver?

To: <>
Subject: [TowerTalk] Do Log-Periodics Stress the Selectivity of theReceiver?
From: (
Date: Fri, 26 Nov 1999 13:48:42 EST

<< Log Periodic Antennas can overload the front ends of so called modern 
receivers and their untuned mixers.  One time 2 years ago 10M was really open 
and I was 40 over 9 four contacts in a row on the East coast.  They 
complained I had distortion until they switched in the attenuator.  Stations 
were breaking in and complaining that weren't even on the frequency and they 
didn't even have LP antennas.  When the bands really open up there is going 
to be a big problem with many untuned mixer receivers. 
     There is a passive circuit that uses 2 tank circuits back to back 
connected with a small capacitor between them.  It inverted the 50 ohms up to 
a Hi-Z and then back to 50 ohms which creates great selectivity.  It has 2 
simple tank circuits per band and fully peakable on any frequency.  I intend 
to build it myself and will have to find the circuit.  In was in CQ.  Look 
under all band preselectors.  Just going through a regular antenna tuner will 
give some selectivity. 
     When the bands open I'd suggest testing a several new rigs first on a 
coax switch on trial to see how selective it is to adjacent 
frequencies--before buying.  There are a few rigs now that are OK.  You don't 
need to switch the attenuator in to solve the problem.  There are advanced 
AVC circuit requirements for DXers that allow working 300/hr on CW in 
contests.  The 1000MP has a modification just for that and it works.  in a 
contest one time a top operator was monitoring another top operator on SSB 
and found that he was missing letters of a call that he wasn't.  They 
switched rigs and determined it was the rigs.  They would have assumed it was 
just too much QRM without the side by side test.  Design requirements are 
very severe for the DXer.

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>