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

[DavidC]

> Log Periodic Antennas can overload the front ends of so called modern
> receivers and their untuned mixers.
>
>      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.

Don't have access to CQ Mag.  If someone finds this sure would love a copy.

>      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.  k7gco

Other than the high-end 1000MP and JRC JST-245 what others, please?
I expect many of us are priced out of those options so the passive circuit
will have to get it done ... in my case for my TS-690S/AT.

BTW:  One need not be a DX contester to need this feature.  Many Nets
suffer intentional and careless-operator QRM ... grossly over-driven amps
and
poorly designed (CB-type) amps exacerbate the problem.  When trying to
assist weak-signal missionary stations with phone patches I have encountered
a real need for high selectivity.

Thanks! & 73, DavidC  K1YP

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