The remote capacitor switching is interesting. Perhaps something like
the switching methodology used with remote antenna switches - a DC
voltage that fires one of N comparators. Thanks for the suggestion.
N4BFD suggested putting a 160m bandpass in series with the ICE highpass.
Also a good idea. Losses aren't a huge problem on 160.
As for using the 5000A RX2 and the phasing features of the upcoming 2.X
PSDR releases with the loops, that hadn't escaped me and it is worth
experimenting with. (I do have the RX2) I'm considering an external box
in the long run only because I could then use my other radios with the
system as well. They're all multiple conversion and most have fairly
solid front ends, but the phase summing/cancellation ability would be
useful there are well.
73,
Jim N7CXI
On 11/3/2010 12:43 PM, Brian Lloyd wrote:
On Wed, Nov 3, 2010 at 12:21 PM, Jim Barber <audio...@charter.net
<mailto:audio...@charter.net>> wrote:
A razor-sharp, canyon-deep 160m-only preselector would be a prized
accessory here, if one existed.
Well, have you considered multiple, loosely-coupled, tuned, parallel LC
networks? It worked for the old TRF receivers.
Even with a ICE BC high-pass in place, when I switch my 160m
"inverted L" antenna in on RX with the 5000A I still get BC images
well above the noise floor, although their amplitude is dramatically
reduced over not using the filter.
BCB signals are *STRONG*. We get so used to signals only a few dB out of
the noise that we forget just how much power reaches an antenna from a
50kW station a few miles away.
(The kids here at school build crystal sets. It is not unusual to see
FOUR VOLTS of audio at the headphone jacks. I would not be surprised if
I could drive a speaker with a proper matching transformer.)
No room here for Beverages, rhombics or other directional wires,
unfortunately.
One of my potential winter projects this year is a pair of remotely
tuned, rotatable shielded loops with a phasing/phase noise
elimination unit in the shack.
If you have the 5000 with RX2 then you already have what you need for that.
I'm hoping to be able to use varactors for tuning the loops, but
given the (very) high BC field strength here and the relative
proximity to my TX antenna (less than a wavelength) I'm not sure yet
whether that will work out.
Remember varactor multipliers? No, that is probably not a great idea. A
series of high-quality caps switched inb parallel in a binary pattern
might be good.
In any case, 160m operation at my QTH with the 5000A is problematic.
I have other radios, but now that I've gotten used to the AGC
threshold feature, the panadapter and the overall sound of the 5000A
receiver, my preference is to use it and "damn the torpedos"... :-)
I know how you feel.
Ideas solicited, of course.
I like your shielded loop idea. And a high-Q loop is going to function
like a preselector too.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
br...@lloyd.com <mailto:br...@lloyd.com>
+1.767.617.1365 (Dominica)
+1.931.492.6776 (USA)
(+1.931.4.WB6RQN)
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