Message	Date	From	Subject
278	2006-12-30 09:55:58	James Duffey	505 kHz Experiment
Rick - You wrote: "The receiver in the Kenwood transceiver tunes to the right frequency, but it isn't very sensitive there. Clearly a 500 kHz preamp is needed for the TS570. Time to dig into EMRFD." If Kenwood used the same philosophy in designing the TS-570 that they did with my TS-850, there is a 20 dB attenuator that is switched in from 500 kHz to 1700 kHz to avoid broadcast band interference problems. There is a mod to bypass it, but I am always leery of modifying commercial equipment. There are significant advantages to homebrew rigs in this respect. I suppose you could put a 20 dB preamplifier in front of it, but that does seem to be the radio equivalent of an oxymoron. I suppose the noise figure will be poor with the attenuator, but that may not be a problem at those low frequencies. Somewhere between the brain cells, the drawing board, and the workbench I have plans for a 500 kHz receiver forming. I thought of starting with a DC receiver, but the VFO inductance is huge and I don't think it is easily realizable with reasonably sized low temperature coefficient iron powder cores. So that means air core inductors I guess, which one would need for the input filter anyway. I am not sure of how stable reasonable air core forms are. I obviously need some more thinking here. I have lots of other ideas for the receiver and with the potential of a new ham band at 495 to 513 kHz, I need to get it all down on paper and implemented in parts. - Dr. Megacycle KK6MC/5 -- James Duffey KK6MC/5 Cedar Crest NM 87008 DM65
279	2006-12-30 10:47:14	Jim Miller	Re: 505 kHz Experiment
i know it sounds like overkill but my first thought is that a dds might work quite well at these frequencies since the sampling rate and therefore many if not all of the spurs should be quite far from the frequency of interest. 73 jim ab3cv

Rick - You wrote:

"The receiver in the Kenwood transceiver tunes to the right frequency,
but it
isn't very sensitive there. Clearly a 500 kHz preamp is needed for the
TS570. Time to dig
into EMRFD."

If Kenwood used the same philosophy in designing the TS-570 that they
did with my TS-850, there is a 20 dB attenuator that is switched in
from 500 kHz to 1700 kHz to avoid broadcast band interference problems.
There is a mod to bypass it, but I am always leery of modifying
commercial equipment. There are significant advantages to homebrew rigs
in this respect. I suppose you could put a 20 dB preamplifier in front
of it, but that does seem to be the radio equivalent of an oxymoron. I
suppose the noise figure will be poor with the attenuator, but that may
not be a problem at those low frequencies.

Somewhere between the brain cells, the drawing board, and the workbench
I have plans for a 500 kHz receiver forming. I thought of starting with
a DC receiver, but the VFO inductance is huge and I don't think it is
easily realizable with reasonably sized low temperature coefficient
iron powder cores. So that means air core inductors I guess, which one
would need for the input filter anyway. I am not sure of how stable
reasonable air core forms are. I obviously need some more thinking
here.

I have lots of other ideas for the receiver and with the potential of a
new ham band at 495 to 513 kHz, I need to get it all down on paper and
implemented in parts. - Dr. Megacycle KK6MC/5

--
James Duffey KK6MC/5
Cedar Crest NM 87008
DM65