[time-nuts] Synths for FMT

Luca Dal Passo iw2lje at gmail.com
Fri May 15 07:52:02 EDT 2015


Hi Tim,
     is the received signals so strong that you can put them directly into
a mixer without amplification and filtering? I.e. without the radio
receiver?
      If not so, you can inject (couple) a local generated RF signal of
well-known frequency into the RF input of the receiver in order to
obtain the beat frequency between the far received signal and the local
oscillator. Don't you?
I've many times used this set-up.
In this case to obtain the various frequency you need, you can simply use a
sinthesized RF signal generator like some old hp, marconi, ReS and other
low cost surplus gears wich can accept an external 10 MHz reference.
In that way you can beat directly the received signal and the sinthetized
signal at the same nominal frequency,  and measuring the Phase difference
between the two signals. If the two frequency are quite similar, you can
measure the period of the movement of the receiver's S-meter. Obviously the
receiver must be set for AM mode in order to shut up the BFO and to measure
the beat on the s-meter
Many RF generators have 10 Hz resolution steps, so it could be impossible
to exactly zero-beat the frequency. In that case you can put an offset (es
. 1000Hz) and put the af beat tone available in the receiver's AF out, into
a low frequency counter (better some reciprocal counter).
Bye
Luca
iw2lje



Il giovedì 14 maggio 2015, Tim Shoppa <tshoppa at gmail.com> ha scritto:

> I'm thinking about sticking my toes in the water with the ARRL Frequency
> Measuring Test. http://www.arrl.org/frequency-measuring-test
>
> Frequencies used on the air, are 14121 khz, 7055 khz, 3598 khz.
>
> A current idea, is to use my Z3801A's 10MHz output to generate a LO that
> would be used with a mixer to convert the FMT's down to audio frequencies,
> to be recorded by a PC's sound card and then post-processed.
>
> Would feed the output from the mixer into one channel of the sound card.
> Would feed 10MHz/10000 = 1kHz square wave (derived from Z3801A) into other
> channel of sound card as a "Calibration" audio signal.
>
> LO Synthesis ideas:
>
> For 3598 kHz, make a 3600 kHz LO this way: Triple 10MHz to 30 MHz, then
> triple again to 90MHz, then divide by 25 to get to 3.6 MHz LO. This will
> result in an audio frequency circa 2kHz.
>
> For 7055 kHz, make 7058.8(...) kHz LO this way: Triple 10MHz to 30MHz. Then
> double and double again to 120MHz. Then divide by 17 to get to 7.0588MHz
> LO. This will result in an audio frequency circa 3.8kHz.
>
> Don't have any good ideas for 14121 kHz.
>
> Any thoughts?
>
> Tim N3QE
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