There are "frequency selective voltmeter receivers" you can pick up at Fair
Radio in Lima Ohio. I use one here. Currently they sell one with digital
readout, good from around 3 kHz to 18 MHz and with some good crystal selections
on the channel bandwidth. These types of receivers may or may not come with
agc! However since the software has agc that is not all that important. So
here you can get an awesome receiver from $100 to $200. Most all of the
circuitry is individually shielded in metal boxes. These have a big calibrated
field strength meter calibrated in dB's and micro volts and is used for
measuring rf in micro volts on antennas and in circuits as well as for closed
circuit cable communications of the fax and digital sorts before the Internet
days. AM and SSB are standard modes with these receivers. Usually the
demodulated audio is for a low powered 600 ohm line output to headphones. If
the current model does not have agc then listening to it straight up with its
own audio is too wild an experience.
I use these types of receivers with the i.f. going to another receiver that
has agc. I get a tunable and selectable front end this way with another
receiver acting as my last i.f. and demodulator section and up to three
receiver conversions in the set up. So I do not have allot of adjacent channel
bleed over and do not suffer i.f. images.
The frequency mixing scheme of the frequency selective voltmeter receiver is
such that you do not have i.f. images nor do you have birdies. These are high
quality test instruments. And although they are single conversion through a
crystal filter, as I mentioned, the rf scheme rids it of i.f. image problems.
Also, these receiver do not use tuned band pass circuits, everything is RC
coupled to maintain a constant impedance over the range of frequencies so the
meter will read the same for the same rf level at input regardless of frequency
{+/- a few dB's.}
Remember that these receivers provide you with an i.f. output jack.
If you want a really cool looking receiver that is also really big in size
and with a digital readout and several poles of filtering as well as SSB but
can not afford a Kenwood or Icom or Drake nor the Grundig Satelit 800 then this
is the radio for you especially if you want to go digital.
It is not a receiver for anyone who is not into electronics however. If you
have the skills to add agc or a detector board etc, then this is your type of
receiver and it doesn't cost as much as the Collin's receivers do.
I like using mine to surf around for BPSK signals.
Go to Fair Radio's site and you might find a photo and details on such a
receiver.
I never really used mine for a test instrument, I am too busy tuning around
on it everyday to listen to broadcast or looking to ease drop on QSO's.
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Also, do not forget that the little digital shortwave radios of the text book
size will look smart and give you some performance especially the dual
conversion models with 1 kHz tuning step resolution. Allot of them have steps
of 5 kHz. You can add an antenna jack if you get one without it.
I usually add one to three turns around the loop stick antenna rod grounded
at the far end and a capacitor to the HF antenna input and run both of these to
a RCA or some other female jack connector. Leaving the telescoping antenna
connected to the FM stereo.
Did you know that it is possible to add auto tuning to these little digital
receivers? It can be done by a Varicap diodes in the front end band pass
sections. It is most practical in the higher HF bands. The diodes alone
wouldn't tune much in range in the lower bands. This requires the main chip to
be programmed to send out a voltage. That will perhaps happen someday.
However you can do it now with a potentiometer to tune things manually. Who
would have thought?
Dan
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