June 2012
Does anyone know of a VHF receiver that will tune in AM/SW signals after they've been frequency shifted up to the 216-302 MHz range? I would like to isolate the 500 kHz - 22 MHz band from a directional AM/SW antenna and use a local oscillator to raise them to 216-237.5 MHz. Then, I'd like to do the same for three other directional antennas to end up with four intermediate frequencies ranging from 216-302 MHz. I'm worried that a typical VHF tuner will only look for FM signals, of the wrong channel width, within the VHF band. These four new intermediate frequencies will now be high enough to make it through amplifiers (usually limited to 54-894 MHz) on our local cable system. I know that a local oscillator could be used at the receiver to bring them back down to their original range for use with a regular AM/SW radio, but I'm looking for an off-the-shelf solution without a hardware modified receiver. Can the "Uniden Home Patrol" or "GRC PSR-800" receivers have their Flash memory stored software modified to do this? The four separate intermediate frequencies will give the end user access to their choice of signals from four different directions. Something low cost, with an internal power supply (no wallwarts), and include Digital or SSB would be ideal. Thanks.
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My Realistic PRO 2004 allows the selection of AM detection at any time, and those receivers can be found on eBay for a pretty low price these days. You would be stuck with a fixed frequency step and no BFO, but that's probably fine for listening to foreign broadcasts. Another approach is a software-defined radio like the Funcube Dongle. That will require a computer, but it is really flexible and there's amazing free software, too. I'm surprised that you have that kind of directionality for such a wide frequency range; I would think that two antennas would be about as good as you can do.
A typical VHF receiver will only look for FM wide/narrow signals. At times I've noticed that even so, this type of receiver can sometimes "hear" an AM signal, not perfectly clear but understandable.
Better would be a wide-band or VHF/UHF "ALL-Mode" receiver that you can select the type of demodulation to use. My Alinco X10 is able to do what you're after. Can you borrow something like that? (There are so many on the new & used market!)
I checked eBay.com for "wideband receiver" and came up with a bunch from ~ $100 - $800 (Kenwood RZ-1 Wide Band Receiver) - (AOR AR-8600MK2/AR8?600MK2 Wide Band & ALL MODE Receiver/Scanner -unblocked- NEW)
Then there are the receivers in the thousands topped off with the new AOR AR5001D Wideband Receiver (DSP receiver) at $5,000.00
If you're going to bid/buy be careful! You need to make sure it can use any demodulation method, in your case AM/FMW/FMN at least, on any received frequency.
73 73 de ke3fl,
Your shortwave distribution via cable TV sounds most interesting!
I have reviewed the specs for the PSR-800 and Uniden Home Patrol receivers and find them to be less than ideal for your purpose.
1) The channel step size for these receivers is 6.25 kHz for the PSR-800 and 5 kHZ for the Uniden. Many longwave and shortwave stations are best resolved on 1 kHz or 9 kHz channel steps or smaller. Your listeners will not be able to tune in all stations.
2) The AM channel bandwidth for these types of receivers is in the order of 12 to 15 kHz which means that several stations may be heard at once.
Most shortwave receivers offer a 3 or 6 kHz filter bandwidth to better resolve shortwave stations.
A receiver such as the AOR8200 MK3 or one of its desktop equivalents, or one of the ICOM professional receivers such as the ICR-8500 (now obsolete) would be a suitable receiver and will permit CW, USB, and LSB reception.
You mentioned the use of a local oscillator as a down converter at the receiving end to facilitate use of a standard shortwave receiver. This would be an excellent option as you could use the frequency selector knob of the LO to directly steer your directional antenna selection (N,E,W,S) without having to retune the receiver. This would be functionally a superior method. Secondly, the use of a down converter frees the listener from having to calculate the LO offset used for each frequency and directional antenna.
The selection of shortwave receiver should be models which permit direct connection of an external antenna (the down converter output). In this way, interference from over the air signal to the cable provided signal can be minimized. There will be a delay, and resulting tone difference between signals leaking in from over the air and those of the cable system, so use of well shielded coax is recommended.
Something you should consider is that the TV channels on the cable system are generally adjusted so that their amplitude is equal on each channel to minimize reception of inter-modulation (IM - channel mixing) artifacts on television channels. Your shortwave channel will demand a larger dynamic range to receive weaker shortwave stations, so it is possible that IM products from the TV channels will be heard within the shortwave pass band. Likewise, the shortwave signals presented to the head end will have to be adjusted so that the aggregate power (in a 6 MHz channel bandwidth) does not exceed that of the channel power of the TV channels, or TV reception may be bothered.
You might also consider use of an FM modulated up converter and FM demodulator/down converter method where the 500 kHz to 22 MHz "base band" is directly applied to an FM modulator and recovered from a demodulator at the receiver. You may be able to find some suitable commercially available CATV FM video modulators and demodulators that will interface directly at the head end.
I experimented with this technique over an FM microwave link and it worked well, and because the base band is faithfully demodulated, there was no frequency translation error in the recovered signal.
Good luck on this project. I would be interested in hearing how it works out.
