Batboard

Every radio product that uses an I/Q modulation scheme is technically capable of operating in AM, FM, phase modulation, or any of a large
variety of phase-shift keying schemes, including C4FM, CQPSK, QPSK, QAM, and others, depending on the properties of the supporting hardware and operating code.

The Astro hardware is definitely CAPABLE of operating in AM mode. The firmware MIGHT be, and certainly could be if it were reflashed as
needed, and then controlled by a modified form of the RSS or CPS knew how to instruct it.

Utility: The VHF Astros will, if opened up by means of the frequency limits hacks, extend well into the aircraft band WITHOUT modifying
the VCO circuitry. A few component value changes to the VCO circuitry would likely allow the VCO to lock up through the entire aircraft
band, and some retuning of the transmitter and receiver circuitry by means of accompanying parts value changes (and maybe some
minor circuit modifications) would allow reasonable performance down at this low range.


So, has anyone ever done any serious exploration along these lines? I for one would like to have an Astro that could be used to monitor traffic
on the aircraft bands, in addition to normal FM traffic.


Elroy

We use it in our newer FPGA controlled digital radios, AM demodulation is simply the
square root of(I^2 + Q^2).

But then you also have to set the band limiting filters IE IIR and FIR digital filters which would be major code change in the radios firmware.

I'm not sure if the Motorola ASTRO radios use a DSP based or FPGA based demod scheme, it is much easier to do in a FPGA than in a DSP but it's theoretically possible if you could get the radios reflashed.


Mike

we use our 800 Mhz Astros to listen to the air band without a problem.
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Okay so I have a reciever permanently patched to a talkgroup on the CEB.

A VHF Astro, taken down into the air band, WILL pick up SOME intelligible signals off of air band transmissions, by "slope tuning" on them,
which is purely a matter of signal strength and luck.

Elroy

That would be awesome if a VHF Astro could Rx/Tx in the aircraft band. Then I can listen to the local PD and use it as a backup aircraft radio! Certainly takes some weight off my flight bag.

Keep in mind the radio won't be wouldn't get you onto the FCC or FAA's chritmas card list if you were caught transmitting there with a non-approved radio.

For safety's sake, I'd stick with a proper airband radio if I were you.

Well, here's some interesting results. I was able to take a VHF Astro Saber down to the ATIS frequency of the local airport (133.100). It locked just fine. And heck, it even received! As you can imagine, receiving AM on an FM radio isn't exactly the best thing in the world, but I found going a few kHz off frequency (as in 133.0875), I was able to actually understand what was being said.

While it's certainly no AM receiver, it does a good enough job providing there's a strong enough signal. I didn't try transmitting, but I can't imagine you'd have much luck.