suggestions on concept : agent to local hq, using MW or FM band to transmit information

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Date: Wed, 6 Apr 2005 03:12:54 -0700

>> How can an agent contact a local HQ using a MW or FM band transmitter and
>> primitive signalling (like polytone or even Morse code) using the most
>> primitive of equipment.

Yes, this is the 'capture effect' very true for FM transmission systems.
>> For MW transmission, frequencies in-between local high power carrier
>> waves seems to be safer with respect to escaping detection as most
>> receivers are digital these days and cannot tune in-between channels. The
>> same concept applies to FM, albeit I suspect that only Morse code would
>> be used to keep the transmission 'narrowband'.
>
> Modern FM tuners, even pre-digital, lock on to the strongest of several
> signals at a give frequency. Casual FM listeners won't hear your agent's
> broadcast unless it's so close that it's the strongest signal. I expect
> there are tricks that HQ can use to extract your agent's signal.

I am not 100% behind morse code as it has a higher EIRP than narrow RTTY
using somthing like BPSK. The signal could be AM modululated, as opposed to
narrowband FM. I assume that the transmitter would lock on to the carrier
and MPX and RDS carriers to guarentee frequency stability.
>> I am assuming some crypto comes into play, but 'simple' hard crypto is
>> preferred conceptually.
>
> You can encipher your message into alphabetic ciphertext, then send the
> ciphertext using Morse code.

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