[ARDF] AM A2A Modulation...

[bruce]

(Re-sent to list on request)

Mark said:
> >     How do you look at a 2m transmitter output?  Are there
> > oscilloscopes that will go that fast, or do you need
> > something like an LO and a mixer?  An HT I was using right

I replied:
> Some cros will go that fast, but you're much better off with a spectrum
> analyser (basically your LO and mixer setup to scan over a frequency range
> automatically).
>
> >     It certainly sounds like the existing ways of achieving
> > A2A (as described by Dale) are simpler than an SSB design transmitter.
>
> Definitely agree there. The first of the 2 methods I mentioned for AM
> modulation is what Dale was describing in detail.
>
> >     My interest in A2A is primarily because I've hunted it,
> > and it's a lot harder than FM MCW.  I want to practice before
> > I have to hunt it in a big competition.
>
> OK I'm still going to diverge from what you say here.
> * Yes the A2A is harder to DF than FM MCW.
> * No, it is not necessary to build or even simulate a proper A2A transmitter
> to practice hunting International transmitters.
>
> The reason for the apparent contradiction in those 2 statements is that it
> isn't the modulation method that makes it harder, it's the fact that the
> carrier is also turned off and on.
>
> Using a whoopee sniffer (which I believe you do), you do not care how the
> audio is modulated because you never listen to it. You are only listening to
> the carrier strength. During a tone (dit or dah), the audio modulation is
> constant, so the sniffer sees it as a constant carrier strength. It makes no
> difference whether the audio is FM modulated, AM modulated or not modulated
> at all (pure CW).
>
> Given that fact, the only people the modulation method makes a difference to
> is those who listen to it and DF using audio strength, rather than whoopee
> tone. Even then, they are likely to be able to hear something, even if it's
> a receiver for a different modulation method (due to in-perfect design of rx
> and tx).
>
> You can go to a lot of effort to make a true AM and carrier pulsed
> transmitter, but if all you want to do is *practice* then I believe you are
> wasting your time. Simply use an FM handheld and control the PTT line
> (assuming the handheld doesn't have too slow a PTT response time) *or* build
> an unmodulated CW transmitter you turn on and off at the Morse rate.

Cheers,
Bruce