Hi,
I tried some googling but nothing useful came up.

I would like to build a lightweight SSB voice keyer for battery
operated portable operations (VHF contests and the like).

MP3 players are getting cheaper every day, they're *small* and
*lightweight* and their batteries last long enough for a typical
contest.

Has anyone seen a design of an interface between MP3 players and HAM
transceivers? Modern RTX could easily use the VOX facility, but older
gear (like my Yaesu FT-290R) would need external PTT keying.

Any idea? Would a "standard" VOX circuit do the trick?

Thanks,
Paolo IK1ZYW

On 8 Aug 2005 01:43:39 -0700, wrote:

[snip]

Has anyone seen a design of an interface between MP3 players and HAM
transceivers? Modern RTX could easily use the VOX facility, but older
gear (like my Yaesu FT-290R) would need external PTT keying.

Any idea? Would a "standard" VOX circuit do the trick?

http://www.tigertronics.com/

73,
Danny, K6MHE

email: k6mheatarrldotnet
http://users.adelphia.net/~k6mhe/

A part of a solution: since pretty much any commercial mp3 player will
handle stereo, assuming sufficient channel separation, put your desired
voice on one channel and a tone on the other channel. Then use a
simple circuit to sense the tone and key a relay (or maybe even just
turn on a FET) to turn on the transmitter. Use a fairly high frequency
for the tone, and the response could be very quick. In simplest form,
the tone detector might not need any frequency filtering at all--just
detect presence vs absence of a signal. Difficulty is that you need a
way to put the tone on with the voice--easy enough if you can
pre-record all you need, but a bit more difficult if you want to change
the messages real-time. An advantage over simple VOX is better control
of the time the xmt line is activated.

I'm not sure if it would be any value, but you could also use different
tones to key different things; standard DTMF would be one way to do it,
but even just properly chosen single frequencies could work. And if
the player can reproduce high audio frequencies OK and you only need
voice bandwidth for your audio out, you could even put both the tones
and the voice on one channel, and filter the tones (or let the xcvr's
audio path-if filters do it).

Cheers,
Tom

K7ITM wrote:

Hi Tom

A part of a solution: since pretty much any commercial mp3 player will
handle stereo, assuming sufficient channel separation, put your desired
voice on one channel and a tone on the other channel. Then use a

I did think of that too, and should be pretty easy to build with a .wav
editor on any PC. My only concern is about channel separation in the
pocket player, and whether MP3 compression would throw away the tone or
not.

Because of MP3 compression I think the tone should not be chosen either
too high or too low.

I'm not sure if it would be any value, but you could also use different
tones to key different things; standard DTMF would be one way to do it,

Well, walking uphill with antenna, RTX and battery (one each) is tiring
enough - that's about 3kg -, having even more radios is not for me. :-)


Thanks for your suggestion,
Paolo IK1ZYW

I did think of that too, and should be pretty easy to build with a .wav
editor on any PC. My only concern is about channel separation in the
pocket player, and whether MP3 compression would throw away the tone or
not.

It depends upon the compressor and the type of compression chosen. There
are three options in most compressors: Mono, Joint Stereo and Stereo.

Keep in mind that MP3 files are really MPG movie streams with no video.

Mono is obvious.

Stereo is two seperate mono channels. This is best for programs with
multi language sound tracks.

Joint stereo is the same system used in FM stereo. FM uses a SUM track
(mono) and a DIFFERNCE track. I think MP3's use one track and a difference
track. Since it is decoded by a computer, this saves processor time
over the sum and difference which requires two tracks to be calculated
after decompression instead of one.

Because of MP3 compression I think the tone should not be chosen either
too high or too low.

Anything in the higher audible range, say 300 Hz on up, but 2600Hz is
sort of a standard in the telephone industry and 1000Hz in the audio visual,
so your choice may be influenced by what you can find easily.

Analog phone cells identified themselves with tones in the 5kHz range.
They were used to determine which cell your phone was actually receiving.
Obvioulsy the phone filtered out the tone.

A simple set of capacitor audio filters such as the ones used in SCAF
units would do the trick and you could use a mono signal. You just make
a 3kHz low pass filter for the audio and a 4khz high pass filter
for the control signals.


I'm not sure if it would be any value, but you could also use different
tones to key different things; standard DTMF would be one way to do it,

DTMF would be simple to use, encoder and decoder hardware is very easy
to get and well documented. The tones are audible so you would need
to use two channels, or introduce a delay to prevent them from being
transmitted.

The old motorola pagers used reeds at very specific filters. Subaudible
for signal identification and audible tones to unlock the recevier.
You may be able to find lots of them in junk bins.


Well, walking uphill with antenna, RTX and battery (one each) is tiring
enough - that's about 3kg -, having even more radios is not for me. :-)

You could just get a bunch of audible greeting cards (or the chips from
inside them) or use a pocket pc or late model Palm.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (077)-424-1667 IL Fax: 972-2-648-1443 U.S. Voice: 1-215-821-1838
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