RadioBanter - View Single Post

Geoffrey S. Mendelson · November 13th 07, 02:39 PM posted to rec.radio.amateur.homebrew

wrote:

When I say long range I am talking open distances between 5 km and 10
km radius where a receiver is established at the highest center point
within this radius and also elevated using a 20 meter antenna.

Is this for licensed or unlicensed operation? This is an amateur
radio group, but will it be extended to non hams?

Is this a "one off" unit, or do you plan to make
5? 10? 1,000? sell them to everyone on the planet?

What do you mean by the word portable?
Pocket sized?
The size of a book?
A small suitcase?

Will it provide it's own power?

How long will it need to run?

Ideally the transmitter will 'send' a three digit numeric code, such
as 101 or 102.

How? CW (switched carrier?) MCW (modulated switched carrier?)
Voice (AM? FM? SSB?), some sort of digital modulation?

Let's take a very specific example he

You want to operate licensed using the 2m Ham band.

You buy a stadard 2m FM "HT" (handheld radio) and add the following
equipment to it:

1. A larger external battery pack.
2. A tone generator for the modulated CW.
3. A device to turn on and off the tones and the transmitter.

Most modern radios can be placed in a standby mode which uses so
little power in relation to the transmitter that it is not needed
to turn them off. Doing so adds complexity to both the computer
program that controls it and the device itself.

A Palm pilot or similar device (think off the shelf technology),
to control it.

The program would be something like:

1. Turn on the radio.
2. Wait 10 seconds for the radio to turn on completely.
3. Turn on the tone generator. (may be generated by the controler itself)
4. Switch the radio into transmit mode.
5. Wait 3 seconds for the transmitter to stabilize.
6. Key the transmitter on and off to generate the message.
Unlicensed operation would use a simpler message, just the
transmitter ID, but some ownership contact information might
be usefull.

Licensed operation would be something like
"DE callsign/p id number". Different countries have different
requirments for unatended operation, including messages.

7. Turn off transmission.
8. Turn off tone generator.
9. Turn off radio.
10. Wait 10 minutes for next transmission.

If you do use CW or MCW, then it should IMHO be no faster than
5 words per minute. The idea is to be identifiable by as many
people as possible.

Range depends upon relative hight to the receiver, antenna type
and power output. It also depends upon what you plan to receive it
with.

I have researched existing products and have found one of the VHF
variety which would satisfy my requirements however it is exspensive
and not exactly of the 'portable' variety.

What I am looking for is suggestions on existing products or designs
that could be used to acheive my requirements.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/