Hello,

I am trying to design and develop a long range portable transmitter.

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.

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

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.


Thank you.

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/

Hello Geoff,

Thank you for your response.

Is this for licensed or unlicensed operation?

Eventually licensed.

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

I plan to replicate approximately 10 to 15 transmitter units and one
receiver. This project is for a volunteer organisation.

What do you mean by the word portable?

When I said portable, I was referring to it being independant of an
external power source or external mounted ariel. It's ideal size would
be similar to that of a book, preferably a cellular phone, however
cost is the main consideration.

Will it provide it's own power?

Yes.

How long will it need to run?

There is no operating time requirement, the only time related
requirement is that the power source lasts long enough to transmit a
simple message.

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

I was thinking AM or FM however CW is an option.

Whichever is the cheapest component wise and irrespective of the power
requirements, is portable and can transmit at the desired range of 5
km to 10 km.

wrote:
Thank you for your response.

You're welcome, I hope this helps.

Is this for licensed or unlicensed operation?

Eventually licensed.

Ok, then I would start off with what is called in the U.S.
Family Radio Service "walkie talkies". They are cheap,
easy to buy and availble almost anywhere. In the U.S.
they operate on 464 mHz, in most other places 446 mHz.

They have a relatively short range. Stated range is 5 to 10
miles, but unless you are on a mountain top talking to someone
on another mountain top, it's more like 1km or less.

However they can be used without a license and as I said,
cheap. Good to experiment with.

I plan to replicate approximately 10 to 15 transmitter units and one
receiver. This project is for a volunteer organisation.

Ok, then I would look into making a controller board or interface
on a printed circuit board. There is plenty of design software
around and you may be able to find a shop that does low quantity
boards for amateur use.

When I said portable, I was referring to it being independant of an
external power source or external mounted ariel. It's ideal size would
be similar to that of a book, preferably a cellular phone, however
cost is the main consideration.

FRS units have permantently attached ariels. Ham radios have removable
ones so you can start with a "rubber ducky" type and upgrade to a
dipole. A 2m antenna is 38 inches long, around 1 meter.

There is no operating time requirement, the only time related
requirement is that the power source lasts long enough to transmit a
simple message.

A battery pack with AA batteries will run one for several hours of
sending short messages. You can use disposable batteries or
NiMH rechargables for longer battery life. NiMH batteries lose
their charge over a week or so, and have problems "floating"
on a charger, so if they have to sit in a box waiting for
an emergency, alkeline disposable batteries are IMHO better.


I was thinking AM or FM however CW is an option.

Cheap handheld units are normally FM, this includes FRS type,
70cm and 2m ham radios and 49mHz unlicensed ones.

27mHz CB type radios are AM (and expensive ones SSB), but in the U.S.
are restricted to voice only by law. They do have a wider range in
most cases.

As for the controllers, the question is exactly how "off the shelf" do
they need to be? If you have someone on the project who can figure out
how to add the switching logic and a someone to modify the operating
system for you, discarded iPods would be perfect. There are lots of
them lying in drawers, being too good to throw out and too expensive
to fix (mostly battery replacement).

You could also do it with old pocket PC's, Palm Pilots, etc. Probably
more easily.

What ever you do, try to get 20-30 of them before you start, several
will fail or be broken in development and it's difficult to start
over again because you ran out of parts.


Whichever is the cheapest component wise and irrespective of the power
requirements, is portable and can transmit at the desired range of 5
km to 10 km.


That will have to be found out by testing. 10km in London, New York, or
Jerusalem will be very difficult, while 10km in a flat area will be
easy.


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/

Geoffrey S. Mendelson wrote:
As for the controllers, the question is exactly how "off the shelf" do
they need to be? If you have someone on the project who can figure out
how to add the switching logic and a someone to modify the operating
system for you, discarded iPods would be perfect. There are lots of
them lying in drawers, being too good to throw out and too expensive
to fix (mostly battery replacement).

After I wrote this I was looking through an old magazine and found a
cicruit to take the output of a tape recorder and use it to key
a transmitter. This one used a single transistor and a relay.

I would update it a bit and instead of using a tape recorder, I
would use a small MP3 player. The kind that use a single AAA battery,
and look like a package of chewing gum sticks.

If you modify them to run from external power, will run for almost a day
on a high capacity AA rechargable battery.

If you create an MP3 file with what you want on it at a low enough bit
rate for "telephone" quality, it would run for an hour on 10 megabytes
of memory. E.g. a 256 megabyte unit will run for 25 hours.

Some of them will play the same file over and over, so you can loop
from when you hit the start button until the battery dies.

The cost is low, WalMart's website has them with 1gigbyte of
memory for $25 and I'm sure you can find 64megabyte ones
very cheap, or even used for free. Since they all would have
the same connection, a headphone jack, getting duplicates
would not be a requirement.

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/