Watt Draw for Common Low Power AM transmitters

The AM transmitter I use here is a home brew unit which operates at 18 VDC and it draws 80 mA which is a power of 1.4 Watts. The 18 volts is internally regulated down to 10 volts so the 18VDC could be lowered to 12 volts which is a power draw of .96 Watts.

18 Volts was chosen to give some "head room" on the supply since the transmitter is outdoors and is fed by a long line. The major power consumer in this transmitter is the modulation circuit which uses a transistor to apply the DC voltage to the final and if a modulation transformer was used instead the power consumption would be on the order of 150 mW.

I estimate that if the design were modified to minimize power consumption it could function at 7V at 50 mA = 350 mW. Using a modulation transformer and IC audio amp. instead of the present circuit could lower this further to perhaps 300 mW.

Another view is to use a final stage input power of 100 mW and add to this the power used by the PLL and audio circuits which I estimate to be about 50 mW for a total of 150 mW minimum.

These numbers are for an unmodulated condition. Modulation can increase this by up to 50% depending on the modulation technique used.

Neil

Thanks Neil.

< 2 watts. Impressive I think.

What sort of signal range are your achieving with your home brew transmitter Neil?

The signal as heard on a car radio is dependably solid out to 1/2 mile and often is listenable out to a mile. The "fringe" was 1.3 miles last time I measured and once it was heard at two miles very weak but this is rare.

It is a ground mounted system with radials.

Neil

Take it you have ground radials in the soil there?

How many radials.

Love the real experience and real ranges by compliant folks. Thanks for sharing!

There are 12 ten foot radials made of #12 insulated wire that I had in my junk box. There are writeups and pictures of this which I will link later. Short on time at the moment.

Neil

I rummaged through the site archives and compiled several posts which I made detailing the design, testing, and construction of my outdoor AM antenna system. These are not "follow the instructions" projects but are intended to give ideas and suggestions.

This thread describes an outdoor test and you can see in the pictures how the radials were laid out.

After the successful test a permanent antenna installation was planned and began with construction and installation of the antenna assembly.

The antenna system was tuned to resonance using a home made RF transformer which is a great way to do so but requires a good scope. Otherwise tuning can be done either by following the transmitter maker's procedure or by monitoring the field strength.

A way to check field strength is a basic loop antenna. This will give a reading out to about 15 feet with the meter shown and a bit further with a DVM. Another good indicator is a radio with a signal strength meter, and not having this, just listen for maximum signal strength.

The last post describes some further observations and improvements

This should keep you busy reading for a while and I hope will give you some ideas. The antenna system with the loading coil can be used with the SSTRAN AMT-3000 and the Ramsey AM-25. Without the loading coil it will should with the SSTRAN AMT-5000 and other transmitters with an internal loading coil (though certification may be an issue when using an antenna other than that specified by the manufacturer).

Some good advice was given earlier which was to start simple and build from experience. Though you can forge ahead with an antenna system similar to that described it may be better to do this step by step, especially by testing a temporary system as I described. Then you will know if it is worth the effort to make it permanent.

Also, don't give up if things don't work as expected first time. It took me a long time to get resonance and that was only after I made the current transformer. It can be done without this but it takes time and patience.

Neil

Thanks for taking the time to post about your antenna builds.

I have lots of reading to do 🙂

I have tried a few different home made antenna types.

Here is a LINK TO MY STORY about one such adventure.

The antenna worked fairly well but shortly after building it I aquired an ATU for my Talking House and didn't pursue it.

My Talking House Model II draws 0.06 amps (6.9 watts) while transmitting.

(Measured by plugging the T.H. Wall Wart into a Kill-a-watt meter )

Thanks @PerryNH.

I tested the TH V or Talking House 5 unit I have here with the Kill-a-Watt meter and we run 4-6 watts consumption depending. That is indoors, with the wire antenna and with the internal speaker on at various volumes.