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(For Europe only),
I have a SSTRAN AM TX that gives me plenty of satisfactions.
(For Europe only),
I have a SSTRAN AM TX that gives me plenty of satisfactions.
Has anyone ever thought to add a small amplifier directly connected to the output of the SSTRAN ? like a 5 watts for example ? (without modifying the ckt of the actual transmitter)
Where could I find a schematic for such an amplifier. I am looking throught the net, but no luck up to now.
Thanks.Denis
Total posts : 45366Not sure of the legal requirements in Europe,but you would need a linear amplifier to boost your output. There isnt any on the market that I am aware of. A better approach would be to get a different transmitter that has the output you need. You can also increase your range with a good antenna setup,again depending on your local rules.
Regards,Lee
http://www.freewebs.com/wilcomlabs/index.htm
Total posts : 45366Denis,
As Lee mentioned, you will need a linear amplifier since the signal is modulated before it is amplified. Also, the amplifier should present a load of approx. 800 ohms to the SSTRAN. Here’s a link which has some circuits and information:
http://web.telia.com/~u85920178/tx/rf_pa_cct_00.htm
Along the lines that Lee mentioned, if I were to do this I would use the SSTRAN to produce an unmodulated carrier, send this to the amplifier, and apply high level modulation at the final amplifier (class C). My reasoning is that unless the PA amplifying a modulated signal is exactly linear it will produce spurs and byproducts which could be a problem. A highly linear amplifier for modulated AM is not trivial.
This is certainly not legal in the US if the final DC input power exceeds 100 mW and I don’t know the rules for Europe.
Neil
Total posts : 45366Using a linear amplifier is a very inefficient way to boost the power of an AM signal. You should not expect to get more than 25% efficiency out of it, because in order to achieve a 5W carrier output you will need an amplifier that is capable of 20W (peak).
As suggested earlier, you could disable the modulation in the SSTRAN and use the output as the drive signal to your amplifier, which I would suggest operating either in Class C or E (non-linear). You should be able to achieve upwards of 70% efficiency in that mode. You could also tap the audio prior to the point where it modulates the carrier in the SSTRAN, and feed that to an outboard audio amplifier, if you would like to take advantage of the preamp and limiter in the SSTRAN.
You should check with your country’s telecommunication authority first, because in most countries, operation at that power level would expose you to severe penalties.
WEAK-AM
Classical Music and More!
Total posts : 45366I did find my copy of another Ernie Wilson/ PanAxis goodie, yes, it is the very circuit you seek.
It’s the AM 5000, a .5 to 3 watt PA.
Ernie used to sell this as a kit back in the 1980s for those who already owned his AM 100, 100mW transmitter and who wanted to experiment with carrier current at higher powers.
If you connect this amplifier to an antenna you might as well just call your name and address into the FCC because you WILL be getting an NOUO, probably within 90 days of putting the fire to the wire.
So, don’t do that.
If, on the other hand, you really want to do some neutral injection Carrier Current, it just might give you the oomp you are looking for.
As the beer people say “Enjoy this quality product responsibly!”
AMA 5000 PA Construction plans, including parts layout and PCB foil pattern
Experimental broadcasting for a better tomorrow!
Total posts : 45366I don’t think efficiency is a concern for someone who wants to boost their power. Efficiency is only a concern when you are trying to achieve max signal within the 100 mW rule.
If you want 5 watts out and the effieciency is 25%, then just make sure the output transistor/heat sink combination can dissipate 15 watts.
Phil B
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