[Lowfer] 1 watt in class " AB " into 32 Ohm load, BW - 600 KHz, and it's an audio amp

[Andy - KU4XR]

--- On Thu, 11/25/10, JD <listread at oswegoblade.com> wrote:

> 
> We also need to bear in mind that Andy was asking about
> Part 15 operation, which is limited to 1 watt DC INPUT.  
> The efficiency of Classes A and AB are pretty poor, 
> and B is barely adequate.
>_________________________________________________________________


Hi JD:

I suppose that this fact is probably one of the biggest reasons
that there are not many lowFERs sending linear modes on 1750 meters.
70% efficiency would be excellent performance in a Class " AB " amp.
Unless I'm mistaken, I think the distortion in a Class " B " amp
might be a little too high, but on the other hand; at LF would it
even be noticable ?? Possibly so if it distorted the transmitted
waveform of a digital mode enough that decoding it would be difficult,
or impossible. I don't have enough experience to know.
I did build an HF to LF Transverter using a SA612, and a TDA7052B.
The IF was at 28 MHz, and I was trying to use an old Radio Shack HTX-100
10 meter mobile as the tunable IF. It works, but the drift in the old
radio is excessive, so not very useful. Antenna current readings with
the QRSS Class " D " setup on the old antenna were 180 Milliamps, and
on the Linear Transverter set for 1 watt DC Input on the TDA7052B audio
amp, the Antenna current was 110 Milliamps. So there is certainly a
drop in output efficiency with any Linear system.
I do still have the desire to get a Linear PA going at some time, and
run something in addition to the QRSS signals on the band. Probably
just need to change the crystal in the transverter, and use another
radio as the tunable IF. I guess that's the most logical route to take.

73: 


Andy - KU4XR - EM75xr - Friendsville, TN. USA