[Lf] Re: LM 1875

[Andre Kesteloot]

Lawrence Stoskopf wrote:

> OK, dumb question.  So the antenna has less than an ohm of input
> resistance and a bunch of capacitance.  You hook it to the output of a
> low impedance output device, maybe a voltage regulator or the LM1875.

several years ago, the British firm Maplin used to sell a kit of parts
that included the LM1875.  This kit is no longer available, to the best 
of my knowledge. I built one of these kits and operated it on 136 kHZ 
without any difficulty.

The two eventual problems with that chip are:
a) it needs 50 to 60 volts (at up to 1 amp) to develop 20 watts (kind of
class AB2)
b) if not used with a good printed circuit board, it may start
oscillating at these higher frequencies.


> I would hate to design a bandpass filter at this frequency with this
> impedance so let't pretend that the output signal is pure.

a simple low-pass filter works well

If you need a copy of the pcb, let me know

73
André N4ICK