Friday, 5 September 2014

A 144MHz preamplifier

As mentioned earlier on my twitter account (@dxing) I have spent much of the day 'fettling' with a PGA103+ preamplifier, getting one ready to use with my Anglian transverter.

                                           



The basic PGA Amp I have been selling has no RF filtering and is subject to overload from nearby strong out of band signals. This is not ideal.

The third order input intercept (IIP3) measured previously seems to have been overly optimistic when compared to recent results. The latest measurements have been done more carefully and at slightly lower levels than previously. Even so, the IIP3 still measures better than +1dBm and is currently beyond the range of my test gear.

By adding a different configuration LPF to the input it has been possible to better noise match the PGA103+input; place a big notch in the middle of the band 2 FM ( possibly still the worst interferer for 144MHz systems in the UK) and yet keep the noise figure low. The LP filter is a variant on a design suggested by G4SWX

A simple 150MHz LPF at the output rolls the gain off above this frequency with minimal impact on gain and reducing 432MHz and 220MHz( DAB) response.
My preamp measures 0.6dB noise figure, 25.4dB gain and >+1dBm IIP3
Stability is excellent. 
An attenuator may be required at the output, in some circumstances, as the gain is rather high for most applications.

I am not planning to produce kits at this stage.

I will produce a full construction article in due course for anyone wanting to build the preamp. First, I want to do some more testing in conjunction with the Anglian transverter.

Sam


1 comment:

  1. Hello Sam,
    here another PGA103 preamp with selection:
    http://www.von-info.ch/hb9afo/articles/PGA103+/default.htm

    vy 73 de Bodo/DL2FCN

    ReplyDelete