Knucker receive system gain

[g8gtz]

When designing your Knucker receive system you need to be bear in mind that the Serit 4762 NIM is designed as a terrestrial tuner for direct connection to an antenna.

This is unlike the Serit 4435 satellite NIM which we use in MiniTiouner which is designed to work behind an LNB with 55dB of gain and needs a preamp + a line amplifier to work properly in terrestrial applications.

Testing has shown that a low noise amplifier does improve system performance by reducing the overall noise figure of the $4762 but should be followed by an attenuator to reduce the risk of overloading the NIM.

The system I ended up with on 70 / 50 MHz was as follows:

Antenna > Bandpass filter > PGA103 LNA with 20 dB gain > 20 dB atttenuator > Serit 4762

So the lesson is you can't just split your signal and feed both tuners with the same signal

73
Noel - G8GTZ

[radiogareth]

In search of suitable 'Band pass filters' I happened across this site:https://pa3csg.nl/?page_id=63

Details for 6,4 & 2 with info on BW changes and insertion loss mods.

For 2m I'm using the Amsat SAW filtered unit https://amsat-uk.org/projects/g0mrf-144 ... e-amp-kit/ which has proved very useful with my Minitiouner. Probably need some attenuation on a Knucker.

These little amps (search eBay for "LNA 0.05-4GHz RF Amplifier SPF5189 Signal Ultra Low Noise High Linearity NF0.6dB") work well for boosting Pluto output power, and are abou8t 1/5th of the price of the PGA103 - would I be getting 'what I pay for' and might they be suitable (I think yes...)??

With the much increased input sensitivity, should I worry about blowing the Knucker front end when I go to TX? Would a relay contact to ground (or 50R) be a wise precaution, or a couple of diodes back to back?

BTW, surely +20dB followed by -20dB equates the well known "4/5th of 5/8th of xxxk all'!!

Gareth (self training underway... )