RF In The Ham Shack

I have had this intermittent problem with RF in the shack. Mainly this was on 20m where when transmitting some digital mode like FT8, the software would crash and the computer would send random serial commands to the radio and just mess things up. Mostly this was on 20m, but also on 15m the wireless mouse would stop working while in transmit. So i had some RF issue happening and by chance I worked out what it was.

Now, for work i spend a good part of my time on a motorcycle out delivering and I like to listen to the radio, podcasts and even ebooks using software that reads the text to me, while i work. I use these cheep arse bluetooth headsets to pipe the audio into my ears from my phone.

It turns out, when i have these plugged in and charging, they are acting as antenna and RF is then being fed into the mouse and keyboard dongle and computer VIA USB and then out the USB to serial cable for the radio’s cat control. Who would have thought that something as simple as USB charging would be the cause of all my problems.

Solution was simple, unplug the bluetooth headsets and everything is tickety boo. Oh and the reason why I have 2 of these, the battery only last 4 hours and 2 means I can work all day and keep the sounds coming. 🙂

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Receiver RF Front End

VK4FFAB Receiver Front End

Ok, I am posting this mostly because I can, but I wont publish the gerbers yet because I actually want to layout the board better, fix some footprints and have the boards remade. Not because they are bad or do not work, but because I know i can make them so much better

So this it my receiver front end. RF comes in from the antenna, through the TX-RX relay into a 0-31dB attenuator module, into a 5 to 15dB RF Preamp.

The RF amp is a pair of J310 as a dual gate mosfet as designed by Pete Juliano here: SimpleCeiver

Variable RF Preamp Schematic
Prototype Built and Tested
PCB as originally laid out.

I might add some more info here later, or will just post anew when i have redesigned the board. The main thing i want to do is to remove those wire links joining the attenuator to the rest of the circuit and replace that with some right angled SMA connectors as the attenuator board comes with SMA connectors on it already. I will probably change the relay also as I now have some better RF relays, not just chinesium grade floor sweepings.

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