We Have Filters!

During the last 2 years, our little group of enthusiastic operators have often thrown bits of equipment at each other, stuck drawing pins in a rival’s coax, and even resorted to a bit of fine tuning in response to the QRM caused by our stations operating close together.  This is, understandably, expected when aerials are less than 30ft apart and usually “full size” – In some situations, we have been able to manage: 40m 100w SSB and 30m CW (in varying power-levels) seems to work well at our Galleywood outings.  Problems arise if the 40m station moves to 20m or 17m.  Operating 40m+15m and 20m+10m obviously pose problems, too.

40m Bandpass FilterAfter umm’ing and arr’ing about the 5B4AGN filters, I settled on the AS-nn series from Array Solutions.  At £52 each plus shipping (and UPS holding their hand out for an import charge), it wasn’t pocket-money but it does mean that we now have the ability to operate at least 4 HF bands without issues.  These filters are invaluable for club/group activities and the “sting” of their price can often be reduced via a “group buy” or a nice word with your local club – assuming that they do some operating, of course!

Luckily, our casual /P brigade of Essex Hams try to generate as much RF as often as possible…  Pete M0PSX bought a 20m one, Peter G0DZB – being really keen – got 30m+17m ones and I got 40m.  These will be used whenever we are out /P as well as during our special-events – this ensures that we can operate on several popular bands without having to move stations apart or restrict ourselves to 1 or 2 bands.

Peter ‘DZB was kind enough to lend me his miniVNA Pro which allows for plotting SWR, Resistance, Loss etc and dump it to an image file.  The graph below shows the performance of the 40m filter across the HF spectrum:

40m Bandpass Filter HF PlotHere are some additional plots: (1) 40m filter at 30m , (2) 30m filter at 20m , (3) 20m filter at 15m , (4) 17m filter HF plot

Bandpass Filter PlotsI also used a narrower sweep to read the individual band attenuation specs: 70db on 160m, 48dB on 80m, 38dB on 30m, 80db on 20m, 83dB on 17m, 73dB on 15m, 70dB on 12m and 70dB on 10m.  Insertion loss is 0.5dB on each filter. During tests, a variety of plots were taken and each filter offered a very respectable set of figures which will make operating more fun/productive from now on 🙂

Post-blog-note: After several outings /P, their performance has been confirmed and using these makes the world of difference!