[arm-allstar] DRA818V VHF and DRA818U UHF Transceiver Modules -- Low Pass filter required!

Christopher Kovacs w0anm73 at gmail.com
Sat Nov 29 19:09:32 EST 2014

I use a lowpass filter on my dra818u module. However, I don't have the test
equipment to check the harmonics. I use this filter my rc gear.

It's a Mini-circuits 15542 low pass filter.


Chris, w0anm
On Nov 29, 2014 12:12 PM, "Doug Crompton" <doug at crompton.com> wrote:

> I only ordered UHF but I suspect they might have the same problem. I will
> definitely check on a spectrum analyzer when I get them. I think these
> modules are designed as part of an overall transceiver and the
> microprocessor, display, output amplifier and filtering are missing. For
> most people it would not be hard to add the proper filtering but few have
> the RF tools to measure the results. So we would have to come up with a
> foolproof filter design that can be easily duplicated. At the same time you
> don't want it to be physically large as that would defeat at least one of
> the advantages of theses modules to begin with. I have a large amount of
> double sided copper PC board and I would probably build a little box out of
> that and put the filter inside along with the module. It would be a matter
> of winding a couple of coils on some common small diameter material like a
> pencil and a couple of chip capacitors. Here are some links I found with a
> quick search on 2 meter filter design.
> http://ve2zaz.net/LowPass_Notch_Filter/144LowPass432Notch.htm
> http://www.radiomods.co.nz/lowpassfilterpage2m.html
> http://www.g4ztr.co.uk/amateur-radio/construction/2m-low-pass-filter/
> http://dutchrfshop.nl/ham-radio/2-meter-band/print-lowpass-filter.html?___store=en&___from_store=nl
> So as Dave pointed out until we come up with some real measurements on
> these, and possible ways to fix the problem, I would be careful about
> putting them on anything but a dummy load. If the 2nd harmonic was 6db down
> running them at the 1/2 watt output level they would be putting out 125mw
> at twice the frequency. Enough to cause interference out to several
> thousand feet at least.
> I wonder if anyone has looked at some of the cheap handhelds that come in
> from China on a spectrum analyzer?  I guess they are type accepted though
> so they should be OK.
> *73 DougWA3DSPhttp://www.crompton.com/hamradio
> <http://www.crompton.com/hamradio>*
> _______________________________________________
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