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

Sun Nov 30 09:33:34 EST 2014

Hi Guys,

The insertion loss looks a little high for that filter (probably > 1.0db). 
But, it sure has a nice small package and attractive price!

I "homebrew" LP filter should be very easy to fabricate. I'll try to come 
up with a small, reproducible design for VHF and a second for 
UHF....Unless someone else wants to give this a whirl?

BTW, for any who haven't seen it, AADE has some nice free-ware software 
for L/C network design. See: http://www.aade.com/filter32/download.htm
I've got one of their L/C meters, too. Very nice equipment.

73, David KB4FXC

On Sat, 29 Nov 2014, Mark Guibord wrote:

> I'd have to call Arrow to get the pricing break down but I don't think they
> would break down a reel. It may be possible to get samples from the factory.
> 
> 
>  
> 
> Here is one for 2 meters.  http://www.minicircuits.com/pdfs/LFCN-120.pdf
> 
>  
> 
>  
> 
> From: arm-allstar-bounces at hamvoip.org
> [mailto:arm-allstar-bounces at hamvoip.org] On Behalf Of Doug Crompton
> Sent: Saturday, November 29, 2014 8:46 PM
> To: BeagleBone Black ARM Allstar
> Subject: Re: [arm-allstar] DRA818V VHF and DRA818U UHF Transceiver Modules
> -- Low Pass filter required!
> 
>  
> 
> Mark,
> 
>   That looks neat. What is the quantity one price? Unfortunately it doesn't
> look like they make a 2 meter equivalent.
> 
> 73 Doug
> WA3DSP
> http://www.crompton.com/hamradio
> 
> 
> 
>   _____  
> 
> From: mark at micro-node.com
> To: arm-allstar at hamvoip.org
> Date: Sat, 29 Nov 2014 20:13:31 -0800
> Subject: Re: [arm-allstar] DRA818V VHF and DRA818U UHF Transceiver Modules
> -- Low Pass filter required!
> 
> Take a look at this one.
> 
>  
> 
> http://www.minicircuits.com/pdfs/LFCG-42+.pdf
> 
>  
> 
>  
> 
> From: arm-allstar-bounces at hamvoip.org
> [mailto:arm-allstar-bounces at hamvoip.org] On Behalf Of Doug Crompton
> Sent: Saturday, November 29, 2014 7:50 PM
> To: BeagleBone Black ARM Allstar
> Subject: Re: [arm-allstar] DRA818V VHF and DRA818U UHF Transceiver Modules
> -- Low Pass filter required!
> 
>  
> 
> It looks like the minicircuits 440mhz filters are pretty effective at the
> 2nd harmonic but the 2 meter ones not so good. These would be good filters
> for 440 low power but they still cost over twice as much as the module so
> unless you have one laying around that kind of defeats the low price point. 
> 
> http://www.minicircuits.com/pdfs/VLF-530.pdf
> 
> http://www.minicircuits.com/pdfs/VLF-490.pdf\
> <http://www.minicircuits.com/pdfs/VLF-490.pdf/> 
> 
> http://www.minicircuits.com/pdfs/VLF-180.pdf
> 
> 73 Doug
> WA3DSP
> http://www.crompton.com/hamradio
> 
>   _____  
> 
> Date: Sat, 29 Nov 2014 18:09:32 -0600
> From: w0anm73 at gmail.com
> To: arm-allstar at hamvoip.org
> Subject: Re: [arm-allstar] DRA818V VHF and DRA818U UHF Transceiver Modules
> -- Low Pass filter required!
> 
> 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.
> 
> 73,
> 
> 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?___st
> ore=en
> <http://dutchrfshop.nl/ham-radio/2-meter-band/print-lowpass-filter.html?___s
> tore=en&___from_store=nl> &___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 Doug
> WA3DSP
> http://www.crompton.com/hamradio
> 
> 
> _______________________________________________
> 
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> 
> Visit the BBB web page -
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> 
> 
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