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

David McGough kb4fxc at inttek.net
Sat Nov 29 04:54:56 EST 2014

Hi Doug,

First, I'll mention that I'll already ordered VHF and UHF modules to test.

I looked at the website that Steve referenced. It shows the 2nd harmonic
(288MHz to 296MHz) down by about 6db and the 3rd harmonic (432MHz to
444MHz) down by about 19db, for a VHF module.  So, assuming the other
modules in this family are similar, a dummy load is the ONLY way to go!
PLEASE DON'T hook an antenna directly to these modules! ....I can easily
key local 440MHz repeaters from 40 miles away, a "rubber duck" and 20mW
using my VX7R---almost the same power as may be present in the 3rd
harmonic from one of these 1W modules!

If you're going to hook this to an ANY antenna, PLEASE add proper
filtering! Another option might be to run the module into an RF switched,
FCC type accepted, power brick. You're then relying on the external power
amp to supply proper filtering, which most should do just fine.

An ham operators, it's our duty to insure our "homebrew" equipment meets
proper FCC (or pick your agency of choice, for different countries) specs
in regard to spectral emissions. And, these boards are, without question,
"homebrew."  If we don't follow these principles, we might get these
privileges taken away (this has already been suggested by some!)---which
would be a shame for all the avid home-brewers out there, like me.

I'll post spectrum analyzer plots when I get the modules I ordered and
test them. Note that the 2nd harmonic from the UHF version falls squarely
in the very busy 800MHz business/public safety/cellular band!!! OUCH!

73, David KB4FXC

On Fri, 28 Nov 2014, Doug Crompton wrote:

> I doubt there would be any problem at the 1/2W or 1W level without an 
amplifier but if you do use one I would be careful on the other hand an 
amplifier just might improve the situation if it had high Q filtering on 
the output. Only testing will tell. Many would use these on a dummy load 
or a minimal indoor antenna for limited range in a local node situation.
> 73 Doug
> http://www.crompton.com/hamradio
> From: ssedgwick at suddenlink.net
> To: arm-allstar at hamvoip.org
> Date: Fri, 28 Nov 2014 14:22:53 -0600
> Subject: [arm-allstar] DRA818V VHF Band Voice Transceiver Module and DRA818U	UHF Band Voice Transceiver Module

Hi David,
I’m sure a LPF will be needed to meet FCC requirement in the US.  This 
is based on the results from the website (needs to be translated, I used Chrome) 
.  This website was based on the DRA818V, but it looks the same as the 
SA-818 so I would expect the same results.  My first test will be on a 
dummy load, hihi
 Hi Chris & Everyone!

First, Happy Thanksgiving!

Has anyone out there taken a look at the transmitted spectrum from either
of these modules to confirm they meet FCC specs??? As small as they are, I
can't imagine there is any low-pass filtering, etc., that is part of the 

...Just wondering!

73, David KB4FXC

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