Re: Duo with pc headset ssb #eladduo

Harke Smits


Allow me to throw some experience in. A couple of years ago I was looking for a decent 2m sdr and I was unimpressed by the market. Either not good enough or too expensive. My application is base station for microwave EME. Then I was informed of the article by G4JNT about using the FDM-DUO at 2 m and I immediately bought a DUO (second hand). It uses the DUO RX in undersampling mode, it's clock is at about 122 MHz. The TX is used normally as the sample frequency is higher than 144 MHz at about 225 MHz. All you need are some filters and amplifiers. It works like a charm and I could even recommend using the DUO as your 2m home base station in all but the most demanding operating conditions. I used a vna to align the filters; with a notch at about 122 MHz. I do not need a low noise figure at 2m obviously, but that is not a problem at all actually with a PGA103 in the front end. With a good signal generator I calibrated the DUO's S-meter by inserting a small attenuator at the RX side in front of the DUO. I found the compression level at 2m to be quite high but unfortunately I can not do NPR measurements at 144 MHz due to lack of a good notch filter.  I have used it at 13 and 3 cm EME without any limitation. I hear beacons, sun- and moon-noise and of course: many stations. For me this has made EME (with my relative small station) really great fun.
I have never operated the DUO in any other operating condition, but at 2 m it's great.
The filters and amplifiers are housed in a small case under the DUO which also contains a Wenzel 10 MHz OCXO to stabilize the DUO.
Just a happy user and no connection to ELAD in any form......
Best 73 de

Harke, PA0HRK

On Sunday, October 18, 2020, 03:31:40 AM GMT+2, Paul Andrews <pandrews@...> wrote:

Are you using this 144 Mhz filter / amp design with your Duo?

The Duo as a 28 MHz IF radio is excellent.  I use it on 432 and 1296 MHz.

No I better understand the limitations at 144 MHz undersampling.

If the Duo is run at 144 MHz with a transverter, is the filtering still required?

73 - Paul - W2HRO

On Sat, Oct 17, 2020, 18:34 Neil Smith G4DBN <neil@...> wrote:
Hi Paul I use a G4DDK Anglian transverter to get the DUO on to 144, but
it is quite simple to get around the mathematical and technological
issues with the DUO at 144 MHz.  Running 144 MHz on a 122.88 MHz sampled
A/D converter means you lose a lot of sensitivity simply because of the
way sampling works. The noise figure of the DUO at 144 MHz is extremely
poor as a result.  Also there is aliasing, so you get noise from the
image frequency as well, and Band 2 FM broadcast breakthrough from
around 100 MHz.

Andy G4JNT has designed a filter and amplifier board to improve the DUO
performance on 144. Have a look at
<> where all is explained...

Neil G4DBN

On 17/10/2020 23:19, Paul Andrews wrote:
> Neil,
> Do you use a 144 MHz IF with your 10 GHz system.   I tried using my
> FDM-DUO configured for 144 MHz with a Khune transverter.  I was not
> successful looking for the beacon.
> 73 - Paul - W2HRO

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