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Sbitx and ad831 mixer

 

Hi to all
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Looking around the net I found this project.
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There he uses an ad831 mixer for a dc receiver.? Got some of them from amazon and put it together with a 10.7mhz 30khz filter I have use on other projects.
This is the setup:
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Im impress of how well these mixers work. Just changing the bfo freq and it receives!!! Actually the rx is very good.??
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Later will try to setup some relays like in the sudden transceiver to switch clock 1 and? 2 to see how the tx looks.??
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Juan WP3DN
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Here is a video of the rx on the bands. The antenna is a 21ft ground mounted vertical with 4 to 1 unun.
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Juan WP3DN
 

Tx works!!!!
Did a little board to swap the clocks and another board to switch rx/transmit audio and tx/receive audio. Very low power but enough to listen on a handheld radio!!!
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Juan WP3DN
 

https://youtu.be/Rn_7CbXwqt0?si=HTt1cNa-2umdUhMc
 

Incredible! Have you tried SSB? That is the proof of overall linearity. What is your bandpass filter?


On Sat, Sep 14, 2024, 7:44 AM WP3DN via <3voltios=gmail.com@groups.io> wrote:
 

Farhan,?
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No band pass filter in place yet. Just wanted to see if it was generating rf.? Need to decide which bands to include since the need to filter per band.
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Juan WP3DN
 

With the AD831 mixer, you should be able to use 3rd harmonic mixing and go upto 435 Mhz


On Sat, Sep 14, 2024, 6:07 PM WP3DN via <3voltios=gmail.com@groups.io> wrote:
Farhan,?
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No band pass filter in place yet. Just wanted to see if it was generating rf.? Need to decide which bands to include since the need to filter per band.
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Juan WP3DN
 

Farhan,?
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This is a video of a ssb tx test and how it looks on sbitx v1 spectrum.?
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For mic bias I used 10k resistor to 5v and 4.7uf capacitor. No mic amp.
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Juan, WP3DN
 

This is a nice setup, can you explain it in a bit more detail, what frequencies are you running on each mixer, I assume the second one is a fixed frequency, and are you pushing the output into something like a zbitx to generate the waterfall ?

On Sat 14 Sep 2024 at 17:16, WP3DN via <3voltios=gmail.com@groups.io> wrote:
Farhan,?
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This is a video of a ssb tx test and how it looks on sbitx v1 spectrum.?
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For mic bias I used 10k resistor to 5v and 4.7uf capacitor. No mic amp.
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Juan, WP3DN
 

Peter,?
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This the normal sbitx software with audio injector card and si5351. Have two ad831 mixers and a 10.7mhz 30khz crystal filter.
To rx clock 2 goes to first mixer and bfo goes to 2nd mixer. Sound output from the mixer goes to the sound input to sbitx software.
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To tx clock 1 bfo goes to 1st mixer and clock 2 to 2nd mixer. Audio output from sbitx sound card goes to 1st mixer, same input from antenna in rx. The antenna is switch to the output of the 2nd mixer.
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To do the clock swap and antenna switching im using two small relays.
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Juan WP3DN
 

Farhan,?
Later I would like learn more about harmonic mixing.
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What I think I would do is to setup the bandpass filters for 10m, 6m, 4m and 2m. If fm is added later, it will be fun to operate on those bands.
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But before all that happens have to box everything and think about power management. There is some artifacts in the audio related to that.?
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Thanks a lot for this amazing software that gives us the oportunity to tinker and do homebrewing easier because half of the radio is done.?
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Thanks again,?
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Juan WP3DN
 

Hi to all!!!
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Scavenging for parts to continue experimenting with the ad831 mixers, I found a 144mhz transverter. First I wanted to use the rd mostet and coil. After inspecting the board found tha it has most of the parts needed after the crystal filter.
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The board has the low pass filter, one mixer for tx and another for rx.
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So now first bfo signal goes to a ad831 mixer. Then passes thru the crystal filter at 40mhz. After it go to the transverter input. Vfo signal replace the fixed crystal on the transverter board.?
Need to add an if amplifier to increase the power output. The transverter can output 10w, but only have 250mw of output. Did a qso today with a mag mount antenna on 144.300 with a nearby ham. But it a start!! 250mw of success!!
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Juan WP3DN
 

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Success!!!
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Added a 20db amp from the cristal output to the transverter and now have 7watts output on 2m!!!
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Now from the codec output the signal goes to the ad831 mixer. Then it goes to the 40mhz crystal filter. After it goes to the amplifier. The output of the amp pass to the low pass filter in the transverter and on to the mixer and final amplifier.
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Juan WP3DN
 

Hi Juan,

Can you share a block diagram so I can better understand your point?

Thanks,
Charudatt VU2UPX?

On Mon, 30 Sept, 2024, 3:14 am WP3DN via , <3voltios=gmail.com@groups.io> wrote:
Success!!!
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Added a 20db amp from the cristal output to the transverter and now have 7watts output on 2m!!!
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Now from the codec output the signal goes to the ad831 mixer. Then it goes to the 40mhz crystal filter. After it goes to the amplifier. The output of the amp pass to the low pass filter in the transverter and on to the mixer and final amplifier.
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Juan WP3DN

IMG-20240929-WA0022.jpeg

 

Charudat,
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This is a quick drawing of the setup
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Also here is the transverter diagram
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What I did to the transverter was removed the cristal oscilator and injected the vfo clock 2. Also modified the low pass so it works exactly like the sbitx.?
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The advantage of the xverter board is that al the 2m circuit stay the same. Also includes a tuned rx preamp and the tx side can output up to 10w.
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Juan WP3DN
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It looks better on the drawing. But it actually works!!!
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144mhz
 

Hi to all!
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Today made my first ft8 dx using the ad831 mixer with 40mhz filter and transverter board.
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I removed the small amplifier before the transverter and improved the vfo feed to the transverter. Gain of the ad831 is at 10db.
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Juan WP3DN

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