10 Ghz Link Receiver Box Project - First attempt

triplestack · Post by **triplestack** » Mon Jul 06, 2015 8:12 pm

builtinashed wrote:It may well be that you broke a hum loop, when you removed the redundant ground connection (as per Analyser's suggestion). Generally, you want to be as close to a "star point earth" model as possible. Doubling up causes multiple paths to mains earth, which leaves different grounds at slightly different potentials, where the potential difference (voltage) is AC hum.
As "S2000" said, the 12V regulator will not do anything worthwhile with only 12V input. It can't provide any regulation, and effects may be unpredictable. I think it will just give a small additional voltage drop, and not much else. Also bear in mind that switching supplies can also radiate the switching frequency, and it can also be present on the output rails. A regulator would normally help to suppress this. It can't do that if it's not regulating, but the 10uF caps should help (although if the supply itself is well filtered, it may not be an issue anyway). I wonder if your PSU has an output voltage adjustment.....

Many thanks for the info builtitnashed, very informative. You mention an output voltage adjustment on the PSU - yes it does have one, and I turned it up when testing until the audio became very clear with no noise/hum.

Analyser · Post by **Analyser** » Mon Jul 06, 2015 8:31 pm

If you can get the output of the power supply to 14V (I think you mentioned that earlier) then the 12v regulator should work ok. This ties in with what you said about everything working and sounding fine. Just to be 100% sure you can check the output of the voltage regulator between the metal satcan body and where the wire goes from the regulator to the big 33 ohm slightly cooked-looking resistor. It should read 12V.

triplestack · Post by **triplestack** » Mon Jul 06, 2015 8:57 pm

Analyser wrote:If you can get the output of the power supply to 14V (I think you mentioned that earlier) then the 12v regulator should work ok. This ties in with what you said about everything working and sounding fine. Just to be 100% sure you can check the output of the voltage regulator between the metal satcan body and where the wire goes from the regulator to the big 33 ohm slightly cooked-looking resistor. It should read 12V.

I just tested the voltage where you advised and it was 11.36V. I tried to turn the PSU up a little higher but it started to cut in and out, the voltages were going up and down until settling on 0.00V!

Not to worry, I turned it back down and it gave a steady reading of 11.36V again.

Analyser · Post by **Analyser** » Mon Jul 06, 2015 11:52 pm

At 11.36V the regulator isn't doing anything so personally I would bypass it. Just unsolder the wire going to the big resistor and attach your 12v from the power supply there. If you can, also keep the 10uF capacitor attached at that point too, so effectively you're just disconnecting the output of the regulator and supplying the 12v from the power supply.

Make sure you set the power supply to 12v before doing this.

If you can't be arsed with all that and it's working fine anyway, don't worry nothing will get damaged leaving as it is.

triplestack · Post by **triplestack** » Tue Jul 07, 2015 7:23 pm

Analyser wrote:At 11.36V the regulator isn't doing anything so personally I would bypass it. Just unsolder the wire going to the big resistor and attach your 12v from the power supply there. If you can, also keep the 10uF capacitor attached at that point too, so effectively you're just disconnecting the output of the regulator and supplying the 12v from the power supply.

Make sure you set the power supply to 12v before doing this.

If you can't be arsed with all that and it's working fine anyway, don't worry nothing will get damaged leaving as it is.

Well I re-tested it again tonight and it sounds bloody awful! The voltage keeps dropping to around 5v and then shoots back up again for 10 secs, then trails off, then up again etc etc. Very unstable. I'm gonna do exactly what you recommend, and unsolder the wire and connect the 12v directly to it.

RF-Head · Post by **RF-Head** » Tue Jul 07, 2015 9:41 pm

Your psu is turned to high and is switching on and off (protecion)
try to lower it to 12V and remove the regulator (7812) and feed the satcan direct

triplestack · Post by **triplestack** » Wed Jul 08, 2015 6:09 pm

RF-Head wrote:Your psu is turned to high and is switching on and off (protecion)
try to lower it to 12V and remove the regulator (7812) and feed the satcan direct

Hi RFHead

I did exactly what you and Analyser suggested, however now i've got a different problem.... The audio signal coming from the satcan is extremely distorted. I have played about with volume controls and no matter how low the volume, the distortion is still there. Any ideas on why this may be? I can't seem to figure out what the problem is!

pjeva · Post by **pjeva** » Wed Jul 08, 2015 6:29 pm

Did you put capacitor between satcan and next stage?
Do you go straight to transmitter or you have some op amp between?

triplestack · Post by **triplestack** » Sat Jul 11, 2015 1:31 pm

pjeva wrote:Did you put capacitor between satcan and next stage?
Do you go straight to transmitter or you have some op amp between?

Hi pjeva - I did re-attach the capacitor between the satcan and next stage, it wasn't attached when I updated last time, but it is now. I have run straight out of the box and into a soundbar (active) so the amp is inside that. So today I decided to test again, and i've had a really good play about with it. I've adjusted the voltage so it reads 12.14V after the capacitor and before the big resistor, so that's good. I diagnosed the problem with the audio drifting in and out today.... IT was the gunn diode that was set incorrectly. I adjusted it and the audio is absolutely crystal clear now! Success! The box is now 100% finished and ready for use as a test box from sites!

I've got to extend a massive thank you to all that have helped me with my first project, you have been really suportive, which is exactly what I needed! Many thanks

Analyser · Post by **Analyser** » Sat Jul 11, 2015 1:37 pm

I was going to say it sounds like the horn was not tuned properly. Glad you got it sorted.

triplestack · Post by **triplestack** » Sat Jul 11, 2015 1:40 pm

Analyser wrote:I was going to say it sounds like the horn was not tuned properly. Glad you got it sorted.

So am I, it was driving me mad! Thanks for all your help man.

s2000 · Post by **s2000** » Sat Jul 11, 2015 3:39 pm

Have a look at this page...

http://ea4eoz.blogspot.co.uk/2012/09/pl ... iodes.html

There is a optimum voltage for every gunn diode, in order to get the best fm modulation.. ie sound quality

Mike Volume · Post by **Mike Volume** » Sun Jul 12, 2015 8:23 pm

To me it looks like the 1uF capacitor and the preset are the wrong way around. I would have thought the - end of the capacitor would need to go to edge connection of the preset, and the middle connection of the preset to the output socket.

triplestack · Post by **triplestack** » Sun Jul 12, 2015 8:26 pm

s2000 wrote:Have a look at this page...

http://ea4eoz.blogspot.co.uk/2012/09/pl ... iodes.html

There is a optimum voltage for every gunn diode, in order to get the best fm modulation.. ie sound quality

Really interesting reading s2000, thanks very much for that. The maker of the gunn exciter box has pre-set the voltage to the horn at 7.2V he's a member on here I think. It's a great bit of kit actually, it works really well.

teckniqs · Post by **teckniqs** » Sun Jul 12, 2015 9:06 pm

Some gunns require only 5v so it's important to make sure the correct voltage has been set accordingly.

triplestack · Post by **triplestack** » Mon Jul 13, 2015 9:09 pm

teckniqs wrote:Some gunns require only 5v so it's important to make sure the correct voltage has been set accordingly.

Good point teckniqs. How would you be able to tell between them?

teckniqs · Post by **teckniqs** » Mon Jul 13, 2015 9:31 pm

You can usually find the data sheets for them on the web.

Shedbuilt · Post by **Shedbuilt** » Tue Jul 14, 2015 1:18 pm

Mike Volume wrote:To me it looks like the 1uF capacitor and the preset are the wrong way around. I would have thought the - end of the capacitor would need to go to edge connection of the preset, and the middle connection of the preset to the output socket.

Yes. I agree. Well spotted. As it stands, at minimum volume setting, the pot is presenting a very low impedance / short circuit to the output of the sat-can. This is not desirable. It's also doing the same to the series cap, which will tend to give increasing low frequency roll-off at decreasing volume settings (albeit this latter effect probably only noticeable at the very low end of the pot). The wiper of the pot should be towards the succeeding circuit, so that it takes it's input to ground. The electrolytic feeding the pot is (if needed at that point), inverted polarity wise. If the output of the satcan is DC coupled (and if you don't know, it's easier to assume it is), it will be more +ve than the pot, which DC wise, will be at ground potential. Also best to add a coupling cap after the pot, in case the next stage is DC coupled (in which case the pot could affect biasing etc, as well as cause noise).

radium98 · Post by **radium98** » Sat Feb 22, 2020 7:18 pm

is this what is called a SAt link .I found it in my junk box .it is a digital satellite receiver ,can this be a link ?

thanks

teckniqs · Post by **teckniqs** » Sat Feb 22, 2020 11:57 pm

10 Ghz Link Receiver Box Project - First attempt

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