Digithin as a starter project

The place for discussion about the RPi add-on RB-TV modulator card developed by G4EWJ and supported by the BATC Shop
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G1LPS Terry
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Re: Digithin as a starter project

Post by G1LPS Terry » Mon Jul 20, 2015 1:20 pm

I had planned to feed a dish with a cut down one for that purpose Brian.
But until theres more activity from the ISS datv tx than the ocasional black screen its not worth the investment and time.

G4EWJ
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Re: Digithin as a starter project

Post by G4EWJ » Mon Jul 20, 2015 1:51 pm

Nice idea, but agreed on the lack of activity.

It's a shame they didn't go for a non-commercial amateur design. They could have used an MK808-DigiLite and had a carousel of test transmissions on an SD card. It would probably have needed some silicone around it to survive the launch though. :D

Brian

g8gtz
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Re: Digithin as a starter project

Post by g8gtz » Tue Jul 21, 2015 9:02 am

Brian,

Had a very good evening last night - at the last minute I went along to the local radio "what's on your bench" evening and took the RpiDATV and Minituner. I showed it and then proposed it could be a club project as kits and full documentation will be available so everyone should be able to get it working and work someone across town. To my surprise several people came up to me afterwards and said they were very interested and could I give them more details - this really has potential so try and talk to your local club about it....

Re SUP2400 - that's really interesting, will try later and do some measurements such as LO leakage on a standard one and then performance on shifted oscillator. We probably ought to go for a standard crystal such as 8 MHz.

G4EWJ
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Re: Digithin as a starter project

Post by G4EWJ » Tue Jul 21, 2015 11:20 pm

That's a good level of interest. Were they newcomers to ATV?

I assumed that the 2400 problem was direct pickup of the SUP-2400 LO by the antenna, because of proximity. It seems to work for Terry.

I kept the modified SUP LO above 2150 to keep it out of the receive band. It has a 2150MHz filter. Maybe that's its purpose.

Brian

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G1LPS Terry
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Re: Digithin as a starter project

Post by G1LPS Terry » Wed Jul 22, 2015 3:18 pm

Changed crystal to 8hmz no joy
Terry :(

G4EWJ
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Re: Digithin as a starter project

Post by G4EWJ » Wed Jul 22, 2015 5:43 pm

>>Changed crystal to 8hmz no joy

In what way? It didn't oscillate or produce an LO?

Brian

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G1LPS Terry
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Re: Digithin as a starter project

Post by G1LPS Terry » Thu Jul 23, 2015 3:10 am

No Lo Brian.
Terry

G4EWJ
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Re: Digithin as a starter project

Post by G4EWJ » Fri Jul 24, 2015 5:41 pm

I had an 8.192MHz crystal installed at one point that I thought was working, but I had a strange fault on the receiver so I didn't try for long. It's probably best to keep the LO above the top of the signal band at 2150 or it might cause some blocking if it gets amplified.

Brian

M0DTS
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Re: Digithin as a starter project

Post by M0DTS » Mon Jul 27, 2015 6:45 pm

I did a sweep this evening of the VCO/lock range of the SUP 2400, see screen shot below. Mine is 9.375MHz reference crystal as standard.
Freq range as-is can be 2300-2560, you could modify the vco components to shift it lower.....
That gives 9-10MHz crystals as a possibility.

73
Rob
Attachments
20150727_194016.jpg
SUP2400 LO range as standard
20150727_194016.jpg (129.9 KiB) Viewed 3174 times

G4EWJ
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Re: Digithin as a starter project

Post by G4EWJ » Mon Jul 27, 2015 7:59 pm

I must have been wrong about the 8.192MHz crystal working and the 8.912MHz crystal was just scraping in.

Brian

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