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
G8DKC
Posts: 138
Joined: Thu Jun 28, 2012 9:39 am
Contact:

Re SUP2400 Xtal Mod 146.5

Postby G8DKC » Thu Aug 27, 2015 1:54 pm

After more tests, I would go for an un-modified Sup2400 with a sat tuner that goes to 13cms,

and use a middle of the band converter say 1Ghz L.O. for 146.5 on a standard sat tuner.

The Global Communications HSU-10 this end is putting the SUP2281.6 into the shade,

maybe some more work on SUP conversion, and or sat tuner deaf on the top end?

I appear to be getting better results from a tuner that goes to 13cms with the SUP2281.6?

Peter

g6pep
Posts: 5
Joined: Sun Nov 22, 2015 10:05 am

Re: Using the SUP-2400 for 146.5 MHz Reception

Postby g6pep » Tue Apr 19, 2016 10:44 pm

I read the CQ-TV 250 article "Using the SUP-2400 for 146.5 MHz Reception" by Dave, G8GKQ, with much interest, I have just bought a pristine SUP2400, from the BATC shop, and am looking to make a similar conversion for 146.5MHz. I had some questions and comments arising from the article.
  1. In unsoldering the crystal provided with the SUP2400, I used a Chip Quik SMD Removal Kit, with its flux and patent alloy to reduce the melting point of the existing solder on the two crystal terminals. Even though those terminals extend underneath the crystal package, the molten alloy appeared to penetrate in there and, at the third cycle of moving the iron between the two terminals, the solder at both ends became molten at the same time and I was able to remove the crystal, apparently without lifting the tracks.
  2. It is a pity that Dave used a replacement crystal (26.825MHz) from his junk box, rather than looking for a commercailly available component. Not exactly easy for others to follow suit.
  3. I found that an E-Bay dealer sells Rx/Tx pairs of radio control crystals of similar frequencies. I bought a pair labelled 26.815MHz and another for 26.835MHz. These were not documented as third overtone crystals but I think that they are likely to be. Under this assumption, these would have fundamentals of 8.938MHz and 8.945MHz, giving L.O. frequencies of 2288.2MHz and 2289.9MHz and would mix down to 2141.7MHz and 2143.4MHz for 146.5MHz input.

    Dave suggests that the minimum L.O. frequency at which lock can be achieved is 2289.1MHz, by cutting just the single inductor track. This would suggest that the 26.835MHz crystal should be used. However, the mixer output for this crystal is rather closer to the edge of the passband of the SUP2400 than that for the "junk box" one.

    The E-Bay crystals are not Surface-Mount devices.
  4. In starting from an unmodified SUP2400, I am in some doubt as to whether all of the mods by Rob, M0DTS, should be disregarded. One such mod involves the "loopy wire" at the SUP2400 input, which is supposed to improved the sensitivity ...
  5. ... also as towhether the "spurs" are expected to occur in the unmodified unit ...
  6. ... also as to whether the casing of the replacement crystal needs grounding with a solder blob, in a similar way to the original. This may be quite a challenge with a non-surface-mount package.

Does anyone have any experience/comments on these points?

Apologies if this posting may sound combative - probably due to my relative inexperience with this device.

John.

G8GKQ
Site Admin
Posts: 441
Joined: Sun Mar 22, 2009 1:21 pm

Re: Digithin as a starter project

Postby G8GKQ » Sun Apr 24, 2016 2:54 pm

John

Apologies for the late reply - I've been concentrating on the Wiki rather than the Forum.

You will see in CQ-TV 251, page 35, that I have described a modification to allow the use of readily-available 8.912 MHz crystals in the SUP-2400.

As long as you can get it to oscillate reliably, you should be able to use your 26.835 MHz crystal (after writing the original article, I found that mine would not oscillate if the unit got too hot). Being close to the edge of the passband should not be a problem. There is room in the case for an hc25/u crystal. If you can ground the crystal case, it will help, but it is not critical.

Lastly, I would recommend doing all the M0DTS mods, as all my measurements were done in this configuration. I would expect the Spurs to be present, even on an unmodified unit.

Hope that helps. Let me know how you get on.

Dave
G8GKQ

M0YDH
Posts: 27
Joined: Sat Dec 31, 2016 5:59 pm
Location: Wolverhampton IO82WO

Re: Digithin as a starter project

Postby M0YDH » Tue Jun 20, 2017 7:47 pm

Hello Dave
I have 2 SUP-2400 upconverters and a Sharp Minitiouner. I want to make the CQTV 251 changes to one of them. Do I go first with the M0DTS DATV converter mods on Rob's website OR the "Zinwell 70cms DATV upconverter v2.pdf" changes off the Wiki? The latter reads clearly and appears less to do.
The 220R resistor and 8.192MHz crystal for stage 2 are on order and I have Chip quik kit to hand.

73
David M0YDH

G8GKQ
Site Admin
Posts: 441
Joined: Sun Mar 22, 2009 1:21 pm

Re: Digithin as a starter project

Postby G8GKQ » Fri Jun 23, 2017 8:44 pm

Hi David

I used Rob's modifications from his website, and don't have experience of the changes described on the Wiki (not that I know of any problems with them).

So, all I am able to recommend is applying Rob's modifications, then the mods in CQ-TV 250 pp 17-19 and then CQ-TV 251 p 35.

An alternative to Rob's modifications is to use the DiSEqC controller described in CQ-TV 250 pp 29 - 30. For best performance at 146 MHz, you can then change the crystal as described in the other articles.

Dave

M0YDH
Posts: 27
Joined: Sat Dec 31, 2016 5:59 pm
Location: Wolverhampton IO82WO

Re: Digithin as a starter project

Postby M0YDH » Mon Jun 26, 2017 6:03 pm

Thank you for the reply Dave. I have working DisEqC as a board mounted on my v1 Minitiouner. In which case [and just to be sure] are you saying that the 3 changes in CQ251 are sufficient for 146.5 [and 437.0] MHz? I hope so because they're clear and achievable!

cheers
David M0YDH


Return to “DigiThin”

Who is online

Users browsing this forum: No registered users and 1 guest