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?
- 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.
- 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.
- 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.
- 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 ...
- ... also as towhether the "spurs" are expected to occur in the unmodified unit ...
- ... 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.
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.
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.
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.
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