BATC Forum

It has been suggested by Brian G4EWJ that it would be a good idea to be able to generate signals on 2m from a 70cms RF modulator output. So I thought it would be a good idea if the community would like to take up this challenge and to that end have now started this thread. Present thinking is 437MHz Tx with an LO of 584MHz would encompass fixed frequency 70cm DigiThin as well as the DTX1 (which is tuneable) into a mixer with appropriate filtering for 2m, plus some amplification to drive into a PA eventually.

12V DC operation and 50 Ohm input and output, maybe with some means of trimming the LO to take account of the 70cms input or LO being slightly out, as frequency errors will be 3 times worse when downconverted, as a percentage.

Sadly I am too busy to get directly involved with actual design work this at present but am very happy to take part in any discussion which I very much hope will now follow on here. I might be able to organise (not make personally) the manufacture of prototypes if Gerbers become available. Small pitch surface mount is no problem at all for volume manufacture.

73

Laurence M0LDZ

Hi

I think the way to go is to use the 200 MHz si570 LO for digithin which can generate 146 MHz and 437 MHz at only a few dB down.

If that's the case then we can use this hardware design forthe much needed 146 MHz rx up converter, so the IF needs to be above 950 (which the DTX1 can generate very nicely) - therefore an LO above 820 MHz is needed.

73

Noel

It could also be used for 50MHz and 70MHz with multiple front ends.

Say a common IF of 1067; 147 requires an LO of 920 (5 x 184, which the cheapest Si570 can do) and the image would be at 1987. Both 920 and 1987 are at gaps in the mobile phone bands, which might be advantageous when on a good portable site.

Brian

Hi

The si570 is not the only option, or necessarily the best one as it needs programming. A common LO of 1 GHz would allow all bands up to 13cms to be upconverted or down converted to the range of a satellite tuner IF. Either a standard module or a PLL. Much simpler than trying to select harmonics from an si570.

The digithin probably needs standard LO and IF (146.5MHz for example) with high quality helical filters to clean it up and then convert to other bands from there with standard transverters.

Mike

Thanks Mike et al;

I am still half asleep so having trouble visualising the block diagram for your and other proposals (I may wake up later!). Any chance of a block diagram?

Right now I don't see how we could combine UP and DOWN functions as the RF matching seems to be frequency dependent on at least this mixer IC from Linear Tech, which has a phenominal range!


http://cds.linear.com/docs/en/datasheet/5510fa.pdf

73 Laurence M0LDZ