- 1296MHz LMW Transverter Troubles
Re: 1296MHz LMW Transverter Troubles
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I have an old LMW 2320 transverter ... it took me 30 years to get it into a state where I could get a single (weak) contact on it ... it spent most of its life oscillating randomly. Having achieved a single contact, I consigned it to the top shelf, where it has remained.
Yes if I place an SMA at the mixer input and then use a separate LNA and filtering as the mixer is a diode mixer and therefore passive, this is something I'm considering as it allows me to play with the gain distribution - There's 42dB gain in the masthead LNA, so it probably wants to see a filter next and then a gain stage before the mixer - 2 LNAs in the RX converter might be too much gain in addition to the masthead LNA. I think some of the problem is the GaAFETS the original design has are NE25137 and mine was supplied with NE25139 which have a different footprint, you can get them to fit and it works but probably not ideal. It did used to work OK on RX, years ago when I lived in Runcorn the Manchester Beacon (long since off air) was a nice signal and that's what I used to align it - on an indoor antenna.
Comments noted about the 6W PA. The PA in mine is different from the LMW design although it does use the same device (BLV93) - I did build this as a separate module in it own box rather than the open boards as used in the rest of the system.
I've not started looking at the TX side yet, I'll do that once the RX is working.
My first 23cm transverter in 1980 something, anyway the problem with these was the 6watt PA stability. Stability from my point of view in the Rx converter was always OK. I would initially try and re tune it. It does have from memory quite a few teflon trimmers and it may be worth trying
BUT you may wish to buy a LNA from Epay that covers 23cm and go straight into the mixer with it, If this works then you could look at some 23cm specific filtering later and other refinements.
On Monday, 3 May 2021, 18:54:24 BST, jimbod1973 . <jimbod1973@...
Well I've discovered the reason I heard nowt at all on 23cm yesterday.
I'm using an old LMW transverter and the 2nd RF stage of the RX converter hoots (I think the 1st stage might be dead altogether) Looking at the layout its not that surprising - there is no shielding around the individual stages and not many ground stitching vias, so I would expect it to lack some stability.
Despite efforts today to add some shielding made from bits of PCB I haven't yet succeeded in taming it. This is a really old design now though (think I built it about 25+ years ago), which has me wandering if I should look at an alternative, more recent approach and just use the remaining parts that work OK (the LO chain, PA and switching all work quite nicely)
The RX conv in its present state would make quite a useful test source for 13cm & 9cm when I eventually get going on those bands.
Robin Szemeti - G1YFG
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