Landwehr 2m Preamp Help/Info & Manual Request
I recently obtained a Landwehr 2m preamp which I plan to use for AO-7 operation. The preamp did not come with any significant documentation besides what is printed on the cover (and thats a bit faded).
The preamp appears to be functional, except that it has a tendency to switch back and forth between RX and TX by itself (when no RF is present and the PTT is not connected). This has made the preamp unusable. Does anyone have experience with this preamp and/or know how this issue can be resolved?
I am looking for any suggestions as well as any documentation (manual/schematic) for this preamp that you might have. Your help is appreciated.
Thanks & 73,
Doug, KD8CAO
Doug,
Great preamp. I am still using mine. I have never had a problem of any sort, but do have the documentation, including schematic. The schematic is typical in that it gives the type components, but not their values. Still, that should give you some ideas. They are 20+ years old, and are perfectly usable, but were not of the best quality originally. I will fiddle with the scanner and send you images tomorrow.
Alan WA4SCA
Doug,
Attached is a PDF of the Landwehr preamp "manual," though the BB copy will strip that off. As I mentioned, they do not give the component values, which was very typical of European products of that period. Landwehr is still is business, though they are no longer selling ham gear, and they may be able to provide some information. http://www.le-tronic.com/
You mentioned that it was switching between RX and TX in receive mode. TX mode is almost identical to unpowered, but there is a way to tell the difference. Hook up a ma meter in the 12 V line. In RX mode, it should draw about 100 ma. If it is in fact switching to TX mode, the draw should be much less, probably around 5-10 ma, as the TR relay is de-energized, and the preamp circuitry is (probably) unpowered. Only the switching electronics should be drawing. If the draw is 0, then you have a loose connection in the 12 volt line, most likely in the connector, which should be easy to locate and repair.
Hope this helps.
Alan WA4SCA
participants (2)
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Alan P. Biddle -
Douglas C. Papay