Re: [amsat-bb] Drake 2880 Converter

[Bill Richarz <wricharz@xxxxxxxx>]

Jesse,

Why not replace the GASFET with the MGA device?
See this websight:

www.g0mrf.freeserve.co.uk/filter.htm

de Bill, N4DH


At 16:48 1/28/01 -0500, Jesse Morris wrote:
>Good afternoon to all,
>
>With a new round of Drake converters apparently on the way I thought
>there might be some in the group that would be interested in the fact
>that I blew the front end GASFET in another converter while testing
>antennas this afternoon.  It apparently happened while swapping the input
>cable from one antenna to another exactly like the last time.  (I've been
>called lots of things in my life but smart is not one of them!)  I had
>planned never to switch antennas with the power on again but somehow I
>was unable to comply with that edict.  (I told you I wasn't smart.)  The
>last time I speculated about static discharge but after this latest
>episode it occurred to me that in the absence of an input (or with a bad
>input) the input stage might just take off and destroy itself.  At any
>rate whatever the cause it would be wise to take all available
>precautions when testing with the converter.
>
>Before I blew up the converter I did manage some antenna tests which
>might be of interest.  I built 1 pound and a 3 pound coffee can horns IAW
>with the article in CQVHF that Jerry pointed me to last week.  The helix
>antenna (21 turns on 1 inch PVC) showed about 3 db better than the 3
>pound can and about 6 to 7 db better than the 1 pound can.  If the 3
>pound can has around 10 dbi gain and I add 3 db for circular vs linear
>polarization (I was using a horizontal dipole for the source)  then that
>would give me about 16 dbi for the helix or a couple of db less than
>calculations.  Given the fact that I don't yet have a way to optimize the
>match and the and my method of measurements is crude at best, the helix
>may well be performing up to specs.  At any rate the PVC and the slightly
>smaller than calculated size is not a killer.  If the best it gets is 2
>db less than calculated then I think I am happy with the helix.  (The
>last time I did this I forgot to add the 3 db for polarization mismatch.)
>  I also was able to again compare the grounded feed helix with the
>ungrounded one and could find no difference so I think I will go with the
>grounded feed.
>
>Now all I have to do is get a couple of converters going again!
>
>73 de Jess - W4MVB
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