On 18 May 2007 at 23:02, Dave G3WCB wrote:
> When you were calling CQ G3YMC called you, but you obviously couldn't
> copy him.
Not surprised.... but welcome to 500kHz. You are a good signal (579-
589) here in Bracknell.
I seem to be having some difficulties with both the antenna (a 10m
base loaded vertical with no top loading) and tx at the moment. Power
seems to have dropped from a good 6-7W when I first finished building
it to 3W or so now and I am eyeing the 1uF output coupling cap in the
PA which I suspect cannot stand the current. Will have a look later
today.
As for the antenna, I was greatly mislead measuring SWR at the shack
end of the coax. One of G4FPQs programs demonstrated quite nicely
that if you have a 300 ohm load at the end of 20m of coax you end up
with a something not that far from 50 ohms at the tx end! I spent
some time getting my noise bridge calibrated and now I can better
work out what is going on (but the resolution of noise bridges is
somewhat deficient for meaningful measurements down at 500kHz). What
it has convinced me is that my ground losses are more like 300 ohms,
just as I had found when I used the same vertical on 136kHz. In the
longer term I need to spend some time getting it lower, but with a
garden with lovely sand about a foot down it is not going to be easy.
Last night (in one of our rain showers) I added a step up toroid
matching transformer at the vertical end (quite a lot of stuff in the
dustbin at the side of it now...). SWR still seems not that bad and
the impedance seems not that far from 50 ohms but more checking is
needed. I called Alan more out of hope than anything, and was not
surprised when he didn't hear me. A QSO with Colin G3VTT earlier in
the week and abortive attempts to call G3UNT shows I have a pretty
marginal signal in Kent at the moment.
Thanks for the reports Dave G3WCB. Bracknell is only around 10 miles
from Taplow so hopefully you should hear me pretty well....
Back to the grind...
73 Dave G3YMC
http://www.davesergeant.com
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