de KT4ZX - Lee Wells - leewells@lexmark.com
Hey everybody....thanks for all the info. A lot of varying
recommendations, but one common one was to test out the
transformers.
So when I got home tonight I pulled the transformer box inside
and took it apart. Oh yeah....first I meant to check the SWR on
the Inv-L, but had the antenna switch in the wrong position. It
appears that I only fried a 50 ohm resistor in the beverage
box that I was switching in to the unused port. The toroids
& relays seem fine.
So on to the testing. I first started testing out the
forward transformer (shown as T2 in ARRL Ant HandBook and ON4UN's
book, the one that is fed from the center tap on T1).
I unsolderd the two signal leads, leaving the other two leads
attached to ground. (I know, I should have wound it with one
piece of wire and then tapped up a few turns from one end,
but I cut the wire too short so I had to but a second winding
on the toroid for the primary) I put a 1K pot on one the hi-Z side,
and attached the lo-Z side to the noise bridge. Here are the
resistances that I found the best noise dips over a range
of frequencies:
freq pot noise bridge
1.85 577 56
3.8 637 55
6.0 740 49
7.1 926 40
This seemed a little off since I had calculated the beverage impedance
to be 407 ohms. And I wound the transformer to match 407 to 50 ohms.
So I decided to go ahead and pull the toroid off the board
so I could take a few turns off of the hi-Z side.
I took about 4 or 5 turns off and the new readings are:
freq pot noise bridge
1.85 715 90
3.8 721 90
6.0 778 92
But this time I didn't tie the grounds together....I noticed that
when I do, the numbers drop on both sides. (1.85 droped to 646/80)
So my main question is how do I interpret this data??? The impedance
ratio is about right now to match 400 ohms to 50 ohms. Another
big question, is why can't I get a good dip with a setting of 50
ohms on the noise bridge??? Am I doing something fundamentally wrong
that causes the readings to be off??
Thanks again & 73's
--Lee - KT4ZX
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