Hi Bob,
yes, most people seem to prefer the SPC these days, although I
have gone back to the simple tee because of the slightly better
power efficiency, given the same components.
I discovered the MFJ case heating problem empirically, by just
putting my hand on the top after an extended over and finding it was
quite warm. Try this with your tuner and see if you get the same.
Every local with an MFJ here who has tried this reports the same
heating.
Regardless, it doesn't make enough difference to tell on the signal
report, but I like to feel that as much of my power as possible is
going out into the wire.
Best wishes for FD next time!
Gary ZL1AN
At 06:27 PM 6/30/03 -0400, you wrote:
>Gary-
>Thanks. Makes sense.
>After looking at your page, I see what you are calling an SPC is what
>I am calling my T. It works great.
>Heating the case, eh? Will try with cover off next FD.
>-Bob
>
>
>
>Gary Bold wrote:
>
>>Bob,
>>
>>both my MFJ tee tuners eat watts, because the coil sits too close
>>to the metal case, which gets warm. I've replaced the case top with
>>cardboard, which increases the Q and decreases the losses.
>>
>>Some years back, I wrote a document describing the theory and
>>design of tee transmatches, which you can find here.
>>
>>http://www.phy.auckland.ac.nz/Staff/geb/transm.pdf
>>
>>For lowest loss, tees should use the largest possible C, as this
>>decreases the voltage across the coil. It's possible to estimate the
>>power loss from the coil Q if you estimate a few other values. I estimate
>>that a good tee transmatch will absorb maybe 5 - 15% of the power
>>applied to it - more for the commercial "miniature, compact" designs.
>>
>>Gary ZL1AN
>>
>>At 03:43 PM 6/30/03 -0400, you wrote:
>>
>>>Well it was the MFJ that seemed to be eatin half my watts.
>>>The T match (hombrew) worked great. Set C's to low value,
>>>find resonance with L, peak with C's.
>>>I suspect the MFJ just loses a lot in the tiny components...
>>>My traveling 'tuner' is a BCB variable cap, a hand wound coil,
>>>and some clip leads. Just lay the parts out on the table top, rock,
>>>or whatever is reasonably flat and non conducting. TX output
>>>is a pair of 24" clip leads to the matchng network and antenna
>>>is wire tossed up and out in opposite directions. Simple and works.
>>>
>>>-Bob
>>
>>
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>
>
>
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