GD-1B 100-250 MHz Coil Info

[Steve Harrison]

Great responses, well over two dozen! My thanks to everyone for taking the
time to measure their coils and write other comments. One chap even
volunteered to send me documents on the meter. I've been able to make a new
coil that works very nicely but am still trying to get some meter grid
current indication on the two highest bands; it will read overscale on the
next two lower bands but nothing on the lowest, either. I suspect a weak
tube although it oscillates nicely way past 250 MHz. The output level on
all ranges is flat to within about 5 dB, better than my old Measurements
Corp. Model 59 meter. I didn't even have to replace the filter cap, the
original holds the B+ up nicely for 10-15 seconds after I turn it off.

73, Steve K0XP

P.S. Following is the actual measurements of the original coil from Dick
Blaney, WB8MHE:
~~~~~~~~~~~~~~~~~~~~~~~
It is, in fact, a 1/2 turn loop.  It is made of brass (I think) tin
plated, 0.1875" (3/16") diameter round stock.  Each end is turned down
to 0.120" (~1/8") by 0.300" long.  Center to center of the ends it is
0.715".  End of pins to top of loop, 0.900".   unturned (full
diameter) portion of loop, 0.600".  There is approximately 1/8" of
straight 3/16" section between the end of the reduced diameter pin and
the start of the arc.  Shouldn't be too much of a problem to make if
someone had a small metal lathe.
~~~~~~~~~~~~~~~~~~~~~~

I was able to make a coil that allows oscillation from 250 to above 500
MHz; but until I can get some grid current indication, this is of academic
interest only, or perhaps it will work as a detector (haven't tried that
yet). For pins, I had to file down the ends of a pair of 6-32 brass screws
and tin them then solder a piece of copper tubing over the cut-down screws.
This allowed the loop length to be somewhat longer than the original coil,
about 1-1/4" for 100-250 MHz. The 250-500+ MHz loop is only 1/2" in height,
very similar to the high band coil for my Measurements Model 59 GDO.

By the way, your TV and FM broadcast radio receiver provide
ready-calibrated "frequency meters" for calibrating V/UHF oscillators! Look
in any ARRL HB for video carrier frequency details of the standard TV
channels.

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