Measuring on a commercial AM-filter from ITT, type 931 AM with my DG8SAQ VNWA
From start the filter specifics
was unknown, so I made an experimental measuring with a 47 OHM resistor in
with a 1 K Trim Pot and made a sweep.
I found that the best and flat top-of-filter was close to, but a little less than 940 Ohm.
Then I figured the transformation between VNWA (50) and the filter (900 Ohm): SQR of 900/50 = ~ 4,25.
I made a Toroid-transformer, 4-filar ( 4 wires wrapped closely with a drillingmashine), type: 4C65 ferrite,
9 windings total, then connected as shown.
|One side to the other.||Then I connected the filter in
2 pc. trimmer at 25 pF is added.
Setting the frequency to 10,7
MHz, plus/minus 250 KHz and CALIBRATING the VNWA,
I connected the WNVA:
You will possibly need to make a screen between filter input and output to avoid overhearing. I did by hand.
And here is the result:
In the 1970'ties I used that filter in a homemade 2 meter SSB-rig and it was working perfectly.
A close-up picture:
The data says:
That is it!!!
OZ6YM, dec. 2011.