The recent posting of receiver test results was very interesting to me.
I have been testing receiver performance for more than 10 years using a
home built test set consisting of 2 filtered,shielded xtal oscillators,
hybrid combiner,and HP attenuators. Frequency spacings of 20,10, and 4.6
khz are available.
I have tested possibly a hundred or so receivers, both new (courtesy
of Texas Towers) and used. I have seen quite a bit of variation in new
as well as used receivers. My test results are quite repeatable and
usually agree well with those made by ARRL.
Last fall I installed a mod in my FT1000D,suggested by Tom Rauch, W8JI
on Top Band Reflector. He has found that one of the fet's in the noise
blanker is not completely disabled when the blanker is "off" and it
generates IMD products. No numbers were given for the improvement
resulting from the mod. I made before and after measurements on my
FT1000D (lot 16, purchased 12/20/91) You are right, it was my Xmas
present, Hi.
The 4.6khz spaced dynamic range before mod was 69db compare with 65db
for the RadCom results. After Tom's mod the dynamic range improved to
79db. My result for 20khz spacing before and after the mod were the
same,92db, compared with RadComs 88db. I believe the RadCom tests were
made with a ssb filter b.w. while mine were made with the 500hz cw
filter. This could account for the difference.
This 10db improvement would put the modified FT1000D near the top of
the list. The mod requires 3 diodes and a 10k resistor. It requires no
board land cutting and could be removed in a few minutes. There are a
number of connectors on the board near the mod location and some care
must be used to tack the diode leads to the connector pins or board
mounted diodes( same electrical points), which I prefer. It takes a
steady hand and a small iron. If anyone wants to make the mod and is
uncomfortable with the verbal description in Toms note, I have made a
sketch of the board area which clarifies the issue. An s.a.s.e will get
you a copy
73, Dan, N5AR
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