I injected the signal straight into the antenna input..................the
same way I test all of my receivers. As an example, the AOR7030, Icom R75,
Palstar R30, Yaesu FRG100, and the Racal 6790/GM all will clearly detect a
signal well below .1uV. This sample of the SW8 loses the signal at the .3uV
range. It sounds like about 10dB of RF gain is missing.
The soft measurement method was used, with a Boonton Model 103D RF generator
connected straight into the antenna input vs running it through a 50 Ohm
thru load. The soft method yields around a 6dB better sensitivity figure.
When I first purchased the receiver, I did purchase the schematic set. Not
a bad deal for around 30 dollars.
I hope that they can figure out what's going on with this unit. Work has
kept me so busy that I just haven't had the time to get to this one.
My latest project has been an AD9851 based RF Generator. I just finished the
board layout, and if this thing works properly, I will make the design
available to interested parties, free of charge.

Pete

"starman" wrote in message
...
Pete KE9OA wrote:

I picked up one of these units last October.................anyway, I
noticed that the sensitivity wasn't as good as my other units, so I
decided
to make some measurements. Across the whole tuning range, the MDS is
..3uV,
while with all of my other receivers (7 of them), the MDS is below .1uV.
Is there any failure mechanism that occurs with this receiver? I do have
the
schematic set.

Hi Pete,

I have the schematic sets for both the early and later SW8. The early
models were reported to have a poor impedance match for the whip
antenna. The later schematics show some changes in the componants of the
double diode circuit which protects for static electricity on the whip.
This circuit is also connected differently to the following circuits in
the later model.

There's a change in value for the series resistor on the gate of Q1
(2SK152), the whip amp'. Some of the capacitor values in this gate
circuit are also changed. Q1 might be running at a higher gain in the
later models but this would only affect the whip sensitivity because the
other HF antenna inputs bypass Q1 through the antenna selection switch
(SW2) on the back of the receiver. I think these changes (above) were
made in 1994. The biggest change occurred in 1996 when the selectable
sideband sync' detector was added. The first digit in the serial number
denotes the year of manufacture.

How did you inject the test signal? Maybe your SW8 is out of alignment.


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