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.

Pete

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.

Pete

Did you buy it new? Is it the 1994 or the 1996 model?

--
Brian Denley
http://home.comcast.net/~b.denley/index.html

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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starman wrote:

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.


I had the early (1994) model and while it was fairly deaf on the whip, it
was very sensitive on my external random wire. Not quite as sensitive as my
R-5000 but not far behind. One of, if not the best audio receiver(s) I have
owned.
Brian Denley
http://home.comcast.net/~b.denley/index.html

Hi Brian,
I would say that it is the earlier model, the one that only
goes down to 500kHz. Since I wanted the upgrade to allow the unit to tune
down to 500kHz, and since it had an intermittent backlight problem, I
decided to ship it out to Drake this afternoon.
Now I understand why the person sold it...........it's always that same old
"I am selling it for a friend, so I don't know anything about its history"
story.
On a good note, Bill Frost, over at Drake told me that it would only run
around 125 dollars for the repair, so I figured, why not?

Pete

"Brian Denley" wrote in message
news:Uqt7c.56179$Cb.879650@attbi_s51...
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.

Pete

Did you buy it new? Is it the 1994 or the 1996 model?

--
Brian Denley
http://home.comcast.net/~b.denley/index.html

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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-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Thanks Brian.....................with the whip antenna, the radio doesn't
sound bad, but on the external antenna inputs, both high and low impedance,
sensitivity isn't too good. I wonder if there was some ESD to the input
stage. I made my measurements at both 700kHz and at 10MHz, so I don't think
that there is an input filter problem, but probably, one of the input
transistors has been damaged. Once I receive the unit back from R.L. Drake,
I will let you folks know what the problem was.
Oh, the S/N starts with a 4, so this would probably be a 1994 model.

Pete

"Brian Denley" wrote in message
news:x1O7c.65561$SR1.112821@attbi_s04...
starman wrote:

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.


I had the early (1994) model and while it was fairly deaf on the whip, it
was very sensitive on my external random wire. Not quite as sensitive as
my
R-5000 but not far behind. One of, if not the best audio receiver(s) I
have
owned.
Brian Denley
http://home.comcast.net/~b.denley/index.html

Pete KE9OA wrote:
Hi Brian,
I would say that it is the earlier model, the one
that only goes down to 500kHz. Since I wanted the upgrade to allow
the unit to tune down to 500kHz, and since it had an intermittent
backlight problem, I decided to ship it out to Drake this afternoon.
Now I understand why the person sold it...........it's always that
same old "I am selling it for a friend, so I don't know anything
about its history" story.
On a good note, Bill Frost, over at Drake told me that it would only
run around 125 dollars for the repair, so I figured, why not?

Pete


Pete:
Let us know how it performs after Drake works on it.

--
Brian Denley
http://home.comcast.net/~b.denley/index.html

I sure will..............as soon as I get it back, it goes on the signal
generator!

Pete

"Brian Denley" wrote in message
news:Yk78c.67932$J05.539677@attbi_s01...
Pete KE9OA wrote:
Hi Brian,
I would say that it is the earlier model, the one
that only goes down to 500kHz. Since I wanted the upgrade to allow
the unit to tune down to 500kHz, and since it had an intermittent
backlight problem, I decided to ship it out to Drake this afternoon.
Now I understand why the person sold it...........it's always that
same old "I am selling it for a friend, so I don't know anything
about its history" story.
On a good note, Bill Frost, over at Drake told me that it would only
run around 125 dollars for the repair, so I figured, why not?

Pete


Pete:
Let us know how it performs after Drake works on it.

--
Brian Denley
http://home.comcast.net/~b.denley/index.html