Hi folks,
I decided to check out my SW8 a little bit more. I measured the
wall wart voltage, and it measured 9.6VDC, so it seemed to be within limits.
Just for the heck of it, I checked the ripple voltage with a scope. 4.6V p-p
of ripple!
I opened up the supply, and discovered that the filter cap had exploded.
Just for the record, this isn't a regulated supply; it is merely a
transformer, four diodes, and a filter capacitor.
I decided to build up my own 10V supply, using a 1000uF cap and a 7810
regulator. I also decided to go with a 3-wire grounded power cord, using
single point grounding on the power supply board.
Now, all of the buzz on the low end of the MW band is gone, and the
sensitivity is much better. Also, the intermittent display backlight problem
is gone.
Still not quite as sensitive as my other receivers, but not bad. MDS is now
down below .1uV, which is pretty ok.

Pete

Pete KE9OA wrote:
Hi folks,
I decided to check out my SW8 a little bit more. I
measured the wall wart voltage, and it measured 9.6VDC, so it seemed
to be within limits. Just for the heck of it, I checked the ripple
voltage with a scope. 4.6V p-p of ripple!
..
..
Still not quite as sensitive as my other receivers, but not bad. MDS
is now down below .1uV, which is pretty ok.

Pete

Good info Pete. I expected you to get more out of the receiver. My SW8 was
a very good radio with a nice mellow sound. It was my favorite receiver for
program listening. The filters do seem a little wider than advertised and
that may be responsible for the nice sound.

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

Pete KE9OA wrote:

Hi folks,
I decided to check out my SW8 a little bit more. I measured the
wall wart voltage, and it measured 9.6VDC, so it seemed to be within limits.
Just for the heck of it, I checked the ripple voltage with a scope. 4.6V p-p
of ripple!
I opened up the supply, and discovered that the filter cap had exploded.
Just for the record, this isn't a regulated supply; it is merely a
transformer, four diodes, and a filter capacitor.
I decided to build up my own 10V supply, using a 1000uF cap and a 7810
regulator. I also decided to go with a 3-wire grounded power cord, using
single point grounding on the power supply board.
Now, all of the buzz on the low end of the MW band is gone, and the
sensitivity is much better. Also, the intermittent display backlight problem
is gone.
Still not quite as sensitive as my other receivers, but not bad. MDS is now
down below .1uV, which is pretty ok.

Pete

I got tired of keeping track of the wallwart for my SW8, which doesn't
fit in the Drake carry bag. The remedy was to cut open the wall wart and
install the parts in the radio. I had to move the battery holder about
an inch to one side to make room for the transformer. It was a tight
fit. I also added a receptacle on the back which accepts a standard
computer power cord. I probably have the only SW8 with an internal AC
power supply.


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I agree.......................with a 3-wire power cord, MW reception is
improved. I niticed the same characteristic with my Palstar R30. The audio
does sound quite good.
On another note, I did finish the RF Generator design. This is a DDS based
unit that covers from 10kHz to 30MHz, in 1kHz steps. Actually, the final
unit will probably tune in finer steps, and it could cover up to 60MHz with
this chip (AD9851) . Modulation range will be from 0 to 100%, with a 1kHz
tone. Tuning method? Rotary shaft encoder, along with keypad entry.
Projected price? I am shooting for the 350 to 400 dollar range.
I characterized the prototype over the weekend. 2nd, 3rd, and 4th harmonics
measured at -25dBc, -35dBc, and -45dBc respectively. I didn't have the
equipment to characterize phase noise, but with this scheme, as used on my
DDS, phase noise measured at -124dBc @ 7kHz offset, using an Epson SG636
packaged 30MHz oscillator as a 30MHz reference.
Frequency error @ 30MHz was only 3Hz. Stay tuned for further developments.
As far at the MW receiver design, all of the RF design is
completed....................I am only waiting for the software person to be
freed up; when this happens, we can move forward.
Right now, I am learning how to use Protel DXP. This is the program that I
will be entering the final design information into.
A nice program............it does PSpice simulations, microstrip
calculations, etc, in addition to the normal schematic capture and board
layout functions.

Pete

"Brian Denley" wrote in message
news:d6Jcc.200431$1p.2281442@attbi_s54...
Pete KE9OA wrote:
Hi folks,
I decided to check out my SW8 a little bit more. I
measured the wall wart voltage, and it measured 9.6VDC, so it seemed
to be within limits. Just for the heck of it, I checked the ripple
voltage with a scope. 4.6V p-p of ripple!
.
.
Still not quite as sensitive as my other receivers, but not bad. MDS
is now down below .1uV, which is pretty ok.

Pete

Good info Pete. I expected you to get more out of the receiver. My SW8
was
a very good radio with a nice mellow sound. It was my favorite receiver
for
program listening. The filters do seem a little wider than advertised and
that may be responsible for the nice sound.

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

That sounds like a good thing to do. An improvement you can make to the
standard Drake power supply is to connect .01uF caps across each of the
diodes. Also, bypass each leg of the power transformer secondary to ground
witha 1uF NP cap. This removes that "flourescent ballast" type of buzzing
hash that you may hear on frequencies below 700kHz. If you have the later
unit that tunes down to 100kHz (which I wish I had), expect much lower noise
performance down there.

Pete

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

Hi folks,
I decided to check out my SW8 a little bit more. I measured
the
wall wart voltage, and it measured 9.6VDC, so it seemed to be within
limits.
Just for the heck of it, I checked the ripple voltage with a scope. 4.6V
p-p
of ripple!
I opened up the supply, and discovered that the filter cap had exploded.
Just for the record, this isn't a regulated supply; it is merely a
transformer, four diodes, and a filter capacitor.
I decided to build up my own 10V supply, using a 1000uF cap and a 7810
regulator. I also decided to go with a 3-wire grounded power cord, using
single point grounding on the power supply board.
Now, all of the buzz on the low end of the MW band is gone, and the
sensitivity is much better. Also, the intermittent display backlight
problem
is gone.
Still not quite as sensitive as my other receivers, but not bad. MDS is
now
down below .1uV, which is pretty ok.

Pete

I got tired of keeping track of the wallwart for my SW8, which doesn't
fit in the Drake carry bag. The remedy was to cut open the wall wart and
install the parts in the radio. I had to move the battery holder about
an inch to one side to make room for the transformer. It was a tight
fit. I also added a receptacle on the back which accepts a standard
computer power cord. I probably have the only SW8 with an internal AC
power supply.


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I was just wondering the other day whether I had added those RF bypass
caps' when I was doing the power supply mod'. I think I replaced the
discrete OEM diodes with a four diode bridge assembly but I may have
forgot the caps'. I'll take a look.

BTW- I might be able to take a picture of the power supply mod' with a
digital camera if you'd like to see how I located the parts in the
chassis.


Pete KE9OA wrote:

That sounds like a good thing to do. An improvement you can make to the
standard Drake power supply is to connect .01uF caps across each of the
diodes. Also, bypass each leg of the power transformer secondary to ground
witha 1uF NP cap. This removes that "flourescent ballast" type of buzzing
hash that you may hear on frequencies below 700kHz. If you have the later
unit that tunes down to 100kHz (which I wish I had), expect much lower noise
performance down there.

Pete

Starman wrote:

I got tired of keeping track of the wallwart for my SW8, which doesn't
fit in the Drake carry bag. The remedy was to cut open the wall wart and
install the parts in the radio. I had to move the battery holder about
an inch to one side to make room for the transformer. It was a tight
fit. I also added a receptacle on the back which accepts a standard
computer power cord. I probably have the only SW8 with an internal AC
power supply.


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That would be good. Another thing...............the 1uF caps that bypass
each leg of the power transformer secondary to ground are even more
effective than the .01s across each diode.

Pete

"starman" wrote in message
...
I was just wondering the other day whether I had added those RF bypass
caps' when I was doing the power supply mod'. I think I replaced the
discrete OEM diodes with a four diode bridge assembly but I may have
forgot the caps'. I'll take a look.

BTW- I might be able to take a picture of the power supply mod' with a
digital camera if you'd like to see how I located the parts in the
chassis.


Pete KE9OA wrote:

That sounds like a good thing to do. An improvement you can make to the
standard Drake power supply is to connect .01uF caps across each of the
diodes. Also, bypass each leg of the power transformer secondary to
ground
witha 1uF NP cap. This removes that "flourescent ballast" type of
buzzing
hash that you may hear on frequencies below 700kHz. If you have the
later
unit that tunes down to 100kHz (which I wish I had), expect much lower
noise
performance down there.

Pete

Starman wrote:

I got tired of keeping track of the wallwart for my SW8, which doesn't
fit in the Drake carry bag. The remedy was to cut open the wall wart
and
install the parts in the radio. I had to move the battery holder about
an inch to one side to make room for the transformer. It was a tight
fit. I also added a receptacle on the back which accepts a standard
computer power cord. I probably have the only SW8 with an internal AC
power supply.


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How did you arrive at the 1uF value for the transformer caps?

Pete KE9OA wrote:

That would be good. Another thing...............the 1uF caps that bypass
each leg of the power transformer secondary to ground are even more
effective than the .01s across each diode.

Pete

"starman" wrote in message
...
I was just wondering the other day whether I had added those RF bypass
caps' when I was doing the power supply mod'. I think I replaced the
discrete OEM diodes with a four diode bridge assembly but I may have
forgot the caps'. I'll take a look.

BTW- I might be able to take a picture of the power supply mod' with a
digital camera if you'd like to see how I located the parts in the
chassis.


Pete KE9OA wrote:

That sounds like a good thing to do. An improvement you can make to the
standard Drake power supply is to connect .01uF caps across each of the
diodes. Also, bypass each leg of the power transformer secondary to
ground
witha 1uF NP cap. This removes that "flourescent ballast" type of
buzzing
hash that you may hear on frequencies below 700kHz. If you have the
later
unit that tunes down to 100kHz (which I wish I had), expect much lower
noise
performance down there.

Pete

Starman wrote:

I got tired of keeping track of the wallwart for my SW8, which doesn't
fit in the Drake carry bag. The remedy was to cut open the wall wart
and
install the parts in the radio. I had to move the battery holder about
an inch to one side to make room for the transformer. It was a tight
fit. I also added a receptacle on the back which accepts a standard
computer power cord. I probably have the only SW8 with an internal AC
power supply.


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It was empirecal......................0.1uf quieted things down pretty well
to around 100kHz, 0.47uF was good down to 50kHz, so I took the next step and
went to a 1uF. Even down at 10kHz, all you hear is atmospheric
noise................no buzzing from the power supply. If you look at the
older TenTec linear supplies, you will see .1uF being used, but these
supplies were intended to be used with rigs that only tuned down to 1.8MHz.

Pete

"starman" wrote in message
...
How did you arrive at the 1uF value for the transformer caps?

Pete KE9OA wrote:

That would be good. Another thing...............the 1uF caps that bypass
each leg of the power transformer secondary to ground are even more
effective than the .01s across each diode.

Pete

"starman" wrote in message
...
I was just wondering the other day whether I had added those RF bypass
caps' when I was doing the power supply mod'. I think I replaced the
discrete OEM diodes with a four diode bridge assembly but I may have
forgot the caps'. I'll take a look.

BTW- I might be able to take a picture of the power supply mod' with a
digital camera if you'd like to see how I located the parts in the
chassis.


Pete KE9OA wrote:

That sounds like a good thing to do. An improvement you can make to
the
standard Drake power supply is to connect .01uF caps across each of
the
diodes. Also, bypass each leg of the power transformer secondary to
ground
witha 1uF NP cap. This removes that "flourescent ballast" type of
buzzing
hash that you may hear on frequencies below 700kHz. If you have the
later
unit that tunes down to 100kHz (which I wish I had), expect much
lower
noise
performance down there.

Pete

Starman wrote:

I got tired of keeping track of the wallwart for my SW8, which
doesn't
fit in the Drake carry bag. The remedy was to cut open the wall
wart
and
install the parts in the radio. I had to move the battery holder
about
an inch to one side to make room for the transformer. It was a
tight
fit. I also added a receptacle on the back which accepts a
standard
computer power cord. I probably have the only SW8 with an internal
AC
power supply.


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