john wrote in message
news:0pWMb.44127$5V2.62848@attbi_s53...
Hi guys and gals. Pretty new to shortwave and I know its late to be asking
but how many of you use a DX-394 communications receiver and what do you
think about it?
I paid $250 for mine on ebay (prolly too much) with a lot of mods done to
it
and got the super Zepp shortwave antwnna. Here are the mods!
1) SWITCHABLE I.F. FILTERS-A switch has been installed to the front panel,
using the Noise blanker switch of the radio that allows listeners to
choose
between Wide or Narrow Bandwidths! The two I.F. Filters have been set up
on
a switch so that you can listen to the wide AM filter for casual, easy
listening or flip over to a narrow bandwidth for Dxing or for listening to
weak signals on a crowded band! The Bandwidth of the narrow, outboard
filter
installed is a tight 3.5-4 KHZ, which is great for SSB and crowded SW band
conditions.

2) The "Chuff Chuff" noise when fine tuning was stopped with a simple mod.

Good mod.

3) Keyboard Beeps mod was done to stop the annoying Beeping.

4) Crosstalk Mod was done by adding components in the ceramic filter
circuit. This greatly reduces the problems from strong adjacent channel
interference or bleed thru from the filters. This narrows the bandwidth by
adding more capacitors to the circuit around Q13 is the second part of
this
mod.

The bandwidth is defined by the filter itself.................you can't
narrow the bandwidth. You can only eliminate the feedaround problem.

5) Weight added to Main tuning dial makes the radio feel like a "Real
Radio"
with a heavy flywheel dial. Approximately 4 oz. of lead was added to the
dial and helps the "Feel " of the dial.

6) RF Gain control mod provides better linearity when adjust gain of
radio.
This makes it much more flexible when tuning and listening to loud or
strong
SW signals. This mod had a big effect on the radio as well!

RF gain isn't that necessary a control, unless you are disabling the AGC. It
might be ok, if you want to eliminate the background noise, but then you
lose AGC control. We are dealing with a closed loop system here.

7) AGC mod done for a slower speed. This makes it easier to listen to on
AM
or Sideband. The original manufacturer had a very fast attack AGC speed.
Up
and down signals will not pump the audio sound unnatural now. In ham
lingo,
the AGC has been modified to compensate for fast QSB.

Good mod, if it is switchable.

8) Audio hiss removed from audio circuit by adding more capacitors to
filter
out some of the higher audio frequencies. Thus, this gives the audio more
punch and makes it easier to listen to. It also helps make up for the
cheap
built in speaker. An external, Good quality speaker is also recommended!

Once again, good mod, if it is switchable; otherwise, you lose high
frequency response. I never noticed a problem with any of my units.

9)Using the frequency counter in my $3000 transceiver the USB and LSB
readouts have been adjusted on the DX-394 to show correct readout with an
internal trimmer capacitor. Typically the frequency readout of the DX-394
shows the center frequency rather than the actual frequency of the SSB
signal.


10)Audio Quality-Additional capacitors have been added to the audio
circuit
which give the radio real bass punch and make it sound like a real
communications receiver!

Why would they add additional capacitors............you only need to
INCREASE the size of the coupling capacitors in order to lower the corner
frequency. (1/2PI RC).

11)Hum Reduction-A 2200 uF capacitor is added to the power supply to
reduce
the hum heard with low audio gain commonly used with headphones. With this
mod the hum disappears! Additional voltage regulation has been added to
the
power supply circuit to make the entire system more stable!

This receiver never had any stability problems. If you really did want to
improve the stability, replace the trimmer capacitors with Voltronics
multi-turn piston capacitors.

12) The top and bottom cases of the radio cabinet have been covered on the
inside with conductive, aluminum tape that will reduce interference. RFI
produced from nearby broadcast stations, computers, TV's and computer
monitors is greatly reduced with this new mod. Birdies, spurious signals
and
heterodynes caused by these and other electronic devices is shielded out
by
this new aluminum tape's shielding.

This was ok from a shielding standpoint, but now the internal loopstick has
been rendered useless. It is now enclosed in a shield!

Please let me know what you THINK!


Not a bad deal for 150 dollars..................you overpaid, but still it
isn't too bad of a radio. Probably, one of the biggest flaws of the design
are the front end filters. Instead of using even a 3 branch type of filter,
the designer decided to use a simple tunable LC filter. This would be ok in
a 50 dollar portable, but is not the way to go in a receiver that originally
was attempted to sell for 400 dollars. The glass epoxy boards are a good
idea. In the Chicago area hamfests, this receiver typically goes for 100 to
150 dollars.

Pete

Interesting observations, Pete. Some I agree with, others I don't. Comments
below.

Tom

Pete KE9OA wrote:
john wrote in message
news:0pWMb.44127$5V2.62848@attbi_s53...
Hi guys and gals. Pretty new to shortwave and I know its
late to be asking but how many of you use a DX-394
communications receiver and what do you think about it?
I paid $250 for mine on ebay (prolly too much) with a
lot of mods done to it and got the super Zepp shortwave
antwnna. Here are the mods! 1) SWITCHABLE I.F. FILTERS-A
switch has been installed to the front panel, using the
Noise blanker switch of the radio that allows listeners
to choose between Wide or Narrow Bandwidths! The two
I.F. Filters have been set up on a switch so that you
can listen to the wide AM filter for casual, easy
listening or flip over to a narrow bandwidth for Dxing
or for listening to weak signals on a crowded band! The
Bandwidth of the narrow, outboard filter installed is a
tight 3.5-4 KHZ, which is great for SSB and crowded SW
band conditions.

If the narrow filter is as described, then either the demodulated SSB signal
will be very thin (audio spectrum mainly 1.5kHz - 5kHz) or the displayed
frequency will be in error by 1-2kHz. That's inescapable with the DX-394's
design. AM tuning accuracy will be unaffected but the filter as described is
perhaps too narrow for double sideband AM and you will find it necessary to
tune towards one of the sidebands to brighten the sound. The switchable
filter mod alone using the stock wide and narrow filters is a super
improvement for AM - wide filter for clear signals, narrow filter for the
tough ones.


2) The "Chuff Chuff" noise when fine tuning was stopped
with a simple mod.

Good mod.

This is debatable. The chuffing noise is caused by a deliberate muting of
audio when frequency is changed or when certain controls are switched - in
order to suppress clicks. Some DX-394's seem to generate stronger clicks
when tuned than others. The clicks can be quite severe when you have the
volume control up high. So the subjective preference for clicks versus
chuffs is a factor - I prefer chuffs. The audio line out jack is not muted
so a chuff-free listening experience can be had by plugging in an external
power amp/speaker - interstingly, IMS, it's click-free, too!


3) Keyboard Beeps mod was done to stop the annoying
Beeping.

This is not a mod (unless he took the cutters to the Beep line). It's a
reversible, operator selectable front panel key combination omitted from the
Owner's Manual but described in the Service Manual .


4) Crosstalk Mod was done by adding components in the
ceramic filter circuit. This greatly reduces the
problems from strong adjacent channel interference or
bleed thru from the filters. This narrows the bandwidth
by adding more capacitors to the circuit around Q13 is
the second part of this mod.

The bandwidth is defined by the filter
itself.................you can't narrow the bandwidth.
You can only eliminate the feedaround problem.

Correct. And perhaps the most important mod - thanks to Frank Cathell - and
makes a huge difference in the amount of interference.


5) Weight added to Main tuning dial makes the radio feel
like a "Real Radio" with a heavy flywheel dial.
Approximately 4 oz. of lead was added to the dial and
helps the "Feel " of the dial.

Very subjective. I have always doubted the virtue of this mod but have never
tried it. Because the DX-394 has keyboard entry, I fail to see the virtue of
a flywheel. There are many ways to jump directly to or close to a desired
frequency that obviate spinning the Main Tuning knob - the Band key, Meter
band selection, direct frequency entry, Monitor key and 160 memories. If the
weighted knob is imbalanced, the knob might fall off frequency. And
excessive weight and use of the knob may accelerate wear and tear on the
rotary encoder.


6) RF Gain control mod provides better linearity when
adjust gain of radio. This makes it much more flexible
when tuning and listening to loud or strong SW signals.
This mod had a big effect on the radio as well!

RF gain isn't that necessary a control, unless you are
disabling the AGC. It might be ok, if you want to
eliminate the background noise, but then you lose AGC
control. We are dealing with a closed loop system here.

I tried and undid the RF Gain modification. I thought it made the
'linearity' of gain vs rotation worse and exacerbated the overload problem
by increasing the maximum gain. There are conditions where you want to
reduce or defeat AGC action, especially in the ham bands on SSB or CW
because the IF is so wide. Strong signals 6kHz away can pump the level
demodulated from the desired signal because they are driving the AGC. I
mod'd one of my DX-394's with an AGC Defeat switch.


7) AGC mod done for a slower speed. This makes it easier
to listen to on AM or Sideband. The original
manufacturer had a very fast attack AGC speed. Up and
down signals will not pump the audio sound unnatural
now. In ham lingo, the AGC has been modified to
compensate for fast QSB.

Good mod, if it is switchable.

Agreed but my research has found that the classic Frank Cathell mod was
designed for the original DX-394 and should not be applied to a DX-394A or B
without also doing a mod to shorten the attack time. That's because the A
and B revisions actually addressed the shortcoming in the original - fast
attack and release was used for both AM and SSB/CW. The A and B models have
a slow release for SSB/CW with an attack time that I would deem to be too
slow. Frank's original mod, when applied to the A and B models,
unnecessarily lengthens both attack and release for the SSB/CW modes. For AM
on all models and SSB/CW in the original model, the increased attack time is
not excessive if the capacitor is chosen for a medium speed release; it's
not a bad compromise and the slower AGC reduces low frequency audio
distortion. It would be preferable to have selectable speeds in all modes to
compensate more optimally for a wide range of conditions. I modified my
DX-394 for selection of fast-medium-slow speed release with as fast an
attack speed as I could get and am looking to improve the attack speed that
I obtained with the fast attack-slow release mod.


8) Audio hiss removed from audio circuit by adding more
capacitors to filter out some of the higher audio
frequencies. Thus, this gives the audio more punch and
makes it easier to listen to. It also helps make up for
the cheap built in speaker. An external, Good quality
speaker is also recommended!

Once again, good mod, if it is switchable; otherwise, you
lose high frequency response. I never noticed a problem
with any of my units.


I agree. I tried the 'hiss' mod and undid it. The preferable mod was the
bass improvement.


9)Using the frequency counter in my $3000 transceiver
the USB and LSB readouts have been adjusted on the
DX-394 to show correct readout with an internal trimmer
capacitor. Typically the frequency readout of the DX-394
shows the center frequency rather than the actual
frequency of the SSB signal.


Not sure that this last statement is true but the author of it has seen many
DX-394's. If the factory aligned the radio according to the instructions in
the Service Manual, then it would be spot on to within +/-200Hz. Aging would
likely reduce accuracy but would a ceramic resonator shift by 0.3% over a
few years?


10)Audio Quality-Additional capacitors have been added
to the audio circuit which give the radio real bass
punch and make it sound like a real communications
receiver!

Why would they add additional capacitors............you
only need to INCREASE the size of the coupling capacitors
in order to lower the corner frequency. (1/2PI RC).


A good mod - adding a capacitor in parallel with the existing was perhaps
easier than replacing it with a larger one!


11)Hum Reduction-A 2200 uF capacitor is added to the
power supply to reduce the hum heard with low audio gain
commonly used with headphones. With this mod the hum
disappears! Additional voltage regulation has been added
to the power supply circuit to make the entire system
more stable!

This receiver never had any stability problems. If you
really did want to improve the stability, replace the
trimmer capacitors with Voltronics multi-turn piston
capacitors.

The 'hum' mod was recently developed and is an excellent improvement. I have
never heard of the 'voltage regulation' mod and am curious what it is and
what was stabilised. I agree that my two A and one B models are very stable,
short and long term, with one exception - some pulling of frequency with
change in RF Gain. I'm not familiar with the Voltronics and will look into
it.


12) The top and bottom cases of the radio cabinet have
been covered on the inside with conductive, aluminum
tape that will reduce interference. RFI produced from
nearby broadcast stations, computers, TV's and computer
monitors is greatly reduced with this new mod. Birdies,
spurious signals and heterodynes caused by these and
other electronic devices is shielded out by this new
aluminum tape's shielding.

This was ok from a shielding standpoint, but now the
internal loopstick has been rendered useless. It is now
enclosed in a shield!

Precisely the purpose! We want just the energy picked up by the antenna
outside the building's environment - not the crap generated inside. And for
LW/MW, we can now use a rotatable, directional antenna whose nulls are not
compromised by the internal antenna. However, aluminum tape is not so very
effective at the lower frequencies; I have used galvanised steel sheet with
better results. And I have even removed the ferrite rod antenna from one of
my radios.


Please let me know what you THINK!


Not a bad deal for 150 dollars..................you
overpaid, but still it isn't too bad of a radio.
Probably, one of the biggest flaws of the design are the
front end filters. Instead of using even a 3 branch type
of filter, the designer decided to use a simple tunable
LC filter. This would be ok in a 50 dollar portable, but
is not the way to go in a receiver that originally was
attempted to sell for 400 dollars. The glass epoxy boards
are a good idea. In the Chicago area hamfests, this
receiver typically goes for 100 to 150 dollars.

Still not a bad deal at $250 - that's near the upper limit of what people
have paid for well modified DX-394's on eBay - and you would be hard-pressed
to find many better radios at this price with the features it has. You could
do worse!


Pete

I agree............it isn't a bad radio, and it does have quite a bit of
potential, especially after replacing those front end filters. It sounds
like you have had more experience with this radio, Tom, and I respect what
you have to say!

Pete

Tom Holden wrote in message
...
Interesting observations, Pete. Some I agree with, others I don't.
Comments
below.

Tom

Pete KE9OA wrote:
john wrote in message
news:0pWMb.44127$5V2.62848@attbi_s53...
Hi guys and gals. Pretty new to shortwave and I know its
late to be asking but how many of you use a DX-394
communications receiver and what do you think about it?
I paid $250 for mine on ebay (prolly too much) with a
lot of mods done to it and got the super Zepp shortwave
antwnna. Here are the mods! 1) SWITCHABLE I.F. FILTERS-A
switch has been installed to the front panel, using the
Noise blanker switch of the radio that allows listeners
to choose between Wide or Narrow Bandwidths! The two
I.F. Filters have been set up on a switch so that you
can listen to the wide AM filter for casual, easy
listening or flip over to a narrow bandwidth for Dxing
or for listening to weak signals on a crowded band! The
Bandwidth of the narrow, outboard filter installed is a
tight 3.5-4 KHZ, which is great for SSB and crowded SW
band conditions.

If the narrow filter is as described, then either the demodulated SSB
signal
will be very thin (audio spectrum mainly 1.5kHz - 5kHz) or the displayed
frequency will be in error by 1-2kHz. That's inescapable with the DX-394's
design. AM tuning accuracy will be unaffected but the filter as described
is
perhaps too narrow for double sideband AM and you will find it necessary
to
tune towards one of the sidebands to brighten the sound. The switchable
filter mod alone using the stock wide and narrow filters is a super
improvement for AM - wide filter for clear signals, narrow filter for the
tough ones.


2) The "Chuff Chuff" noise when fine tuning was stopped
with a simple mod.

Good mod.

This is debatable. The chuffing noise is caused by a deliberate muting of
audio when frequency is changed or when certain controls are switched - in
order to suppress clicks. Some DX-394's seem to generate stronger clicks
when tuned than others. The clicks can be quite severe when you have the
volume control up high. So the subjective preference for clicks versus
chuffs is a factor - I prefer chuffs. The audio line out jack is not muted
so a chuff-free listening experience can be had by plugging in an external
power amp/speaker - interstingly, IMS, it's click-free, too!


3) Keyboard Beeps mod was done to stop the annoying
Beeping.

This is not a mod (unless he took the cutters to the Beep line). It's a
reversible, operator selectable front panel key combination omitted from
the
Owner's Manual but described in the Service Manual .


4) Crosstalk Mod was done by adding components in the
ceramic filter circuit. This greatly reduces the
problems from strong adjacent channel interference or
bleed thru from the filters. This narrows the bandwidth
by adding more capacitors to the circuit around Q13 is
the second part of this mod.

The bandwidth is defined by the filter
itself.................you can't narrow the bandwidth.
You can only eliminate the feedaround problem.

Correct. And perhaps the most important mod - thanks to Frank Cathell -
and
makes a huge difference in the amount of interference.


5) Weight added to Main tuning dial makes the radio feel
like a "Real Radio" with a heavy flywheel dial.
Approximately 4 oz. of lead was added to the dial and
helps the "Feel " of the dial.

Very subjective. I have always doubted the virtue of this mod but have
never
tried it. Because the DX-394 has keyboard entry, I fail to see the virtue
of
a flywheel. There are many ways to jump directly to or close to a desired
frequency that obviate spinning the Main Tuning knob - the Band key, Meter
band selection, direct frequency entry, Monitor key and 160 memories. If
the
weighted knob is imbalanced, the knob might fall off frequency. And
excessive weight and use of the knob may accelerate wear and tear on the
rotary encoder.


6) RF Gain control mod provides better linearity when
adjust gain of radio. This makes it much more flexible
when tuning and listening to loud or strong SW signals.
This mod had a big effect on the radio as well!

RF gain isn't that necessary a control, unless you are
disabling the AGC. It might be ok, if you want to
eliminate the background noise, but then you lose AGC
control. We are dealing with a closed loop system here.

I tried and undid the RF Gain modification. I thought it made the
'linearity' of gain vs rotation worse and exacerbated the overload problem
by increasing the maximum gain. There are conditions where you want to
reduce or defeat AGC action, especially in the ham bands on SSB or CW
because the IF is so wide. Strong signals 6kHz away can pump the level
demodulated from the desired signal because they are driving the AGC. I
mod'd one of my DX-394's with an AGC Defeat switch.


7) AGC mod done for a slower speed. This makes it easier
to listen to on AM or Sideband. The original
manufacturer had a very fast attack AGC speed. Up and
down signals will not pump the audio sound unnatural
now. In ham lingo, the AGC has been modified to
compensate for fast QSB.

Good mod, if it is switchable.

Agreed but my research has found that the classic Frank Cathell mod was
designed for the original DX-394 and should not be applied to a DX-394A or
B
without also doing a mod to shorten the attack time. That's because the A
and B revisions actually addressed the shortcoming in the original - fast
attack and release was used for both AM and SSB/CW. The A and B models
have
a slow release for SSB/CW with an attack time that I would deem to be too
slow. Frank's original mod, when applied to the A and B models,
unnecessarily lengthens both attack and release for the SSB/CW modes. For
AM
on all models and SSB/CW in the original model, the increased attack time
is
not excessive if the capacitor is chosen for a medium speed release; it's
not a bad compromise and the slower AGC reduces low frequency audio
distortion. It would be preferable to have selectable speeds in all modes
to
compensate more optimally for a wide range of conditions. I modified my
DX-394 for selection of fast-medium-slow speed release with as fast an
attack speed as I could get and am looking to improve the attack speed
that
I obtained with the fast attack-slow release mod.


8) Audio hiss removed from audio circuit by adding more
capacitors to filter out some of the higher audio
frequencies. Thus, this gives the audio more punch and
makes it easier to listen to. It also helps make up for
the cheap built in speaker. An external, Good quality
speaker is also recommended!

Once again, good mod, if it is switchable; otherwise, you
lose high frequency response. I never noticed a problem
with any of my units.


I agree. I tried the 'hiss' mod and undid it. The preferable mod was the
bass improvement.


9)Using the frequency counter in my $3000 transceiver
the USB and LSB readouts have been adjusted on the
DX-394 to show correct readout with an internal trimmer
capacitor. Typically the frequency readout of the DX-394
shows the center frequency rather than the actual
frequency of the SSB signal.


Not sure that this last statement is true but the author of it has seen
many
DX-394's. If the factory aligned the radio according to the instructions
in
the Service Manual, then it would be spot on to within +/-200Hz. Aging
would
likely reduce accuracy but would a ceramic resonator shift by 0.3% over a
few years?


10)Audio Quality-Additional capacitors have been added
to the audio circuit which give the radio real bass
punch and make it sound like a real communications
receiver!

Why would they add additional capacitors............you
only need to INCREASE the size of the coupling capacitors
in order to lower the corner frequency. (1/2PI RC).


A good mod - adding a capacitor in parallel with the existing was perhaps
easier than replacing it with a larger one!


11)Hum Reduction-A 2200 uF capacitor is added to the
power supply to reduce the hum heard with low audio gain
commonly used with headphones. With this mod the hum
disappears! Additional voltage regulation has been added
to the power supply circuit to make the entire system
more stable!

This receiver never had any stability problems. If you
really did want to improve the stability, replace the
trimmer capacitors with Voltronics multi-turn piston
capacitors.

The 'hum' mod was recently developed and is an excellent improvement. I
have
never heard of the 'voltage regulation' mod and am curious what it is and
what was stabilised. I agree that my two A and one B models are very
stable,
short and long term, with one exception - some pulling of frequency with
change in RF Gain. I'm not familiar with the Voltronics and will look into
it.


12) The top and bottom cases of the radio cabinet have
been covered on the inside with conductive, aluminum
tape that will reduce interference. RFI produced from
nearby broadcast stations, computers, TV's and computer
monitors is greatly reduced with this new mod. Birdies,
spurious signals and heterodynes caused by these and
other electronic devices is shielded out by this new
aluminum tape's shielding.

This was ok from a shielding standpoint, but now the
internal loopstick has been rendered useless. It is now
enclosed in a shield!

Precisely the purpose! We want just the energy picked up by the antenna
outside the building's environment - not the crap generated inside. And
for
LW/MW, we can now use a rotatable, directional antenna whose nulls are not
compromised by the internal antenna. However, aluminum tape is not so very
effective at the lower frequencies; I have used galvanised steel sheet
with
better results. And I have even removed the ferrite rod antenna from one
of
my radios.


Please let me know what you THINK!


Not a bad deal for 150 dollars..................you
overpaid, but still it isn't too bad of a radio.
Probably, one of the biggest flaws of the design are the
front end filters. Instead of using even a 3 branch type
of filter, the designer decided to use a simple tunable
LC filter. This would be ok in a 50 dollar portable, but
is not the way to go in a receiver that originally was
attempted to sell for 400 dollars. The glass epoxy boards
are a good idea. In the Chicago area hamfests, this
receiver typically goes for 100 to 150 dollars.

Still not a bad deal at $250 - that's near the upper limit of what people
have paid for well modified DX-394's on eBay - and you would be
hard-pressed
to find many better radios at this price with the features it has. You
could
do worse!


Pete