"mike maghakian" wrote in message
...
Pete G on this group raves about how great it is.

however it does not mean it is fun to use. commercial receivers are not
always fun to use.

I have a Drake maritime 5000 dollar receiver, I find it no fun at all to
use compared to the satellit 800 or a modded DX-394 or similar fun to use
receiver.


The 6790 is a good receiver........if you want all of the "creature
comforts", this isn't the receiver to use. It is my favorite as far as
performance, but it is so DEEEEEEEEEEEEEEEEEEEEEEPPPPPPPPPPPPPPPP! We are
talking about over 20 inches of depth.
The gain of the I.F. system is higher than any of my other receivers. The
MDS measures less than .1uV over the whole tuning range, which is in line
with just about every other receiver being sold today.
My favorite receiver? My Lowe HF-150.
I also have the HF-225, but it doesn't compare with the 150 for MW
reception, because of the lossy duplexer that it uses on the MW range (why
they don't use a bandpass filter for this range, I don't know).
My 2nd favorite is my NRD-515, followed by the Palstar R30, Yaesu FRG-100,
Icom R75, AOR7030, SW-8, and all of the others (I lost count).
Many folks are concerned about getting ahold of parts for the 6790, but the
same could be said about the Cubic, WJ, Collins, and all of the other
premium receivers. The main advantage of the super high end receivers is
that most of them can be used for shipboard operation, where they will be
co-located with high power transmitters.
An example is the Collins HF-2054 or the 851S-1 receiver............these
receivers can handle 100V of RF at the antenna input without damage to the
receiver, whether it is powered on or turned off.
Is this kind of robustness needed for the home receiver. Probably not. The
ESD protection that these receivers afford would be helpful, as evidenced by
the number of Lowe receivers that I have replaced the 1st mixer in recently.
Somebody made a comment about how cool the Icom R-75 runs..........I bet
that you haven't attempted to touch that internal 5V regulator.
There have been some failures with this regulator recently. The failure
mechanism is caused by the fact that Icom chose to use an 18V supply to
power the radio. Dave Zantos has modified his power supply by adding a
pre-regulator that brings the voltage down to 13.5V before it enters the
radio.
My advice? Either modify that Icom power brick or replace it with a
regulated 13.5V power supply.
Looking inside of that supply, you will find spots on the circuit board for
adding bypass caps across each rectifier diode.
Add .01uF caps in these places and it will prevent the diodes from
rectifying RF. Another good mod for this power supply is to add a 1uF NP cap
from each leg of the SECONDARY of the power transformer to ground. This
snubs the switching noise from the rectifier diodes.
I have heard mention on this NG that purchasing a good regulated supply gets
rid of these emissions........this is not really the case. Any power supply
can be made quiet by using the aforementioned techniques.
The AOR7030s power supply can also benefit from these mods.

Pete

Hi Pete,

I was the one who mentioned the cool-running R-75. I should have also
mentioned I *only* power it by a 13.5vdc Astron supply. I've never used the
ICOM power brick.

Guy


"Pete KE9OA" wrote in message
...

"mike maghakian" wrote in message
...
Pete G on this group raves about how great it is.

however it does not mean it is fun to use. commercial receivers are not
always fun to use.

I have a Drake maritime 5000 dollar receiver, I find it no fun at all to
use compared to the satellit 800 or a modded DX-394 or similar fun to use
receiver.


The 6790 is a good receiver........if you want all of the "creature
comforts", this isn't the receiver to use. It is my favorite as far as
performance, but it is so DEEEEEEEEEEEEEEEEEEEEEEPPPPPPPPPPPPPPPP! We are
talking about over 20 inches of depth.
The gain of the I.F. system is higher than any of my other receivers. The
MDS measures less than .1uV over the whole tuning range, which is in line
with just about every other receiver being sold today.
My favorite receiver? My Lowe HF-150.
I also have the HF-225, but it doesn't compare with the 150 for MW
reception, because of the lossy duplexer that it uses on the MW range (why
they don't use a bandpass filter for this range, I don't know).
My 2nd favorite is my NRD-515, followed by the Palstar R30, Yaesu FRG-100,
Icom R75, AOR7030, SW-8, and all of the others (I lost count).
Many folks are concerned about getting ahold of parts for the 6790, but
the same could be said about the Cubic, WJ, Collins, and all of the other
premium receivers. The main advantage of the super high end receivers is
that most of them can be used for shipboard operation, where they will be
co-located with high power transmitters.
An example is the Collins HF-2054 or the 851S-1 receiver............these
receivers can handle 100V of RF at the antenna input without damage to the
receiver, whether it is powered on or turned off.
Is this kind of robustness needed for the home receiver. Probably not. The
ESD protection that these receivers afford would be helpful, as evidenced
by the number of Lowe receivers that I have replaced the 1st mixer in
recently.
Somebody made a comment about how cool the Icom R-75 runs..........I bet
that you haven't attempted to touch that internal 5V regulator.
There have been some failures with this regulator recently. The failure
mechanism is caused by the fact that Icom chose to use an 18V supply to
power the radio. Dave Zantos has modified his power supply by adding a
pre-regulator that brings the voltage down to 13.5V before it enters the
radio.
My advice? Either modify that Icom power brick or replace it with a
regulated 13.5V power supply.
Looking inside of that supply, you will find spots on the circuit board
for adding bypass caps across each rectifier diode.
Add .01uF caps in these places and it will prevent the diodes from
rectifying RF. Another good mod for this power supply is to add a 1uF NP
cap from each leg of the SECONDARY of the power transformer to ground.
This snubs the switching noise from the rectifier diodes.
I have heard mention on this NG that purchasing a good regulated supply
gets rid of these emissions........this is not really the case. Any power
supply can be made quiet by using the aforementioned techniques.
The AOR7030s power supply can also benefit from these mods.

Pete

Ok, that makes sense..............on 13.5V, the Icom runs great. I still
have to do the audio mods to mine one of these days. It is a super
performer, RF wise.
Right now, I am revamping a McKay Dymek DR-33C. I just measured the LO
injection from the synthesizer. At +17dBm, I would expect much better IM
performance. LW is laden with multiple MW signals.
I am going to replace that whole kludge of a 1st mixer with a Mini-Circuits
TAK-3H. This device has an IP3 of +29dBm.
The 2nd mixer is getting a Siliconix E431..............this device has an
IP3 of +30dBm.
It should be a very good receiver when I get through with it. I used the
TAK-3H when I upgraded my KWM-380. With a wide open front end on MW / LW, no
IMD products were noted.
These mods should improve the MDS of the DR-33C. I will post my results.

Pete

"Guy Atkins" wrote in message
...
Hi Pete,

I was the one who mentioned the cool-running R-75. I should have also
mentioned I *only* power it by a 13.5vdc Astron supply. I've never used
the ICOM power brick.

Guy


"Pete KE9OA" wrote in message
...

"mike maghakian" wrote in message
...
Pete G on this group raves about how great it is.

however it does not mean it is fun to use. commercial receivers are not
always fun to use.

I have a Drake maritime 5000 dollar receiver, I find it no fun at all to
use compared to the satellit 800 or a modded DX-394 or similar fun to
use receiver.


The 6790 is a good receiver........if you want all of the "creature
comforts", this isn't the receiver to use. It is my favorite as far as
performance, but it is so DEEEEEEEEEEEEEEEEEEEEEEPPPPPPPPPPPPPPPP! We are
talking about over 20 inches of depth.
The gain of the I.F. system is higher than any of my other receivers. The
MDS measures less than .1uV over the whole tuning range, which is in line
with just about every other receiver being sold today.
My favorite receiver? My Lowe HF-150.
I also have the HF-225, but it doesn't compare with the 150 for MW
reception, because of the lossy duplexer that it uses on the MW range
(why they don't use a bandpass filter for this range, I don't know).
My 2nd favorite is my NRD-515, followed by the Palstar R30, Yaesu
FRG-100, Icom R75, AOR7030, SW-8, and all of the others (I lost count).
Many folks are concerned about getting ahold of parts for the 6790, but
the same could be said about the Cubic, WJ, Collins, and all of the other
premium receivers. The main advantage of the super high end receivers is
that most of them can be used for shipboard operation, where they will be
co-located with high power transmitters.
An example is the Collins HF-2054 or the 851S-1 receiver............these
receivers can handle 100V of RF at the antenna input without damage to
the receiver, whether it is powered on or turned off.
Is this kind of robustness needed for the home receiver. Probably not.
The ESD protection that these receivers afford would be helpful, as
evidenced by the number of Lowe receivers that I have replaced the 1st
mixer in recently.
Somebody made a comment about how cool the Icom R-75 runs..........I bet
that you haven't attempted to touch that internal 5V regulator.
There have been some failures with this regulator recently. The failure
mechanism is caused by the fact that Icom chose to use an 18V supply to
power the radio. Dave Zantos has modified his power supply by adding a
pre-regulator that brings the voltage down to 13.5V before it enters the
radio.
My advice? Either modify that Icom power brick or replace it with a
regulated 13.5V power supply.
Looking inside of that supply, you will find spots on the circuit board
for adding bypass caps across each rectifier diode.
Add .01uF caps in these places and it will prevent the diodes from
rectifying RF. Another good mod for this power supply is to add a 1uF NP
cap from each leg of the SECONDARY of the power transformer to ground.
This snubs the switching noise from the rectifier diodes.
I have heard mention on this NG that purchasing a good regulated supply
gets rid of these emissions........this is not really the case. Any power
supply can be made quiet by using the aforementioned techniques.
The AOR7030s power supply can also benefit from these mods.

Pete

In article
,
"Pete KE9OA" wrote:

Snip

Somebody made a comment about how cool the Icom R-75 runs..........I
bet that you haven't attempted to touch that internal 5V regulator.
There have been some failures with this regulator recently. The
failure mechanism is caused by the fact that Icom chose to use an 18V
supply to power the radio. Dave Zantos has modified his power supply
by adding a pre-regulator that brings the voltage down to 13.5V
before it enters the radio. My advice? Either modify that Icom power
brick or replace it with a regulated 13.5V power supply. Looking
inside of that supply, you will find spots on the circuit board for
adding bypass caps across each rectifier diode. Add .01uF caps in
these places and it will prevent the diodes from rectifying RF.
Another good mod for this power supply is to add a 1uF NP cap from
each leg of the SECONDARY of the power transformer to ground. This
snubs the switching noise from the rectifier diodes. I have heard
mention on this NG that purchasing a good regulated supply gets rid
of these emissions........this is not really the case. Any power
supply can be made quiet by using the aforementioned techniques. The
AOR7030s power supply can also benefit from these mods.

You are right about the 5V regulator. These are series regulator
elements and the higher the input voltage the more power they must
dissipate to regulate the voltage down to the lower voltage.

People don't seem to get the diode rectifier concept here though. The
diode in the power supply passes current when the voltage polarity is in
the right direction and blocks it in the reverse. This is the
rectification function. When the diode switched from on to off the
circuit goes to high impedance. This results in a voltage spike that can
damage the diode if the voltage goes above the PIV rating. PIV stands
for Peak Inverse Voltage. It is this voltage spike every time the diode
switches off that causes EMI/RFI depending on the path. It could be
either or both but is usually mostly EMI.

If it is mostly EMI, the usual case, then a common mode choke will block
the majority of the diode switching noise on the cord to the radio.

The power supply terminology to reduce the PIV voltage across the diode
so as to not damage it is a "snubber" circuit. This is usually made of a
cap and resistor across the diode. The cap/resistor time constant value
is determined by the duration of the reverse spike it design to absorb.
The resistor burns the power.

If the spike is small and you want to suppress it for RF reasons only
then it can be just a cap. The capacitor will circulate the current from
the voltage spike around the diode, which is a small RF current loop,
instead of allowing it to propagate away from the diode through the rest
of the power supply circuit up the power cord and into your radio and
make a buzz at 60 or 120 Hz.

You can use a cap to the AC outlet ground on the secondary side of the
transformer but it might not be the best thing to do as it or a pair on
either side on the secondary will generate a continuous current down the
AC mains ground lead at 60 Hz. It might be better to use one cap on the
negative side of the DC output to ground in order to reduce this common
mode switch noise. Alternatively you might try a cap on the positive
output to ground in addition to the one one the negative side. Here you
will only be sending the noise currents down the AC mains leads and not
the 60Hz components.

--
Telamon
Ventura, California

Telamon wrote:
In article
,
"Pete KE9OA" wrote:

Snip

Somebody made a comment about how cool the Icom R-75 runs..........I
bet that you haven't attempted to touch that internal 5V regulator.
There have been some failures with this regulator recently. The
failure mechanism is caused by the fact that Icom chose to use an 18V
supply to power the radio. Dave Zantos has modified his power supply
by adding a pre-regulator that brings the voltage down to 13.5V
before it enters the radio. My advice? Either modify that Icom power
brick or replace it with a regulated 13.5V power supply. Looking
inside of that supply, you will find spots on the circuit board for
adding bypass caps across each rectifier diode. Add .01uF caps in
these places and it will prevent the diodes from rectifying RF.
Another good mod for this power supply is to add a 1uF NP cap from
each leg of the SECONDARY of the power transformer to ground. This
snubs the switching noise from the rectifier diodes. I have heard
mention on this NG that purchasing a good regulated supply gets rid
of these emissions........this is not really the case. Any power
supply can be made quiet by using the aforementioned techniques. The
AOR7030s power supply can also benefit from these mods.


You are right about the 5V regulator. These are series regulator
elements and the higher the input voltage the more power they must
dissipate to regulate the voltage down to the lower voltage.

People don't seem to get the diode rectifier concept here though. The
diode in the power supply passes current when the voltage polarity is in
the right direction and blocks it in the reverse. This is the
rectification function. When the diode switched from on to off the
circuit goes to high impedance. This results in a voltage spike that can
damage the diode if the voltage goes above the PIV rating.

A voltage spike occurs when interrupting power to an inductive load.
There is no indictive load in what you are describing.


PIV stands
for Peak Inverse Voltage. It is this voltage spike every time the diode
switches off that causes EMI/RFI depending on the path. It could be
either or both but is usually mostly EMI.

If it is mostly EMI, the usual case, then a common mode choke will block
the majority of the diode switching noise on the cord to the radio.

The power supply terminology to reduce the PIV voltage across the diode
so as to not damage it is a "snubber" circuit. This is usually made of a
cap and resistor across the diode. The cap/resistor time constant value
is determined by the duration of the reverse spike it design to absorb.
The resistor burns the power.

A snubber circuit is used to protect a driver from the transient when
switching power to an inductive load. See,
http://focus.ti.com/lit/an/slup100/slup100.pdf

The radio power supply is not that type of circuit.


If the spike is small and you want to suppress it for RF reasons only
then it can be just a cap. The capacitor will circulate the current from
the voltage spike around the diode, which is a small RF current loop,
instead of allowing it to propagate away from the diode through the rest
of the power supply circuit up the power cord and into your radio and
make a buzz at 60 or 120 Hz.

The diode is acting as a mixer. It is combining the 60 Hz line voltages
and the signals at the radio frequencies creating a signal at RF with a
large 60Hz modulation. Adding a cap bypasses the diode at RF,
significantly reducing the mixing action.


You can use a cap to the AC outlet ground on the secondary side of the
transformer but it might not be the best thing to do as it or a pair on
either side on the secondary will generate a continuous current down the
AC mains ground lead at 60 Hz.

You need a complete circuit for current to flow. At 60 Hz, what is the
rest of the circuit?


It might be better to use one cap on the
negative side of the DC output to ground in order to reduce this common
mode switch noise. Alternatively you might try a cap on the positive
output to ground in addition to the one one the negative side. Here you
will only be sending the noise currents down the AC mains leads and not
the 60Hz components.


I suggest looking at the whole picture and look at what this does at 60
Hz and at RF frequencies.


Later,

Craigm

In article , craigm
wrote:

Telamon wrote:
In article
,
"Pete KE9OA" wrote:

Snip

Somebody made a comment about how cool the Icom R-75
runs..........I bet that you haven't attempted to touch that
internal 5V regulator. There have been some failures with this
regulator recently. The failure mechanism is caused by the fact
that Icom chose to use an 18V supply to power the radio. Dave
Zantos has modified his power supply by adding a pre-regulator that
brings the voltage down to 13.5V before it enters the radio. My
advice? Either modify that Icom power brick or replace it with a
regulated 13.5V power supply. Looking inside of that supply, you
will find spots on the circuit board for adding bypass caps across
each rectifier diode. Add .01uF caps in these places and it will
prevent the diodes from rectifying RF. Another good mod for this
power supply is to add a 1uF NP cap from each leg of the SECONDARY
of the power transformer to ground. This snubs the switching noise
from the rectifier diodes. I have heard mention on this NG that
purchasing a good regulated supply gets rid of these
emissions........this is not really the case. Any power supply can
be made quiet by using the aforementioned techniques. The AOR7030s
power supply can also benefit from these mods.


You are right about the 5V regulator. These are series regulator
elements and the higher the input voltage the more power they must
dissipate to regulate the voltage down to the lower voltage.

People don't seem to get the diode rectifier concept here though.
The diode in the power supply passes current when the voltage
polarity is in the right direction and blocks it in the reverse.
This is the rectification function. When the diode switched from on
to off the circuit goes to high impedance. This results in a
voltage spike that can damage the diode if the voltage goes above
the PIV rating.

A voltage spike occurs when interrupting power to an inductive load.
There is no indictive load in what you are describing.


PIV stands for Peak Inverse Voltage. It is this voltage spike every
time the diode switches off that causes EMI/RFI depending on the
path. It could be either or both but is usually mostly EMI.

If it is mostly EMI, the usual case, then a common mode choke will
block the majority of the diode switching noise on the cord to the
radio.

The power supply terminology to reduce the PIV voltage across the
diode so as to not damage it is a "snubber" circuit. This is
usually made of a cap and resistor across the diode. The
cap/resistor time constant value is determined by the duration of
the reverse spike it design to absorb. The resistor burns the
power.

A snubber circuit is used to protect a driver from the transient when
switching power to an inductive load. See,
http://focus.ti.com/lit/an/slup100/slup100.pdf

The radio power supply is not that type of circuit.

The snubber protects the rectifier diode from the transformer and
series inductors in the power supply LC output filtering.

There is a reason why most diodes have a PIV much higher than the
voltage in the circuits they operate in. Ever wonder why?

If the spike is small and you want to suppress it for RF reasons
only then it can be just a cap. The capacitor will circulate the
current from the voltage spike around the diode, which is a small
RF current loop, instead of allowing it to propagate away from the
diode through the rest of the power supply circuit up the power
cord and into your radio and make a buzz at 60 or 120 Hz.

The diode is acting as a mixer. It is combining the 60 Hz line
voltages and the signals at the radio frequencies creating a signal
at RF with a large 60Hz modulation. Adding a cap bypasses the diode
at RF, significantly reducing the mixing action.

Thanks for writing that. The reason I have written this now overly long
thread is to explain the reason for by passing and how it works and why
the thinking that the diode is switching RF ground on and off is
generating the noise is rubbish.

You should connect an oscilloscope to a power supply rectifier diode in
operation. If you would do that you will see a large voltage spike
based on the inductance of the circuit and how fast the diode switches.
Faster diodes are more efficient but the spike voltage will increase
with the faster switch time so faster diodes will need a higher PIV
rating.

A fairly slow diode switching at 60 or 120 Hz depending on the
rectifier circuit in a low current supply may not develop a very high
PIV so a capacitor by itself may do the job.

Low current supplies likely have slower diodes because the heat they
dissipate results from the product of the switch time and current going
through them. Larger supplies will have more current through the diodes
and so that they don't burn up they have to switch faster. Bigger
supplies have bigger inductors and faster diodes with larger PIV as a
result.

Switching more power means you need a snubber RC across the diode
instead of just a capacitor.

You can use a cap to the AC outlet ground on the secondary side of
the transformer but it might not be the best thing to do as it or a
pair on either side on the secondary will generate a continuous
current down the AC mains ground lead at 60 Hz.

You need a complete circuit for current to flow. At 60 Hz, what is
the rest of the circuit?

One side of the capacitor is grounded through the AC mains ground lead
and on the other side is alternating voltage at 60 Hz.

It might be better to use one cap on the
negative side of the DC output to ground in order to reduce this
common mode switch noise. Alternatively you might try a cap on the
positive output to ground in addition to the one one the negative
side. Here you will only be sending the noise currents down the AC
mains leads and not the 60Hz components.


I suggest looking at the whole picture and look at what this does at
60 Hz and at RF frequencies.

I did and have. It is common practice to use a small value capacitor to
ground on or near the power supply outputs where any common mode
noise from switching transients is coupled to ground. You can do this
at the transformer secondary but why generate the 60 Hz current if you
don't have to do that? The object is to conduct noise currents to
ground not 60 Hz mains supply.

--
Telamon
Ventura, California

I remember...........you have come up with some pretty good ideas about this
subject in the past. Thanks!

Pete

"Telamon" wrote in message
...
In article
,
"Pete KE9OA" wrote:

Snip

Somebody made a comment about how cool the Icom R-75 runs..........I
bet that you haven't attempted to touch that internal 5V regulator.
There have been some failures with this regulator recently. The
failure mechanism is caused by the fact that Icom chose to use an 18V
supply to power the radio. Dave Zantos has modified his power supply
by adding a pre-regulator that brings the voltage down to 13.5V
before it enters the radio. My advice? Either modify that Icom power
brick or replace it with a regulated 13.5V power supply. Looking
inside of that supply, you will find spots on the circuit board for
adding bypass caps across each rectifier diode. Add .01uF caps in
these places and it will prevent the diodes from rectifying RF.
Another good mod for this power supply is to add a 1uF NP cap from
each leg of the SECONDARY of the power transformer to ground. This
snubs the switching noise from the rectifier diodes. I have heard
mention on this NG that purchasing a good regulated supply gets rid
of these emissions........this is not really the case. Any power
supply can be made quiet by using the aforementioned techniques. The
AOR7030s power supply can also benefit from these mods.

You are right about the 5V regulator. These are series regulator
elements and the higher the input voltage the more power they must
dissipate to regulate the voltage down to the lower voltage.

People don't seem to get the diode rectifier concept here though. The
diode in the power supply passes current when the voltage polarity is in
the right direction and blocks it in the reverse. This is the
rectification function. When the diode switched from on to off the
circuit goes to high impedance. This results in a voltage spike that can
damage the diode if the voltage goes above the PIV rating. PIV stands
for Peak Inverse Voltage. It is this voltage spike every time the diode
switches off that causes EMI/RFI depending on the path. It could be
either or both but is usually mostly EMI.

If it is mostly EMI, the usual case, then a common mode choke will block
the majority of the diode switching noise on the cord to the radio.

The power supply terminology to reduce the PIV voltage across the diode
so as to not damage it is a "snubber" circuit. This is usually made of a
cap and resistor across the diode. The cap/resistor time constant value
is determined by the duration of the reverse spike it design to absorb.
The resistor burns the power.

If the spike is small and you want to suppress it for RF reasons only
then it can be just a cap. The capacitor will circulate the current from
the voltage spike around the diode, which is a small RF current loop,
instead of allowing it to propagate away from the diode through the rest
of the power supply circuit up the power cord and into your radio and
make a buzz at 60 or 120 Hz.

You can use a cap to the AC outlet ground on the secondary side of the
transformer but it might not be the best thing to do as it or a pair on
either side on the secondary will generate a continuous current down the
AC mains ground lead at 60 Hz. It might be better to use one cap on the
negative side of the DC output to ground in order to reduce this common
mode switch noise. Alternatively you might try a cap on the positive
output to ground in addition to the one one the negative side. Here you
will only be sending the noise currents down the AC mains leads and not
the 60Hz components.

--
Telamon
Ventura, California

The diode is acting as a mixer. It is combining the 60 Hz line
voltages and the signals at the radio frequencies creating a signal
at RF with a large 60Hz modulation. Adding a cap bypasses the diode
at RF, significantly reducing the mixing action.

Thanks for writing that. The reason I have written this now overly long
thread is to explain the reason for by passing and how it works and why
the thinking that the diode is switching RF ground on and off is
generating the noise is rubbish.

I didn't say anything about switching RF ground......................I said
that the diode is radiating the noise.

You should connect an oscilloscope to a power supply rectifier diode in
operation. If you would do that you will see a large voltage spike
based on the inductance of the circuit and how fast the diode switches.
Faster diodes are more efficient but the spike voltage will increase
with the faster switch time so faster diodes will need a higher PIV
rating.

A fairly slow diode switching at 60 or 120 Hz depending on the
rectifier circuit in a low current supply may not develop a very high
PIV so a capacitor by itself may do the job.

Low current supplies likely have slower diodes because the heat they
dissipate results from the product of the switch time and current going
through them. Larger supplies will have more current through the diodes
and so that they don't burn up they have to switch faster. Bigger
supplies have bigger inductors and faster diodes with larger PIV as a
result.

The mechanism I am talking about isn't isolated to just high current
supplies, unless you are talking about a 200mA supply as being high current.

Switching more power means you need a snubber RC across the diode
instead of just a capacitor.

You can use a cap to the AC outlet ground on the secondary side of
the transformer but it might not be the best thing to do as it or a
pair on either side on the secondary will generate a continuous
current down the AC mains ground lead at 60 Hz.

At 60Hz, a 1uF cap has a considerable amount of capacitive reactance, so
very little current would go through this loop.

You need a complete circuit for current to flow. At 60 Hz, what is
the rest of the circuit?

One side of the capacitor is grounded through the AC mains ground lead
and on the other side is alternating voltage at 60 Hz.

It might be better to use one cap on the
negative side of the DC output to ground in order to reduce this
common mode switch noise. Alternatively you might try a cap on the
positive output to ground in addition to the one one the negative
side. Here you will only be sending the noise currents down the AC
mains leads and not the 60Hz components.


I suggest looking at the whole picture and look at what this does at
60 Hz and at RF frequencies.

I did and have. It is common practice to use a small value capacitor to
ground on or near the power supply outputs where any common mode
noise from switching transients is coupled to ground. You can do this
at the transformer secondary but why generate the 60 Hz current if you
don't have to do that? The object is to conduct noise currents to
ground not 60 Hz mains supply.

--
Telamon
Ventura, California

No problem. I used to work on switching power supply designs.


In article ,
"Pete KE9OA" wrote:

I remember...........you have come up with some pretty good ideas about this
subject in the past. Thanks!

Pete

"Telamon" wrote in message
..
.
In article
,
"Pete KE9OA" wrote:

Snip

Somebody made a comment about how cool the Icom R-75 runs..........I
bet that you haven't attempted to touch that internal 5V regulator.
There have been some failures with this regulator recently. The
failure mechanism is caused by the fact that Icom chose to use an 18V
supply to power the radio. Dave Zantos has modified his power supply
by adding a pre-regulator that brings the voltage down to 13.5V
before it enters the radio. My advice? Either modify that Icom power
brick or replace it with a regulated 13.5V power supply. Looking
inside of that supply, you will find spots on the circuit board for
adding bypass caps across each rectifier diode. Add .01uF caps in
these places and it will prevent the diodes from rectifying RF.
Another good mod for this power supply is to add a 1uF NP cap from
each leg of the SECONDARY of the power transformer to ground. This
snubs the switching noise from the rectifier diodes. I have heard
mention on this NG that purchasing a good regulated supply gets rid
of these emissions........this is not really the case. Any power
supply can be made quiet by using the aforementioned techniques. The
AOR7030s power supply can also benefit from these mods.

You are right about the 5V regulator. These are series regulator
elements and the higher the input voltage the more power they must
dissipate to regulate the voltage down to the lower voltage.

People don't seem to get the diode rectifier concept here though. The
diode in the power supply passes current when the voltage polarity is in
the right direction and blocks it in the reverse. This is the
rectification function. When the diode switched from on to off the
circuit goes to high impedance. This results in a voltage spike that can
damage the diode if the voltage goes above the PIV rating. PIV stands
for Peak Inverse Voltage. It is this voltage spike every time the diode
switches off that causes EMI/RFI depending on the path. It could be
either or both but is usually mostly EMI.

If it is mostly EMI, the usual case, then a common mode choke will block
the majority of the diode switching noise on the cord to the radio.

The power supply terminology to reduce the PIV voltage across the diode
so as to not damage it is a "snubber" circuit. This is usually made of a
cap and resistor across the diode. The cap/resistor time constant value
is determined by the duration of the reverse spike it design to absorb.
The resistor burns the power.

If the spike is small and you want to suppress it for RF reasons only
then it can be just a cap. The capacitor will circulate the current from
the voltage spike around the diode, which is a small RF current loop,
instead of allowing it to propagate away from the diode through the rest
of the power supply circuit up the power cord and into your radio and
make a buzz at 60 or 120 Hz.

You can use a cap to the AC outlet ground on the secondary side of the
transformer but it might not be the best thing to do as it or a pair on
either side on the secondary will generate a continuous current down the
AC mains ground lead at 60 Hz. It might be better to use one cap on the
negative side of the DC output to ground in order to reduce this common
mode switch noise. Alternatively you might try a cap on the positive
output to ground in addition to the one one the negative side. Here you
will only be sending the noise currents down the AC mains leads and not
the 60Hz components.

--
Telamon
Ventura, California

--
Telamon
Ventura, California

In article ,
"Pete KE9OA" wrote:


The diode is acting as a mixer. It is combining the 60 Hz line
voltages and the signals at the radio frequencies creating a signal
at RF with a large 60Hz modulation. Adding a cap bypasses the diode
at RF, significantly reducing the mixing action.

Thanks for writing that. The reason I have written this now overly long
thread is to explain the reason for by passing and how it works and why
the thinking that the diode is switching RF ground on and off is
generating the noise is rubbish.

I didn't say anything about switching RF ground......................I said
that the diode is radiating the noise.

Yeah, that was someone else responding to my response to your post.
I hope that makes sense.

You should connect an oscilloscope to a power supply rectifier diode in
operation. If you would do that you will see a large voltage spike
based on the inductance of the circuit and how fast the diode switches.
Faster diodes are more efficient but the spike voltage will increase
with the faster switch time so faster diodes will need a higher PIV
rating.

A fairly slow diode switching at 60 or 120 Hz depending on the
rectifier circuit in a low current supply may not develop a very high
PIV so a capacitor by itself may do the job.

Low current supplies likely have slower diodes because the heat they
dissipate results from the product of the switch time and current going
through them. Larger supplies will have more current through the diodes
and so that they don't burn up they have to switch faster. Bigger
supplies have bigger inductors and faster diodes with larger PIV as a
result.

The mechanism I am talking about isn't isolated to just high current
supplies, unless you are talking about a 200mA supply as being high current.

Not 200mA. Things don't get interesting until you are above a few amps.

Switching more power means you need a snubber RC across the diode
instead of just a capacitor.

You can use a cap to the AC outlet ground on the secondary side of
the transformer but it might not be the best thing to do as it or a
pair on either side on the secondary will generate a continuous
current down the AC mains ground lead at 60 Hz.

At 60Hz, a 1uF cap has a considerable amount of capacitive reactance, so
very little current would go through this loop.

Well, that depends on the secondary voltage. A few tens of volts would
generate current in the milli amp range, which is not a lot but it's
not necessary.

You need a complete circuit for current to flow. At 60 Hz, what is
the rest of the circuit?

One side of the capacitor is grounded through the AC mains ground lead
and on the other side is alternating voltage at 60 Hz.

It might be better to use one cap on the
negative side of the DC output to ground in order to reduce this
common mode switch noise. Alternatively you might try a cap on the
positive output to ground in addition to the one one the negative
side. Here you will only be sending the noise currents down the AC
mains leads and not the 60Hz components.


I suggest looking at the whole picture and look at what this does at
60 Hz and at RF frequencies.

I did and have. It is common practice to use a small value capacitor to
ground on or near the power supply outputs where any common mode
noise from switching transients is coupled to ground. You can do this
at the transformer secondary but why generate the 60 Hz current if you
don't have to do that? The object is to conduct noise currents to
ground not 60 Hz mains supply.

--
Telamon
Ventura, California

--
Telamon
Ventura, California