Static discharge protection questions
 

Hey group,

I have a portable radio with no external ground.

Recently I built a PI network antenna tuner in a metal box and
included an output for earth ground. So the outer sheild of my coax
inputs as well as outputs and the variable capacitor frames are on
this ground to earth. The random wire input goes strait to the tuning
capacitor thus needs some kind of static drain off.

I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in
between the inputs and ground would discharge static buildup and give
me some warning of build up conditions.

I am also concerned about limiting the voltage to the receiver front
end to prevent damage. I have heard installing back to back high speed
diodes between the imputs and ground would acheive this.

I understand everything but the diodes. What does back to back mean. I
recall diodes are one way, but which way goes where? Should I look for
a certain type or rating of diode?


Thanks for your help,

Mike

Back to back: Take your two diodes and install them in parallel, but
with one 'pointing' in the opposite direction. The idea is that, because
each diode will conduct when the voltage rises above it's threashold, it
doesn't matter if the spike is positive or negative. A radio signal is
highly unlikely to be powerful enough to force either diode to conduct
(and if it did, they'll protect the RX front end).

I don't think they'd help much however! You only have to think about the
kind of potential in a static build-up to decide that you do not want to
rely on a pair of diodes to keep everything calm. Far better to make
sure your aerial has a DIRECT path to earth - a low impedence one at
that. Best way to avoid static damage? Disconnect the hardware from the
wire when you think there's static about. Oh - and avoid using
headphones....


Good luck.
K



mike wrote in
:

Hey group,

I have a portable radio with no external ground.

Recently I built a PI network antenna tuner in a metal box and
included an output for earth ground. So the outer sheild of my coax
inputs as well as outputs and the variable capacitor frames are on
this ground to earth. The random wire input goes strait to the tuning
capacitor thus needs some kind of static drain off.

I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in
between the inputs and ground would discharge static buildup and give
me some warning of build up conditions.

I am also concerned about limiting the voltage to the receiver front
end to prevent damage. I have heard installing back to back high speed
diodes between the imputs and ground would acheive this.

I understand everything but the diodes. What does back to back mean. I
recall diodes are one way, but which way goes where? Should I look for
a certain type or rating of diode?


Thanks for your help,

Mike

Back to back: Take your two diodes and install them in parallel, but
with one 'pointing' in the opposite direction. The idea is that, because
each diode will conduct when the voltage rises above it's threashold, it
doesn't matter if the spike is positive or negative. A radio signal is
highly unlikely to be powerful enough to force either diode to conduct
(and if it did, they'll protect the RX front end).

I don't think they'd help much however! You only have to think about the
kind of potential in a static build-up to decide that you do not want to
rely on a pair of diodes to keep everything calm. Far better to make
sure your aerial has a DIRECT path to earth - a low impedence one at
that. Best way to avoid static damage? Disconnect the hardware from the
wire when you think there's static about. Oh - and avoid using
headphones....


Good luck.
K



mike wrote in
:

Hey group,

I have a portable radio with no external ground.

Recently I built a PI network antenna tuner in a metal box and
included an output for earth ground. So the outer sheild of my coax
inputs as well as outputs and the variable capacitor frames are on
this ground to earth. The random wire input goes strait to the tuning
capacitor thus needs some kind of static drain off.

I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in
between the inputs and ground would discharge static buildup and give
me some warning of build up conditions.

I am also concerned about limiting the voltage to the receiver front
end to prevent damage. I have heard installing back to back high speed
diodes between the imputs and ground would acheive this.

I understand everything but the diodes. What does back to back mean. I
recall diodes are one way, but which way goes where? Should I look for
a certain type or rating of diode?


Thanks for your help,

Mike

On 21 Sep 2003 21:30:28 GMT, Kieren wrote:

Back to back: Take your two diodes and install them in parallel, but
with one 'pointing' in the opposite direction. The idea is that, because
each diode will conduct when the voltage rises above it's threashold, it
doesn't matter if the spike is positive or negative. A radio signal is
highly unlikely to be powerful enough to force either diode to conduct
(and if it did, they'll protect the RX front end).

I don't think they'd help much however! You only have to think about the
kind of potential in a static build-up to decide that you do not want to
rely on a pair of diodes to keep everything calm. Far better to make
sure your aerial has a DIRECT path to earth - a low impedence one at
that. Best way to avoid static damage? Disconnect the hardware from the
wire when you think there's static about. Oh - and avoid using
headphones....


Good luck.
K


OK I get it now.

As for an earth ground......I found a nice fat copper braided wire
coming off the metal roof lightning protectors (this is an old
farmhouse) down the side of the house going deep into the ground.

I suspect if I solder a nice fat 12 guage wire to my random wire where
it meets my coax it would suffice in this regard. Additionaly I will
run another wire to this ground from my tuner.

thanks,

mike

On 21 Sep 2003 21:30:28 GMT, Kieren wrote:

Back to back: Take your two diodes and install them in parallel, but
with one 'pointing' in the opposite direction. The idea is that, because
each diode will conduct when the voltage rises above it's threashold, it
doesn't matter if the spike is positive or negative. A radio signal is
highly unlikely to be powerful enough to force either diode to conduct
(and if it did, they'll protect the RX front end).

I don't think they'd help much however! You only have to think about the
kind of potential in a static build-up to decide that you do not want to
rely on a pair of diodes to keep everything calm. Far better to make
sure your aerial has a DIRECT path to earth - a low impedence one at
that. Best way to avoid static damage? Disconnect the hardware from the
wire when you think there's static about. Oh - and avoid using
headphones....


Good luck.
K


OK I get it now.

As for an earth ground......I found a nice fat copper braided wire
coming off the metal roof lightning protectors (this is an old
farmhouse) down the side of the house going deep into the ground.

I suspect if I solder a nice fat 12 guage wire to my random wire where
it meets my coax it would suffice in this regard. Additionaly I will
run another wire to this ground from my tuner.

thanks,

mike

In article , mike
writes:

Hey group,

I have a portable radio with no external ground.

Recently I built a PI network antenna tuner in a metal box and
included an output for earth ground. So the outer sheild of my coax
inputs as well as outputs and the variable capacitor frames are on
this ground to earth. The random wire input goes strait to the tuning
capacitor thus needs some kind of static drain off.

I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in
between the inputs and ground would discharge static buildup and give
me some warning of build up conditions.

A small neon bulb was used in thousands of ARC-5 Command Set
receivers in WW2 for static bleed-off. Similar to an old NE-2 bulb.
No need to use a resistor. The neon will conduct somewhere around
70 Volts and shunt any static pickup to ground...then goes into non-
conducting state until the next static potential build-up.

I am also concerned about limiting the voltage to the receiver front
end to prevent damage. I have heard installing back to back high speed
diodes between the imputs and ground would acheive this.

I understand everything but the diodes. What does back to back mean. I
recall diodes are one way, but which way goes where? Should I look for
a certain type or rating of diode?

You can use practically anything modern in the way of diodes there
but the high-speed types such as 1N914 and 1N4148 are very cheap
and available many places. Varistors could be used (GE "movisters")
or even 1N4000 series rectifier diodes. Diodes have a 0.6 to 0.7 VDC
forward conduction voltage if silicon.

Put them side by side with the anode of one to the cathode of the
other at each end. That will limit voltage input to about 1.4 V peak-to-
peak. You could put a small series resistor, say 22 Ohms or so,
between antenna input and the diodes to limit peak diode current on
conduction. Your option...since the series resistor will drop the RF
input level slightly.

You could also use a high-inductance RF "choke" in place of diodes
and neon bulb. 1 to 5 mHy would work at HF bands. That forms a
constant low-resistance DC path from antenna to ground and keeps
static accumulation bled off immediately.

Len Anderson
retired (from regular hours) electronic engineer person

In article , mike
writes:

Hey group,

I have a portable radio with no external ground.

Recently I built a PI network antenna tuner in a metal box and
included an output for earth ground. So the outer sheild of my coax
inputs as well as outputs and the variable capacitor frames are on
this ground to earth. The random wire input goes strait to the tuning
capacitor thus needs some kind of static drain off.

I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in
between the inputs and ground would discharge static buildup and give
me some warning of build up conditions.

A small neon bulb was used in thousands of ARC-5 Command Set
receivers in WW2 for static bleed-off. Similar to an old NE-2 bulb.
No need to use a resistor. The neon will conduct somewhere around
70 Volts and shunt any static pickup to ground...then goes into non-
conducting state until the next static potential build-up.

I am also concerned about limiting the voltage to the receiver front
end to prevent damage. I have heard installing back to back high speed
diodes between the imputs and ground would acheive this.

I understand everything but the diodes. What does back to back mean. I
recall diodes are one way, but which way goes where? Should I look for
a certain type or rating of diode?

You can use practically anything modern in the way of diodes there
but the high-speed types such as 1N914 and 1N4148 are very cheap
and available many places. Varistors could be used (GE "movisters")
or even 1N4000 series rectifier diodes. Diodes have a 0.6 to 0.7 VDC
forward conduction voltage if silicon.

Put them side by side with the anode of one to the cathode of the
other at each end. That will limit voltage input to about 1.4 V peak-to-
peak. You could put a small series resistor, say 22 Ohms or so,
between antenna input and the diodes to limit peak diode current on
conduction. Your option...since the series resistor will drop the RF
input level slightly.

You could also use a high-inductance RF "choke" in place of diodes
and neon bulb. 1 to 5 mHy would work at HF bands. That forms a
constant low-resistance DC path from antenna to ground and keeps
static accumulation bled off immediately.

Len Anderson
retired (from regular hours) electronic engineer person

On 22 Sep 2003 01:32:08 GMT, (Avery Fineman)
wrote:


A small neon bulb was used in thousands of ARC-5 Command Set
receivers in WW2 for static bleed-off. Similar to an old NE-2 bulb.
No need to use a resistor. The neon will conduct somewhere around
70 Volts and shunt any static pickup to ground...then goes into non-
conducting state until the next static potential build-up.

Wow.....70 volts seems a tad high to be protective in my solid state
portable. I suspect the older vacuum tube sets were far more static
resistant. I've read the limit for my sony portable should be kept
below 0.7volts to keep the sensitive front end electronics safe.




You can use practically anything modern in the way of diodes there
but the high-speed types such as 1N914 and 1N4148 are very cheap
and available many places. Varistors could be used (GE "movisters")
or even 1N4000 series rectifier diodes. Diodes have a 0.6 to 0.7 VDC
forward conduction voltage if silicon.

Put them side by side with the anode of one to the cathode of the
other at each end. That will limit voltage input to about 1.4 V peak-to-
peak. You could put a small series resistor, say 22 Ohms or so,
between antenna input and the diodes to limit peak diode current on
conduction. Your option...since the series resistor will drop the RF
input level slightly.

You could also use a high-inductance RF "choke" in place of diodes
and neon bulb. 1 to 5 mHy would work at HF bands. That forms a
constant low-resistance DC path from antenna to ground and keeps
static accumulation bled off immediately.

Len Anderson
retired (from regular hours) electronic engineer person


I've read suggestions for resistors ranging from 2.2 k ohms to 56 k
ohms all the way up to 100 k ohms. The most recent information being
the lowest value resistors. From the schematics I have seen, the
resistors were placed in parralel between the antenna input and ground
input. Or in the case of a two wire unbalanced input, between each
wire and the case of the tuner which is grounded.

Guess I might have to just play resistor values and see what doesnt
hurt signal strenth (another suggestion I read).

good information though, thanks. - mike

On 22 Sep 2003 01:32:08 GMT, (Avery Fineman)
wrote:


A small neon bulb was used in thousands of ARC-5 Command Set
receivers in WW2 for static bleed-off. Similar to an old NE-2 bulb.
No need to use a resistor. The neon will conduct somewhere around
70 Volts and shunt any static pickup to ground...then goes into non-
conducting state until the next static potential build-up.

Wow.....70 volts seems a tad high to be protective in my solid state
portable. I suspect the older vacuum tube sets were far more static
resistant. I've read the limit for my sony portable should be kept
below 0.7volts to keep the sensitive front end electronics safe.




You can use practically anything modern in the way of diodes there
but the high-speed types such as 1N914 and 1N4148 are very cheap
and available many places. Varistors could be used (GE "movisters")
or even 1N4000 series rectifier diodes. Diodes have a 0.6 to 0.7 VDC
forward conduction voltage if silicon.

Put them side by side with the anode of one to the cathode of the
other at each end. That will limit voltage input to about 1.4 V peak-to-
peak. You could put a small series resistor, say 22 Ohms or so,
between antenna input and the diodes to limit peak diode current on
conduction. Your option...since the series resistor will drop the RF
input level slightly.

You could also use a high-inductance RF "choke" in place of diodes
and neon bulb. 1 to 5 mHy would work at HF bands. That forms a
constant low-resistance DC path from antenna to ground and keeps
static accumulation bled off immediately.

Len Anderson
retired (from regular hours) electronic engineer person


I've read suggestions for resistors ranging from 2.2 k ohms to 56 k
ohms all the way up to 100 k ohms. The most recent information being
the lowest value resistors. From the schematics I have seen, the
resistors were placed in parralel between the antenna input and ground
input. Or in the case of a two wire unbalanced input, between each
wire and the case of the tuner which is grounded.

Guess I might have to just play resistor values and see what doesnt
hurt signal strenth (another suggestion I read).

good information though, thanks. - mike

For Static control, I have a 1 megaohm 1/2 watt resistor to ground from
each side of my antenna. I do this because my balanced antenna tuner does
not have a DC path to ground.

Notice I said STATIC control, not Lightening arresting.

You can use a much lower value. The resistor should be large compared to
the impeadence of your anteanna. So if the antenna is 4,000 ohms, even a
400,000 ohm resistor would be 100 times the antenna value.

KA9CAR




"mike" wrote in message
...
Hey group,

I have a portable radio with no external ground.

Recently I built a PI network antenna tuner in a metal box and
included an output for earth ground. So the outer sheild of my coax
inputs as well as outputs and the variable capacitor frames are on
this ground to earth. The random wire input goes strait to the tuning
capacitor thus needs some kind of static drain off.

I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in
between the inputs and ground would discharge static buildup and give
me some warning of build up conditions.

I am also concerned about limiting the voltage to the receiver front
end to prevent damage. I have heard installing back to back high speed
diodes between the imputs and ground would acheive this.

I understand everything but the diodes. What does back to back mean. I
recall diodes are one way, but which way goes where? Should I look for
a certain type or rating of diode?


Thanks for your help,

Mike