My suggestion to reduce the possibility of static damage is to install two
good quality 3dB SMA attenuators to the two ports and leave them in place.
You will sacrifice 6dB of dynamic range, but otherwise have the same
accuracy. You could also place the pads at the DUT end of the test cables
if you plan to leave them in place. This will also serve to protect the
SMA connectors from damage and ware.

My suggestion is to get into the habit of discharging EVERY cable which you attach to a radio or any other instrument.  Just momentarily shorting the inner and outer conductors against the shell of the target connector is sufficient.
73, Don N2VGU

Correct. Especially antennas. The fair weather electric field or worse the fields around thunderstorms can cause charging of the antenna(s). Wire and verticals should be equipped with noninductive resistors to ground of 5k ohms or so to keep them discharged. Will not interfere in any way with especially 50 ohm systems.


From: "Donald S Brant Jr via groups.io" <dsbrantjr=gmail.com@groups.io>
To: "NanoVNAV2" <NanoVNAV2@groups.io>
Sent: Sunday, July 6, 2025 5:56:10 AM
Subject: Re: [nanovnav2] Static Protection

My suggestion is to get into the habit of discharging EVERY cable which you attach to a radio or any other instrument. Just momentarily shorting the inner and outer conductors against the shell of the target connector is sufficient.
73, Don N2VGU



--
------------
Don Latham
PO Box 404,
Frenchtown, MT, 59846
406-626-4304

I'm not sure a 3dB pad is worthwhile. A 3dB pad would only add 3dB of
protection headroom. It would reduce voltage and current surges to about
71% of the original non-padded amounts.

The best way to protect the unit would be to be sure cables are
discharged before being connected, not test in storms or with nearby
transmitters active, and not have any kind of voltage source connected
to the system being measured.

73 Tom

On 7/5/2025 1:48 AM, Bob W0EG via groups.io wrote:

> My suggestion to reduce the possibility of static damage is to install
> two good quality 3dB SMA attenuators to the two ports and leave them
> in place.  You will sacrifice 6dB of dynamic range, but otherwise have
> the same accuracy.   You could also place the pads at the DUT end of
> the test cables if you plan to leave them in place.  This will also
> serve to protect the SMA connectors from damage and ware.
>

--
This email has been checked for viruses by AVG antivirus software.
www.avg.com

A 3dB pad will also discharge the cables. It will also help stabilize the
impedance of the test cables and can improve phase stability. Anyway, when
I was working, we always had pads on the far end of our test cables.

On Wed, Jul 9, 2025 at 1:05 AM Tom W8JI via groups.io <w8ji=
w8ji.com@groups.io> wrote:

> I'm not sure a 3dB pad is worthwhile. A 3dB pad would only add 3dB of
> protection headroom. It would reduce voltage and current surges to about
> 71% of the original non-padded amounts.
>
> The best way to protect the unit would be to be sure cables are discharged
> before being connected, not test in storms or with nearby transmitters
> active, and not have any kind of voltage source connected to the system
> being measured.
>
> 73 Tom
>
> On 7/5/2025 1:48 AM, Bob W0EG via groups.io wrote:
>
> My suggestion to reduce the possibility of static damage is to install two
> good quality 3dB SMA attenuators to the two ports and leave them in place.
> You will sacrifice 6dB of dynamic range, but otherwise have the same
> accuracy. You could also place the pads at the DUT end of the test cables
> if you plan to leave them in place. This will also serve to protect the
> SMA connectors from damage and ware.
>
>
>
> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
> Virus-free.www.avg.com
> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
> <#m_9067127468306050979_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>
>
>

Just adding to the discussion for a couple of reasons - 1 confirming my understanding / if correct may add to the thinking of the subject ?
2 If any part of my description / perspective is incorrect - then to get a better understanding myself ;)

With out mentioning too many other causes , the 2 most common causes of charge / current buildup in the antenna system would be lightning , and static - as I understand , static major buildup is during dry conditions + wind moving particles past the antenna system - this could be dust & low humidity / or very cold conditions with snow - so cold that no humidity --- all the humidity is in the frozen snow " dry particles being moved by wind " .

Need to change my name to call sign KD0CAC

Another practice I have exercised for decades is the following. Whenever
you pick up a coaxial cable which you intend to connect to
something....anything electronic, I press my finger over the end between
the center conductor and the braid or backshell of the connector. This
will slowly (relative to Vp) discharge the cable. You may receive a small
"surprise", but that's better than bricking the piece of electronics.

Besides lightning and static, there are other acts of nature than can and
will charge an antenna and feedline. You might also consider wind, blowing
dust, snow, and rain. Those can also deposit a healthy charge on antennas
and feedlines.

Dave - WØLEV

On Wed, Jul 9, 2025 at 5:59 PM Bob W0EG via groups.io <morrisnc7=
gmail.com@groups.io> wrote:

> A 3dB pad will also discharge the cables. It will also help stabilize the
> impedance of the test cables and can improve phase stability. Anyway, when
> I was working, we always had pads on the far end of our test cables.
>
> On Wed, Jul 9, 2025 at 1:05 AM Tom W8JI via groups.io <w8ji=
> w8ji.com@groups.io> wrote:
>
>> I'm not sure a 3dB pad is worthwhile. A 3dB pad would only add 3dB of
>> protection headroom. It would reduce voltage and current surges to about
>> 71% of the original non-padded amounts.
>>
>> The best way to protect the unit would be to be sure cables are
>> discharged before being connected, not test in storms or with nearby
>> transmitters active, and not have any kind of voltage source connected to
>> the system being measured.
>>
>> 73 Tom
>>
>> On 7/5/2025 1:48 AM, Bob W0EG via groups.io wrote:
>>
>> My suggestion to reduce the possibility of static damage is to install
>> two good quality 3dB SMA attenuators to the two ports and leave them in
>> place. You will sacrifice 6dB of dynamic range, but otherwise have the
>> same accuracy. You could also place the pads at the DUT end of the test
>> cables if you plan to leave them in place. This will also serve to protect
>> the SMA connectors from damage and ware.
>>
>>
>>
>> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
>> Virus-free.www.avg.com
>> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
>> <#m_2750739383376910598_m_9067127468306050979_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>>
>>
>
>

--

*Dave - WØLEV*

A VNA is primarily a lab bench instrument. Not designed for antenna
testing, although it can be used that way with appropriate caution. Much
better is a dedicated antenna tester, like the excellent products from
RigExpert. Well protected and can be used one-handed (like on a tower).
Never had a problem with these. However, they are more expensive. Built
in the Ukraine, not China.

On Wed, Jul 9, 2025 at 1:59 PM John Faughn via groups.io <johnfaughn=
gmail.com@groups.io> wrote:

> Just adding to the discussion for a couple of reasons - 1 confirming my
> understanding / if correct may add to the thinking of the subject ?
> 2 If any part of my description / perspective is incorrect - then to get a
> better understanding myself ;)
>
> With out mentioning too many other causes , the 2 most common causes of
> charge / current buildup in the antenna system would be lightning , and
> static - as I understand , static major buildup is during dry conditions +
> wind moving particles past the antenna system - this could be dust & low
> humidity / or very cold conditions with snow - so cold that no humidity ---
> all the humidity is in the frozen snow " dry particles being moved by wind
> " .
>
> Need to change my name to call sign KD0CAC
>
>
>

The field under a thunderstorm can be tens of kV/m even if there's no lightning.
So the antenna being "in that field" can put voltage on the coax.

But there's actually more subtle way - you have a high field, and that causes corona or sparking somewhere else in the system, and that corona sprays charge into the antenna system.

You can get an interesting phenomenon where you hear a buzz that changes in frequencies. That's from multiple things storing charge, and as the voltage increases, the buzz rate increases.

And of course, particulates can carry charge (dust and snow and rain all do it) - the thing about rain is that usually, for antennas, there's some resistive path from the antenna to ground that gets wet, and is a leakage path to discharge the charge. Airplanes don't have this, so they have to worry about rain caused P-static.

I guess the upshot is that you can get charging from "other things that are charged" near by.

almost. Lightning causes both an induction pulse and an RF pulse at the same time, but does not leave the antenna "charged". particles striking the antenna will carry off charge, leaving the opposite charge on the antenna. Also, under large electric fields such as thunderstorms, sharp pointy places on the antenna can go into discharge, leaving the opposite charge on the antenna.


From: "John Faughn via groups.io" <johnfaughn=gmail.com@groups.io>
To: "NanoVNAV2" <NanoVNAV2@groups.io>
Sent: Wednesday, July 9, 2025 8:24:11 AM
Subject: Re: [nanovnav2] Static Protection

Just adding to the discussion for a couple of reasons - 1 confirming my understanding / if correct may add to the thinking of the subject ?
2 If any part of my description / perspective is incorrect - then to get a better understanding myself ;)
With out mentioning too many other causes , the 2 most common causes of charge / current buildup in the antenna system would be lightning , and static - as I understand , static major buildup is during dry conditions + wind moving particles past the antenna system - this could be dust & low humidity / or very cold conditions with snow - so cold that no humidity --- all the humidity is in the frozen snow " dry particles being moved by wind " .
Need to change my name to call sign KD0CAC



--
------------
Don Latham
PO Box 404,
Frenchtown, MT, 59846
406-626-4304

Hi Bob,

If the pad is connected to the analyzer and then the analyzer is
connected to the antenna a 3dB pad can't possibly do much. It would
simply make the VNA have  ~71 % of the current and voltage surge without
the pad. I wouldn't consider that worthwhile protection.

If the pad is connected to the antenna and then the VNA is connected the
pad would have discharged any static currents prior to VNA connection.
This would be major, although someone could do just as well by shorting
the shield to center right before connecting (if they remember to do that).

73 Tom

On 7/9/2025 7:25 AM, Bob W0EG via groups.io wrote:
> A 3dB pad will also discharge the cables.  It will also help stabilize
> the impedance of the test cables and can improve phase stability. 
> Anyway, when I was working, we always had pads on the far end of our
> test cables.
>
> On Wed, Jul 9, 2025 at 1:05 AM Tom W8JI via groups.io
> <http://groups.io> <w8ji=w8ji.com@groups.io> wrote:
>
> I'm not sure a 3dB pad is worthwhile. A 3dB pad would only add 3dB
> of protection headroom. It would reduce voltage and current surges
> to about 71% of the original non-padded amounts.
>
> The best way to protect the unit would be to be sure cables are
> discharged before being connected, not test in storms or with
> nearby transmitters active, and not have any kind of voltage
> source connected to the system being measured.
>
> 73 Tom
>
> On 7/5/2025 1:48 AM, Bob W0EG via groups.io <http://groups.io> wrote:
>
>> My suggestion to reduce the possibility of static damage is to
>> install two good quality 3dB SMA attenuators to the two ports and
>> leave them in place.  You will sacrifice 6dB of dynamic range,
>> but otherwise have the same accuracy.   You could also place the
>> pads at the DUT end of the test cables if you plan to leave them
>> in place.  This will also serve to protect the SMA connectors
>> from damage and ware.
>
> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
> Virus-free.www.avg.com
> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
>
>
> <#m_9067127468306050979_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>
>

--
This email has been checked for viruses by AVG antivirus software.
www.avg.com

Anything that charges the feedline and/or antenna is an issue. We built
baluns here at one time. They were tested with a three step test on an
expensive Agilent VNA for RF function and on a high pot for voltage
breakdown.

The sequence was always connect the balanced terminals to the load
fixture then to the VNA. The high pot, which would go 5kV or better with
UHF connectors and normal coax like RG8X, was last.

Someone did the high pot first then connected to the VNA before the load
fixture was connected. That little mistake cost over $2500.

We also had directional coupler bridge failures in tuners caused by
static when using T network tuners when on lower bands. The T network
output capacitor and feedline were the culprits. The feedline and
antenna would build a slow charge until the voltage breakdown reached
the level of the output cap in the T. The output capacitor would arc and
ring the inductor hard enough to take out the diodes in the directional
coupler.

This was cured by adding a 100k 2 watt bleed resistor.

I measured one of my insulated base 300ft towers. On a dry windy day it
had picoamperes of current to ground. But even with that small current
letting the tower float would charge that tower to several thousand
volts. The tower's capacitance would give me a good slap on the fingers
and arm if I touched it. It would take maybe five or ten minutes, maybe
longer, to recharge.

73 Tom



On 7/9/2025 10:24 AM, John Faughn via groups.io wrote:
> Just adding to the discussion for a couple of reasons - 1 confirming
> my understanding / if correct may add to the thinking of the subject ?
> 2 If any part of my description / perspective is incorrect - then to
> get a better understanding myself ;)
> With out mentioning too many other causes , the 2 most common causes
> of charge / current buildup in the antenna system would be lightning ,
> and static - as I understand , static major buildup is during dry
> conditions + wind moving particles past the antenna system - this
> could be dust & low humidity / or very cold conditions with snow - so
> cold that no humidity --- all the humidity is in the frozen snow " dry
> particles being moved by wind " .
> Need to change my name to call sign KD0CAC
>

--
This email has been checked for viruses by AVG antivirus software.
www.avg.com

Even unrolling a cable can build up a considerable triboelectric charge due to the dielectric layers rubbing together.
73, Don N2VGU

User 1 1db pad, and calibrate it out. It will give you a way to minimize any static problems. Nothing will help with a lightning hit except a really good lightning arrestor….and some luck



Frank

KA2FWC

This is called sferics as we studied it in 1960-1972.



200 V/m as one goes up into the atmosphere; but of little concern to amateur radio operators with proper grounding scheme.

Precaution we to use a 2.2M resist in parallel with aNE-2 neon bulb connected to the antenna lead and to ground. A cheap but effective sferics bleeder.



Joseph D. Yuna (LCDR USN/ret.)

W4JDY / EM79XR

OK, I recently read something about this. The potential at about 6'
above ground is around 250 volts. How can one actually measure this? Or
can't you?

Yes, I've seen a spark generated across an antenna connector where the
antenna isn't DC grounded. It seemed to only happen on dry, windy days
however.

Chuck



On 7/12/2025 3:39 PM, W4JDY1953_G via groups.io wrote:

>
> This is called sferics as we studied it in 1960-1972.
>
> 200 V/m as one goes up into the atmosphere; but of little concern to
> amateur radio operators with proper grounding scheme.
>
> Precaution we to use a 2.2M resist in parallel with aNE-2 neon bulb
> connected to the antenna lead and to ground.  A cheap but effective
> sferics bleeder.
>
> *Joseph D. Yuna (LCDR USN/ret.)*
>
> *W4JDY / EM79XR*
>
>

On Mon, Jul 14, 2025 at 12:58 AM, Chuck Kelsey wrote:

>
> How can one actually measure this?

A field mill is one method: https://en.wikipedia.org/wiki/Field_mill
73, Don N2VGU

100-200 V/m is the “fair weather” electric field. Near storms, it can get up
to kV/m pretty quickly, even without lightning in the picture. See
<https://www.missioninstruments.com/pages/learning/elec_fields.html>








As to how one measures it - you use an electrostatic field meter - usually
called a “field mill”, which is basically a very high input impedance volt
meter with a shutter that alternately exposes and shields the measuring
electrode. The shutter is a disk with sectors cut out to match the shape of
the electrode under it, and it spins. That turns the measured voltage into
AC, so you can use synchronous detection and AC coupling, and it also helps
eliminate DC drift. (Just like chopper amplifiers in the days of yore).





> On Jul 13, 2025, at 21:59, Chuck Kelsey via groups.io
<wb2edv=gmail.com@groups.io> wrote:
>
>

>  OK, I recently read something about this. The potential at about 6' above
ground is around 250 volts. How can one actually measure this? Or can't you?
>
> Yes, I've seen a spark generated across an antenna connector where the
antenna isn't DC grounded. It seemed to only happen on dry, windy days
however.
>
> Chuck
>
>
>
>

>

> On 7/12/2025 3:39 PM, W4JDY1953_G via groups.io wrote:
>

>

>> This is called sferics as we studied it in 1960-1972.

>>

>>
>>

>> 200 V/m as one goes up into the atmosphere; but of little concern to
amateur radio operators with proper grounding scheme.
>
> Precaution we to use a 2.2M resist in parallel with aNE-2 neon bulb
connected to the antenna lead and to ground. A cheap but effective sferics
bleeder.

>>

>>
>>

>> **Joseph D. Yuna (LCDR USN/ret.)**

>>

>> **W4JDY / EM79XR**

>>

>>
>>

>>
>

_._,_._,_

* * *

It can be measured but the source impedance is about 10^14 ohms. Usually measured with an instrument called a field mill. Antennas are usually charged due to this field by a process called triboelectric charging.


From: "Chuck Kelsey via groups.io" <wb2edv=gmail.com@groups.io>
To: "NanoVNAV2" <NanoVNAV2@groups.io>
Sent: Sunday, July 13, 2025 12:06:26 PM
Subject: Re: [nanovnav2] Static Protection

OK, I recently read something about this. The potential at about 6' above ground is around 250 volts. How can one actually measure this? Or can't you?

Yes, I've seen a spark generated across an antenna connector where the antenna isn't DC grounded. It seemed to only happen on dry, windy days however.

Chuck



On 7/12/2025 3:39 PM, W4JDY1953_G via groups.io wrote:





This is called sferics as we studied it in 1960-1972.



200 V/m as one goes up into the atmosphere; but of little concern to amateur radio operators with proper grounding scheme.

Precaution we to use a 2.2M resist in parallel with aNE-2 neon bulb connected to the antenna lead and to ground. A cheap but effective sferics bleeder.




Joseph D. Yuna (LCDR USN/ret.)

W4JDY / EM79XR









--
------------
Don Latham
PO Box 404,
Frenchtown, MT, 59846
406-626-4304

Tribocharging is (generically) charging by contact with something and then removing contact. Dust particles are the most common, but rubbing a balloon on a cat is also a form of tribocharging. Pulling plastic (or tape, or wire) off a reel is a classic tribocharging. There's a reason you see "christmas tinsel" (or explicit ESD charge removal sprayers) on machinery that has a feed of insulating material. (I built a machine that pulled plastic sheet off a big real and cut it to length. It was spectacular how much charge would build up. And since the machine was fairly large, the total energy was enough to be painful if it discharged to you.)

The other way things pick up charge is by induction - coming near something charged, without actually touching it. A Wimshurst or Van deGraaff or Pelletron or Kelvin Water dropper work by induction (mostly). The idea is you bring something charged near something else - the charge on the "something else" matches the charged object:
Let's say we have a big blob of charge that gets near an antenna.. The antenna picks up charge, through the feedline, to match the charge on the blob. If we now open the feedline, and then take the blob away, the charge remains on the antenna.

This is also how a charged balloon (or Van de Graaf) attract things (like pieces of paper) without being touched. The charged balloon induces a charge on the paper.

Wind picks up nano-sized dust and even macro-sized particles. Those small
dust particles transfer charge to your antenna and charge the coax. No
surprise.

Dave - WØLEV

On Mon, Jul 14, 2025 at 4:59 AM Chuck Kelsey via groups.io <wb2edv=
gmail.com@groups.io> wrote:

> OK, I recently read something about this. The potential at about 6' above
> ground is around 250 volts. How can one actually measure this? Or can't you?
>
> Yes, I've seen a spark generated across an antenna connector where the
> antenna isn't DC grounded. It seemed to only happen on dry, windy days
> however.
>
> Chuck
>
>
>
> On 7/12/2025 3:39 PM, W4JDY1953_G via groups.io wrote:
>
> This is called sferics as we studied it in 1960-1972.
>
>
>
> 200 V/m as one goes up into the atmosphere; but of little concern to
> amateur radio operators with proper grounding scheme.
>
> Precaution we to use a 2.2M resist in parallel with aNE-2 neon bulb
> connected to the antenna lead and to ground. A cheap but effective sferics
> bleeder.
>
>
>
> *Joseph D. Yuna (LCDR USN/ret.)*
>
> *W4JDY / EM79XR*
>
>
>
>
>
>

--

*Dave - WØLEV*

Seeing all of these reminds me of a video I once saw of a large/tall crane with the boom up at maybe 30° from vertical with the cable dangling about 4' above the ground, and a fairly large arc going from the end of the cable to ground. The tractor part was on the ground, so...
There was an AM radio station less than 1/4 mile away, and the boom/cable/ground made a big loop antenna.
So don't forget about other sources of RF getting picked up by your antenna before connecting that cable to the VNA.

Arnold, KQ6DI

> On 07/14/2025 7:56 AM PDT Don Latham AJ7LL <djl@montana.com> wrote:
>
>
> It can be measured but the source impedance is about 10^14 ohms. Usually measured with an instrument called a field mill. Antennas are usually charged due to this field by a process called triboelectric charging.
>
>
> ---------------------------------------------
> From: "Chuck Kelsey via groups.io" <wb2edv=gmail.com@groups.io>
> To: "NanoVNAV2" <NanoVNAV2@groups.io>
> Sent: Sunday, July 13, 2025 12:06:26 PM
> Subject: Re: [nanovnav2] Static Protection
>
> OK, I recently read something about this. The potential at about 6' above ground is around 250 volts. How can one actually measure this? Or can't you?
>
> Yes, I've seen a spark generated across an antenna connector where the antenna isn't DC grounded. It seemed to only happen on dry, windy days however.
>
> Chuck
>
>
>
> On 7/12/2025 3:39 PM, W4JDY1953_G via groups.io wrote:
>
> >
> > This is called sferics as we studied it in 1960-1972.
> >
> >
> >
> > 200 V/m as one goes up into the atmosphere; but of little concern to amateur radio operators with proper grounding scheme.
> >
> > Precaution we to use a 2.2M resist in parallel with aNE-2 neon bulb connected to the antenna lead and to ground. A cheap but effective sferics bleeder.
> >
> >
> >
> > Joseph D. Yuna (LCDR USN/ret.)
> >
> > W4JDY / EM79XR
> >
> >
> >
>
> --
> ------------
> Don Latham
> PO Box 404,
> Frenchtown, MT, 59846
> 406-626-4304
>
>

Thank you to all whom responded. I have a better understanding now.

Chuck




On 7/14/2025 10:56 AM, Don Latham AJ7LL via groups.io wrote:

> It can be measured but the source impedance is about 10^14 ohms.
> Usually measured with an instrument called a field mill. Antennas are
> usually charged due to this field by a process called triboelectric
> charging.
>
> ------------------------------------------------------------------------
> *From: *"Chuck Kelsey via groups.io" <wb2edv=gmail.com@groups.io>
> *To: *"NanoVNAV2" <NanoVNAV2@groups.io>
> *Sent: *Sunday, July 13, 2025 12:06:26 PM
> *Subject: *Re: [nanovnav2] Static Protection
>
> OK, I recently read something about this. The potential at about 6'
> above ground is around 250 volts. How can one actually measure this?
> Or can't you?
>
> Yes, I've seen a spark generated across an antenna connector where the
> antenna isn't DC grounded. It seemed to only happen on dry, windy days
> however.
>
> Chuck
>
>
>
> On 7/12/2025 3:39 PM, W4JDY1953_G via groups.io wrote:
>
> This is called sferics as we studied it in 1960-1972.
>
> 200 V/m as one goes up into the atmosphere; but of little concern
> to amateur radio operators with proper grounding scheme.
>
> Precaution we to use a 2.2M resist in parallel with aNE-2 neon
> bulb connected to the antenna lead and to ground.  A cheap but
> effective sferics bleeder.
>
> *Joseph D. Yuna (LCDR USN/ret.)*
>
> *W4JDY / EM79XR*
>
>
>
>
> --
> ------------
> Don Latham
> PO Box 404,
> Frenchtown, MT, 59846
> 406-626-4304
>

Two different charging mechanisms … at sea or land in military ops. Never saw sand, dust or the wind cause extreme charges; but the atmosphere on dry days surely did.

Sferics was researched to death as far back as 1932-193w6 in French Indochina and contemporarily by NASA.



If you have a conventional grounding system, you are good to go in most cases.



Joseph D. Yuna (LCDR USN/ret.)

W4JDY / EM79XR