[Elecraft] Antenna static charge precautions - any tips?

Sun Sep 9 09:28:49 EDT 2012

Which begs the question...why isn't a 100K across the antenna jack in the original design?
BTW, I use a choke across the antenna leads.

Chuck, KE9UW
aka Jack, BMW Motorcycles BMWMOA #224

________________________________________
From: elecraft-bounces at mailman.qth.net [elecraft-bounces at mailman.qth.net] on behalf of Fred Jensen [k6dgw at foothill.net]
Sent: Saturday, September 08, 2012 10:16 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Antenna static charge precautions - any tips?

Don is totally right.  But, cutting to the chase, put a 100K resistor
across your coax before it gets to the receiver.  Easy, no RX mods, just
put a 100K resistor ... 1/2W will do fine ... into a PL259.  Put a UHF
T-connector on your radio, put the antenna on one leg, put your
resistive PL259 on the other.

Trust me, you *CAN* fry the input stages to your radio and it won't even
look like you're doing it as you are.  Been there -- done that, more
than once, we all learn slowly. :-)  No bleed = charge builds up in the
input capacitance, it will eventually take something out.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org

On 9/8/2012 8:03 PM, Don Wilhelm wrote:
> OK a bit of explanation is in order.  The K2 (and K3 as well as the K1)
> control power based on measuring the actual output power and adjusting
> the drive to provide the requested power level.  That means a device
> capable of measuring the RF output is necessary.
> Well, that is the wattmeter in the KPA100 - it uses Schotky 1N5711
> diodes because those have been chosen to provide the best response with
> respect to frequency and power level.
>
> Yes, those diodes are a bit "tender" with respect to static.  Those
> diodes live right at the antenna terminals and are quite susceptible to
> static charges.  The K2 (K3) power control system will give you the most
> consistent power control (because it is a closed loop), but to operate,
> it must be able to measure the output power. and the diodes that do that
> task are susceptible to static discharges.
>
> Yes, go out and find yourself some resistors between 22k and 100k and
> connect them across your feedlines.
>
> Note that I do not care about the path to (earth) ground - while that
> may be nice, IMHO it will not help with the equipment damage from
> antenna induced static charges.  Yes, the station should be connected to
> earth ground, but for purposes of lightning protection rather than
> static discharges from antennas.
>
> There are 3 grounds in a ham station - AC safety ground (see NEC
> requirements), Lightning safety grounding (see Ron Block's papers at
> Polyphaser,.com) and RF ground.  The RF ground is the most elusive,
> because it does not include any hard connection to mother earth.
> "Ground" in this sense is a point of commonality, or a point where the
> RF voltage is zero.  That condition occurs at the feedpoint of a
> balanced antenna - the zero voltage point directly between the feedpoint
> terminals.
>
> OK, I am mixing a bit of the theoretical and the practical, but take to
> heart, it is not hard.  When the wavefront moves from the feedline into
> the antenna, the conditions change from conduction (obeying Kirchoff's
> laws)  to radiation (obeying Maxwell's wave equations). Where the
> transition point occurs is indeed a mystery.
>
> That has nothing to do with the "ground question"..  Everything needs to
> have a return path, and I believe that is valid for RF as well as for DC
> conditions.  This is the Kirchoff stance,, but there are those who argue
> than the Maxwellian equations offer a better explanation.  That  may be
> true, but there is little difference.
>
> My goal is not to "solve" this inconsistency, but just to add a bit more
> information (OK, to justify my conclusions be they right or wrong).
>
> 73,
> Don W3FPR
>
> On 9/8/2012 10:07 PM, stan levandowski wrote:
>> Thanks, Don.  I have a homebrew doublet with a gas discharge center
>> insulator and I have been under the (apparently incorrect) assumption
>> that I've been well protected from static buildup.  I've also got a
>> coaxial switch which is dialed into the dummy load when not in use.
>>
>> Guess, I better go out and buy a 22K resistor now and fnish the job ;)
>>
>> Appreciate the tip.
>>
>> 73, Stan WB2LQF
>>
>>
>> On Sat, Sep 8, 2012 at 9:17 PM, Don Wilhelm wrote:
>>
>>
>>>
>>> The Gas discharge tubes are effective against large charges - the
>>> ones I have will squelch a voltage in excess of 600 volts, but below
>>> that level, they will do nothing.  That 600 volt surge is enough to
>>> take out the diodes in the K2 KPA100.  The K3 has more protection.
>>> but still should not be trusted when it comes to static charges.
>>>
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2012.0.2197 / Virus Database: 2437/5257 - Release Date: 09/08/12
>
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html