On medium wave broadcast stations they fit quite large rf chokes across the
antenna terminals. I've seen some a foot long by 2" diameter. The self
discharge any build up on the antenna. Of course if there is a direct
> Hi David,
>
> Thank you for the info,
>
> It is good to know how this problem was addressed on a ship board radio
> installation.
>
> I understand that when the bleeder resistor is at a high impedance point
> in the antenna circuit it will need to dissipate power.
>
> In a 50 Ohm circuit operating up to 100 W (70.7V) I think that the 47K
> 1/2W resistor should be sufficient with a reasonable safety factor unless
> there is a high potential due to a nearby lightning strike etc.
>
> I know that a 47K resistor will heat up from RF if it is connected across
> the antenna coupler output when it is tuned to a high impedance antenna
> even at QRP power levels.
>
> The L network used in the Elecraft ATU designs provides DC coupling
> through the series inductors so even though the bleeder is connected to
> the 50 Ohm transmitter output it should be effective in keeping a static
> charge from building up on a long wire antenna. The concern here is that
> if the charge builds up to several thousand volts, dielectric breakdown
> of coupling capacitors can occur which may cause damage to the diodes in
> the RF bridge etc.
>
> 73,
> Bob Johansen WB2SRF
>
> On Sun, 12 Nov 2006 15:37:26 -0000 "David Cutter" <
[hidden email]>
> writes:
>> In the marine set I went to sea with, 2 x 10k 25W carbon resistors
>> in
>> parallel were fitted as an antenna bleed. This was on the MF/HF
>> set: all
>> valves in those days. Antenna was end fed inverted L and the tx was
>> about
>> 150W.
>>
>> David
>> G3UNA
>>
>> ----- Original Message -----
>> From: "Robert Johansen" <
[hidden email]>
>> To: <
[hidden email]>
>> Sent: Saturday, November 11, 2006 4:42 PM
>> Subject: [Elecraft] KPA100 rev D
>>
>>
>> > Hi Wayne,
>> >
>> > There a reason for concern for eliminating the choke in the
>> antenna
>> > circuit. I noticed that there is no DC path to ground to
>> eliminate the
>> > chance of static potenital build up on an antenna from discharging
>> a high
>> > voltage into the rig. This may be the reason why some builders
>> have
>> > experienced blown detection diodes in some ATU's etc.
>> >
>> > I think that is a good practice to install a 47K 1/2W carbon
>> resistor
>> > across the antenna terminals to act as a bleeder resistor when
>> there is a
>> > capacitive coupled output.
>> >
>> > 73,
>> > Bob Johansen WB2SRF
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