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" <[EMAIL PROTECTED]> 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" <[EMAIL PROTECTED]> > To: <elecraft@mailman.qth.net> > 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 > > _______________________________________________ > > Elecraft mailing list > > Post to: Elecraft@mailman.qth.net > > You must be a subscriber to post to the list. > > Subscriber Info (Addr. Change, sub, unsub etc.): > > http://mailman.qth.net/mailman/listinfo/elecraft > > > > Help: http://mailman.qth.net/subscribers.htm > > Elecraft web page: http://www.elecraft.com > > > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
