Hi Bob, If I recall (correctly).<and you should double check> The D40 is completely isolated from the mast, so it would be nearly invisible to your 160m RF...given all the other loading you have going on there. I don't know a thing about the Optibeam...is it also isolated or grounded? I am guessing grounded, as you now have a change. If that IS the case, you'll need more capacitance to counteract the loading you've added. As to the amount, I could only hazard a guess. If you've maxxed out your 1000pF air variable, you can add some random length of RG-214 or other coax in parallel and start hacking off a foot at a time, and then tweak with the cap as neccessary. It's cheap and saves climbing ! I forget at the moment how many pF RG-214 or other similar dielectric coax is, but maybe 10-15pF per foot springs to mind. Try adding 10 or 15' on and see what you can do with your cap.
My brain is still numb from ARRL-10 CW this weekend...I keep hearing "T E S T, V E 9 A A" in my ears , hi ! DIT dit, MIke ----- Original Message ----- From: Bob Garrett To: 'Jim F.' ; 'top Band' Sent: Sunday, December 11, 2011 1:21 PM Subject: Topband: Changes To My Shunt Fed Tower Hello Topbanders, It is getting cold in the Northeast and as I get older, I dislike the cold even more. In April of this year, I replaced my Cush craft D40 40 meter rotable dipole with an OptiBeam OB-4030 dipole for 30 and 40 meters right at the top of the mast. The overall length of the antenna is about ten feet longer and I am assuming that it has added some additional capacitance to my 100 foot shunt fed tower with a Cush craft X7, A3WS, 5 EL M2 6 meter yagi and the new OptiBeam dipole. My match on the tower went from 1.0 x 1. To 1.9 x 1 after I installed the new antenna. In terms of loss, this isn't a huge change but my amplifier doesn't like the change. Before I spend a lot of time running back and forth to the tower making random changes, any thoughts as to what I can do to improve the match. I'm currently using one series capacitor 1000PF for the matching network. I have attempted to adjust this capacitor but it looks like the 1.9 x 1 is the low point. Perhaps some thoughts - increase or decrease the spacing of the shunt wire? Move the connection up or down on the tower? Before I get to crazy, just wanted to look to the base of knowledge on this reflector for your input. 73 and tnx in advance. Bob K3UL _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK ------------------------------------------------------------------------------ No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.454 / Virus Database: 271.1.1/4071 - Release Date: 12/09/11 20:51:00 _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
