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W1VT

Joined: Sat, Apr 4th 1998, 00:00 Roles: N/A Moderates: N/A

Latest Topics

Topic Created Posts Views Last Activity
QST Downloads Feb 19th 2016, 16:34 1 735 on 19/2/16
March 2016 QST Compact Multiband Dipole Feb 19th 2016, 15:23 1 638 on 19/2/16
Antenna analyzer vs feedline type Sep 21st 2012, 14:37 1 2,552 on 21/9/12
USB to Serial Port problems--Prolific Drivers Aug 3rd 2012, 18:27 2 3,083 on 26/12/15
Italian Phishing emails! Dec 13th 2011, 14:20 1 2,215 on 13/12/11
John K0GMO needs help designing SS Amp Nov 17th 2011, 15:53 1 2,049 on 17/11/11
1 Farad Capacitor to Eliminate Headlight Flicker? Oct 19th 2011, 13:14 4 3,595 on 9/11/11
History of Relay Rack Dimensions? Oct 17th 2011, 12:58 2 2,323 on 25/10/11
Miswired Selsyn Oct 13th 2011, 17:51 1 2,214 on 13/10/11
Stealth Antenna wire Sep 12th 2011, 12:51 2 2,867 on 13/9/11

Latest Posts

Topic Author Posted On
Large yagi SIZE358 5 days, 4 hours ago
http://www.ifwtech.co.uk/g3sek/diy-yagi/dipoles.htm

No, DL6WU Yagis are old designs that are not optimized for direct 50 ohm feed. They are designed to be fed with folded dipoles, as described on the page above. A folded dipole provides a fixed 1:4 impedance step-up, raising the 12.5 ohm impedance of the Yagi to 50 ohms.

Zack W1VT
ARRL Senior Lab Engineer

feed line length question KK4BHS 5 days, 4 hours ago
Quote by KA8WBF
Hello

I notice older Handbooks suggest a 1/4 wavelength feeder (or multiple) to a 1/2 wavelength zepp, while later ones list a length that appears to be a multiple of 1/3 wavelength (42 feet). Parallel currents or feedline radiation are mentioned, but not a lot of explanation of why they exist or where they come from.. Can anyone add more details?

Cordially
KA8WBF

The older Handbook advice still works well for a single band antenna, but I tried for years to sell that idea to beginners without much success. Modern hams want multiband antennas. The older Handbook advice doesn't work for multiband antennas and modern tuners. A multiple of a 1/2 wave antenna is high impedance, and the feeder presents a high impedance to the tuner. Tuners like the AH-4 and others specifically tell you not to do that. Actually, you can if you run very low power, like 5 watts, but that idea is even harder to sell than starting off with a simple single band antenna.

The modern Handbook advice is a compromise based on the idea that a modern ham wants to run as much power as they can on as many bands as possible.

One of a kind high voltage vacuum variable capacitors are still available on Ebay if you wish to homebrew a tuner that will handle very high voltages.

Zack W1VT
ARRL Senior Lab Engineer.
Drone aka UAV to put up stationary antenna? xof7fox 5 days, 15 hours ago
http://www.sonic.net/~n6gn/SWTL_Powered_Drone_Antennas.html

I think it a good question, but answers may be hard to get because this technology is still quite expensive for the average ham. I'm still waiting for the prices to come down even more before I get one to install my antenna ropes higher in the air.

Zack W1VT
ARRL Senior Lab Engineer
Power measurements, what am I doing wrong? ON4DD 1 week, 3 days ago
It may be a bad connector.
Power measurements, what am I doing wrong? ON4DD 1 week, 3 days ago
0.261 volts/2=0.13 volts peak
0.13 volts peak/1.414=0.092 volts rms
(0.092volts)^2/50ohms=0.17 x 10^-3 watts or 0.17 mW
10*log(0.17)dBm =-7.7 dBm

Zack Lau W1VT
ARRL Senior Lab Engineer

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