ARRL

W1VT

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

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Topic Created Posts Views Last Activity
Antenna analyzer vs feedline type Sep 21st 2012, 14:37 1 1,178 on 21/9/12
USB to Serial Port problems--Prolific Drivers Aug 3rd 2012, 18:27 1 1,438 on 3/8/12
Italian Phishing emails! Dec 13th 2011, 14:20 1 1,257 on 13/12/11
John K0GMO needs help designing SS Amp Nov 17th 2011, 15:53 1 1,136 on 17/11/11
1 Farad Capacitor to Eliminate Headlight Flicker? Oct 19th 2011, 13:14 4 1,975 on 9/11/11
History of Relay Rack Dimensions? Oct 17th 2011, 12:58 2 1,355 on 25/10/11
Miswired Selsyn Oct 13th 2011, 17:51 1 1,202 on 13/10/11
Stealth Antenna wire Sep 12th 2011, 12:51 2 1,741 on 13/9/11
Designing a ham bench Aug 29th 2011, 12:38 2 1,815 on 29/8/11
Can't find recent Hint and Kink Aug 26th 2011, 13:01 1 1,735 on 26/8/11

Latest Posts

Topic Author Posted On
Dipole or loop? KO0Y 13 hours, 14 minutes ago

You could easily lose half the power in the balun--typical baluns are designed for 200 ohms at the output, not 2000ohms. Ideally, you would use a balun optimized for 1.8 to 8MHz, rather than something that tries to cover the entire HF spectrum.

A good all-around compromise, given that you have a radial field already installed, is an inverted-L. The feedpoint impedance is roughly half that of a dipole of twice the length, plus a bit of ground loss. With an autotuner, you typically want to avoid multiples of resonant half wavelenths, to keep the impedance down and within the autotuner matching range.

http://www.g8jnj.net/usingautotuners.htm
If you are using a longer length of wire, perhaps as a Sloper or inverted ‘L’ good lengths to choose are either 19.4, 22.8 or 34.3m long, as these avoid high impedances on most of the Amateur bands from 160 to 6m.


Zack Lau W1VT
ARRL Senior Lab Engineer
Dipole or loop? KO0Y 14 hours, 11 minutes ago

While a larger loop has more resonances in the HF spectrum, the resonances become more narrow, so I doubt the large loop will meet your SWR objective.

YT-100 specification Tunes 4 to 800 ohms. (16 to 150 on 6M)

This suggests using a 4:1 balun at the feedpoint of the dipole.
This isn't ideal--at low impedances the loss of a tuner tends to be much higher, but it may work well enough for your needs. Beware of SWR drift--this indicates that a lot of power is being lost in the balun--which is actually quite likely given the limitations of balun technology.

Zack W1VT
Digital QST crashes constantly on iPad3 K9AO 2 weeks ago
http://www.arrl.org/news/updated-qst-ios-app-now-available

The Digital QST iOS app has been updated with bug fixes and new features. Please download Version 2.1.0.226. You may view the fixes and changes in the “What’s New in Version” section in the iTunes App Store.
hf radio direction finder? tuulen 2 weeks, 1 day ago

Most of the time, the beam heading is along the great circle path.

http://www.njdxa.org/dx-tools/beam-headings.php
Here is a calculator that will create a list of custom headings for your station.

For someone just starting out in the eastern part of the country, a good compromise is to point the antenna toward Europe--where there is a very high level of activity on the amateur bands. However, for many hams just starting out, it is more important to get the antenna high, rather than in a particular direction. A low antenna will have high ground losses, and a more or less omnidirectional pattern. You should try to get the dipole up at least half wavelength on the band you want--this is 35 ft on 20M and 17 ft on 10M.

A second choice may be to orient the antenna to cover as much of the continental USA as possible.

Zack Lau W1VT
ARRL Senior Lab Engineer


High SWR Inverted L KC7QHE 3 weeks, 3 days ago

One would expect a 3rd harmonic resonance around 4MHz. The resistance should be a bit lower, around 100 ohms.

The most likely issue is pickup from local broadcast stations. The MFJ 259 uses broadband diode detectors--they have no way of telling these signals from the low level test signal generated by the analyzer.

http://www.mfjenterprises.com/Product.php?productid=MFJ-731
MFJ does sell a filter to improve the accuracy of the measurements.

I would use an ordinary SWR meter and higher power to tune up the inverted-L. Interference can be minimized by tuning when the bands are closed.

Zack Lau W1VT
ARRL Senior Lab Engineer

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