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[TowerTalk] Fw: quad tuning, etc. et al

To: towertalk@contesting.com
Subject: [TowerTalk] Fw: quad tuning, etc. et al
From: "larryjspammenot@teleport.com" <larryj@teleport.com>
Reply-to: "larryjspammenot@teleport.com" <larryj@teleport.com>
Date: Sat, 24 Jun 2006 21:13:53 -0700 (GMT-07:00)
List-post: <mailto:towertalk@contesting.com>
-----Forwarded Message-----from the [HAMQUADS] mailing list


>From: ac5e@comcast.net
>Sent: Jun 24, 2006 4:38 PM
>To: HAMQUADS@yahoogroups.com
>Subject: Re: [HAMQUADS]  quad tuning, etc. et al
>
>Trying to tune any antenna with elements tied together has always been an 
>exercise in futility for me. Trim one element - and the next is now too long. 
>Or short. Or no longer seems to be connected. Or something! You will be much 
>happier with separate loops, since they will behave as you expect, not as you 
>wish. 
>
>I second the suggestion to remove the balun. Don't throw it away, the core may 
>come in handy some day. 
>
>But do use a remote control switchbox that leaves the unused driven loops OPEN 
> to change loops/bands.  That is, if the 20 meter driven loop is in use all 
>the other loops should be open. Neither antennas nor transformers work well 
>with a shorted turn in close proximity to the primary, and RF power is too 
>expensive to heat shorted loops with. 
>
>Even with all unused DE's open I have had much better luck running my various 
>and assorted quads with only 20/15/ and 10 Meter loops.  The pattern is much 
>cleaner, and the FB is better. Sorry, I could not strip the 17 and 17 Meter 
>loops off fast enough to make a direct comparison in gain. 
>
>You can use either Bill Orr's loop lengths, the ARRL Antenna handbook sizes, 
>or calculate them yourself with a five buck calculator. I do suggest finding a 
>100 foot steel tape with incremental inch markers to the 1200 inch end, and 
>multiplying the 1005 in 1005/f by 12 (giving you 12060/f) to give you loop 
>lengths directly in inches. One gets you 71.02474 feet, the other 852.3 inches 
>for a quad's DE at 14.150.  Not having to convert from one to the other saves 
>time and uncertainty. 
>
>High quality 72/75 ohm RG11 is recommended for quarter wave sections. This 
>will have a velocity factor (propagation velocity as a percentage of the speed 
>of light) CLOSE to .66 - and the foam core version will have a VF close CLOSE 
>to 0.82. Lower quality stuff is likely to be further from nominal - but if you 
>don't have an Autek, MFJ 259 or some other antenna analyzer you can make sure 
>you have the good stuff and use antenna manual lengths.  
>
>If you do have an analyzer, cut the coax "long," connect it to your analyzer, 
>and trim until you get the LOWEST impedance possible on the analyzer. Verify 
>the length by shorting the end, and the impedance should become very high. 
>
>And, if you don't want to run the full legal limit, smaller size "75" ohm coax 
>such as RG59 will also do. But the stuff I have measured is variable enough to 
>make me throw the cookbook away. 
>
>The third element is well worth while - and the longer the boom and wider the 
>spacing between spreaders the happier you will be. Quads are funny, you don't 
>gain much with four elements - but if you can manage 5 with at least 10 feet 
>of spacing (40 foot boom) you should be a very happy camper. 
>
>If you are interested, besides Bill Orr's and the various handbook articles, 
>Bob Haviland's "The Quad Antenna" is an excellent resource as are the Cebik 
>books available from AntennX. 
>
>73  Pete Allen  AC5E
>
>Amateur Radio, emergency communications when all else fails
>
>
>
>
>
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