[NLRS] 6 and 2 meter antennas

[Dr. Gerald N. Johnson]

Actually I found nearly all the pattern changes from close stacking of 
horizontally polarized yagis was in the back half elevation. Totally 
useless directions accompanied by a feed point impedance change. Indeed 
Tilton in 1948 found he couldn't match the 6m beam 3" from the 10m beam.

What I've concluded is that the RF in the high band yagi couples from 
each element to individual elements of the low band yagi and the low 
band yagi elements radiate mostly as a broadside up and down. There is 
no traveling wave on the low band yagi on the high band because the 
elements are too far apart to couple. The resulting pattern is way 
different from that caused by feeding the low band yagi on its third 
harmonic, illustrated near the front of my paper.

73, Jerry, K0CQ

On 1/25/2012 11:30 AM, w0zq at aol.com wrote:
>
>
>
> Hello Kirk&  all.
>
> Good discussion on antennas .... here is some more cheap advice!
>
> Regarding the Force 12 low noise LFA yagi's, here is a cut&  paste from their website at http://www.texasantennas.com/index.php?option=com_content&view=article&id=207&Itemid=205  .
>
> "The LFA does not use a dipole at the feed point of the antenna. Instead it uses a large, rectangular loop laid flat on the boom between the parasitic elements and this loop serves several purposes. First of all, a closed loop helps to reduce the pickup of any man-made noise/static. Next, it helps to broadband the antenna resulting in the LFA producing some very wide, low and flat SWR curves. Finally its size in both X and Y plots are dynamically altered by the G0KSC optimizer in order to maintain a natural 50 Ohm feed point impedance ensuring any connection losses are kept to an absolute minimum."
>
> The first claim, that a closed loop helps to reduce the pickup of any man-made noise/static, is at least part snake oil.  Yes, you may be able to rationalize some situations, but I think its a weak claim.  The next claim, that this type of matching/driven element design provides a more broadband SWR, is probably true albeit being too narrow band is not usually a problem for modern 6m&  2m yagis.  An exception may be on 2m if you are trying to cover 144 to say 146 or 147 .... however, this is not an issue for most weak signal VHFers who hang around 144.200.   That the design of this driven element results in a "natural" (vs an artifical?) 50 ohms feed point is probably true too.  It is a good way to match a VHF yagi to 50 ohms, but there are other ways too.  The upside of such a design is that is simplistic (good for reliability?), the down side is that there is more wind load (which isnt usually too much of an issue for VHF yagis).
>
> Also, remember that its important to consider your application.  If you are into EME, antenna pattern is VERY important because signals are weak and you want to hear only the signal that you are pointing at and not any noise coming from all other directions.  At EME signal levels antenna pattern plays a major role.   If I was looking to put up an EME array, I would look seriously at the LFA yagis.   However, for us "normal" terrestrial guys, pattern is usually less important, and in some cases it can be a hindrance.  For example when contesting, sometimes its an advantage to being able to hear (somewhat) off the sides or back of your antenna in order to be able to hear someone calling you.  On the other hand, if you live in the big city and have some directions that are noisy, having an antenna that has a clean pattern could be a plus to help reduce noise from one direction when pointed in another direction.  As Jerry points out, rovers have successfully used very closed s
pac
>
>   ed yagis for years.  Close spacing seems to have less affect on gain than it does on pattern .... pattern is the first thing that gets hosed up when you start to "contaminate" the near field with "stuff".   If that "stuff" is resonant, say like a 2m antenna on 432, the effect is stronger.  If that stuff is not resonant, for example say a 2m antenna on 222, the effect is milder.  I use a CC 4 element yagi for roving that has a homebrew 4 element 222 yagi interlaced on the same boom, and it works very well ..... measured it at AU one year and it had the expected gain numbers on both bands.
>
> Myself, I have always been a K1FO, Directive Systems, fan.   Steve is one of us, provides outstanding service and support, shows up at many of the VHF conferences, stands squarely behind his products and company, and the K1FO thru the boom elememt mounts are rugged, lighweight, and provide minumum wind load.
>
> Not sure how much mast space you have.  If you have a HF triband beam, then you would be looking at 6, 2, and 432 above that?   I think putting a small 432 yagi at the top of the tower will significantly outperform a larger yagi at 20' .... this may not be true if you live out in the country in say North Dakota, but we have lots of 40 to 50' maple trees and attenuation due to foliage starts to become more significant as you move up the bands starting with say 432.  I would suggest a small 432 yagi at the top.  So one thought would be to mount the bigger 2m yagi above the HF tribander, say the DSFO144-12 (17' boom, 1.5 sqft), then above that the 6m yagi, say the DS50-4 (12' boom, 1.3 sq ft), then at the very top a 432 antenna, say the DSFO432-15RS (8' boom, 0.7 sq ft).  This gives you the best separation you can get for the 432 antenna away from the 2m antenna, and for the 6m antenna away from the HF tribander.  The HF tribander will be unaffected.  So you would be looking 
at
>
>   a stack of four antennas .... HF on the bottom, then 2m, then 6m, then 432 at the top.
>
> What about 1296?
>
> My two bits.
>
> 73, Jon
> W0ZQ
>
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