[TowerTalk] (no subject)

[K7GCO@aol.com]

In a message dated 7/31/00 9:36:14 PM Pacific Daylight Time, poster@gate.net 
writes:<< 
 
For a 6el 5 Band Quad would 500 segments be enough or would the Pro version 
be needed?   Jack  WB4ROY

Jack:  My current opinion is "No" & "Yes."  This is subject to change after 
my next project. You will end up with damn few segments per element when you 
have that many elements.  I wouldn't even attempt a 5 band 6 element (per 
band) design with only 500 segments.  First off your testing program in Eznec 
is going to be very extensive.  Making all the necessary adjustments to tweak 
it physically will then take a long time needing a full time crane.  Are you 
using "optimum or compromise" spacing for each band to save supports, weight 
and wind resistance?  Are you using a proven design and would like to improve 
it or just check it out?  Better use a prop pitch rotator or you will have 
another headache.  If you use compromise spacing you seriously reduce the 
justification of building it.  If you tie all the DE's together--forget the 
whole thing.

I have a progressive program I'm using to avoid time wasting rat holes.  I'm 
starting with a 3, 4, 5 then 6 band 2 element tapered quads and then 
determining the actual variables if any from Eznec with pattern measurements 
and a test dipole.  By using the same electrical spacing for each band I can 
see how the reflector lengths are altered on each band to get the same 
pattern and the DE lengths need to be altered to get resonance.  Then I'll 
try 3 elements for 2,3,4,5 then 6 bands.  I'll compare it to monobanders of 
the same number of elements at the same height.  If it's manageable I'll try 
4 elements if I live long enough. This way I learn the variables and get 
better at adjusting for them.  You are jumping into a tuning mess even in 
Eznec of 5 bands and 6 elements right away.  I wish you the best of luck but 
in my opinion with only 500 segments you have a potential accuracy deficiency 
against you already.  I just want it as close as possible before I construct 
the antenna.   

See the article in the in July 2000 CQ by Beezley on Global Optimization of 
Yagi Designs.  He goes into great detail of all the variables just to get the 
ultimate. He didn't give any final dimensions.  If I'd been the editor I'd 
have asked for some.  Many of 5,6,7&8 element yagi designs have been pretty 
well optimized although I did improve one 7 element version for F/B all the 
way around.  M Squared has a great 7 element yagi I've used that you can put 
up and forget.  If I install anything that big and even a monobander, I want 
it "finalized" and with ZERO joint resistance that stays ZERO.  My goal is 
"ZERO MAINTENANCE."

I plan to see if I can come up with a quad that will compare.  Use the M 
Squared 7 element as your reference and the antenna to beat.  Or use a 
Raibeam 5 element monobander.  If you can beat these, let me know and then 
try a 2 bander, then 3 on and on.  In my opinion that gives you a progressive 
data program that assures you are accomplishing something worth the effort.  
I jokingly and seriously often state--"I humbly believe that everyone is 
entitled to my opinion."  My goal is always to end up with something better 
and advise how to get there in the least time and with the least expense.  At 
69 my tuning time is limited and just want to operate with the best beams I 
can still install all by myself.  After 60 years of tuning beams I can see 
too many variables in a 5 band 6 element (on all bands) quad and tweaking 
them on a big beam is a very time consuming and mechanically challenging job 
even with a crane.  Getting 5 or 6 bands and 6 elements tuned up and knowing 
it's maximized at gain or F/B requires very accurate pattern testing to 
verify and to justify all the work just for a few dB more gain and the 
convenience of 5 bands on one boom.  I will have a test pick up dipole about 
10 WL away for pattern tests.  I'll transmit at it and measure the pattern on 
a graphic recorder I made.  The speeded up prop pitch motors I use are ideal 
for F/B checks also and I can pretty well see what I have with a fast turn.  
F/B is the one easy test everyone can do.

I heard a software authority gave data for high gain monoband quads that some 
made and they didn't check out.  Multiple that by 5 bands.  It becomes a 
mechanical and electrical Albatross on your back or I should say on your 
tower.  Some guy with a 2 element quad properly designed will ace you 
out--I've done it.  Stacked 2 element beams is a great system and with the 
least cost, headaches and variables to worry about. 

Some seem to like to express their "opinions" without checking ones data on 
TT as their "final ego authority"--rather as just an opinion.  When I don't 
know for sure I do a test to determine what is right.
  
Remember.   "One Test Is Worth 1000 Opinions" (Old K7GCO Axiom)  

In my case I will determine the lengths for the 2 element and 6 bands needed 
with what I think is enough segments and the Eznec "tapered segment" feature 
and then reduce them to 500 or less for the whole array and see what 
difference Eznec shows.  Before I start I have reduced my variables.  Then I 
will build the antenna and carefully check the pattern and the feedpoint Z 
which I will measure at the end of the feedline being 1/2 WL multiples.  If 
that checks out I found out what I wanted to know.  I've had several 
critically tuned monoband yagi's for gain or F/B check out exactly for 
pattern and Z which has given me great confidence in Eznec for yagi's but 
monoband and multiband quads are a different bird with "the bends".  

I have a 3 element yagi tuned for absolute max gain of 10.2 dBi on a .35 WL 
boom.  The Eznec predicted F/B of 8 dB and 8 ohm Rr--checked out and I was 
impressed.  I don't know the exact gain but the pattern suggests I'm getting 
the gain.  It's real close to my 5 element design on a .8 WL boom.  I used a 
sneaky way to feed it directly with 50 ohm coax and NO RF Spill Over.

So I often over test in Eznec before the final cut and try sessions if 
necessary when possible and you will like the additional features of Eznec 
Pro even if you find you don't need the extra segments.  I'd get the fastest 
computer also which I'm doing to save time with over 500 segments.

I have an "ace in the hole" I will be doing to my 2 element configurations.  
The only tuning variable I have for pattern is the reflector.  I'm adding a 
variable capacitor after initial tests in each reflector (reflector has to be 
made longer doing this) all ganged together on an insulated shaft driven by a 
selsyn on the mast made mechanically possible by tapered spacing.  I can make 
reflector error corrections and any other variables on any part of the band.  
I can tune it for max gain also.  I will feed it with 100 ohm balanced coax 
GD'd to a 1/2 wave multiple on 5 bands (91' 2" for .66 vf) into a Johnson 
Match Box.  The Z is around 100 ohms when tuned for max F/B for a monobander. 
 A 2:1 balun could be used in the shack.  Not so on every band when 5 bands 
are combined.  When tuned for max gain the Z is also lower and reactive.  The 
amount of reactance depends on how the DE length is compromise tuned at 
either setting.  But that's where the Johnson MB comes to the rescue as all 
impedance matching is done in the shack.  It will handle large amounts of 
reactance, typical Rr values and deliver the RF into the coax.  The balanced 
100 ohm coax requires no balun and is forgiving to SWR and 2nd only to open 
wire line.  I've reduced my variables greatly but this will still take some 
tine--with just 2 elements.

You have a huge project that only a contester can really justify.  Actually 
if I was a contester I would have 4 or more element monobanders on separate 
towers to make sure I had them all maximized without wondering if there was a 
way I could improve them.  This requires land that I happen to have now.

The cost of Eznec Pro is small compared to the cost and time of your project. 
 Are you a contester?  I agree every dB you can get is needed to be a winner 
or just to justify the cost of any antenna for routine contacts.  I 
frequently have this nagging feeling--have I maximized everything?  Do I have 
loss centers?  Using open wire line and the right tuner eliminates feedline 
questions.  I actually obtain final designs that I can't improve, use them 
awhile and get interested in something else

Now there is another factor that is potentially worth pursuing.  I found with 
a 2 element 5 band quad the patterns were improved over a monobander.  That's 
the first time I ever saw that with multiband beams and I've never ever seen 
this reported anywhere.  Look for it in your program as that can justify it. 
If that holds for multiband quads of 3 or more elements also--that even 
interests me as that is advancing the state of the art.  That is where the 
real technical fun is but it can be very time consuming and expensive.  
Reduce the variables where even you can.  This started out as a "no" and a 
"yes" answer to your question but "I've been there and done that" on a lot of 
projects.  I no longer tolerate wasted time. I don't know how much I have 
left and hate to see anyone waste it.  K7GCO

 K7GCO@aol.com wrote:
 > In a message dated 7/31/00 4:43:50 PM Pacific Daylight Time,
 > k7ox@pipeline.com writes:
 >
 > <<
 >  Hello TT
 >
 >  I am interested in purchasing some software to model various ant
 >  configurations.  I was looking at EZNEC 3.0 but it is my understanding 
that
 >  after 300 models it will no longer work ???  I would like to keep the cost
 >  reasonable.  What is out there ? looking for opinions, pro or con.  Thanks
 >  in advance for any info you would care to share.
 >
 >  73 Gary >>
 > Gary:  I've done over 1000 models and it still worked.  I have Eznec Pro 
now
 > and I love it.  I can use more than 500 segments.  I needed that for a 6 
band
 > 2 element quad I'm designing I'm adding a 4 element 144 and an 8 element 
450
 > quad out the back also.  Both are easy to use although I sent Roy 30 pages 
of
 > suggestions on how to make it even more user friendly and 3 pages recently 
on
 > making the Pro version even more user friendly.  I'm updating my computer 
the
 > to fastest one available also.   k7gco
  

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