[TowerTalk] Re: Stacked Skip Log and Normal LP's and the Maligned L
Network
Jay Terleski
wx0b@arraysolutions.com
Fri, 08 Dec 2000 14:42:43 -0600
Ken,
This is way to much for me to respond to.
Bottom line:
Your L-network is way to difficult for anyone to make. A Wide band
transformer works every time and and for everyone.
I Have stacked over 1600 yagis, quads, LPDAs, and Tribanders, and
verticals with this technique. The interaction is minimimal if
noticable at all at .5 WL.
I just did a big deal on a VHF/UHF radar set up with two T31 Teannadyne
Logs (nice beam!)
110mhz to 500 Mhz and the wide band xfmr I made for them works.
I doubt very much if an L network would ever work with out a ton of
switching out of L and C.
Plus the relay or switch inductance would be impossible to predict and
correct for in my lifetime.
Its not worth the effort to use L netorks over one band.
Sorry to disagree with you but your not going to convince me it will
work otherwise.
What your saying is you have 4 L networks for each band segment. This
is not a practicle solution.
Use an Un-UN and enjoy being on the air.
Love to continue but there is a contest on in a few hours, and I have 3
stacks to play with all using Un-Uns.
73,
Jay
K7GCO@aol.com wrote:
>
> TT: I apologize but I sent this a few minutes ago accidentally without a
> spell check. Please DELETE the previous one even from the Archives if
> possible and use this one. I'll try not to do that again. k7gco
>
> << In a message dated 12/6/00 8:22:32 PM Pacific Standard Time,
> wx0b@arraysolutions.com writes:
> <<
> That's not really a good idea Ken, I would point out that an L network
> has a very small bandwidth. I suggest to do it a different way. Use a
> matching network that is broadbanded. Like the StackMatch wideband UN-UN
> transformer.
>
> Then the logs will have the proper impedance matching over their entire
> bandwidth.
>
> So this the technique.
>
> Run equal lengths of 50 ohm coax to a central point between the logs
> place your Stackmatch here, it will match the logs properly to select
> U/L/Both. Then run a line of hardline down to the shack. It can be CATV
> to save more money and have less loss. Match it with a couple of 50:75
> ohm UN-UN Xfrms.
>
> L networks are work at one frequency. And I know that K7GCO knows this,
> he probably just was in a hurry.
>
> Jay, WX0B
> >>
> Jay: I will take some exception to your views based on a lot of use of the L
> network (and I was in a hurry). I have a great system for stacked beams that
> you would even like but didn't have time to describe it. Without attachments
> even a simple circuit is hard to describe without a bunch of E-mails to
> follow. I will have a Web Site in SD as the SD Antenna Club with my old call
> W Zero Lice, Mice & Bedbugs for material like this and some of the mags like
> AntenneX which every TTer should read. Cebik had a great LP with F/B like I
> have never seen and will build.
>
> First off it's assumed the Skip Log or Normal LP's that are horizontally
> spaced (in this example) wide enough to minimize the affect each has on the
> other when used individually and the different Z's presented at the
> feedpoints due to the difference in heights off the ground. For this
> installation one would have to live with the vertical pattern affects and Z's
> on each other individually when only one or the other is used and the
> different Z affects on each one from the ground. A compromise spacing was
> suggested not for 15M but 17M just to minimize this coupling problem. I've
> never read anyone warning of the affect one stacked beam has on the other
> when used individually as I can do with my switching harness. I saw the
> interference in Eznec. Most use both together full time which is a serious
> mistake. The spacing I suggested is most likely too wide on 10M. On 10M it
> sharpens the free space vertical lobe even more but doesn't increase the gain
> and 2 ears start to form. On 20M the spacing is too close and the full 3 dB
> gain is not obtained but it's less of a compromise than if they were
> optimally spaced for 15M.
>
> The pattern distortion when either one is used alone (to make use of the
> different angles of radiation between the 2 beams) is a problem that I tried
> to minimize. Fortunately this problem is minimized the higher the gain of
> the beams used in stacks for 2 reasons. The vertical patterns are
> progressively sharper with gain which means less coupling between them
> vertically when used separately and the spacing also has to be wider to
> obtain the max gain with stacked beams--both +'s. The LP's would couple to
> each other more as their vertical patterns are much broader (why they work so
> well close to the ground), and a closer electrical spacing is required when
> stacked. So the assumption is made that with equal length feedlines the Z at
> the end of each feedline will be very close to each other and you will have
> to live with it. I also use my "Magic Length" of 91' 2" (.66 VF) or
> multiples as it will be a 1/2 wave or multiples at 3.562, 7.125, 10.67,
> 14.25, 17.81, 21.375, 24.937& 28.5 MHz. Resonant coax lengths reduce
> reactance's and repeats the R value of the Z at the feedpoint. If longer
> lengths are needed, you can add lengths of 45' 6.9" and the 1/2 wave
> relationships will still hold.
>
> I have a very simple matching harness that goes on a coax switch for this
> application that allows full power to each beam individually or both together
> using 2-75 ohm 1/4 wave stubs with a unique switching feature. It has a big
> bonus of giving additionally bandwidth when both are used due to the opposite
> reactance the 75 ohm 1/4 wave stubs create above and below the center
> frequency. I've got a lot of rave notices of this system (at least worth a
> dinner) from many on it including DXer Lou Gordon K4VX. I didn't mention it
> as the 1/4 wave stubs would have to be changed for each band.
>
> Now for those who suggested the typical V stacking where both feed points
> are tied together for simplicity and 1 feedline, this is a bad application
> for this concept when using short boom Skip Logs. It's the most useful and
> effective for very long boom LP's. This physical configuration essentially
> maintains the same and optimum electrical spacing for the entire frequency
> range and has a minimum V angle. With short boom LP's, the beams would have
> to be up to 90 degrees or more to each other to optimize and balance the
> electrical spacing on the upper and lower bands. Furthermore the part of the
> vertical pattern pointing forward from each Skip Log would be down several dB
> and pattern addition straight forward is not at all optimum--forget it.
> Note! When 2 long wires are used in a Vee Beam configuration, they are
> aligned so that each has a lobe going forward and parallel and only 3 dB is
> obtain in an optimum configuration. I have such a V log here for the TV
> Channels of minimum elements using also a staggered element elimination
> design and the Vee stacking didn't do a thing for it. Another compromise
> failure. We need more of those who maximize their designs (I've been known
> to lean that way), not this damn "Minimal Design Bankruptcy" constantly
> jammed down our throat that wastes everyone's money.
>
> My L networks seem to be a bit broader than yours or I didn't think they
> were narrow on applications just like this 25 proposed ohm load. I also have
> what I call "One Knob Antenna Tuners" in 4 switchable L network
> configurations, shunt and series capacitance and inductance. It does lots of
> things. Visualize this. The variable Xc (I use them a lot) is on the same
> shaft as on the inductor. As I rotate the inductor through each turn, the Xc
> goes through 2 complete cycles and in about 5 seconds, I can tune through the
> entire range of many many Z's it will match--in 4 different configurations.
> So I find 1:1 SWR real fast and can touch it up quickly off frequency if
> needed.
>
> I've used this L Network configuration in a similar application. Visualize
> 2 yagi's on the same boom at right angles to each other in the "X
> Configuration". Each yagi is fed with equal length feedlines. CBer's had a
> similar beam in a + configuration where they selected either horizontal or
> vertical polarization. The vertically polarized DE had to be a different
> length and had other adjustments than the horizontal DE used due to the heavy
> coupling to the mast. The tower was excited and lift off of the vertical
> pattern was substantial. I used the X configuration to reduce this coupling
> and to balance it up so the load of each beam for the coax was the same. It
> still coupled but I have a way to get rid of the tower interference now when
> vertically polarized. I'm adapting it to a quad DE--when I get time.
>
> I have a switch box that allows me to select 6 different polarization's from
> this "X Beam." I can select either beam for 45 degree polarization left or
> right (direct feed), horizontal polarization (1/2 power in each beam in
> phase), vertical polarization (1/2 power to each beam 180 degrees out of
> phase) and turnstile polarization CW or CCW with 1/2 power in each 90 or -90
> degrees out of phase. To obtain 90 or 180 degree phasing I switch in these
> lengths of coaxes in series with one coax in the proper way. For matching
> in-phase, the coaxes are paralleled for 25 ohms and matched with (you guessed
> it) an L Network. It uses relatively small coils and variable Xc's for 1 KW
> levels without heating or arcing in a small space--3 of them. Once the
> proper inductor of the L Network was found and tuned up in the middle of the
> band I seldom had to adjust the Xc in the band edges. I had all the
> bandwidth I needed with the matching and phasing hardware in a small box and
> saw no need to look for a better system. I could have used 2-75 ohm stubs
> for the matching part but didn't for reasons I don't remember--some 50 years
> later. A CB mfg in Chicago tried to swindle the design out of me--but
> failed. I seems that most mfgs want everything I got free despite contracts.
> He could have had a great money maker for us both laid in his hands but out
> right greed cost him (and me) dearly. He could have had several other unique
> designs also. Industry is notorious for this practice but there are
> exceptions.
>
> Anyhow horizontally stacked Skip or Norma Logs is a similar Z matching
> design and by having a calibrated variable inductor and Xc you can preset for
> each band or in-between frequency very quickly instead of changing 1/4 wave
> stubs for each band or frequency for a match. I'm eager to try my "L-Network
> Match Box" on horizontally stacked LP's myself. I see no reason to use
> another matching system at this time but would like to see a better system
> for flexibility. Send me the details of the Stack Match and I'll see if I
> can adapt it. I have the flexibility of selecting the top, bottom or both
> LP's in the shack--without relays. I like to maximize the full potential of
> any system. If I can get more bandwidth I'm interested. I think I'll have
> plenty of bandwidth as with the LP's I won't have the reactance swings
> typical with parasitic beams. Now I bet you knew that. Your concern of L
> Network use has been diminished by LP's. Long live the L-Network until
> something else comes along that's better for this application.
>
> Although I was in a hurry I arrived at my suggested simple design I posted
> on TT in about 5 seconds considering all these details I've explained here as
> I've "been there and done that" in similar applications. It took about 10
> minutes to Post--but many hours to answer. I've found that if I give too
> much info or too little (and without attachments) I have to justify or supply
> even more info--which I always do. I would hope that you TTer's would by now
> have a little more confidence in my suggestions. If I say it works--it
> works. I'd like to remind you that you also got the info free of charge.
> There are some with limited insights that make "great demands" for more and
> more free info as they can't derive it themselves. They are a form of
> "Technical Parasites" on "Technical Welfare." I normally charge for
> technical information. (If I charged you for what I said, would you have more
> confidence in it?) I thought I'd make a quick suggestion, I was properly
> challenged and I may and often learn of new techniques myself which I'm
> always open for.
>
> Horizontally Stacking LP's is a great idea that I started getting myself
> about 15 years ago with the availability of them from 14 MHz to higher
> frequencies and I knew how to match 2 of them stacked real easy. About 40
> years ago I tested one of the first LP's of the first designers of it by the
> name of Dwight Isbel came up with. It was flat from 60 to 150 MHz at 93
> ohms. I still have a picture somewhere of it and Isbel. He worked for
> Boeing in a fancy Antenna Lab and I didn't, yet I was testing it for him.
>
> The lower gain of LP's is no detriment--it's an asset most of the time when
> properly used. It's been a victim of uninformed critics who have never used
> one. I'll have 2 M2 Skip Logs's stacked in SD (if I ever get there)
> matched--you guessed it--with L Networks or a better systems if there is one.
> This should explain why I do what I do (have I ever misled you?). During
> the mean time there should be some serious study of the life and times of the
> "unseen vertical pattern" as you rotate the beam, its size relationship (it's
> wider) to the horizontal pattern, gain and Reflection Factors. It's time for
> more of you to get on Eznec and read AntenneX mag on Internet. It's read in
> over 170 countries now. K7GCO
> "Now you know the rest of the L Network
> story."
>
>
>
> --
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--
Jay Terleski
WX0B - Array Solutions
www.arraysolutions.com
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