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Author Topic: Phased Verticals  (Read 441 times)
N4JTE
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Posts: 1155




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« on: August 05, 2008, 07:06:38 PM »

Now that I have enough first hand knowledge on 40 meter phased verticals to realise how much I don't know, it's time for some elmering. According to most radiation patterns for two element vertical arrays the most gain(4.5db) will occur at 1/4wl spacing using a 135 degree phase line. Unfortunatly ON4UN only describes this design at 1/8 wl spacing, page 11-33. I'm wondering if the feedline and phaseline lengths could be used at the 1/4 wl spacing. Never afraid to show my ignorance, hi.
Also I never got the CD he refers to which would probaly answer my own question, is it sold seperately ? Google tells me I have to buy the book again. Would appreciate any help on this as that 4.5dbd looks inviting.
Tnx
Bob
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WA3SKN
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« Reply #1 on: August 06, 2008, 05:07:36 AM »

Don't worry about the gain!
It’s the cardioid "front-to-back" ratio that is important here.  You will want 90 degree phasing with 1/4 wavelength spacing.  You can get close enough using open-wire.  Space the antennas 1/4 wavelength apart and use 1/4 wavelength of open-wire between them.  Add a relay to switch them in or out-of-phase for 2 directions.  The front-to-back ratio with this arrangement is impressive, enjoy!
73s.


-Mike.
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KZ1X
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« Reply #2 on: August 06, 2008, 05:18:09 AM »

You should be able to model this with the free version of EZNEC.  It has a segment limitation but simple verticals are low-segment count so, try it out!  While you are at it, consider making end-fed halfwave verticals instead of quarter waves.  It's a lot of work to out in a radial field for good 1/4 wave performance.  Yes, you have to match the feedpoints but this is easy to do with a piece of airdux or similar and a variable capacitor.  Takes hours to make the match boxes versus days or weeks to lay radials, and these days the parts can cost less than the wire.  Plus the halfwave is a better DX antenna IMHO.
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KE2TR
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Posts: 134




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« Reply #3 on: August 06, 2008, 07:30:08 AM »

I have read most all the on4un books on low band dxing and what it gives you is a starting point. If you want plug and play 40mtr verticals I would recomend Comteck phasing boxes, they make it real easy. But if you dont want to invest in these types of boxes and want to roll your own its time to be a ham again and try different types of spacing and feedlines to obtain your best results. IMO I have used 3/8 wave spacing and 72 degree phase lines plus feed each vertical with 1/4 wave electrical feedlines. This has worked out very well both with inverted vee's and verticals but for some reason the verticals do work better with 1/4 wave spacing as far as FB. Also use current baluns at the base of each antenna.
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WA1RNE
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« Reply #4 on: August 06, 2008, 07:42:59 AM »

 
One of the easiest ways to do this is by using coaxial lines of the correct type and lengths calculated using the program Simpfeed from W7EL:


 http://www.eznec.com/Amateur/Articles/Simpfeed.pdf


 You can use the dimensions in Table 1 if they match your current configuration or model your configuration using EZNEC Demo and enter the individual and mutual feedpoint impedances into the program.

Alternatively, you can use an L Network and quarter wave lines, setting the desired phasing using a scope, but the Simpfeed method is about as cheap and easy as it gets and works well.


 ...WA1RNE
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K0OD
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Posts: 2546




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« Reply #5 on: August 06, 2008, 08:20:15 AM »

DX Engineering also now makes phasing boxes. 4-Square is a good antenna, especially on receive. It's mostly about the noise rejection from the sharp pattern which is better than a 2-element yagi. Instant rotation is a great feature. Mine was quite broad banded too. The DXE box also allows a 360 degree pattern.  
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WA3SKN
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« Reply #6 on: August 06, 2008, 10:36:53 AM »

Both Kraus and the ARRL Antenna Handbook cover two 1/2 wavelength antennas with various spacings and phasings.  The two of interest are 1/8 wavelength spacing and the 1/4 wavelength spacing, both cardioid patterns.  The 1/8 wavelength has a very narrow bandwidth, the 1/4 wavelength is much more forgiving!
The next step up is three 1/2 wavelength antennas,  with two in-phase and one out-of-phase, making a steerable array just with relays.  Then comes the variable phasing steerable arrangement, with either three or four elements.  DX Engineering is the place to go for this design.
The problem on 40 meters is that most hams are working with 1/4 wavelength antennas, and all the problems of a counterpoise/groundplane at that frequency.  Great front-to-back ratios can be obtained, but you are limited to single band operations.
Note that commercial stations are assigned a single frequency to operate on, while an amateur needs to consider a "range" or "bandwidth" in their plannings.
Hope this helps!
73s.

-Mike.
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N4JTE
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Posts: 1155




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« Reply #7 on: August 06, 2008, 01:03:19 PM »

WA1RNE, tnx for the closest response to what I asked, I have a full version of the eznec but it is a bear to use with raised radials.
Mike, SKN, to me, it's ALL about gain.
As far as running 1/2 WL  40 meter verticals, I'm fresh out of 70 ft. towers and  would not bother trying to phase an unloadable design with less gain then I already have.
What I  am trying to do is phase with 135 degrees, not quadruture 90 degrees, been there did that.
Tnx,
Bob
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W4VR
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« Reply #8 on: August 06, 2008, 02:52:44 PM »

Bob:  I'm not a big fan of 2-element phased vertical arrays, but if I remember correctly the classic design with nearly optimal gain is the one using 1/8-wave spacing and 135-degree phasing.  Most folks I know using phased verticals on 40 or 80 meters use this combination.  It also works well for a horizontal array, as W6VOD (SK) clearly demonstrated in his experiments from Pagosa Springs, CO.  The nice thing about using this combination, as I recall, is that the feedpoint resistance of both radiators are nearly identical which makes it easier to feed from a power division standpoint.  The 1/4-wave, quadrature phased, arrays have vastly different feedpoint resistances and are more difficult to phase, unless you use current forcing techniques as described by ON4UN and Christman.  Ron, W4VR
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N4JTE
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Posts: 1155




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« Reply #9 on: August 06, 2008, 03:06:17 PM »

Ron, W4VR, exactly what I was referring to but I was wondering if that whole feedline/ phase loop would work better at 1/4 spacing. I think I'll try the 1/8 when I get back to NY next week and forget about the 1/4 w/l spacing till I figure it out on eznec. Also realized I can broadside by shorting out the loop, I think, I know that works on quadrature not sure on 135 degrees. I can always go back to reversible quad when I'm  finished exploring the vertical thing. But the 2 ele vertical worked so well I figure I've got a few more experiments left before getting back to horizontal wires.
Tnx,
Bob
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N4JTE
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Posts: 1155




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« Reply #10 on: August 06, 2008, 07:43:58 PM »

Actually all the antenna books I have show maximum gain for any 2 element antenna results from 135 degree phasing at 1/4 W/L spacing. ZL special etc.
I will try to extrapolate on4un's measurements for 1/8 spacing and see what happens before I give up  the opportunity to acheive 4.5dbd with 2 elements. Was hoping somebody had actually tried this and give me some insights. The christman method appeals to me as I have gained confidence with that method as used in my article posted last week so please no more tutorials on 1/4 W/L 90 degree feedlines, trying to push the envelope, hi.
Tnx,
Bob
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W4VR
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« Reply #11 on: August 07, 2008, 08:42:27 AM »

Bob:  I believe you're using the current forcing method, so every time you change the feedpoint impedance by increasing or decreasing the element spacing you will need different line and phasing loop lengths...if I'm not mistaken.  
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W6OP
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Posts: 338




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« Reply #12 on: August 08, 2008, 04:23:15 PM »

I have 20 meter phased verticals. Phasing is 90 degrees and spacing is 1/4 wavelength, each with 32 overlapping bonded radials. Works great. definite increase in gain over my 6BTV on 20 meters. Right now I am getting ready to change the phasing to 135 degrees switchable.

I use what is called a C-Match by Lee Barret K7NM. Basically you make both verticals about 5 degrees long and match them with variable capacitors. I salvaged mine from some MFJ tuners I bought cheap on eBay. You don't need very high voltage caps since you are at a current maximum and voltage minimum. Lee has published a book on designing the C-Match and determining capacitor values for different bands. It was being sold by Universal Radio but if they don't have it just contact Lee directly. Real nice guy and answers emails promptly.

Pete W6OP
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