Switching multiple monoband antennas 180/0 degrees for vertical TO angle control

[K1JJ]

With many 10M antennas being built lately, some guys have asked about switching the phase 180/0 degrees to obtain a low or high take-off angle. This helps enhance local or DX work.

The objective was to switch my 3-stack    0-180-0  or  0-0-0  degrees.   By adding a double pole, double throw relay, a 1/2 wavelength piece of coax can be switched in or out to give this 180/0 degree feed ability.

When adding in a relay system, we must determine how much extra length is added to the feedline because of the relay and cable path. In my case I am adding 46" with the connecting cables and relay contacts. Thus, I need to cut 46" off of the antenna feedline where the relay system is inserted.

When the relay is off, there is a short path thru the contacts and the three antennas have identical feedline lengths. This is 0 degrees, or fed in-phase giving the lowest vertical takeoff angle.  

When the relay is energized, the extra piece of 1/2 wave coax (11' 2" for 29 mhz) is added to the one Yagi's feedline length. This makes the center antenna 180 degrees out of phase compared to the other two.

If we use two antennas, it does not matter which one is phase switched, the top or bottom - it will have the same effect.

The formula for the 180 degree feedline length is 492/f  X  velocity factor.  For RG-213 coax, the vel fac is about 0.66.  So 492/29mhz * .66 = 11.19' = 11' 2".  I also measured using an MFJ 259B and found the 1/2 wave coaxial system tuned to about 28.7 mhz, to match the other two antenna feedlines.

I used a standard plastic box with tight lid found at Home Depot to waterproof the relay system. It will be mounted on the tower at 66' and painted for UV protection.   A lighter and smaller arrangement could be worked out for a stacked wire array like what Steve/HX has been describing in other posts.

I realize some purists might say there will be some swr induced because of the open frame relay contacts and layout, but from experience on 6M, I have found that this is a very minor effect and swr stays down in the 1.1:1 range.  If the overall antenna phase is maintained within <10-20 degrees of error, modeling shows the pattern to still remain quite sharp and robust. [caw mawn]   I try to do things on the cheap if possible.

There is a diode across the relay coil to help clamp lightning strikes. I have lost relay coils in the past without a diode.


Tom, K1JJ


Pic 3:  5el homebrew Yagis at 99', 66' 33' heights.    The middle Yagi gets the relay system to give it 0/180 degrees out relative to the other two. This will give vertical angle selections between ~7  or 15 degrees.    

[WBear2GCR]

Ah, c'mon!

That's effectively cheating, having ants like that!

               _-_-bear

[Steve - K4HX]

It is a sickness but mostly a healthy one (as long as you stay on the tower).

[flintstone mop]

We're glad Tom is around here. Be careful on those towers!!
He proves out what we read in antenna books.

To be able to switch and hear the difference. OK by me.

He did a similar study of various times of early evening into the late night on 80M...I think, where his various antenna heights proved out that the low angle and high angle signals are constantly changing throughout the night.

[K1JJ]

It is a sickness but mostly a healthy one (as long as you stay on the tower).

Yep, guilty as charged...


The challenge now is to get out there in this 30 degree WX and hang onto the cold rails to install this contraption. All for the love of hearing a Pascal somewhere say, "OMG OM, you 59  - chow!"    [sigh]


It's just like a nightmare, isn't it?   [Tom Cruise in Color of Money]

T

[Steve - K4HX]

Ha! 5/9 Microphone for you!

It's only really worth it when you get on the air and enjoy the fruits of your labors. Then it doesn't seem so sick.

[KL7OF]

I'm waiting for you to point that array out west for some 10M  checks (ant"A"...ant "B" etc) ........I'm PW on 10 with 40 watts and 4 element monoyagi...Good luk Tom..

[K5IIA]

let the fun begin. i hope to be adding a second 4 element yagi this weekend. i have one at 53 foot and will mount another a little lower on towwer. will be fun to work you on 10m steve. you had a nice sig last night i think it was on 75m.

[K1JJ]

Climbed the tower and installed the new 10M 180/0 switcher.  With a toggle switch in the shack I can get the 10M stack to be in/out of phase giving about 7 or 15 degrees of TO angle selection.

On first trial, I saw a station out west come up about 10db with the out of phase.  But then the next hour I saw most stations about 10-15 db louder on the in-phase.  I heard Brandon/ K5IIA come up about 15 db when in-phase, thus lower angle between us.

Just copied a VE6 who was the same on both phases.

The swr changes from about 1.3: 1  to 1.1:1  when I switch out.

I noticed that the general noise floor drops down about an S unit when I go out/higher angle. This seems to indicate that the noise is coming in at lower angles.

In pic #1, the black box strapped to the tower is the remote switcher.

Pic 2 shows the Yagis presently staggered to cover NW, W and SW directions, USA.

So, bottom line, I need to spend some more time over various conditions to see the patterns of propagation.  It appears to be a worthwhile addition, but we will have to see.

The 40M stack pictured in the last pic may get the same treatment next year if this works out.

T

[K1JJ]

While outside, I couldn't resist:

Yaz at 8.5 years old.

The 40M stack that may get the 180/0 switcher too.

T

[Steve - K4HX]

NICE! You and Brandon will be the Channel Masters!

[WA1GFZ]

I thought I would get on 10 this morning. Fired up the TR7A and everything was dead. Reflected power equals forward power. Very sinking feeling that LOG is broken. Ohm out antenna and measure 1 ohm. Cable or ant not open.
Then connect LOG to HPSDR and YEA! lots of signals. EU strapping in at 20 over S9. HPSDR TX not connected so didn't try to TX. I want to remove all the JSs first. Gee I could have tried the Viking 2 HMMM.
I think the problem is in the TR7A low pass filter section switch may not be tracking properly. Heck only 35 years old. It happened once before.

[WBear2GCR]

Mister JJ,

I can't figure it out from the pix, but how do you rotate those beams?

                      _-_-bear

[K1JJ]

Mister JJ,
I can't figure it out from the pix, but how do you rotate those beams?
                      _-_-bear

Bear,

The Yagis are hung on homebrew swing gates that give about 330 degrees rotation around the tower.  Each Yagi gate is tied off with a strong rope to the ground. To position them I use the "Armstrong Method."

I set them up for SW for a while, then manually turn them NE to work Eur, etc.

These days, I would probably go with a rotating tower, but it's too easy to blow $15K for a full system.    Instead, I used sections from a Rohn 45 that I helped dismantle for free.  

Rotators could be added to the swing gates, but I don't think I will bother at this point.  

I have gates on the 20M beams too. So far, never had a problem with them over about 10 years of use.   Rotator problems? Don't even axe me...

T