Search

Title

Author

Article Body

Manager


Manager - AB7RG
Manager Notes

Smaller Backyard, Revised 40-Meter Beam!

Created by Bob Raynor, N4JTE on 2020-02-02

"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the eHam.net team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 07/28/2014

 

Smaller Backyard, Revised 40-Meter Beam!
40 Meter 3 element reversible vertical wire beam
Submitted by N4JTE

Things have changed in my neighborhood! A family from LI. NY now occupies the house/backyard next store, which had been vacant for years. Why anyone would move from Babylon to Ellenville is a question I will ask as soon as I finish taking down my "annoying" string ends from his newly acquired backyard trees.
Say goodbye to an amazing 80 meter reversible wire beam , a 40 meter EDZ and one lousy string on 40 wire beam intruding! Yeah yeah truth be told, I was a spoiled little brat that lost his antenna playground, hi
My yard is only 48 ft wide in a north south direction so once again necessity being the mother of invention; let the adventure begin.

The Plan:

I wanted to at least match my 40 meter 2 element previous existing wire dipoles beam's excellent performance based on spacing and was/is a full length reversible flat top at 40 ft as seen on my qrz page. With only 48 ft of space now available, it was time to shrink everything to be able to fit in my yard.


Heck, even without my adventuring into the 3rd element this baby at two elements with only 16 ft spacing will double your ERP in reversible directions with 30 db front to back!! Yada Yada; as per all the books at least, hi.


Note; Yes this will be a rather "technical" article in which I will present a bunch of stuff that will hopefully resonate with a few antenna nuts on the same path that I have been navigating for many years.


And, I am confident that there is some good info presented here for anyone who wants a tremendous mono band cheap antenna with useable gain and substantial front to back in relatively small backyard.


And please note that this monoband phasing concept can be extrapolated for any band from 160 meters to 2 meters.

HOWEVER; If you want a 6 band, I hear everywhere, "tunes?" all bands dc to daylight DX buster antenna, or a 7 ft. tall antenna on your kitchen toaster for 10 bands, than stop reading and head off to "Ham Universe.com" or some other magic antenna site.
Study this chart and begin the adventure into phased vertical and wire dipoles!
Spacing in W/L between elements is on the top and phase angles are on the side if diagram is hard to read as eventually posted here.


Figure Polar plots of spacing vs phase angle with resultant gain over a single element.

I have used two element vertical driven arrays, and lately, dipole phased driven arrays on 80, 40 and 17 meters for years with amazing results based on 1/4wl spacing with quadrature Christman feeding utilizing ON4UN and VK1OD's feed line studies. Their work proved that 84 degrees works better than 90 degrees with a lag/lead line of 71 degrees adding up to 155 degrees. Having tried the 90 /180degree versions, I can attest to the 84/155 degrees being lights out better! -- Especially in flattop dipole configuration. However, I never had the need till now, to go back to a vertical design, at a new to me, 1/8wl spacing, with non (90 degree) quadrature phasing, so it came down to the usual build it and see what happens exercise!


I have used many variations/ number, of raised radials in the past and decided to use just two in this experiment. Reason being I knew I could real time test it against a two wire beam and it's too darn cold for more!

Well, back to my new limitations, that extra tree or two in my new neighbor's backyard are now off limits, so what to do?

Besides nasty thoughts of directing a couple of skunks into his living room or worse, to welcome them to the "country", common sense prevailed.
I have often been intrigued with 135 degree phasing as it is the optimum end fire gain achievable on any 2 element system be it vertical or horizontal. Best part is the slightly better gain and front to back with only 16 ft of spacing on 40 meters. My plan was to build the 2 element phased system with 1/8 WL spacing as inverted vee's, and when optimized and tested the next step was to be adding a switchable parasitic director/ reflector vee as a third element! Spoiler alert; after many hours of construction the two element inverted vee configuration was an abysmal failure! No front to back even with forced phased feeding so it's apparent the Vee configuration is not the way to go with 1/8 wl spacing!

Quick Phasing Primer:

I have been singing this song about phasing in previous eham articles and extolling the virtues intrinsic to the design and have seen a growing interest from many emails from around the world who have heard and worked me especially interested in my use with dipoles as opposed to verticals, as the ground losses of dipoles at 1/4wl plus tall, are minimal as compared to the average vertical install.

Achieving all those wonderful gain and pattern pictures in all the antenna books will only be achievable if the voltage/magnitude is exactly the same on both phase lines at the element wires. There are a couple of sweet spots on the coax but never exactly at the published polar plots phasing numbers like the ones pictured above from the ARRL antenna books.


Case in point; a 90 degree spaced cardioid end fire needs 84/155 degrees to reach design paradigms.
And 135 degree phasing is actually happier with 157/39 degrees with 1/8wl spacing as shown below on the polar plot from ON4UN's book.


Figure 135degree phasing with 16ft spacing.

157 degree phasing with 39 degree lag line
3 db beam width=142degrees
Gain=4.3dbd

So, with the new backyard constraints and after the Inverted vee fiasco, I figured why not try out the 1/8wl spacing with two full size vertical elements and then add a switchableparasitic 3rd element director/ reflector for maybe even a super ah ah moment. -- About same East/West footprint as previous 2 element wire beam. My center frequency of choice is 7160 so the following formula plugs that number in along with needed phase line degrees, no need to worry about velocity factor except when picking starting length of coax.
Caveat; do not cut phase lines based on VF alone without doing the frequency method, waste of time and accuracy!

Formula: 157/90 = 7.160/X = 4.104 meg

That's the frequency, 4.104 meg that you want to see the lowest SWR displayed when trimming the 157 phase line lengths. Remember this method requires the ends shorted when using transceiver with 50 Ohm dummy load in parallel with tested feed line.

Scan the vfo, run around 30 watts on rtty until you find the sweet spot/ lowest swr, remember a low frequency tells you that your line is still long, that's a good thing, tedious but effective! The 39 degree line lag/lead line for reversibility is figured and cut with the same method for a frequency of 16.4 Meg. This formula gives you the means and method with your transceiver to cut phase lines correctly without expensive test equipment.


I got this epiphany/formula about 6 years ago and I have concentrated on phased experiments since then. And when you build one you're going to be as addicted to phasing as I am!


I put in the two 4x4 pt poles at 16 ft. spacing and a third in the west direction at 20 ft. spacing for the future parasitic director/reflector. Big guess on that parasitic dimension with phased elements involved when reversible!


And then the weather showed up big time!

Time to cut the phasing lines and elements inside, 5 degrees out there! That's 10 unwelcome inches of snow!
All element poles are spider poles from the previous 80 meter wire beam and were eventually 43 ft tall and strapped to the 4x4 posts with no guying needed as at that height the 60 ft spider poles were nicely nested and stable in the wind at 43 feet. The wire elements are 33 ft with two raised radials at about 10ft off the ground.

Results:

Had enough left of the flattop 40 wire 2 element beam to compare the new vertical antennas in real time. Neighbor has not seen the one remaining masonry string still over there yet, hi. With just the two vertical elements in the new configuration it was definitely noisier in the East direction than the flattop, that building 50 ft away in the photo is an extended care facility with lots of medical noise. Signal strength reports in Europe were a couple of S units down from flat top so there was a little drop off with the new smaller footprint design and change of polarization.


The original beam is E/W and the new one is now NE/SW, so one never knows if that figured in.


BUT:
With the addition of the switchable director/ reflector the differences were not really a big deal, some nites the verticals beat the horizontal and vice a versa. The extra parasitic element was the big equalizer in getting closer to 2 element horizontal beam performance.


The parasitic element was the biggest challenge, radials or not etc. Going from the 30 to 36 ft length, director/reflector, with the relay was a no brainer but tuning it up near 7160 was a chore because I figured I needed radials or something for the other half of a non-driven thingy as I up to now, never had any real, write home about, performance from parasitic vertical, multi element designs. I kept the length of the director wire at 30 ft. and added one 33 ft. long radial laying on the snow and trimmed it till I got to 7518 (director) using a separate feed line back to shack to check for freq/swr. I have the MFJ and Autek analyzer but way too cold! Strange approach but hey it worked, (till the snow melts!). Then I attached the relay along with 6 ft. of extra wire to the vertical wire to make it into a reflector.

I was worried that with an additional element the front to back/gain would be impacted, and it was, for the better. The 3 verticals do not have the usual 25db front to back that the 2 dipoles showed, but similar gain, a fair trade off in tight space.


I am aware that the parasitic vertical element will probably work even better with some due diligence as at this point it is a low inverted L!


Actually most things I try are a big guess until in the air! Not a very good modeler with real world phase systems and unknowable near and far field enhancement on verticals. Also this time every year while I am writing this, mid-February after dark from Hudson Valley, NY, the band is horrendous/ qsb etc. stateside but still relatively good out east and long path to VK. -- Absolute worst time of year to try a new antenna design on 40 meters from NY but no choice.


Obviously a two element reversible monobander, even at 40 plus feet, is hard to beat but this experiment been has convinced me of what can be accomplished in a small backyard with 1/8wl spacing for 40 meters.

If you build it: 1: All wires 12g insulated and each of the two phased elements are 33 ft. long, the two raised radials on each of those elements were not measured but were tuned for 7.160 as low dipoles.
2: Phase lines at 157 degrees and 39 degrees are rg8x. -- About 48ft.long and 12 ft. long respectively.
3: Optional dir/ref is 30ft long wire, (give or take, never measured it after tuning) with a dtdp {could be spdt but have lots of the dpdt12v relays laying around} with 12 volt relay at director length bottom with 6ft added at the normally off terminal for needed reflector length. Both relays when normally off, were for West direction and switched from shack 12 volt supply with $3 light switch on ground leg to add reflector length and lag line for East direction. Radio shack relays used are sold online at around $6.
4: I use the LDG auto tuner but a matching network of parallel wl 75ohm coax feed line probably easy to do.
5: Relay wiring is available on my QRZ page and previous eHam articles.
6: Radio is IC 751a with ICM microphone and AL80b amp usually at 600 out.

Final thoughts:

The soon to be removed 2 element flat topped phased dipoles, http://www.eham.net/articles/26865 will be missed but this vertical design has achieved very satisfying results in a much smaller space.
I believe that getting a two, or the optional parasitic 3 element, widebeam width, reversible high gain, low angle short "boom" vertical beam is very achievable on 40 meters in a typical backyard and of course it all gets easier and smaller when designed for the upper bands.
With a little sweat equity you can compete very effectively with any store bought tower and commercial trapped beam costing probably 20 times as much.


The alternative!!!

Tnx for reading
Bob
N4JTE

 

 

N4PIE2020-07-18
Smaller Backyard, Revised 40-Meter Beam!
Another great, thought provoking article, Bob. All of this is giving my brain a cramp. I will revisit in the morning hi hi.