Here is a slideshow of my 20 meter phased verticals. The slideshow is a little slow to start so be patient after hitting the start button.
The slideshow widget is old and has quit working so I will just show a gallery of the pictures.
All of my antennas are made to be quickly and easily taken down. I can take take everything down including my Steppir BigIR in about ten minutes. I do it by having PVC or metal pipe in the ground with threaded connectors. PVC pipe is used for all of the small antennas and metal for the bigger ones. The ground is soft here without big rocks so I can pound in a 24 inch long PVC or metal pipe easily. This really works out well for having a BBQ or party, especially with kids and dogs around. It also makes it easy to mow the lawn though I usually just mow around them. I use LMR400 coax which is pretty stiff so I can just go over it with the mower. The radials are all buried in the grass, I just use 22 or 24 gauge insulated wire and tack them to the grass in the spring and shortly the grass has completely covered them.
The matching circuit at the base of each vertical is a split capacitor network designed by Lee Barrett K7NM and called a C-Match. Lee wrote a book about the C-Match and how to calculate the capacitance needed and the length of the elements, very interesting reading. Basically the elements are cut long so they are inductive and the capacitance both matches the impedance and ensures equal poet goes to each element. Lee’s book also comes with a CD with spreadsheets on it do do a lot of the calculations.
The coax to each antenna is equal in length and I have built a switching network to connect in a 90 degree phasing line to direct the antenna east or west. It works pretty well and the gain from a phased array often makes the difference between not copying a DX station and making the QSO.
I love your antenna set up! That is exactly what I would like to do in my back yard – can you give me more details about how you built the ground mounts? I want to be able to put these verticals up and take them down as needed so they aren’t a permanent fixture. Also, what did you use for the vertical elements?
Thank you!
Mark, W9MS
You’ve done a very neat installation, most impressive.
I’m presently experimenting with a Christman phasing system with 2el 20m verticals. Looking at you very professional like work, I wonder if those long interconnecting leads and the relays add to the length of the phasing lines? I tried to add a pigtail of about 1.5 inches to the end of one of my phasing lines and measures the frequency jump down over 100 khz. Thus, I was wondering if all the emphasis on a phasing g line having to be exact up to a khz or so, is overstated?
Thank you John for the kind words. I found the ground wire to the radials had an effect but I kept them as short as possible. Each vertical element was made with telescoping tubing so I adjusted their length to make up for any other changes. My primary goal was just to make sure the current going to each vertical was equal which is what the C-Match did. I am not a theoretical person but I suspect there is a fair amount of fudge factor you can use without any problems. My feeling is anything less than 1 db isn’t worth worrying about.
Thanks for your helpful response Peter. As a matter of curiosity, measure the cables going and and out of the relay box. For example, when a 84 degree line connects to the 71 digress line it becomes a continuous 155 differ line. That then becomes 1/4 wave at approximately 8.245 Mhz (if the system is designed for 14.200 antenna resonance). What. found was that it was measuring 8.050, a whopping 205 Khz added by the connectors, interconnects and the relay contacts. I measured both sides of the 155 degree lines by switching the relay back and forth. Not wanting to mess up two good 84 degree lines, I fine tuned the 71 degree line till I reached a compromise. As you say Peter, the difference is not monumental but I “think” front to back has improved. I’m not even sure what I did is the right way to go about it.
It also leads me to the point that F/B is not always indicative of maximum gain or where that falls. There is a guy on youtube that does many videos on phased verticals and it seems he is always after max FB, whereas phased verticals are no different to Yagis or any other parasitic antennas where gain and FB are never on the same frequency. ON4UN in his book says that a badly tuned system can still show FB but actually be -4 to -5 db down on gain!
If one is fussy, I’m sure the only way to get it right is to use a dual channel scope and make sure the phase difference is spot on!
At the end of the day, it’s a great learning curve!
I think you are right John, about F/B and max gain not being at the same settings. I was always interested in maximizing the gain and whatever F/B I had was a bonus. Since most dxpeditions run split I didn’t have a problem with stations behind me. My vertical elements were made of telescoping aluminum so I adjusted them for resonance. I don’t remember what I did about the cables. I probably tested them once and didn’t think to do anything else. Unfortunately I can’t measure anything now. I have my phased verticals down and don’t intend to put them back up. We did a bunch of landscaping in the backyard and I only have a single Steppir vertical now. I also have a portable mount for my 6 meter moon in the summer and a short 160 meter vertical in the winter.
I would suggest you get a hold of Lee Barrett K7NM. He invented the C-Match and knows all the answers. You should be able to get his email address off QRZ.com I’m not sure where you might get a copy of his book.
I have a writeup on the switching considerations I will email to you.
Thanks again Peter, that’s very helpful. I will look out for your email.
I live in a gated community and my little backyard is postage stamp sized, so getting even thus far has been an achievement. I enjoy the tweaking and learning aspect very much. It seems to
me that many people like myself at the start, are happy to follow the basics and not beyond. They are forgiving, but with a max of 3db to gain, and I doubt many of us get even that, perhaps it’s not really FB we should chase.
Season’s greetings and the best for the coming New Year.
73
John