Verticle Tent Pole HF Antenna
(Last update: 01-01-2019)
Hello, I keep finding vague hints at building a tent pole online, but can not find anyone who has done it. Finally today, I went in to Burnaby Radio Communications Ltd.. If you need anything to do with HAM, he ether has it or knows where to find it. And just about the nicest guy I have ever met. A great experience. But whats sitting in his front room? (by his HAM shack! that he has setup at work and why not?) The antenna that he is about to put outside, the same one I have been wanting to build:
This is a tent pole antenna with a 9:1 Balun at the bottom of it. Sitting on a surveyors tripod. That is EXACTLY what I want to build and exactly how I was thinking on doing it but I primarily interested in 10m 6m 2m. This antenna is made by Alpha Antenna (http://alphaantenna.com/index.php?main_page=index&cPath=5), look at it, what a beauty! So. I am making one. here we go. (I want to add here. the build quality of this antenna is amazing. If you can afford it, I highly recomend it. When I saw it in operation I was blown away, where it works and how well it worked.)
First of all my B.O.M. as I think I see it.
-Aluminum tent poles
-Brass fitting for the bottom of the tent poles
-some kind of base
-and why would I need a Balun? I am to new at this to understand fully, so I am trying it without.
-50' of RG58
-UHF Male (PL259) connector
Regarding the Balun, I dont know enough to understand the reason, so I am going to build it without it, then use an antenna analyzer before hooking it up to a radio. You can use your bed frame as a radio, TO LISTEN, but don't try and TX. you will convert all those nice electronics to carbon.
So, Tent poles. THANK YOU BRAD! My buddy Brad Allan (who came to Burnaby Radio with me) pipes up with "Oh, I have a whole bunch of aluminum tent poles", Big grin from me he responds "Ok, when we get to Kamloops, I will dig em out" The poles were 16ft long, but had a bend in them to shape the tent. But only 6 poles had bends in them 7 do not. Including the top piece. This means I can start my build and still be around 10'
I decided to reach out to the armature radio operators group on facebook, just to see what they thought about this idea. At the bottom of this page you will find a document titled "tent pole antenna - facebook post.docx" that is a copy of the conversation. Very helpful. (I actually end up talking with Steve, the Founder of Alpha Antenna).
On: http://www.hamuniverse.com/hamantennalengths.html the antenna lengths chart: (I put the chart here, because information always vanishes on the internet.)
This means I should be able to use the antenna for 10m on down if I cut the poles. well first I need an electrical connector at the bottom. Right now however, these are at ether end.
This means, I need some kind of electrical connection to the body of the pole AND it needs to retain this elastic string. So I did up a drawing:
Thankfully Rob from the Kamloops maker space had a lathe (mine is still in Calgary). He made the part and it looks great, Unfortunately, the part is about 0.001 to small for friction fit. To solve this I built it back up using silver solder. This also is soft enough that when it slid in, it made a fantastic electrical connection. No detectable loss.
Now with the string attached to the brass connector and a M8 .125 thread cut in the end (tap the threads BEFORE you install the brass), I am ready to assemble. I used a I used a Dremel with a wire brush and cleaned the anodizing from inside the tent pole, but only where it mates to the male parts. I later had to disassemble everything because I damaged the threads. Also I want this to be male thread. So I made an adapter to go from M8 to 3/8x24, threaded it in and silver soldered it in place. See picture bellow:
To tension the elastic cord inside, I repeated the tension the manufacturer had put on it. They had 2 and a half poles of tension pulled in to it. If that doesn't make sense, here is diagram: (So if there are 7 poles, then the elastic is pulled to 9.5 poles)
This helps to hopefully ensure a solid electrical connection from my basic testing. Still haven't hooked it up to a radio. I did decide at this point to check continuity between the aluminum linking pole and the black part of the pole. There is nothing. I bet there is paint between the black pipe and the inserted linking pole.
*** Side Note: Regarding ground radials. this guy says, may not be needed (I am going to add grounds anyhow) here is his somewhat related and interesting video. But I will add them as needed. Anyhow, just spitballing right now. ***
I tried removing the coating that is covering the shiny aluminum pole that links each section together and still got nothing. So after a lot of effort I managed to get the linking pole to come out of the black pole and sure enough, its been painted inside the pipe so it was blocking the electrical connection between sections. That together with the clear cote on the linking pole... I should have tested this earlier.... Dam. Ok. Moving forward. I can ether try and remove the anodizing from both the black pipe and the linking pipe or I can build something from scratch. The point of this is to make an easy antenna, so I will try and re-purpose the linking pipe.
After simply cleaning the antenna linking pole, and the inside of the black pole, the connection is still not ideal. Using an el'cheepo multimeter shows 28ohm oh resistance between two sections of the tent pole. I was able to fix this by using a centre punch on the end of the black pipe (the "female" end) this made the pipe fitting very tight and the multimeter now shows it as a dead short between two sections and about .05 ohm over 8feet.
Photos of the base I started experimenting with:
I used a #4 40 tap to put 8 holes around the base. The hole in the base for the 3/8 to UHF connector is over sized and the coupler nut is being used to keep the aluminum ground ring centred. This ensures the center conductor does not come in contact with the ground. The UHF connector side is centered by a plastic ring. So as long as its tight, it wont short out.
Holly crap, I think I am done!?!?!?
This is no longer the direction I will go. please look bellow this section
To make a new insert, I need to understand the pressure fit from the old linking pole:
So, it appears that only the last .25" inch has a larger diameter and its only bigger by 0.01" (10 thou) I find that interesting. I actually think, I have a few choices here. For starters, if I made an identical replacement for this, I would make it 0.38" on one end and 0.375 on the other, this would give a tighter connection between segments. For now my plan is to do an experiment with making a screw together section from aluminum. Though I am concerned about how strong it would be in wind.
It might be that I just didn't leave enough thread, but this does NOT feel strong enough to me. I had left a hole in the center of the two parts to ensure that the elastic cord could be put back in the poles. but whatever the case, this does not seem to cut it. Its to bad really, because I already made a whole bunch of these, thinking it would solve my problem. I should have known better. but I was excited.
The next design is to make it friction fit on one side and slip fit on the other.