.64λ Homebrew

[Needle Bender]

Yeah, I just thought I'd throw that out there, just in case anyone reading along planned to home-brew their own Sigma_5/8 or equivalent.

I'm loving this thread. I'm so caught up in reading it that I just haven't had time to post much at all.

I'm a little surprised that the 1/2 wave of coax didn't roughly equal the readings from the 6 x 1/2 waves.

I use 11811 divided by the freq in MHz(27.185) to find one wave length in inches, then multiply by .625 or .64 for the full length of the radiating part of the antenna, minus the average circumference which I get by adding the diameter of the bottom to the diameter of the top, then dividing by 2, then multiplying that by pi, 3.1416.

That always gets me close to X=50 & 1.0:1 if the matching network is dialed in and there's no top hat. I don't worry about the velocity factor of air since it's so close to 1.

For band center: 27.185MHz, a 1/4 inch less than 23' is about right for the radiating part of a .64, 22' 5" for a 5/8, according to my precise miscalculations.

__________

I used to think I was smart, but now that I'm briliiant, I realize I'd be stupid to think I'm that intelligent.

 

[HomerBB]

Great info. Something to keep onhand.
I was a little put off by the difference between the single and 6 x 1/2 wave, too. The single 1/2 wave and direct connect are the closest.

 

[Marconi]

Great info. Something to keep onhand.
I was a little put off by the difference between the single and 6 x 1/2 wave, too. The single 1/2 wave and direct connect are the closest.

Homer, assume we might not really know what the matching values are at the feed point...for any antenna in the beginning, and would only know if we're able to test it accurately. Try this and record you results for me if you would.

Always keeping the frequency the same, how does your dummy load report the values noted below...when connected directly to your analyzer? I suggest you record the values for R,X,SWR,Z at the same frequency in all tests. Then do it again using several different lengths of coax. Record those values too, and compare your results for me.

If you see differences, how do we explain that in light of our having a nearly perfect load to test, where theory tells us the line length should make no difference in the SWR results that we see at the feed point?

Based on theory, I would expect you to see no differences if we tested using a perfect load, but when I do such a test with my loads, I get obvious differences with different lengths, and I've wondered why. I'll be the first to admit that my dummy loads and my VA1 are not perfect. They are close, but maybe these imperfections are enough to cause my issues and my confusion.

Can you tell me what's going on with you in this regard?

 

[HomerBB]

I think you are asking me to use my feedlines into a dummy load, correct?

If so, I can do that.

 

[Marconi]

I think you are asking me to use my feedlines into a dummy load, correct?

If so, I can do that.

Yep, I'm just curious what you might be seeing with your meter. I'm not particularly interested in your feed lines per se, so it's OK if you just use a couple or three short jumpers, so you won't have to disconnect your antenna. Just a brief description of the line and the length will do, and then the analyzer details you get with each. Be sure and do the dummy load connected directly, by itself, as a base line to represent what the dummy load should show us.

I'll look for my old notes of my report and post it to see what differences I got.

 

[Needle Bender]

Homer, is it possible to do the tests with the radials 18' above ground?

__________

I used to think I was smart, but now that I'm briliiant, I realize I'd be stupid to think I'm that intelligent.

 

[HomerBB]

When I get the modifications on the tip over mast done I will be able to do it. I'm working on it today after work.

 

[HomerBB]

Yep, I'm just curious what you might be seeing with your meter. I'm not particularly interested in your feed lines per se, so it's OK if you just use a couple or three short jumpers, so you won't have to disconnect your antenna. Just a brief description of the line and the length will do, and then the analyzer details you get with each. Be sure and do the dummy load connected directly, by itself, as a base line to represent what the dummy load should show us.

I'll look for my old notes of my report and post it to see what differences I got.

View attachment 7002

ok. got it.

 

[HomerBB]

I have made some modifications to the tip over tower that will beef it up.
It is now comprised primarily of an ?- beam constructed of treated 2 x 10 x 16' and 2 x 4 marrying them together.
Inside the beam I have mounted my 40' push-up so that the bottom of it is 1' above the break-over point. This allows me to extend the upper 30' of the pole when once I have the mast standing straight up. In the photo there is a 5' additional section of pipe between the top of the PU pole and the antenna which I will be removing in order to kee the antenna within reach when scoped in. i will be adding some ladder spikes in the top of the wooden portion of the mast to stand on so ads to have a better position for extending the PU pole rather than the top of my step ladder.
I had to go to work so I didn't get it completed. Soon. BTW, it works quite well so far. In the photo the antenna sits at 23.5'.

 

[HomerBB]

I have a little more work to do on the tower to get it where I want it to be.
One more innovation will be an 18" x 30" platform near the top of the wooden section that I can raise when I want to stand up there and work with the antennas, and will fold downward against the side of the tower when not in use. But so far I am adding a few more photos of the tower, and a link to a video of me lowering and raising it.
Almost ready to get back to work on the antenna.

TipOver01.wmv - YouTube or In Touch - TipOver01.wmv

 

[HomerBB]

Soon I'll get back to the antenna.

I have added the platform to work from to the top of the wooden section.
As with all things I do, there is a little at each stage that tells me I have a liitle more to do.
I am going to add some more guys, especially at the top of the wood section, if I'm going to send any time on that platform.
I have been on it already, but want the added assurance that it remains rock steady when I am up there.

 

[HomerBB]

Yep, I'm just curious what you might be seeing with your meter. I'm not particularly interested in your feed lines per se, so it's OK if you just use a couple or three short jumpers, so you won't have to disconnect your antenna. Just a brief description of the line and the length will do, and then the analyzer details you get with each. Be sure and do the dummy load connected directly, by itself, as a base line to represent what the dummy load should show us.

I'll look for my old notes of my report and post it to see what differences I got.

View attachment 7002

27.400 Mhz

dummy load direct ----------- 1.0 -------- R/50 -------- X/0
RG59 x 2' coax --------------- >25 ------- R/6 --------- X/82 (tried 2 different 2' jumpers)
RG59 e1/2λ ------------------ 1.0 -------- R/50 -------- X/0
RG8 mini 7.5' ----------------- 1.3 -------- R/39 -------- X/7

 

[Marconi]

Homer, you get an extra 7' feet of height in the push up pole with your setup, but is it safe? Form the perspective of the images I hope I see that you're sitting some while working, with your feet on the ladder spikes when pushing up, right?

How high is you antenna in the last pictures? Are both sections out full length?

I wouldn't do it that high, but you're a lot younger. My feet are never more that about 6' above the ground when I work my antennas. However, I would add maybe two more ladder spikes to each side to spread out the pressure on your arches, and add much more support that you might need while pushing the pole up. You sure don't want an arch to go out on you while up that high a load in your hands. The last time I had an arch go out on me, my eyes crossed and my leg went limp for a brief moment, but luckily I didn't have any load pushing down on me at the time.

Be careful you're working three times as high as I did.

 

[Marconi]

27.400 Mhz

dummy load direct ----------- 1.0 -------- R/50 -------- X/0
RG59 x 2' coax --------------- >25 ------- R/6 --------- X/82 (tried 2 different 2' jumpers)
RG59 e1/2λ ------------------ 1.0 -------- R/50 -------- X/0
RG8 mini 7.5' ----------------- 1.3 -------- R/39 -------- X/7

That is a very good dummy load and the connection looks totally transparent which is good. I wish mine would do that in the 27 mhz band. I blame my little error on my Heathkit DL and that may possibly be due to the connector I used too.

Now Homer, take your RG59 e1l/2 wave tuned line at 27.400 mhz, and move your frequency to 26.965 mhz and see what happens.

I am surprised at your 2' jumper results, so I did a video showing my results.

Marconi's Autek VA1 to a Heathkit dummy load via a RG58/u jumper 2' feet long. - YouTube

I think this confirms, more or less, what I was trying to explain about feed line length effects. Dose this surprise you?

 

[HomerBB]

Marconi, both of those saying they are RG59 are in error. They are RG58.
I am never surprised with things anymore. I will try another 2' jumper tomorrow.
For the purposes of this test I used for a dummy load 2 parallel 100 ohm resistors attached via antenna connector to feedline/analyzer.

The bottom of the antenna is only 28' in the photos. No the sections lack a little yet, and one section is still unextended. I will be adding guys for more support. I sit as much as I can. Just ask my wife.