.64λ Homebrew

[Marconi]

In the shack, antenna at 42' height:

28.265 ------------ 2.0 R=61 X=34
27.979 ------------ 1.5 R=49 X=22
27.571 ------------ 1.0 R=45 X=1
27.555 ------------ 1.0 R=46 X=1
27.405 ------------ 1.2 R=49 X=9
27.185 ------------ 1.5 R=55 X=21
26.965 ------------ 1.8 R=74 X=27
26.549 ------------ 2.0 R=108 X=0

It is much narrower banded, and friendly higher up the band.

What the SWR meter in the shack says:

28.485 ------------ 2.0
28.305 ------------ 1.5
27.555 ------------ 1.0
27.405 ------------ 1.0
27.185 ------------ 1.05
26.965 ------------ 1.25
26.800 ------------ 1.45
26.600 ------------ 1.0

Seems the SWR meter has a different point of view on the whole thing.

Homer, I just don't get it. Is this right, 26.600 = 1.0, or should that be 2.0?

I think we might possibly see something like a repeat in the SWR curve at some harmonic frequency...maybe far beyond our normal bandwidth. Your SWR seems to have reversed course within only .200 khz, and that is really strange. I would check and see if you see that happens with one of the other coils. IMO, something has to be messing up to do that, and I would suspect it was either the antenna or a mistake in reading the meter.

The variations I see in your unique style of bandwidth procedure creates an irregular bandwidth curve. IMO, that may be because you don't use a controlled step rate for the frequencies you record, and that tends to make your curves look unusual. However, I don't think we would expect what happened to you at 26.600, being as you were within a normal bandwidth range of about 5 mhz or less for such an antenna.

From a point of resonance, we might tend think of SWR, as changing in a linear direction just like the typical change in frequency we might make is linear. Within reason, I don't think your SWR meter should indicate what you reported. We may see the reactance respond this way, but the SWR changing like you indicated...seems pretty unusual.

I wish I could help you explain this one.

Happy Easter to all of you guys.

 

[AudioShockwav]

when I first got my I10K, I had an unusually wide bandwidth, in fact it was SO wide that I called Jay on the phone to talk about it.....I wish like hell now that I kept things like you guys do, I had actually charted it.....
There was two dips in SWR across a large frequency range with a slight rise in the middle.
Jay suggested to me that I might have a Coax issue, because he had seen something like this before.
I dismissed it, because I felt the coax was fine, and loved the increased bandwidth.
Almost a year later, I installed A Yagi for 2 meters, and while doing that replaced the old I have no idea what brand it was RG8 with a new chunk of Belden coax
I lost the wide bandwidth just like Jay told me I would, and got a smooth regular bandwidth curve just like you would expect.

Just something I wanted to throw out there.
Homer I know you already tried to read your antenna at the feed-point, if it is not to much trouble, I think if you could get the MFJ to read properly with a very short jumper, say 12 inches or less it will help remove any results that are being influenced by feed-line.
You really are going to have to invest in a trained antenna monkey, just satisfy all the rest of us with our never ending Request`s/Questions.

73
Jeff

 

[HomerBB]

Jeff,
I have a plan that may resolve some of this line length thing. I am going to modify my tip over mast by replacing the solid 2" pipe with my 40' push up pole likely using only 30" of it. In this way I can simply use my 12' step ladder and lower the push up pole to within my reach, then push it up after adjustments. In this way I can check things at differing heights using as short a feedline length as is required for each height.

I have numerous 2' jumpers to try the direct feed approach again.

I do have to wonder if direct attachment to an A99 might behave differently than to an antenna with radials like mine has.

I no longer have an A99, so I may have to construct a 1/2λ bottom fed antenna like the Station Master just to test this idea.

Eddie,
is your Station Master convenient to get me some measurements of the lowest end of it?
If not I'll hunt it down.

 

[Marconi]

Jeff now that you mention it, I've seen such broad banding results with a 100' foot piece of used RG8x...that happened to have a clear outer cover so I could see the shield inside. I got it from a buddy that had it on his A99, for maybe 8-10 years and it still looked good and he claimed it worked good. I installed it on my Starduster, and much later on I discovered that the coax suffered a lot of attenuation, and checking it close the issue looked to be due to water deterioration on the shield.

Long before I figured it out, I noticed several things were happening, none of which might be considered bad. My antenna seemed unusually quiet even compared to my neighbors who complained of bad static, the SWR was very low, and several local and DX contacts started reporting my signals were noticeable less than several of my close by neighbor buddies. This said however, the antenna still seemed to work just as well as the neighbors and they said as much. I felt that was due to the fact that I wasn't missing any contacts, both local and DX. It also seemed to me a big plus was, I was hearing better and still making the same contacts that my buddies were.

I also noticed that I could go well into 10 meters without noticeable change in SWR, and I could even go to 17 meters and the SWR would remain at less than 2.00:1. For a year or so, I was giving all the credit to old SD'r for what I was experiencing, even though several buddies around said their SD'r didn't appear to be that broad banded or that quiet. Before I discovered the water problem, I would tell the guys they shouldn't expect the SD'r to make as good a signal as all of their bigger antennas.

On taking the antenna down I discovered the shield had turned green or black in several large spots along the line. When I tested the line using a dummy load with an RF meter I saw 100 watts input only produce 10 watts of output. Considering these issues, the line still seemed to performed pretty well. I guess that goes back to my old saying,

"...it don't take much power to make a contact, and we are just lucky that Mother Nature don't require our systems to be perfect in order to work our radio."

Homer, maybe I was just lucky to experience what I did, so if your line is old, then maybe you're seeing some attenuation due to age or water that makes your bandwidth real wide. I never did a bandwidth curve on it back in those days, but you could check the thru-put, like I did, and maybe that would suggest something to consider.

Maybe that is what was happening with Jeff's I-10K as well.

 

[Marconi]

Jeff,
I have a plan that may resolve some of this line length thing. I am going to modify my tip over mast by replacing the solid 2" pipe with my 40' push up pole likely using only 30" of it. In this way I can simply use my 12' step ladder and lower the push up pole to within my reach, then push it up after adjustments. In this way I can check things at differing heights using as short a feedline length as is required for each height.

I have numerous 2' jumpers to try the direct feed approach again.

I do have to wonder if direct attachment to an A99 might behave differently than to an antenna with radials like mine has.

I no longer have an A99, so I may have to construct a 1/2λ bottom fed antenna like the Station Master just to test this idea.

Eddie,
is your Station Master convenient to get me some measurements of the lowest end of it?
If not I'll hunt it down.

Homer, I don't have a Station Master antenna, I've never physically even seen one.

Sometime back I did a lot of work with my analyzer hooked direct to my A99, with without radials, and with both horizontal, slanted radials. I even tested more radials and I never noticed my meter acting strange. The main point I was trying to make was what match would the A99 show without a feed line, and that was based on all the information we get about the Imax/A99 having a terrible match device that caused the antenna to required the feed line to be used as the counterpoise.

But what I failed to consider back then was the mast was still in the mix. So, that real world testing needs to be done again, if I'm to prove my point. To be fair, I would also have to isolate the antenna and mast.

Maybe I'm repeating myself, but with that said Homer, I didn't see my meter acting strange while being connected directly to the feed point.

 

[HomerBB]

Homer, maybe I was just lucky to experience what I did, so if your line is old, then maybe you're seeing some attenuation due to age or water that makes your bandwidth real wide. I never did a bandwidth curve on it back in those days, but you could check the thru-put, like I did, and maybe that would suggest something to consider.

Maybe that is what was happening with Jeff's I-10K as well.

I suppose I could do the the thru-put on the coax, but all of it is less than 2 months old.

 

[HomerBB]

Homer, I don't have a Station Master antenna, I've never physically even seen one.

Sometime back I did a lot of work with my analyzer hooked direct to my A99, with without radials, and with both horizontal, slanted radials. I even tested more radials and I never noticed my meter acting strange. The main point I was trying to make was what match would the A99 show without a feed line, and that was based on all the information we get about the Imax/A99 having a terrible match device that caused the antenna to required the feed line to be used as the counterpoise.

But what I failed to consider back then was the mast was still in the mix. So, that real world testing needs to be done again, if I'm to prove my point. To be fair, I would also have to isolate the antenna and mast.

Maybe I'm repeating myself, but with that said Homer, I didn't see my meter acting strange while being connected directly to the feed point.

Okay. Fair enough. I'll just have to go back to it and see what I really see.

My error on the antenna. It was you Wolf 1/2λ I was thinking of.

 

[Marconi]

I suppose I could do the the thru-put on the coax, but all of it is less than 2 months old.

Well, with that being the case don't even bother to test. The problems with water in the feed line probably doesn't work that quickly.

Okay. Fair enough. I'll just have to go back to it and see what I really see.

My error on the antenna. It was you Wolf 1/2λ I was thinking of.

That's Ok.

 

[Marconi]

Hope this helps.

Coil diameter is about 16.5" x .25" rod with return legs = 8.25". This may be the wrong size coil. The bottom bolt for the coil also looks to be a bad design idea as well. The hose clamp you see in image #1 was my effort to repair after this bolt stripped out the few threads in the 1/8" wall thickness of the base mount.

The base mount is 12" x 1.6875" x .125 wall thickness.

The insulator slides free inside the mount and is secured using the top 2-1/4" bolts located in the top portion of the mount. Over time these two bolts burr up the insulator and this can make adjustments difficult to impossible over time.

The small bolt head seen between 2-1/4" bolts in the middle of the mount serves as a stop for the insulator from the top, and for the mast from below. I think the radiator is glued inside of the insulator.

There are 2-1/4" bolts either side of the small bolt head noted above. The bolt above secures the insulator and the bolt below secures the mast inserted in the mount from below.

The bottom 1/4" bolt also helps secure the mast

 

[HomerBB]

Thanks, Marconi. That should be useful.

 

[HomerBB]

These readings are on the antenna after I brought it back down to 13' height so I can modify my tip over tower to make it more testing friendly.
What we have is several readings of the antenna with the latest matching system as previously posted. The readings are 4 different sets consisting of the
MFJ-259B connected to the antenna by e1/2λ x 6 coax, e1/2λ, 2' jumper, and directly mounted to the antenna feed point with a coupler connector.
This time around I found the analyzer behaved as it should directly against the bottom of the radials . . .

Apparently I failed to get a reading at the 1.5 bottom reading in the e1/2λ set,unless it was also 26.965 reading.

 

[Needle Bender]

FYI, the Avanti Sigma_5/8 uses a 16" diameter ring and is fed at the bolt holding the bottom ring-supporting arm. The entire ring is 'hot'.

The antenna is .625 (5/8) and measures 22' 4" tall, and averages a 2.5" circumference.


__________

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]

That's a mighty thick vertical antenna. The bottom of it must be at least 3" - 4 " diameter. . .

 

[Marconi]

That's a mighty thick vertical antenna. The bottom of it must be at least 3" - 4 " diameter. . .

Homer, I think NB said the antenna averages about 2.5" in circumference which is probably about 3/4" in diameter. When I don't use taper on an Eznec model for a 5/8 wave, I use 3/4" for most and sometimes all of the radiator portion.

BTW, what kind of battery life are you getting so far with the 259B?

 

[HomerBB]

Homer, I think NB said the antenna averages about 2.5" in circumference which is probably about 3/4" in diameter. When I don't use taper on an Eznec model for a 5/8 wave, I use 3/4" for most and sometimes all of the radiator portion.

Duh

BTW, what kink of battery life are you getting so far with the 259B?

As much as I have been using it, I'd say with alkaline batteries I have gotten about 3 hrs. I've been using it with AC adapter since it went too low to want to work.

I found the results of the 4 different feedline lengths, or the 3 lengths and a direct connection to the antenna interesting. At least this time the analyzer worked as expected. Post #71