My Latest Homebrew 5/8 Base Antenna

[HomerBB]

I'd like to enter this into the Spring contest, please. Antennas are all I do . . .

I put up the 4 element Yagi my neighbor and I built, and put a vertical dipole above it. The dipole seemed to work as well as any dipole I'd had, but I was accustomed to vertical antennas with gain, so I decided to put something else up. I pulled down the dipole and put up a 1/4ƛ GP which actually proved to serve me better than the 1/2ƛ dipole above the Yagi. However, I was going to turn the dipole into a vertical GP, and went with a 5/8ƛ. I wanted less wind load than I had experienced with my previous 5/ƛ antennas, and thought I could accomplish this by reusing the dipole materials, and using shorter, smaller diameter radials. I chose to use 3' long x 12 radials for a full equivalent of 9' long x 4 radials.

Here's what I did:

I started with a common wire spool available for free from Home Depot if you catch them before the throw them out.

I purchased 12 0f these 3' garden stakes for radials. They are light, of small diameter, and are plastic coated metal.

I removed the ends of the cable spool from the core.

I drilled holes through the disc for attaching the radials with cable ties, and threaded the cable ties through.

I started putting the 12 radials on the disc in this fashion.

You'll notice I use the built in ridges on the disc to maintain my exact distances apart for each radial.

I used self-drilling screws at the inner end of each radial to both secure the radials, and to use for wiring them together. The inside circular hub of the disc was a natural marker for getting all the radials at exact length.

The completed radial set gets a coat of silver paint to improve its appearance

The coil.

These items, a spacer, which will be used to mount the coil, and the coupler will be used to mount the radials disc to the antenna shaft.

The dipole consisted of two aluminum tubes 3/4" x 6', and two aluminum tubes 1/2" x 2.5'. They were bonded in the center by a 1/2" x 1' PVC tube inside the 3/4" aluminum tube, and a 3/4" x 1' PVC tube outside the 3/4" aluminum tube. The dipole was separated by 1" of space. For the 5/8ƛ I closed the gap, and tied them together on the outside of the PVC tubes by use of metal Duct tape, and copper wire between self-drilling screws. The 5' long fiberglass post hole digger handle will be the bottom shaft of the vertical as it was for the dipole.

I have the entire vertical assembly together here. For the additional top length needed an old A99 top peice was inserted and secure with screws tapped into the metal knurl at the bottom of the whip.

The coupling is assembled to the fiberglass base shaft, and the hub is attached to the coupler. All this is accomplished with tape for spacing, and self-drilling screws. All is together and the tap point is being sought for.

The antenna is in the air on a temp mast in a temporary place.Its final location will be over the Yagi on the tip over mast. The entire thing will be painted silver in it final condition.

Where it is currently mounted is is nearer the house than I like. And there is also a tree nearby. The photo angle gives a false impression of its nearness to the roof ridge. It is about 12' the other side of the ridge, and two feet higher. In this location the SWR curve is:

28.755 ---------- 2.3:1
28.305 ---------- 2.3:1
27.855 ---------- 1.9:1
27.555 ---------- 1.4:1
27.405 ---------- 1.3:1
27.205 ---------- 1.1:1
26.965 ---------- 1.0:1
26.515 ---------- 1.3:1
26.065 ---------- 2.1:1
25.615 ---------- 3+

I hope the curve will settle a little flatter with distance from the ground on the permanent mast. However, it is good for my usage as it is.

 

[mackmobile43]

You have way too much free time my friend. cool antenner.

 

[HomerBB]

You have way too much free time my friend. cool antenner.

Thanks

 

[BOOTY MONSTER]

looks real nice homer . that spool end worked perfectly for you
there gonna have to make a new forum section here just for your antenna projects .

 

[Marconi]

looks real nice homer . that spool end worked perfectly for you
there gonna have to make a new forum section here just for your antenna projects .

Hey BM, how is you 5/8 wave GP coming along, it has been some time and no word?

Way to go Homer. How does the 5/8 wave compare to the AstroPlane?

 

[HomerBB]

Just got it up above the Yagi a few minutes ago. Well have to see. Give me a few days to check it out. I will run it this way and see how it acts. At the moment it is hearing some Hawaii slightly better than the the Yagi is, but we know DX is a different animal. I've got it in the air over the Yagi, and the SWR is even more widebanded than it was.

SWR @ 36' above ground, and 8' above the Yagi.

28.755 ---------- 1.2:1
28.305 ---------- 1.1:1
27.855 ---------- 1.1:1
27.555 ---------- 1.05:1
27.405 ---------- 1.0:1
27.205 ---------- 1.0:1
26.965 ---------- 1.1:1
26.515 ---------- 2.2:1
26.065 ---------- 2.9:1
25.615 ---------- 2.6:1
25.165 ---------- 1.9:1

Bit of a puzzler. We shall see.

 

[hotrod]

very nice job. reminds me of a sirio 827

 

[Marconi]

28.755 ---------- 2.3:1----- 28.755 ---------- 1.2:1
28.305 ---------- 2.3:1----- 28.305 ---------- 1.1:1
27.855 ---------- 1.9:1----- 27.855 ---------- 1.1:1
27.555 ---------- 1.4:1----- 27.555 ---------- 1.05:1
27.405 ---------- 1.3:1----- 27.405 ---------- 1.0:1
27.205 ---------- 1.1:1----- 27.205 ---------- 1.0:1
26.965 ---------- 1.0:1----- 26.965 ---------- 1.1:1
26.515 ---------- 1.3:1----- 26.515 ---------- 2.2:1
26.065 ---------- 2.1:1----- 26.065 ---------- 2.9:1
25.615 ---------- 3+ ------ 25.615 ---------- 2.6:1

Homer, it appears that your antenna made some significant frequency changes on raising. Being as the changes appear positive in affect and direction. Maybe you're not interested in why, but I think some of my work with my antennas may suggest a couple of things to consider...if I sat down and studied the results with this situation in mind. I am curious and have studied this affect before.

On some of the Bandwidth work I did recently and in 2009, I tested both high and low heights, and changing feed line length, etc., and everyone fussed about the point in using different heights, saying "...nobody in their right mind does that." You know the drill.

Of course my main thought in mind was to test to see if location made a big difference, since I was comparing antennas side by side. As yet I have not decided to try and analyze what I can from all the data I took, and then to possibly make some reasonable conclusions.

Did you add feed line when you moved and raised your antenna?

Right off the top of my head I would think the change was due to the antenna being originally mounted very close to the house, or if you added length to your feed line to get higher then the frequency difference could be feed line transformation going on. Just my opinion.

Keep us posted.

 

[pro151]

Man is an antenna building fool I tell you!

But then again that is why we are all in this hobby isn't it.

Keep on keeping on.

(Makes me both jealous and ashamed at the same time that I have never found or made the time to get my TAK-11 in the air and play with it.)

 

[HomerBB]

@ Pro151: I drive myself nuts doing this. Just enjoy your peace of mind.

@Marconi: Yes, I had to add feed line - about 50' - and it was near the house. It has been suggested the Yagi beneath it has added more effect, too. Given some time I will know whether it outperforms the AP. I already know it is better than the dipole. The 1/4 GP was better than the dipole.

 

[Marconi]

@ Pro151: I drive myself nuts doing this. Just enjoy your peace of mind.

@Marconi: Yes, I had to add feed line - about 50' - and it was near the house. It has been suggested the Yagi beneath it has added more effect, too. Given some time I will know whether it outperforms the AP. I already know it is better than the dipole. The 1/4 GP was better than the dipole.

Homer, I would think if the vertical was affected much, it would be either good or bad. We have to assume there is some affect however, and the general consensus would be it is bad. I had a Starduster on a 10' foot mast mounted above my horizontal 4 element and I could not tell any difference in match or in on-air operations. The SD'r does have a different radial design however, being almost vertical vs. your radials being totally horizontal, so there may be some difference there. In my case both antennas seemed to work just fine, but I did not actually try and compare them together or with another antenna up at the same time on another mount. The only comment I recall making at the time was that the SD liked it up there and the ears were quite good sitting up above my beam...even while the ends of the down radials were within 2' feet of the beam. The beam didn't seem to care either way, and I believe that was due entirely to the polarity difference which is quite strong, possibly the strongest response to be noted in antenna design... and your vertical is higher up by a considerable amount over the similar height for my SD'r.

If you ran a bandwidth curve on the beam before this addition to the environment, how does it compare now? That should suggest something. When we hear talk about an antennas responding to another that is close by, the reference is usually decidely a bad influence, right or wrong? In my thinking this affect can be bad, good, or transparent with the latter two never really being discussed.

In some cases similar to your install the elements are all conductive, and can add to or take away from performance. Assume the affect is to add to performance, then we can assume that some return currents are utilizing this added element. Now, consider the affects or your non-conductive roof, it to can add capacitance to the antenna, but it surely will not return any currents, so there is added loss on both counts via capacitance and the lack of a return path. Personally I would consider being too close to the non-conductive roof a worse case senario than being too close to your beam.

I hope I made my point clearly here.

 

[HomerBB]

Your point is clear, and I appreciate you making it. I have not really sensed anything negative, and the presence of verticals over beams is a common thing. What put me in the questioning mood was that I've never used so many so short GP radials, and someone thought they would be less than optimal. So the increased bandwith when it went over the beam was wht I hoped was not a suggestion that the radials were not in fact the true GP of my vertical, but the beam was. In either place, near the house without the beam under it, and up over the beam, the vertical is hearing and transmitting very well it seems so far, and definitely better than the dipole.
What I'm waiting for to answer your question of how it compares to the AP is to catch the stations that were readable with the AP on the air again to get a comparison.

Thanks.

 

[Marconi]

Your point is clear, and I appreciate you making it. I have not really sensed anything negative, and the presence of verticals over beams is a common thing. What put me in the questioning mood was that I've never used so many so short GP radials, and someone thought they would be less than optimal. So the increased bandwith when it went over the beam was wht I hoped was not a suggestion that the radials were not in fact the true GP of my vertical, but the beam was. In either place, near the house without the beam under it, and up over the beam, the vertical is hearing and transmitting very well it seems so far, and definitely better than the dipole.
What I'm waiting for to answer your question of how it compares to the AP is to catch the stations that were readable with the AP on the air again to get a comparison.

Thanks.

Homer, I hope I didn't suggest above that you should have sensed something negative in your results, because in my reading of your results I understood that you sensed an improvement...and you were pretty clear about that.

I've read that some do put verticals like the Imax, A99, or similar, right above their horizontal beams, but I think most think twice about placing their ground plane antennas with horizontal radials right above a beam, and if they do they are likely to raise it up a 1/4 wavelength or more out of some fear that there may be a negative response to one or the other are both antennas...just like you probably did. This is not to say I support this idea, because I think I've already told you that I put a Starduster above my beam and the bottom of the radials were within 2' feet of the beam with little or no affect as best I could tell. I'll check my notes back to that time and see if I happened to have done a bandwidth curve, but I'm pretty sure I wasn't thinking about such in those days.

Personally I believe all radial systems tend to ill-affect (reduce) the bandwidth even while being necessary for some antennas to operate effectively and efficiently. In all cases where I've ever installed radials on a no-radial antenna or I've added additionally radials to the typical ground plane type antenna, I've always noticed a reduction in the bandwidth creating a less flat curve in favor of a more bowl like curve that we might expect from such a test. Therefore I think you might be wrong about the beam adding more ground plane and expanding the bandwidth. But, I could be wrong.

Attached below are three Antenna Worksheets indicating bandwidth curves for an A99 with 3 horizontal 72" GPK radials, and two reports for the same antenna without any radials. You will note both the SWR and the VA1 analyzer curves went in the opposite direction from what you are suggesting. I doubt seriously that the beam has much if any return currents flowing, but if it does can only help. You could test what you claim here and prove me wrong, just by lowering the setup and removing all the radials on the 5/8 wave. If you're right then the antenna should still basically work as though it still had the ground plane you removed.

View attachment A99 Bandwidth Curves 01 2011.pdf Look close at this pdf file and see how the bandwidth was affected by adding and removing the GP radials to this A99. I think all vertical antennas with horizontal GP radials will likely react in a similar way.

I asked you in my post above if you did a bandwidth curve on the beam before adding the vertical, and if so...how did the results compare? I would think that might tell you a bit more about the likely side affects if any. How say you?

BTW, I assume that you might have a rig with a small frequency range, but if I'm wrong could you give us bandwidth data for the <2.0:1 SWR range. I believe I was right about why you saw the frequency change albeit you when higher. When an antenna is more or less out of match at or near resonance, showing excessive reactance the feed line will surely be reactive and transformation will result in a frequency change which I seen many times equal or better 50% or more of the CB bandwidth. This happens in spite of the SWR you are seeing at the radio, or the inline meter, resulting in a nice increase in bandwidth. I'll bet you that transformation is what made your apparent bandwidth increase and not the affects from the beam.

 

[HomerBB]

I did a SWR check on the Yagi, but I don't know where I put it. It certainly isn't as wide as the vertical. Unless I find the paper I wrote it on I wont know without taking the 5/8 off the tower. Not happenin' today

Your SWR chart is interesting on the A99. Amazing what paying attention can reveal.

The only reason I speculated about the influence of the Yagi on the vertical was because of someone on another forum suggesting the same.

I made this 5/8 less robust because it was going on the wooden tower with the Yagi. I hoped for less wind load on the tower. I knew Sirio used shorter radials with more in number of them for GP on some of their antennas, so I went that direction. So far, the idea still appeals to me.

No. I didn't think you were suggesting I was experiencing anything negative.

 

[Moleculo]

Homer, I would think if the vertical was affected much, it would be either good or bad. We have to assume there is some affect however, and the general consensus would be it is bad.

What general consensus? I don't see anyone else saying that what he did is bad? It's only bad if it's producing a result that he didn't want. Especially on HF, generally adding more radials is more better to some ridiculous point that is impossible to build

Personally I believe all radial systems tend to ill-affect (reduce) the bandwidth even while being necessary for some antennas to operate effectively and efficiently. In all cases where I've ever installed radials on a no-radial antenna or I've added additionally radials to the typical ground plane type antenna, I've always noticed a reduction in the bandwidth creating a less flat curve in favor of a more bowl like curve that we might expect from such a test. Therefore I think you might be wrong about the beam adding more ground plane and expanding the bandwidth. But, I could be wrong.

By putting the antenna over the yagi, you have changed the characteristics of the radial system (I'm guessing that the mast between the yagi and vertical ground plane radials is metal). What this will do is change the antenna's resonance. In the 21st edition of the ARRL Antenna book on pages 6-16 to 6-17, the section on Elevated Radials and Counterpoises says, "By raising the radials above ground most of the current will flow in the radials, which are good condutors. This allows a simple radial system to provide a very efficient ground. However, there is a price to paid for this. The ground system now has a direct effect on the feedpoint impedance, introducing reactance as well as resistance, and is relatively narrow band. For a given vertical height, the radial length must be adjusted to resonate the antenna." So, height above ground, length and number of radials affect resonance. There is more in the book that explains these concepts which is worth reading.

Adding more radials isn't necessarily a bad thing, but it does change things as you found out. Using just your SWR meter to tell you whether what changed is either good or bad is not really going to tell you much.