DIYing a QRO cobwebb

[G3TXQ]

What should the effect of raising the cobwebb from say a few feet above the ground to around 23 feet be in regards to tuning? Will the resonant frequencies shift a lot?

Jeff,

All I can tell you with any certainty is that the tuning is likely to go up in frequency as you lift the antenna; how much is tough to say - it's dependent on factors like your local ground characteristics.

If I were you, I'd reckon on having to do one "iteration". If you note the resonant frequencies with the antenna low down, then note them again with it 23ft up, you should be able to calculate how much to "aim off" when doing the final tuning low down.

If I get a chance this afternoon, I'll check mine at a couple of different heights; that might give you some indication of likely shifts. But that job is well down the priority list handed me by my local "senior management"

73,
Steve G3TXQ

[G3TXQ]

Jeff,

Just managed to sneak in a quick antenna scan

At its lowest, my cobweb was about 10ft above ground but only 2ft clear of the garage roof. I then moved it up to 20ft. These were the frequency shifts going from 10ft to 20ft:

20m: +64kHz
17m: +43kHz
15m: +21kHz
12m: +22kHz
10m: No change

Of course, if you are tuning at a height much below my 10ft you can expect bigger shifts.

73,
Steve G3TXQ

[KC8VWM]

I don't have specific data to post but I found it interesting (using my twin wire folded dipole type) for some apparent reason to observe how the antenna's vswr remained low and yet became more broadbanded on bands like 10m when it rains. Not my typical experience using antennas in wet weather conditions.

[NH7RO]

Jeff,

Just managed to sneak in a quick antenna scan

At its lowest, my cobweb was about 10ft above ground but only 2ft clear of the garage roof. I then moved it up to 20ft. These were the frequency shifts going from 10ft to 20ft:

20m: +64kHz
17m: +43kHz
15m: +21kHz
12m: +22kHz
10m: No change

Of course, if you are tuning at a height much below my 10ft you can expect bigger shifts.

73,
Steve G3TXQ

OK, Steve, that info (although under somewhat different conditions) is very helpful to me. Thank you for taking the time and trouble to do so. I will adjust the elements a tad less from now on to compensate a bit for when it's aloft. I' may also readjust the bands I've already done ever so slightly as I might just "luck out" the first time it goes up.

It's clouding up outside so I better scoot outside and finish it up before the blasted rains return.

73, Jeff

[NH7RO]

I don't have specific data to post but I found it interesting (using my twin wire folded dipole type) for some apparent reason to observe how the antenna's vswr remained low and yet became more broadbanded on bands like 10m when it rains. Not my typical experience using antennas in wet weather conditions.

That is also very interesting, Charles; I've never had that happen with any other antennas of mine. I wonder why and how that can be?

73, Jeff (QSY to the back yard)

[KC8VWM]

That is also very interesting, Charles; I've never had that happen with any other antennas of mine. I wonder why and how that can be?

73, Jeff (QSY to the back yard)

Not sure exactly but I would speculate the "wet" adds more skin effect to the elements causing them to appear fatter from an electrical perspective thus increasing the bandwidth. However, it's just a theory and I have not confirmed this.

I've never had the vswr remain relatively constant on most other antennas in wet weather either. Typically the vswr goes up when it rains but this hasn't been my experience with the twin element cobbweb.

That is to suggest when other antennas couple to thier surroundings and when that surrounding enviroment in the radiation field changes, perhaps this also causes additional reflections to occur etc. resulting in an increased vswr on most other antennas.

Again, I can only theorize, but it may be due in part to the confined electrical field involving its design and since the cobbwebb is less susceptible to coupling to surrounding objects like other antennas might do, perhaps this also means it's less affected when those surroundings become wet.

[N8WWM]

Missy wants a date with Guido, Jeff. She says that she will only go if chaperoned by Lindy, the black 11 yr old little monster. And Guido has to take BOTH of them to a catnip bar afterward, not to mention mouse-tracks ice cream for dessert.

[NH7RO]

Charles; Your hypothesis makes sense but I have noticed a huge jump in the swr when operating the antenna in the rain---but that's while the antenna is only 5' off the ground so I suppose my results so far don't really count.

The rain is continuing and my plans for putting the cobweb up are in a holding pattern so far. I'm getting impatient with our typical lousy weather so will probably go ahead and put it up this afternoon regardless of the rain. I figure I'll have to see how it tunes at height before I take it back down for additional/final tunings on another day.

Doug; I told Guido about Missy's request and he seemed to meow an approval of sorts. I got the feeling, though, that he has a more than a fleeting suspicion that they may be related (albeit distantly) as they look so doggone* much alike (perhaps I should say"catgone" instead?)! We looked you up on QRZ and saw your photo of Missy and Lindy there; we were both shocked to see Guido's and Missy's strong resemblance---so much so that I'm beginning to wonder, too.

Guido does know all the local hangouts around here well (as he doesn't work much) and he has a good source for top-grade catnip, too. While he doesn't like to share much he might be cajoled if he was offered some Mouse Cream frozen dessert; is there any possibility that Missy & Lindy could bring an ice chest with some when they come?

73, Jeff and the cats

KH6 Cat Farm/Antenna Farm

[NH7RO]

The cobweb and new coax is all hooked up on the tilt-over mast and ready to go aloft today; Guido and I are just waiting for the xyl to get home from work so she can hold the mast while I run around and tie off the guy ropes (as Guido chases them).

Will report back later tonight with more pics and (hopefully) a good report of how it is working on the air. The rain is off and on but the main thing bothering us now is all the vog (volcanic smog) drifting over from the crater nearby; it's really noxious stuff (and one of the main reasons we're leaving
KH6 for good). Doug---tell Missy & Lindy to bring gas masks!

73, Jeff

[NH7RO]

The cobweb is up and is working well on 20 and 15 meters. The swr is a bit high on 17 and 12 so I plan to take it down tomorrow after work and retune those bands. 10m is OK so I may leave it alone or else lengthen the elements 1/4" or so to lower the resonant frequency a tiny bit (it's now around 28.500which is fine but a bit lower might be more practical).

I also worked outside until it was dark as I had a lot of other antenna work to finish up. I took down my delta loop and a lot of other wire and rope remnants from previous antennas still hanging off of trees and things in the jungle. The rains didn't return for a change and all the noxious vog seemed to have warded off the mosquitos ( I didn't notice any at all tonight!).

While I've downloaded a good number of new pics it may be sometime tomorrow evening before I get them posted here. I'll also have a more detailed report on the cobweb to follow as well. It was a long day and I'm tired---but relieved to see the cobweb up in the air at last. It really is a fine little skyhook and the signals I heard were surprisingly good for an omnidirectional one at that. More tomorrow.

Goodnight all,

Jeff