DIYing a QRO cobwebb

Heads-up:

For those interested I'm finally uploading the latest pics to my Photobucket site now and will post them here shortly.

73, Jeff

Upon Charles' suggestion I shortened one of the leads going from the feepoint to the choke so that they are now of equal length (as best as I can determine). Before and after:
http://i701.photobucket.com/albums/w...ldPart2011.jpghttp://i701.photobucket.com/albums/w...thFeb12001.jpg

Then I mounted the balun on the feedpoint support arm and began attaching the elements:

http://i701.photobucket.com/albums/w...thFeb12002.jpg

http://i701.photobucket.com/albums/w...thFeb12006.jpg

Meanwhile, two of my three onsite supervisors, well, supervised:

http://i701.photobucket.com/albums/w...thFeb12013.jpg (Guido)
http://i701.photobucket.com/albums/w...thFeb12014.jpg (Guffino)

My cobweb in rough draft form:

http://i701.photobucket.com/albums/w...thFeb12007.jpg

Yep them cats know how to supervise!! And when whey arnt they do this....

Attachment 86858

After I got the basic cobweb put together we started having some torrential rains and flooding. Those combined with a busy work week prevented me from doing more.

I also needed to take down my 6m, 12m and 15m antennas in preparation for moving house as well as some repair on the 15m Moxon which had a broken spreader. I decided that I would install the cobweb atop what was originally my 15m mast as that antenna was going back up on the rotatable mast after it was fixed.

Here's some pics of that operation which took all day (or most of it) and required a bit of help from my xyl:

12m dipole comes down (actually lowered it by cutting sections of the long bamboo mast off the bottom before tilting it over!)
http://i701.photobucket.com/albums/w...thFeb12035.jpg

Guido can be seen checking for power line clearance here, too---he's top-notch!
http://i701.photobucket.com/albums/w...thFeb12037.jpg

When I fixed the 15m Moxon I also decided to make a feedline choke before I put it back up.

Used a couple of "painter's pyramids" and a slew of cable ties for that:

http://i701.photobucket.com/albums/w...ebPart4001.jpg

In this shot (taken a bit earlier, before the 6M Yagi came down) you can see the 15m Moxon mast (on the right side) which is where the cobweb will be soon (provided we get a good break in the monsoonal rains):

http://i701.photobucket.com/albums/w...thFeb12043.jpg

With the xyl lowering the main guy line via a pulley up in the trees we gently set the 6m Yagi down:

http://i701.photobucket.com/albums/w...thFeb12062.jpg

Later the following day we put the 15m Moxon in it's place---atop the Yaesu rotator/mast combo---so now I can turn my beam without having to run outside all the time ( had been using the armstrong method):

http://i701.photobucket.com/albums/w...ebPart4003.jpg

Now I've got the other (old 15m) mast ready to put up once the cobwebb is all done. I still need to finalize the element spacings and test it for SWR come the next dry day that I have off. Yesterday a 400' roll of Times Microwave LMR-400 arrived (I'd ordered it in early January but since it was shipped via Parcel Post it ended up taking 5 weeks; typical for that method to/from Hawaii) and I quickly measured out 50' from the hefty spool and cut it for my cobweb feedline.

I may try to put new PL-259s on that later today so I can get the cobweb up sooner than later, otherwise I'll get that chore done later this week when I have a couple more days off.

This is a quick shot of the cobweb today during a lull in the downpours (believe me, we've been getting drenched---our drought is over!). I held my camera out the side porch door so I didn't quite get all of it but you get the idea:

It's almost ready!
http://i701.photobucket.com/albums/w...ebPart4004.jpg

I plan to trim off the spreader ends with my Dremel before I put it up so it will be as compact as I can make it. I am also considering adding large ferrite beads to the other end of the feedline (where it connects to my remote antenna box outside) since I have a Palomar BA-8 balun kit sitting around collecting dust. I suppose it can't hurt, despite the choke current type balun I have at the feedpoint, right? (In case there are stray currents from radiation ).

Roger on the supervising and other "activities" cats like to do---just saw your post, KAK!

The xyl is glaring at me so I know it's time to do some household chores before the day is done so that's it for now---except one last pic that I almost forgot to post---here's a scene with most of my antennas during the big rearrangement:

My Delta Loop is on the left, 6m Yagi mast is laying over in the foreground, the 15m Moxon is in the middle atop a pot, the Yagi is on the lawn in back of it and the cobweb is sitting on top of a clay pot over on the far right---believe it or not that pot was halfway submerged in a little rainwater lake yesterday!

http://i701.photobucket.com/albums/w...thFeb12066.jpg

73, Jeff

Nice laundry line you have there... The cat did a great job too.. :)

Like you said, tuning and treaking should be done when its dry. Great pics Jeff.

Thanks, Charles. I look forward to getting on the air with it by the weekend if the rain will ever stop.

I got a nice new 50' section of coax all ready to connect to it, too. As usual, stay tuned and I'll be posting my results as soon as I'm QRV with it.

73, Jeff

Jeff - the package arrived and once again, thank you!
I read your message that you wrote on the back and yes sir we will do that some day and I am looking forward to it!

RR, Nick; Thanks again and GL with your cobweb build. Feel free to post pix of yours here, too, if you like.

If we don't work before I leave KH6 then we'll have a NM to AZ QSO for sure.

Going outside to adjust the element spacings now as the rains have taken a break this afternoon---will try to get the darn thing up in the air as soon as possible; I'm itching to try it out (and compare it to my Moxons).

Btw, if it performs well I'll probably use it during the ARRL and CQ WPX DX Phone contests that are just around the corner---and I plan to concentrate my efforts on 15m (maybe even operating single band high power there as I really want to acheive DXCC on that band before we move mid-April).

73, Jeff

The Tuning Begins...

The sun was back out late this afternoon when I got home from work so I went outside and continued the final work on the cobweb.

First, I affixed some Gorilla Tape around the element attachment points on the spreaders so the cable ties wouldn't slip. Then I tightened the elements up until they looked to be in order.

I cut off all the excess fiberglass on the spreaders and put more tape on the open ends so the antenna will be as compact as possible.

Finally, as the sun began to set behind Mauna Loa I hooked up a length of coax to the antenna and to my remote switchbox inside our garden shed.

When I began checking the swr on my Elecraft K3 (in the nifty TUNE mode) I came up with very high readings---but the antenna was only 5 feet above the ground to start with.

All the bands varied between 5>1 and 7>1 swr so I quickly set about trimming the element ends.

Folding back the wire onto itself (as KC8VWM did in his build) several inches or more began to yield the kinds of numbers I was looking for;

here's a brief summary so far:

10 meters: 28.450 =2.1:1
28.500 =1.5:1
28.550 =1.6:1 (with 3.5" trim on each side)

12 meters: 24.930 =1.0:1 (I started out with 6.4:1 all across the band! These figures were acheived after trimming 2 3/4" per side)
24.990 =1.4:1

15 meters: 21.225 =1.3:1
21.250 =1.0:1
21.450 =1.9:1 (after trimming a whopping 8 3/4" per side!)

I was beginning to work on the 17m elements when it started sprinkling a few drops and the mosquitos also began to attack so I packed up my tools, disconnected the coax and put the SO-239 cap back on. It was also getting too dark to work, anyway.

I hope to finish adjusting it tomorrow but it all hinges on the weather(as usual). I have two days off work so hopefully the weather will cooperate again.

One question I have that hopefully someone here* can answer before then is:

*("Steve, G3TXQ, white courtesy phone, please!")

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?

I want to aim strictly for the upper phone portions of all the bands as I only operate there. I suppose worst case scenario I'll have to take the antenna back down to readjust everything if it goes out of whack when I hoist it up in the air.

73, Jeff