My v37bqh 12-EL ch7 attic yagi

[mrpeter105]

Majortom:

I can't take it outside. I don't have a boom long enough. This thing is 15.5 ft. long. I used the truss beam holding up the roof as my boom. You see I wanted to build a bigger yagi but I didn't have anything to use as the boom. Then I thought why not use the truss beam as the boom. I was using the beam to lash my K6STI to so it was pointed in the right direction more or less.

Choclab:

Yes, I was thinking to use the K6STI model to find the best signal in the attic, which so far I think is probably better near the front of the attic where I always put it. What I should do is station the K6STI along the length of the yagi again and monitor for a longer interval than I originally did to confirm.

As for the driven element I wasn't sure what to use there. So I just used the lengths specified by ve7bqh but I used the swept back outline from the K6STI model. I slapped it together hurredly so I took it down and i'm gonna redo it more carefully. I'm also going to make a straight split dipole version to test. I was up there yesterday and I bent one of the DE elements forward a bit and noticed a jump in ch9 signal so I want to look into that more. Finally i've built a couple of SBGH antennas out of skid strapping as well as the DE of the K6STI which works. I've had excellent results with my SBGH builds as well. So I'm not totally convinced that it can't be made to work. For now I will try to keep using it.

[mrpeter105]

Originally Posted by holl_ands

To shift frequency, Rescale lengths of ALL Elements. It would take nearly
2/10ths of an inch shortening for ALL Element lengths to shift it UP by 1 MHz,
so SMALL dimensional errors aren't much of a problem. And since it looks
like the "boom" is non-metallic wood, there is no Boom Correction needed.

From his webpage it said that if your using a non-metallic boom then remove just over 4mm from the length of each element. Mine are within the range of those two points. Some nearer one side than the other.

I was thinking about it yesterday and looking at image7 again the dropoff is at 187mhz. Ch 7 starts at 174 mhz. So 13 mhz difference which corresponds to about 2.5 inches assuming the dropoff occurs right before ch7. My element diameters are about what is specified. Except for the driven element. So i've followed his dimensions pretty closely. That's alot. Could it really be off by that much?

Tweaking X-Azis location of D1 adjusts SWR with minimal effect on Gain.

Yeah, I was up there yesterday and was adjusting it and the only thing I could see change was the rapidity with which the signal meter on the Access DTA-1080 converter box that I borrowed was cycling between 0 and 15%. Right where the change was the most was right where it was supposed to be according to the plans, more or less.

I tried rescaling the length of Just the Driver Element +/- 10%, with ZERO
effect on the 187 MHz roll-off point, although it does shift SWR Curve a bit.....

Thanks.

[holl_ands]

You can't just replace K7MEM's Stick Dipole with K6STI's Swept Back Dipole
without first modeling it to find WHERE to attach it along the X-Axis and how
much Sweep is needed....and probably also retweak other dimensions......
It's a DIFFERENT design....

[mrpeter105]

Originally Posted by holl_ands

You can't just replace K7MEM's Stick Dipole with K6STI's Swept Back Dipole
without first modeling it to find WHERE to attach it along the X-Axis and how
much Sweep is needed....and probably also retweak other dimensions......
It's a DIFFERENT design....

Hi:

Thanks. I redid a new DE with straight elements with maybe a 10 to 15 mm feedgap . One of the wires to one of the elements is maybe twice as long as the other. Anways there was a marginal increase from say 8-11% to a new range of 11-15% on the meter. My next guess is that the area that i've been putting my K6STI into is a hotspot. I guess i'll have to think about moving it forward and see if that does anything.

[mrpeter105]

Hi:

I've reinstalled the v37bqh yagi forward in the area where I used to mount my K6STI yagi. With my K6STI the baseline signal range would be in the 15 to 20 % range. With the v37bqh the baseline range seems to now be about 18 to 23 % on the signal meter. With the K6STI it would usually shoot up into the 30 - 40 - 50 % range and produce momentary decode. I am also now seeing the same type of behaviour with the v37bqh. I've seen instances where it would shoot up into the high 40% range so far with some momentary decode. That type of behaviour was almost nonexistant at the old spot. Its only been a day so I don't know yet if it's any better for that than the K6STI since there would also be days where it was much lower than usual as well. I doubt it, but we'll see. When the tropo picks up a bit more then i'll have to see how it behaves in those type of conditions. I also have to add another line up to the attic so I can observe both yagis at the same time to get a better idea. One member suggested that I use better materials for the DE. I may give that a shot in the future to see if it will really help when I find something I can use.

This yagi was an expedient experiment just to see if I could get better results than my K6STI was getting. I was hoping that the higher gain would overcome the attic attenuation, probable station off angle and its own smaller beamwidth as well as my subpar build quality. If I would have seen the baseline signal range on the tv up in the say 30-35% range then I would say that it was a successful result. As it stands now its not. I will play around with it some more and see what I can come up with.

I'm not going to let this stop me from investigating this signal. I will probably build another yagi, with its own boom. It will definately be shorter than this one which is 15.5 ft long (too damn long!). I may also try to build another K6STI and try ganging them. Come summer I
will definately be experimenting outside and seeing what that yields. I hope as time goes on that we will see more members trying for this signal and updating us with their results and their setups.


Something I noticed as I was experimenting with this signal:

I have a small Sharp 19" lcd about 3 ft from my Panasonic 32" lcd. I've noticed this effect with both yagis. When tuned into WBBZ on the Panasonic that turning on the Sharp lcd would do a number on the signal by 5 or 10% on the signal meter on the panny. One night I was getting decode with slight breakup on the K6STI on the panny. I would turn the the little lcd on and the picture would enter into total breakup on the panasonic. Turned it off and the picture would recover. Tried it a few times and same result. They also share the same plug outlet. So I tried running an extension cord from the other room and it still seems to happen. When the signal on the panny was strong and sustained then turning it on would not induce breakup. This could be due to the dollar store coax that i've been using so far. I will try a dedicated line with quality coax to see if it makes a difference. Just something I thought other people would be interested in knowing in case it may apply to them in some way.


Finally I would like to thank all the members who have given their advice. I will update the thread if anything changes.

[rob50312]

Mr Peter WBBZ is just too weak for attic reception.Even with a 30 foot tower it would be difficult.Hows your reception of CKVR ? CKVR is much stronger at your location.Even Global 7 from Midland signal is likely as strong as WBBZ despite what TV fool says.

[mrpeter105]

Originally Posted by rob50312

Mr Peter WBBZ is just too weak for attic reception.Even with a 30 foot tower it would be difficult.

I'm trying to see how much I can improve the signal. While I know it's a tough one I want to see if I can get a good enough system in place to at least be able to get reliable reception for the spring/summer/fall tropo seasons. That would be worth it. The experience will also give me an idea if it is feasible to use an outside antenna for winter. I might get up the gumption to put up something outside if I am sure it will work. Maybe.

Hows your reception of CKVR ? CKVR is much stronger at your location.Even Global 7 from Midland signal is likely as strong as WBBZ despite what TV fool says.

I am able to get CKVR with the K6STI 5-EL yagi that I made at a hotspot in the attic. Reception was about 45 to 55 area on the signal meter with 40 needed for decode. I then added 28-in straight narods to one of my gen1 sbgh and was able to get right around 40 on the signal meter but with periods of falling below decode at the same spot. I am now going to redo those with added narod reflectors to see if I can get rf10 from behind. Member 300ohm gave me a tip of how to redo the narods/narod reflectors to increase ch7 gain from the front and ch10 from behind. I will then try to use this at another spot where I get PBS on rf43 but the rf10 signal is weaker.

So I just want to see what is possible. I won't know unless I try and i'm curious.