OTA antenna info, Mt. Wilson foothill area with severe multipath - Page 10 - AVS Forum
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post #271 of 342 Old 04-03-2002, 09:05 AM
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Nick,

The first one I purchased was $85 w/frt.This last one was $130.I think they nipped me,but it's not easy to do business with overseas suppliers,except for Blake Aerials.Lee Mellor & company do a nice job with export sales.

I'm not sure if it would be an improvement over the U-92,but it could be.Glenn had one for sale-don't know if he still has it.

Sales info:

Combined Precision Components (CPC)

www.cpc.co.uk
www.televes.com

Ph# using cheaper dial-around (thanks cymro!) 1016868 011 44 8701 202530
CPC part # AP00759
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post #272 of 342 Old 04-03-2002, 09:37 AM
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MAXHD:

Nice to see you are posting again.

FYI, there is an excellent tutorial on stacking, including sidelobes, here:

http://www.grantronics.com.au/docs/StkYagis.pdf

For horizontal stacking he recommends a spacing, in wavelengths, of 52/(3db beamwidth degrees).

Since the beamwidth of Yagis narrows as you go up in frequency (i.e down in wavelength) it turns out that the best stacking distance is roughly independent of the channel you are tuning to.

For example, using measured beamwidth data (supplied by Lee Mellor at Blake) for the Blake JBX21WB:

Ch14, Wavelength = 24"; 3 db beamwidth = 50 degrees.
So, spacing = (52/50)*24 = about 25 inches

Ch69, Wavelength = 14"; 3db beamwidth = 25 degrees.
So, spacing = (52/25)*14 = about 29 inches

Of course, experimenting with different spacings, starting with the above values, is vital.

I suspect that the Televes beamwidth is probably somewhat greater than the JBX21WB.
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post #273 of 342 Old 04-03-2002, 09:44 AM
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GlennL

Thanks. I think my Winegard is the 9095, but have found that the U-92 has fewer dropouts on digitals than the Winegard, so would probably prefer to vertically stack the U-92 by buying another of those.

Since I'm primarily looking for deep fringe signal gain and no multipath seems to be effecting my analog reception, I'm assuming that the vertical stack is the ticket.

I will check back with you on the tilter, as well as some pre-terminated RG-6 cords and a signal combiner with low loss.

Using baluns at the antenna and a 75 ohm combiner, how does one determine if the phasing is correct?

Don't confuse information with intelligence.
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post #274 of 342 Old 04-03-2002, 11:28 AM - Thread Starter
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Quote:
Originally posted by WHEELO1
Using baluns at the antenna and a 75 ohm combiner, how does one determine if the phasing is correct?
Barry made a nice tester for this http://coyotecreekranch.com/DTV/

-Glenn
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post #275 of 342 Old 04-04-2002, 04:11 PM
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Quote:
Originally posted by MAX HD
Nick,

The first one I purchased was $85 w/frt.This last one was $130.I think they nipped me,but it's not easy to do business with overseas suppliers,except for Blake Aerials.Lee Mellor & company do a nice job with export sales.
Thanks Max for the info. I checked with one Canadian distributor that offered to get the antenna at cost from Televes shipped to me for $170. Just a little too rich for me at this time. As far as the Blake is concerned, I think it is just too big for where I wanted to put it.

nick
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post #276 of 342 Old 04-04-2002, 08:39 PM - Thread Starter
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zmeister,

For a tighter turning radius, take a look at using two stacked JBX14's. They are about half the length and perform better than a single JBX21.

-Glenn
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post #277 of 342 Old 04-04-2002, 11:40 PM
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Glenn & cymro,

I let the tower down this evening and moved the stack from 57" down to 29". It really helped the pattern,knocking down those tall,nasty sidelobes.I don't know where those engineers came up with that spacing,but this works much better.

I thought while I was at it I'd put the DY28A back on the mast just below the stack to see how they would compare on low UHF channels.

They run neck and neck up to Ch28,then the stack took off. I have a 9" Panasonic PV-C931W that has a very sensitive tuner,that I use for DX,and it went into overload.Even a 7Kw LP at 54mi was causing bleedover two channels deep.Didn't think that was possible.

Anyway,I don't think I can go much further with this antenna tweaking for fear I'll blow my TV's up!


Hmm...wonder what a quad stack......?
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post #278 of 342 Old 04-05-2002, 03:43 PM
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Quote:
Originally posted by Glenn_L
zmeister,

For a tighter turning radius, take a look at using two stacked JBX14's. They are about half the length and perform better than a single JBX21.
True an option but I'm concerned about the cost of going full tilt to do stacking right. But anyway what is the length of the JBX14?

nick
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post #279 of 342 Old 04-05-2002, 04:35 PM
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nick,

The length of the JBX14 is 1.8 meters.
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post #280 of 342 Old 04-05-2002, 06:48 PM - Thread Starter
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Well, I did not have four identical antennas, so I decided to try a quad using two 14's and two 08's. I just connected all four antennas to a 4-way splitter with equal length coax and it worked great! I would say it is just about equal to two JBX21WB's. This is not really a practical setup though, since the cost and weight are more than using two 21's, but since I had these antennas laying around, I just had to give it a try. It would be a option for someone looking to put something powerful in a attic.

The turning radius for stacked JBX14WB's is 48". You could do a quad stack with the 08's and get the turning radius down to 36". Certainly worth thinking about to get around the "wife acceptance factor" compared to a roof antenna.

http://atechfabrication.com/images/quad_014.jpg

edit:
Looking at the above picture, it looks like the antennas are pointing up at a 45 degree angle, but actually they are set to only six degrees. I am taking this picture with my camera aimed upwards, so those mountains you see are much, much higher.

-Glenn
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post #281 of 342 Old 04-06-2002, 09:31 AM
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MAX HD

Are you using JBX21WB's or Televes in the stacking test that you just performed?

According to Glenn's and my tests, 36" spacing seems to work a little better than 28" for the JBX21WB's.
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post #282 of 342 Old 04-06-2002, 07:57 PM
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cymro,

I'm using 2 Pro Range 75's for the stack.I thought I'd take it down to 29",which would be about the minimum for Ch14. It didn't seem to hurt the gain and brought down the first two lobes off the main beam(grating lobes), considerably.I think if I move them further apart it will raise those nasty sidelobes,which is a real nuisance while Dxing.

If it's nice tomorrow,I'm going to mount them in a vertical stack and see how that compares.I read somewhere that vertical stacking can improve weak signal fade,which would also be beneficial.


Glenn,

It would be neat to see what a matched Quad stack would do pointed towards SD,compared to a dual stack.

Looks like you done some mix&match with the reflectors to save some work<grin>

Keep up the good work!
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post #283 of 342 Old 04-07-2002, 11:14 AM - Thread Starter
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Max,

How did you measure the side lobes? I have found the stack to get more directional the farther apart you place the antennas. At a minimum spacing of 20-28", the spectrum analyzer waveform shapes were nearly identical to a single antenna, but with more gain. As you move the antennas apart, the signal shape flattens out, a sign of reduced multipath. If you don't have any multipath, vertical stacking will give you more gain. But if you do have multipath, vertical stacking will make it worse.

I did not want to do any custom work with the quad, so I used the smaller reflectors in the middle (good eye!). It may work better to have the large reflectors with the antennas farther apart, but this would also make the vertical angle more sensitive.

A quad stack of 21's would be awesome! This setup is only equal to two 21's.

-Glenn
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post #284 of 342 Old 04-07-2002, 10:06 PM
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Glenn,

I rearranged the Pro 75's today to a vertical stack.The gain seemed to increase slightly,but the pattern in the E plane(horizontal) is much wider,causing strong analogs to overload adjacent channels regardless of which direction the antennas are pointed.

What I think I'll do is try a CM 7775 preamp with the 0538 coupler and see if I can tone things down some.If that proves out to work better,I'll sell one of the Televes preamp/couplers(I have two),to someone that lives farther out in the boonies and needs a dual stack setup.

Also,I think I'll go back to the horizontal stack and play with the spacing some more.

BTW,no fancy testing equipment here.I just use a couple of RS -20db adjustable attenuators,tune to an analog station thats slightly snowy,turn the rotor and adjust the attenuators to determine the difference in the peaks and valleys of the polar patterns,and also observe the azimuth headings on the rotor control readout.
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post #285 of 342 Old 05-21-2002, 09:44 AM - Thread Starter
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http://www.atechfabrication.com/imag...tilter_059.jpg

ATF-V200 Economy Tilter

This new tilter uses a standard Channel Master rotator and controller to reduce cost. For use with single antennas only.

-Glenn
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post #286 of 342 Old 05-21-2002, 09:53 AM
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Very clever and very slick...nice design!
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post #287 of 342 Old 06-17-2002, 08:49 AM - Thread Starter
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I just did a test comparing different signal combiners used for stacking antennas:
  • Winegard #SP-1002 5-1000MHz Splitter
  • Channel Master #0538 Antenna Joiner/2-Way Splitter
  • Labgear #6011/00 UHF Combiner/Splitter

I was looking to see which one had the lowest loss.

Results can be found here:
Antenna Combiner Test

-Glenn
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post #288 of 342 Old 06-17-2002, 06:33 PM
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Quote:
Originally posted by Glenn_L
[B
This new tilter uses a standard Channel Master rotator and controller to reduce cost. For use with single antennas only. [/b]

Interesting design, but I wonder if a plain vanilla screw-jack style BigUglyDish actuator would give more range, etc. Might just try to make my own.

No warranty is either expressed or implied. The universe is a figment of its own imagination. Your milage may vary. Not responsible for lost homework, missed bus transfers, or forgetting to buy a lottery ticket the day they run your birthday. Have fun.

Have spectrum analyzer, will travel.
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post #289 of 342 Old 06-17-2002, 07:00 PM
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Hi Glenn,

I've always heard there wasn't a big difference in good quality splitter/combiners.Now you've just confirmed that.Appreciate all your great testing!

What would you recommend to combine a quad stack?

Thanks,

Greg B
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post #290 of 342 Old 06-17-2002, 07:03 PM
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Oops, duplicate post.

No warranty is either expressed or implied. The universe is a figment of its own imagination. Your milage may vary. Not responsible for lost homework, missed bus transfers, or forgetting to buy a lottery ticket the day they run your birthday. Have fun.

Have spectrum analyzer, will travel.
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post #291 of 342 Old 06-18-2002, 01:33 AM - Thread Starter
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Quote:
Originally posted by glgorman
I wonder if a plain vanilla screw-jack style BigUglyDish actuator would give more range, etc
Do you mean something like this?

http://www.atechfabrication.com/imag..._051_small.jpg
Precision Tilter

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post #292 of 342 Old 06-18-2002, 01:44 AM - Thread Starter
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Greg,

I used a standard 4-way 1Ghz splitter (similar to the 1002 I tested) on that quad I built , works just fine. There is a picture of the quad a few posts up.

You could also use the other types of 2-way combiners. You would need three of them and another set of matched length cables to combine the two pairs. As long as everything stays in phase, they don't have to all combine at the same point. But due to the velocity factor, I like to keep harness cables as short as possible.

-Glenn
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post #293 of 342 Old 06-21-2002, 06:09 AM
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Hello everyone,

There are four way inductive splitters available, I used one of these for my transmitting quad at our development site in Sheffield. We were in the process of making one ourselves using ferrite beads and a PCB made by ourselves but gave it up because the 4 way we tested was perfect for the job. The splitter is made by Fringe and I recomend it highly for anyone attempting a quad.

I do not think that there will be many of you guys that really, really need a quad, but if any one requires these external 4 way inductive splitter please let me know.

Good luck with all your work chaps

Lee

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post #294 of 342 Old 07-07-2002, 11:09 AM - Thread Starter
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Antenna Stacking Test - ATF-X300

This is a new antenna I built specifically for being stacked, but it works fine by itself too. It is high performance in a small package at half the weight of comparable antennas. I have been running them successfully for two months now. I only plan to build more if there is enough interest.

-Glenn
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post #295 of 342 Old 07-07-2002, 11:41 AM
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Hello Glenn,

Congratulations on your new design.

It's amazing how much difference just 4 feet makes with antenna performance. Also, I'm surprised that the optimum azimuth changes by a few degrees over that 4 foot displacement. I like your "toe-in" idea. No doubt different receiving locations with different multipath will require different "toe-in" for best results.

After "toe-in", what next? camber adjustment?

Thanks again for your informative posts.
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post #296 of 342 Old 07-07-2002, 01:06 PM - Thread Starter
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""After "toe-in", what next? camber adjustment?"" hehe, that's a good one!

Hi cymro,

Actually, living on the side of a hill, I did try angling the antennas to be parallel to the angled ground plane. I found that if the antennas were slightly off level, it was better to be off with the terrain rather than against it, but since I rotate toward San Diego, I just set them up level.

As for toe-in, I swapped antennas A and B around and got identical results, so the antennas are exactly the same. I figured each antenna should be optimized before combining. With ch53, the horz. angle needed to be within 2 deg. to get a signal. Testing them separately showed a 5 deg. difference, so I re-aimed them on the boom and picked up a noticeable improvement in signal when combined. The vertical angle was the same for A and B, so I left that angle the same for each antenna.

-Glenn
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post #297 of 342 Old 07-07-2002, 06:39 PM
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Very impressive, Glenn. Thanks for keeping us in the loop as you develop better & better OTA reception solutions.

'Better Living Through Modern, Expensive, Electronic Devices'

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post #298 of 342 Old 08-03-2002, 06:47 PM
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Hi Glenn

I am interested in your ATF-X300 design. Thanks for all the info on this.
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post #299 of 342 Old 08-06-2002, 09:46 PM - Thread Starter
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Hi Ed,

I might be building a few more of these in a couple months. Right now, I only have the two I built for myself.

-Glenn
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post #300 of 342 Old 08-07-2002, 11:15 AM
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Thanks Glenn

I sold my other Antenna so I am looking for one in the next two weeks. If anyone has a BLAKE JBX21WB they want to sell send me a private message. Glenn: my tilter should arrive from you soon and I have everything ready to install it. I will post pictures of the installation and my Samsung SIR-T165 tuner as soon as it arrives. Thank you and all the other people on this forum for all the info.
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