Gray-Hoverman - early prototyping and modeling posts

[Autofils]

First, let me send kudos to DjiPi, for his reception report in this post: http://www.digitalhome.ca/forum/show...4&postcount=52

That was a significant amount of work and provides members of this forum with an excellent comparison of the Gray-Hoverman with a Screen Reflector, to the CM4221 clone.

DjiPi's results (post #322) would seem to confirm the EZNEC modeling results.

Copyright 2008, and distributed under the GPLv3 license:

I have now completed the optimization of the reflector screen for the SingleBay and the following graph shows the Net gain for:

1. Full Reflector Screen [Overall size is 30 x 40 inches]
2. Split Reflector Screen [Each section is 14.5 x 40 inches, with a separation of 1 inch]
3. 6 Pair Rod Reflectors
4. Channel Master CM-4221 for comparison

The spacing between the array and reflector is 100mm.





This shows the additional gain that a optimal screen reflector provides, compared to the 6 pair rod reflectors.

For the reflectors screen, there is a slight increase in gain, if the reflector screen is split into two sections with a 1 inch separation.

For those that are looking for #9 Al wire, I found some on Ebay; just search for "Aluminum Ground wire".

If you try this antenna, please post your results to this forum.

[DjiPi]

Originally Posted by Autofils

First, let me send kudos to DjiPi, for his reception report in post #322.
That was a significant amount of work and provides members of this forum with an excellent comparison of the Gray-Hoverman with a Screen Reflector, to the CM4221 clone.

DjiPi's results (post #322) would seem to confirm the EZNEC modeling results.
(...)

Thank you Autofils, and you should be sent kudos as well for the modelling work that you have done, as well as any person that helped in any way. This helped me a lot (and convinced me) to build the SBay-Gray-Hoverman !

My wish now is to try the Double-Bay, with a similar reflector size adapted for the double-bay. I'll let everyone know the results. If you had some spare time to model the double-bay with optimal reflector size, that would be very appreciated. In the mean time I'll experiment.

Great work !

[DjiPi]

Hi t/s (or s/t),

I would suggest that you build yourself the Gray-Hoverman instead of the CM4221 clone. The Gray-Hoverman is a little bit better, so unless you want to build different antennas for fun or curiosity, this would be the shortest way to acheive your primary goal . By the way, where are you located to get 16 digital channels ?

Everybody: I rearranged the pictures of my album from my post #322, now comparing the channels is a lot easier, and the way I did it will allow me to post pictures when I'll compare the CM4221 vs Double-Bay Gray-Hoverman.

[Autofils]

The EZNEC v3 modeling of the Double Bay Gray-Hoverman have been completed and are presented in this posting.

The graph below compares the Net Gain of the Double Bay Gray-Hoverman to the Channel Master CM-4228 for the following versions:

1. DoubleBay Array-Only (No reflector)
2. DoubleBay with 11 pair Colinear Rod reflectors
3. DoubleBay with Screen Reflector 30x75 inches
4. Channel Master CM-4228 (kq6qv Nec4 data for CM-4228)



These results indicate the the DoubleBay Gray-Hoverman (Colinear Rod reflector and Full Screen reflector versions) are a bit better than the Channel Master CM-4228.

I initially thought it strange that the screen reflector had a "bump" in gain from Ch40, but when compared to the DoubleBay Array-only, you can see that "bump" is also present. I did not find any significant gain difference between full or split screen, as was found for the SingleBay.
The gain decreased for wider screens, so I believe 30x75 inch screen is very close to optimal for the DoubleBay.

If you are considering an outdoor installation, the collinear rod reflectors will have a much lower wind load.

If you try this Gray-Hoverman DoubleBay, please post your reception results.

[stampeder]

Originally Posted by Autofils

These results indicate the the DoubleBay Gray-Hoverman (Colinear Rod reflector and Full Screen reflector versions) are a bit better than the Channel Master CM-4228.

Now if we can come up with an easy-to-read set of schematics on the physical contruction we will have a real winner!

DjiPi, will you be fabricating the Double Bay Gray-Hoverman any time soon?

BTW, Autofils doesn't mind if we refer to it as the DBGH for short.

Given all the focused R&D about the Hoverman I was contacted by DjiPi about putting it all into its own thread. Now that we are seeing concrete successes I've moved all of the Hoverman-related posts here.

[Autofils]

Originally Posted by stampeder

Now if we can come up with an easy-to-read set of schematics on the physical contruction we will have a real winner!
...

The dimensions for the SingleBay and DoubleBay, Gray-Hoverman with colinear rod reflectors, are specified in this post: http://www.digitalhome.ca/forum/show...6&postcount=31

Copyright 2008, and distributed under the GPLv3 license:

Reflector screen for the singleBay is 30x40 inches overall. The split screen is two sections 14.5 x40 with a separation of 1 inch, between each vertical section.
Reflector screen for the DoubleBay is 30x75 inches.
The reflector screen used in the model was based on a wire grid structure of 2"(hor) x 1" (vert), same as CM-4221.
For indoor applications, tin-foil will work quite well.
For outdoor applications, the colinear rod reflectors will have a much lower wind load.

The reflector screen is centered with respect to the array(s) and the reflector spacing is the same as the colinear rod reflectors, at 100mm.

[DjiPi]

Originally Posted by stampeder

(...)
DjiPi, will you be fabricating the Double Bay Gray-Hoverman any time soon?
(...)

Yes, in fact the DBGH was the antenna I made first, but to report results on the SBGH, I took apart the second bay. Now it's time to put it all back together again and to install the reflector.

Just a note about my pictures on SBGH reception report: I just took out the CM4221 clone and put the SBGH pointing in the exact same direction, so I didn't try to pinpoint each channels for best results. That was a very rough comparison.

Autofils noted that channel 44 and 62 didn't seem to match the model, so I double-checked if I had mixed up the pictures. It appears that I didn't.

So, yes, I will be able to report results soon (I'm very excited now that I see that the performance would exceed in theory the CM4228 ).

[99gecko]

Thanks to Autofils, as well as DjiPi, Gerry B, Old Sparks, Kro, (and any others I may have missed) for your informative posts. I think many of us can't really appreciate the modeling work you have done here.
I have a partially completed 4228 clone in my workshop (which I started last summer! ), which I'm now thinking I might scrap and try my hand at your modified DBGH. I have very limited spare time so don't expect to see any results for a very long time , but I promise to post when I get done!!

The reflector screen used in the model was based on a wire grid structure of 2"(hor) x 1" (vert), same as CM-4221.

Unfortunately I only have 1" square construction screening to use as my reflector. What do you think I should expect since my screen material has twice as many vertical wires? If needed I can easily cut out the extra wires.

As well, perhaps I missed this, but do you have any idea what the overhead plot will look like for your modified DBGH ? Has anyone generated a reception pattern for this?

[Autofils]

99gecko,

Your 1"x1" construction screen would be fine as is; no need to cut out any wires.
The reflector screen for outdoor applications, is generally made with the largest grid structure based on the highest operating frequency of the antenna, to minimize the wind load, so a 1"x1" will probably be a bit better.

I assume by overhead plot, you mean the polar plot. I have those results at 500 and 660Mhz for the DBGH, colinear and screen reflector. I'll get the photos posted soon and that will show the improved Front/Back ratio for the reflector screen compared to the 11 pair colinear rod reflector.

I look forward to your DBGH progress.
For me, the outdoor install has to wait until spring and at the rate we are getting snow here in Ottawa, it may well be a late spring this year.

[99gecko]

Yes I meant polar plot.

at the rate we are getting snow here in Ottawa, it may well be a late spring this year.

If you lived in Ottawa during the winter of Feb 1971, this winter should be a breeze . My parents took a photo of me standing on the snow looking in my bedroom window..... it was on the 2nd story !!

cheers

[Autofils]

PolarPlots for the Gray-Hoverman were run on EZNEC v3 at two frequencies.
500MHz (Ch19) and 660MHz (Ch45).

Single Bay


(a) SBGH Collinear Rod Reflector vs Split-Screen Reflector



(b) SBGH Split-Screen vs CM-4221



Double Bay Polar Plots

(a) DBGH 11 pair Collinear Rod Reflector vs 30x75 Screen



(b) DBGH 30x75 Screen vs CM-4228

[DjiPi]

Thank you for your polar plots Autofils, very, very interesting...

Based on these plots for the DBGH, it indicates that there would be a significant gain at the back of the antenna for the refector rods: this is very interesting for me considering my location between Montréal and US.

I think that I will end up building the rod reflectors DBGH because in my situation, it would allow me to catch the Montreal stations with better gain, with little impact on the reception strength for the US stations. Does my reflexion make sense ?

But for the testing purpose of the antenna and report, I'll experiment with the full-splitted-grid first.

DjiPi.

[stampeder]

DjiPi, what if you build it with the full reflector to test if the back door gives you the Montreal signals, then switch to the rods if its not good enough?

My own situation is very similar, with Mt. Seymour and SeaTac stations being almost 180deg apart, but I'm quite close to the Canadian ones so I might test to see if the full reflector's back door is generous enough.

[DjiPi]

Originally Posted by stampeder

DjiPi, what if you build it with the full reflector to test if the back door gives you the Montreal signals, then switch to the rods if its not good enough?

That is effectively my plan as I said before (well maybe not that clear ), but I'm curious about the rod reflectors gain pattern. My interrogation would imply the possibility of multipaths/problems, etc. resulting from the gain at the back. Wouldn't it be like building 2 CM4221 and putting them back to back ?

[Autofils]

This is a correction for previous SBGH polar plots that I have posted on this forum.

On the AVS forum " New DIY antenna design from Slashdot", vman41 asked the following question...

BTW, can someone explain to me why the polar plots from this NEC2 modeler are often asymetric? One would presume the geometry input for the antenna was idealized, so getting oddball lobes on side of the axis that aren't reflected on the other side is disconcerting.

I had a quick look into this and found that it occurred only with the SBGH over the freq range 600 to 700Mhz, but I did not have any explanation. I sought help from old sparks, and he quickly identified the problem.

The SBGH modeling files did not have the voltage source located in the exact middle of the wire tag. (The DBGH files were correct and did not show the asymmetrical lobe)

Here is the link to the AVS forum for the explanation of the asymmetrical lobe, including my red face ...
I want to thank vman41 for spotting this and old sparks for the solution..

And here are the corrected SBGH polar plots.
( Stampeder: These should be added to the GPL web site with a short explanation)