"Top Hat" GH with NARODs for VHF-HI: Major GH Improvement

[gcd0865]

In considering wrapping Al tape around fiberglass rods for the main reflectors and NAROD reflectors for a GH10n3, I understand that the 5/16" diameter fiberglass rods are considerably stiffer than the 1/4" ones. Does switching to the 5/16" size significantly affect performance, or would the overall dimensions of the antenna need to be changed? Could you still use 1/4" Al rod for the driven elements with the 5/16" main reflectors and NAROD reflectors, or would that just throw everything out of whack?

[nikiml]

nec2 predicts differences within .1 dB.
On some channels you get a bit more on others a bit less, but nothing major.

[gcd0865]

Awesome, thanks nikiml. Was thinking that the 5/16" rods would hold up better to wet snow and ice storms.

[jflarin]

Originally Posted by rvsixer

Antenna will go in a townhouse top loft, indoors if possible (immediately behind a sliding glass door which faces our Mt. Wilson antenna farm at 325 deg perfectly). Due to the indoor location I am most interested in the physically smaller GHn2 lineup, but before building thought I would post my TV fool to see if the smaller designs have any hope of working for me:
http://www.tvfool.com/?option=com_wr...361688726e6ed5

Opinions/advice most welcomed. Moving up to a GN4n and or outside remains a possibility if needed.

You TVFOOL shows 2 edge for almost every signal. This isn't looking good. On my location, I couldn't get anything below +10dB of NM even in the attic. When I moved outside, I got everything solid, even some channel that are so low that they are not shown in my tvfool... and I still get them today. So whatever plans you do, build it cheap and fast to test if it works inside, then put it outside just to check it the result is better and I guess you'll want to build something sturdy to go outside pretty fast.

jf

[rvsixer]

Originally Posted by jflarin

You TVFOOL shows 2 edge for almost every signal...So whatever plans you do, build it cheap and fast to test if it works...jf

jf thanks for the reply. Very good advice, and coincidentally exactly what I have been up to how weird is that : ?!

I just built and tested the Mcclapp M4 bowtie design (UHF gain comparable to, VHF-hi gain lower than GH NAROD variants). Indoors absolutely nothing. M4 outside without reflector received only the strongest UHF station on my tvfool, and the two weakest VHF stations. M4 with reflector locks on most stations having an NM 10-11dB or higher, variable reception on those having NM 8-11dB, and nothing below NM 8dB. The one elusive channel is KABC (the strongest station) .

This experiment gives confidence on moving forward with the highest gain GH variant I can physically fit on the patio.

[theMikeD]

Hi there,

Are there instructions somewhere to build one of these for those of us who are not engineers and don't want to learn the physics behind antenna design? All I'm after are dimensioned drawings. Can someone point me to that?

Thanks so much!

...Mike

[nikiml]

the dimensions can be taken of the 3D models on my web-site.
for help see
http://clients.teksavvy.com/~nickm/help.html
and
http://www.digitalhome.ca/forum/album.php?albumid=714

You can also view any of the models in full screen, print and add dimensions by hand...

[theMikeD]

Thanks thats a big help. It looks like your site has dimensions for a few varieties. I've already added numbers to the n3 variant. Now I just need to figure out a frame to hold it all!

Are the green rods in the bg intended to replace the mesh I have seen in photos of other designs?

...Mike

[300ohm]

Now I just need to figure out a frame to hold it all!

Most build nikiml's models using a "H" or ladder type pvc frame. The grey pvc pipe is much cheaper than the white and is UV resistant to boot. You will still have to use white pvc fittings though because of the unavailability of grey fittings.

Are the green rods in the bg intended to replace the mesh I have seen in photos of other designs?

Yes, there are two basic types of GH reflectors, the rod models and the mesh/solid surface models. The mesh/solid surface reflector models cant receive vhf-hi as of yet, only the rod reflector models can.

[theMikeD]

Great, I'll try to whip something up, pipe-wise. I'll just have to remember to hold off on final assembly until I get it through the attic doorway!

One last question: is there a difference in the wire material/diameter between the zigzag part and the reflector part? Or can I make all the metal parts from the same wire?

Oh, and will any old balun work? Or is there a preferred model?

...Mike

[nikiml]

All of the models I've posted were optimized for 1/4 inch aluminum wire for all elements.

Small deviations in the wire thickness should be ok. For example I have checked the performance with 5/16 inch for the reflectors and it was very close.

Any balun covering both the UHF and the VHF-hi spectrums should work.
but of course some baluns are made better than others...

[300ohm]

I'll just have to remember to hold off on final assembly until I get it through the attic doorway!

When working with pvc pipe for antennas, DONT glue, use a #4 wood screw instead to hold the fitting.

[theMikeD]

Good tip on the flexible copper tubing...I found that in the plumbing department. The straightening trick with the dril won't work with tubing though...I'll have to roll it or something.

I found this

http://www.instructables.com/id/GH10...an-TV-Antenna/

but no cutting diagrams, which is a real shame as that seems like a sturdy way to do it. Guess I'll hack around and see what I come up with. Sure missing my workroom right now.

We have an industrial wreckers in town, I think I may swing by there tomorrow to see what I find. Maybe they have old antennas or scram aluminum.

...Mike

[nikiml]

the model unclesam built is the GH10n3 and you can also find his posts and albums here on this forum, in this thread and also in the metal working and plastic working threads.

[stampeder]

A reminder about the great antenna metal-working thread here at our site:

Best Metals for Antennas: Performance, Soldering, Welding, Bending, Working

I've put some of the recent posts from this thread over there into that one for the benefit of all our readers.