building a narrow band GH (targeting 536mhz) - Canadian TV, Computing and Home Theatre Forums

 
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post #1 of 3 (permalink) Old 2017-07-16, 08:36 PM Thread Starter
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Question building a narrow band GH (targeting 536mhz)

I would like to build a narrow band Hoverman to focus on 536 mhz. I plan on building it based on the design on JED’s website, but I have a few questions about the design. Hoverman HDTV UHF antenna


If I am reading the section on narrow band design correctly, a 10 1/8” square zig zag should be my starting point? If I scale the feed gap the 1.0727611 (575/536), then the gap is slightly over 6” wide.

I’m a novice antenna builder. Is there a point of dimensioning returns in feed gap spacing? Can I get too wide?


It looks like the screen on the scaled design is roughly 5” back. Is there a point where a simple screen reflector is too far behind the elements?


I see on JED’s website that there was a GH10rev0 in which he used to compare the frequency range to the newer wider band GH’s. Was this simply a 10” square zig zag? Does anyone still have a link to that one?

Thank you,
wbm
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post #2 of 3 (permalink) Old 2017-07-17, 03:12 AM
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Dimensions for JED's GH6-574MHz "Narrowband" Antenna [Tuned for 575 MHz = Ch31] are found here:
Hoverman HDTV UHF antenna

As described by JED, nearly ANY Antenna can be RESCALED for Operation in another Band by changing ALL of the Dimensions [incl. Wire Size] by:
Rescale Factor = F = Current Design Frequency / New Design Frequency

Hence F = 575/536 = 1.07276 [All Dimensions are LARGER....as you calculated above]
So JED's a = 9-7/16 inches would be Rescaled to 10-1/4 inches.
BTW: The Zig-Zag Angles are NOT "square".

Since the difference is small, the SAME Wire Size can be used with negligible change to Gain and SWR.

Note that although JED provided all of the OTHER 4nec2 Files, he FORGOT to include the 4nec2 File for the Narrowband G-H. If you NEED it to say view ALL of the Dimensions, I should be able to regenerate it without TOO much difficulty.....Let me know.....

=======================================
Unless you are using a Design Optimization Tool, such as nikiml's Python Optimization Scripts, I do NOT recommend changing ANYTHING in the posted Design Dimensions.....it can quickly turn to MUSH.....and BTW: why would you even WANT to change anything????

=======================================
FYI: For comparison purposes, it would take a [much simpler to build] 15-El FD-Yagi to provide same 16+ dBi Gain, using K7MEM type design [which means I SHOULD be able to match that with an OPTIMIZED 14-El FLF-Yagi (Flat-Loop-Fed) such as my 9-El FLF-Yagi]:
http://www.k7mem.com/Electronic_Note.../yagi_vhf.html

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands

Last edited by holl_ands; 2017-07-17 at 04:16 AM.
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post #3 of 3 (permalink) Old 2017-07-17, 07:46 PM Thread Starter
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Thank you for the reply. I didn't mean squares, but rather each zig zag was the same dimension. I noticed that the GH10's from both NikiMl and JED's websites are showing various lengths of zig zag's, but I suspect that is due to how broad of frequencies that those antennas were meant to cover.


I'm not quite sure I'm ready to tackle a Yagi yet. I've built a couple of GH's with good success, but I would I couldn't consistently pick up channel 24 (broadcast at 536) which was my weakest local feed. I think it is due to the higher tuned frequency of the original GH. I'm willing to bend some wire to find out either way.


The only thing I don't like about the scaled narrow band is the size, but I guess that's the price you pay for a lower peak frequency range.
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