Transcript VHF Propagation Modes
“Cheap” Yagis
Rochester VHF Group 09 February 2007
“Cheap” Yagis
Presenters: Mark Adams, K2QO Bill Rogers, K2TER 4/25/2020 Rochester VHF Group 2
Introduction
“ This year, I just scraped together enough ‘bottle and can’ money to buy my VHF radio equipment. Do I have to wait till next year for the antennas I need to put a decent signal on the air?
” 4/25/2020 Rochester VHF Group 3
Introduction
“ Having never homebrewed an antenna other than a HF dipole, I don’t think I have the skills or experience to replicate the NBS yagis in the ARRL Antenna handbook. Now what?” 4/25/2020 Rochester VHF Group 4
Introduction
“ I’d like to try roving on the bottom 6 bands but I don’t want to spend an arm and a leg on another set of antennas that are 6 feet or less in length. What’s an avid VHFer to do?” 4/25/2020 Rochester VHF Group 5
Introduction The Answer… You need “Cheap” yagis.
Cheap yagis were originally conceived by Kent Britain, WA5VJB, in an effort to assist Cuban operators in getting on the VHF bands. Cheap yagi construction plans are readily available for all bands from 144 MHz to 1296 MHz. These designs are scalable for use at other frequencies, as well.
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Why “Cheap” Yagis?
Simplicity – Mechanical construction and Feed point impedance matching.
Availability – Common materials can be obtained with one stop to a hardware store. No special tools needed. Plans are in public domain.
Repeatability – It’s hard to mess these up.
Time efficiency – You could build a set of these antennas in a Saturday afternoon.
Affordability – Less than $10/antenna at retail rates.
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The “Cheap” Yagi Driven Element
No balun req’d 4/25/2020 Rochester VHF Group 8
144-1296 Cheap Yagi Stack
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144 MHz Yagi dimensions
144 MHz Driven El. = 38.5" and H = 1.0" - All 1/8" dia. elements
3 Element 3 Element 4 Element 4 Element 6 Element 6 Element Length Spacin g Length Spacin g Length Spacin g
Reflect or Driven Direct or 1
41 0 42 0 40.5
0 8.5
8.5
7.5
37 20 37.5
19.25
37.5
16.5
Direct or 2
33 40.5
36.5
34
Direct or 3
36.5
52
Direct or 4
32.75
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222 MHz Yagi dimensions
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432 MHz Yagi dimensions
432 MHz Driven El. = 13.0" and H = 3/8" - all 1/8" dia. Elements
6 Element 6 Element 8 Element Length Spacin g 8 Element 11 Element Length Spacin g Length 11 Element Spacin g
Reflec tor
13.5
Driven Dir 1
12.5
Dir 2
12
Dir 3
12
Dir 4
11
Dir 5
0 13.5
0 13.5
0 2.5
2.5
2.5
5.5
12.5
5.5
12.5
5.5
11.25
12 11.25
12 11.25
17.5
12.00
17.5
12 17.5
24 12 24 12 24 12 30.75
12 30.75
Dir 6
11.25
38 12 38
Dir 7
11.75
45.5
Dir 8
11.75
53
Dir 9
11 59.5
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903 MHz Yagi dimensions
902/903 MHz Length Spacing Reflect or 6.2
0 Driven * 2.4
Direct or 1 5.6
3.9
Direct or 2 5.5
5.8
Direct or 3 5.5
9 Direct or 4 5.4
12.4
Direct or 5 5.3
17.4
Direct or 6 5.2
22.4
Direct or 7 5.1
27.6
Direct or 8 5.1
33
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1296 MHz Yagi dimensions
The driven element is small enough to allow 0.141 semi-rigid coax to be used instead of RG 58. Silicon Bronze welding rod was used for the elements but any material can be used. Driven element dimensions are L = 4.0" and H = 1/2" Elements are 1/8" diameter.
Measured gain: 12.5 dBd
1296 MHz
10 Element 10 Element 4/25/2020 Length Spacin g
Reflect or
4.3
Driven Dir 1
3.9
Dir 2
3.8
Dir 3
3.75
Dir 4
3.75
Dir 5
3.65
Dir 6
3.6
Dir 7
3.6
Dir 8
3.5
0 1.7
2.8
4 6.4
8.7
12.2
15.6
19.3
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K2QO/R Antenna Setup
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K2QO Rover
We use Cheap Yagis on 2, 222, 432 and 903!
1296 is a Quagi from the Handbook. This is an easy to make antenna too.
Performance of 6-el 2M Yagi same as driven section of my FO-12.
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Construction Notes:
Start with the exact dimensions as published by Kent Use a file to remove any sharp edges Consider plastic caps for element tips 4/25/2020 Rochester VHF Group 17
More Tips
Consider surplus patch cables. Cut off one end and attach to feed. Best if connection at antenna is a female.
Use $2.99/Gal Redwood stain.
Radio Shack mast clamps are FB.
Wind loads are virtually nil.
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Closing
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