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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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1st Jun 2021, 5:12 pm | #1 |
Hexode
Join Date: Dec 2018
Location: Lugo, Spain
Posts: 483
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VHF Yagi Gamma match opinions
In the process here of building a 2 metre yagi with the intention of using the gamma match.
I,m not totally sure if the outside gamma tube should slide over the inner feed conductor for critical adjustment or should it be the shorting bar that only is sliding ?. |
1st Jun 2021, 5:33 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,998
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Re: VHF Yagi Gamma match opinions
I've always done Gamma-matches where the braid of the feeder is connected to the boom at the zero-voltage centre-point of the driven-element, the centre of the feeder connects to the 'inner' end of the gamma-rod [nearest the boom] and the gamma-rod-to-driven-element connection is the adjustable bit.
Also perhaps worth googling 'Clemens Match' - which is a sort-of capacitively-end-loaded Gamma-match! See https://www.iw5edi.com/ham-radio/4509/the-clemens-match for example. |
1st Jun 2021, 5:59 pm | #3 |
Hexode
Join Date: Dec 2018
Location: Lugo, Spain
Posts: 483
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Re: VHF Yagi Gamma match opinions
Clemens , looked at that , that's different , hmmm.
Using the inner of RG213 here ( with the dielectric included) had to heat shrink it over to take up the slack inside the ali tube, lord knows what the capacitance is going to be LOL. Doing some mock ups on each part before i commit to the complete antenna, parts making and acquisition stages !. I made a 50mhz cubical quad with gamma and it works very well but not with coax as a capacitor only an old style ceramic vhf cap. |
2nd Jun 2021, 12:39 am | #4 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,340
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Re: VHF Yagi Gamma match opinions
I use the slider option - http://www.users.on.net/~endsodds/yagi3elgamma.jpg
This is the full details of this particular antenna - 3 element 2m Yagi - http://www.users.on.net/~endsodds/yagi3el.htm All above links the original designers site. |
2nd Jun 2021, 9:44 am | #5 |
Hexode
Join Date: Dec 2018
Location: Lugo, Spain
Posts: 483
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Re: VHF Yagi Gamma match opinions
Thanks for the tips fellas.
That also looks very interesting Terry , i think i will have a go at all these , must admit the Clemens is balanced so that could be the way to go . Would it work with RG58 ?. First i have to make one as a reference. Never made a VHF yagi before so all new ground. i think the solar cycle is increasing now so i would like to see what 2 Meters can do on SSB. I just did not want to go down the road of a split radiator element and all that insulator lark with the boom. |
2nd Jun 2021, 11:29 am | #6 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,340
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Re: VHF Yagi Gamma match opinions
Not having built one, my guess is the tube diameter may need to be smaller to use RG58. |
2nd Jun 2021, 11:48 am | #7 |
Hexode
Join Date: Dec 2018
Location: Lugo, Spain
Posts: 483
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Re: VHF Yagi Gamma match opinions
Yes , a lot smaller , not sure how the ali tube diameters interact with the transformer action taking place with the driven element , all very interesting stuff, i could spend days on this kind of thing , just wish i had a HP VNA with the smith chart read out LOL.
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