VHF Yagi Gamma match opinions - UK Vintage Radio Repair and Restoration Discussion Forum

Malcolm T · 1st Jun 2021, 5:12 pm

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 ?.

G6Tanuki · 1st Jun 2021, 5:33 pm

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.

Malcolm T · 1st Jun 2021, 5:59 pm

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.

Terry_VK5TM · 2nd Jun 2021, 12:39 am

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.

Malcolm T · 2nd Jun 2021, 9:44 am

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.

Terry_VK5TM · 2nd Jun 2021, 11:29 am

Quote:

Originally Posted by Malcolm T

Would it work with RG58 ?.

Not having built one, my guess is the tube diameter may need to be smaller to use RG58.

Malcolm T · 2nd Jun 2021, 11:48 am

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.

1st Jun 2021, 5:12 pm	#1
Malcolm T Hexode Join Date: Dec 2018 Location: Lugo, Spain Posts: 483	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
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	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
Malcolm T Hexode Join Date: Dec 2018 Location: Lugo, Spain Posts: 483	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
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,339	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. __________________ Terry VK5TM https://www.vk5tm.com/

2nd Jun 2021, 9:44 am	#5
Malcolm T Hexode Join Date: Dec 2018 Location: Lugo, Spain Posts: 483	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, 11:48 am	#7
Malcolm T Hexode Join Date: Dec 2018 Location: Lugo, Spain Posts: 483	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.