[VHFcontesting] Tech Help needed

[nosigma at aol.com]

Interesting thread.  I face a similar band width problem but fortunately conquered it with a lot of help. 

 I need to run SSB, FT8 at the low end (50.125-50.313) and FM (52.525) at the high end.  With the Gamma match Cushcraft (go ahead, hate on me for using it) 5 element I was able to get well under 1.5:1 except from 51.100 to 51.800.  It was a full days work with a blue tooth wireless head on a spectrum analyzer that let us test with the mast up and down (fold over on Jeep).

The Gamma match settings are way off the mfg spec to make it work.  The critical tuning was to the reflector and first two directors.  The reflector is marginally asymmetric (probably due to 45 deg polarization with mast interference) and much wider than the SSB spec with the first two directors being a bit narrower than the SSB spec.  FM to 400mi and SSB (running W4IY KW amps & heliax) going from Va to  Europe and the Pacific Northwest.  4000ft elevation didnt hurt.

The ability to slide the reflector  and directors in and out to change width was the enabling capability of the antenna that allowed the silly wide bandwidth to be achieved.  

I know the M2's are fixed width elements, but if you the time to experiment playing with sleeves of tubing on the reflector and first couple directors you might get good results.

73
John
KM4KMU 
On Saturday, January 2, 2021 chetsubaccount <chetsubaccount at snet.net> wrote:
This brings up again the age old question: do I want to DX or contest?

A high gain, narrow band antenna does not send a CQ in a wide azimuth. But today's rules allow you to call someone on your cellphone and ask them to get on and give you their grid while you beam there way. 

Vs.

Less elements on the yagi (but you can stack them  for more gain or have multiple yagis) and call CQs that may be heard over a wider coverage azimuth. 

Kind of like fishing- try by yourself to read the areas to fish vs. other boats telling you where to go. Either way you will catch fish and have fun.

Your station, your choice!

Hoping to catch many fish this January.

73,
Chet, N8RA



-----Original Message-----
From: VHFcontesting <vhfcontesting-bounces+chetsubaccount=snet.net at contesting.com> On Behalf Of Dan Evans via VHFcontesting
Sent: Saturday, January 2, 2021 7:59 PM
To: 'Jim Worsham' <wa4kxy at bellsouth.net>; Paul Rollinson <Paulrollinson at sbcglobal.net>
Cc: 'VHF Contesting Reflector' <vhfcontesting at contesting.com>
Subject: Re: [VHFcontesting] Tech Help needed

Hi Paul,No help here with the issue, but I wanted to thank you and the list for the topic.
I currently have a CC 6 element on a small tower.  I have a bigger tower I hope to put up soon, and I've been wanting to upgrade to the 6M7 if I ever get the tower project off the ground.  So I will likely face the same issues.
I've been following with interest.
73Dan
-- K9ZF  President, Clark County Amateur Radio Club,Amateur Radio Emergency Service, Clark County Indiana. EM78el The once and future K9ZF /R no budget Rover  ***QRP-l #1269 Check out the Rover Resource Page at:  List Administrator for: InHam+grid-loc+ham-books  Ask me how to join the Indiana Ham Mailing list! 

    On Saturday, January 2, 2021, 11:55:03 AM EST, Paul Rollinson <paulrollinson at sbcglobal.net> wrote:  
 
 Good morning all,

It appears that I'm not alone with this issue. It's a great antenna until you try to push up the band for the digital modes, with potential for more to come.

So far I've learned this from this list and other friends in the VHF spectrum:

The theory behind moving the shorting bars out to more the freq up the band may be based on simple J pole type design, when you short higher up the driven element, it increases in resonate freq.
The 70 ohm (RG-6) phasing line might be able to raise the center freq if shortened. If anyone has done this, please reply with length to attempt.
The driven element might be able to be sleeved increasing the diameter and potential bandwidth, which is the biggest problem with this design.
Electrically lengthening the T match bars using  retaining rings at the end may create an aching point at hi power and wet environment. This may be catastrophic for an amp and will not be explored.
Repositioning D1 may help but this has unknown effect of performance.
Finding a better, free space test range will be first on the list. I have 90Ft trees here so spanning 2 trees and hanging the antenna in the middle show be effective.
I still plan on calling M2 on Monday to see if I'm missing something

I will say this, great responses from the VHF community. Thanks to all.

73,

Paul Rollinson, KE1LI
Rollinson Associates
860-928-5147
860-208-8814 Cell/Text
Paulrollinson at sbcglobal.net

Representing Component Part 
Manufacturers for over 35 years

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