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Philuk
Junior Member
Username: Philuk
Post Number: 23
Registered: 4-2009
| | Posted on Sunday, July 01, 2012 - 4:41 pm: | 
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I have been off 11m for quite a while now and a friend told me 555 was picking up so I have decided to try and build a vertical 5/8 or even better.64wl antenna for the band as I have a vacant wall bracket looking bare without one, by the way I am not tight the reason for building is I am disabled and only work part time and do not claim any benefits therefore every penny is needed for the household bills.
I have looked at quite a few options but the one that intrigues me most is the Gain-master by Sirio I have the plans with all the details but for the life of me I cannot work out what this antenna is? its reported to be a .64 wave vertical but to me it looks like an end fed dipole with a matching coax stub 1/4 wl up from the feedpoint after an ugly balun (air wound choke with 16 turns)and at the halfway point is a 15pf? coaxial capacitor feeding the 330cm radiator, strange looking thing any ideas please?
Phil
M6MRP Yaesu FT817nd, FT840 FT51R.
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Marconi
Advanced Member
Username: Marconi
Post Number: 812
Registered: 11-2001
| | Posted on Saturday, July 07, 2012 - 11:20 am: |
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Phil, IMO the GM is a center fed 5/8 wave radiator. It is kind of different to say the least. The coax choke, at the base, is the cut of point for the bottom element, and the element radiates due to the Common Mode Currents flowing on that coaxial portion, that lower 1/2 of the coaxial radiator. The top portion of the radiator is just a simple wire element about the same length as the bottom portion.
The stub and the capacitor handle the matching at the center of this 5/8 wavelenth radiator, and according to my Eznec model...this one appears to be well balanced, just as Sirio describes. |
Philuk
Junior Member
Username: Philuk
Post Number: 30
Registered: 4-2009
| | Posted on Sunday, July 08, 2012 - 8:03 pm: |
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Well there is a handle Ive seen before, that is if it is the same Marconi from another forum I have recently joined for HB build advice?
What gets me is the center fed bit? as it looks to be fed from the base, does the feed start at the base of the capacitor or the point where the stub match connects? its sure is a strange one.
I was experimenting with my HB version today on my FT817ND on 20m the HB GM was erected low down in the garden and tuned with my mfj tuner, I could clearly hear distant very weak stations (2 or 3 S points) like Japan and India that were not audible on my delta loop or inverted V! I must get this thing working properly " truly amazing design"
Catch you on the other side.
73
Phil
M6MRP Yaesu FT817nd, FT840 FT51R.
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Press_man
Advanced Member
Username: Press_man
Post Number: 561
Registered: 5-2008
| | Posted on Sunday, July 08, 2012 - 8:40 pm: |
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Hi Marconi ! Where ya been? You OK?
73
73 Pressman
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