1.5 KW PEP Gain-Master Modification

[PhilipB]

Gainmaster

What overall measurements are you using for your home built Gainmaster?

Hi Needle Bender, as per the plans Ive posted on the home brewing a gain master thread on this site, plans were given to me by a kind ham/cber in Portugal but Im having problems with the cap (I think?) as my ugly balun is a different diameter former and less turns, not going for high power just a low cost low power home built version for 10/11m.
Now it is resonant on 12m with a very low swr at the moment good tx/rx and low noise also no tvi on my old test portable TV which gets trashed by most other antenna's
Having another play about with it today while the weather is good and may try the recomended coil turns if I can find a correct size former and also going to try a medium sized variable open plate cap from my home brew low power mag loop which I know is good as that tunes fine from 10 to 20m.
regards
Phil

 

[simonradioman]

Sirio are now working on another version of the antenna. It was started in July and still under review. I heard this last week directly. So wait and see, maybe a higher power version will come and this will solve many issues people had in the past

 

[Needle Bender]

I'll take TWO please!!

I have two GMs up prsently due to having a radio in the kitchen AND the shack, but I won't risk running the 2K amp into either, only a Tx Star 500 and no issues with that yet on 10-12m, but I'd sure like to warm up those tubes into a high power version. I hope the new one handles at least 2500w pep.

 

[camaro1]

so what happens when then stock cap burns?? what are the signs?

 

[Shockwave]

When the capacitor shorts out in the GM, you will not be able to see an SWR below 1.7:1 over its normal operating range. This problem is rare today since the cap was upgraded.

 

[Needle Bender]

Hey Shockwave, upgraded to what? What's the new power handling claim/ guarantee?

Twice now, (different locations & antennas) I've witnessed an Imax2000 outperform a Gainmaster.

I wonder if there's a specific height where the Gainmaster either works best or poorly?

 

[Shockwave]

They just widened the gap between the conductors on the cut end of the coax to increase the breakdown voltage. I don't think they increased the power rating because the goal was to provide a comfortable degree of headroom to prevent the failures we saw on the first production run.

With respect to the Imax beating the GM in two installations, the GM is sensitive to objects around its base just like most antennas are effected by objects around their tops. The top and bottom of the GM are energized equally so close proximity to other conductive things would have a bigger impact on the GM. Although I'm using one just 10 feet above a 4 element Yagi with very good results.

 

[Needle Bender]

- Just an observance:

The diameter of the 16T coaxial coil is right about 3", ending up with right about 148" of coax in the coil.

At it's VF of 70% that equals right about an electrical 1/2 wave length of 18'.

Hmmm. Interesting coincidence.

 

[vkrules]

16t on 65mm (not 3 inches) is even closer. When are you guys going to catch up with the rest of the world and go metric! Good cmc choke, much better than the old 5 turns on a 100mm former,

 

[vkrules]

the tuned stub is a 1/4 wave( from shorted end to cap x vf) as well.Just another observation.