Gamma Matches

[TheRealPorkchop]

Where’s a good source of information to properly build a high wattage gamma?

More specifically, the in’s & out’s of which material to chose and why, how to build one that will handle higher power input. I’m aware I could buy one but what fun is that?

I’d like to build one that’ll handle at the very least 5kw.

Which brings the question to the table, the ratings offered by Maco, is that PEP figures or CW/AVG?

 

[groundwire]

Arrl handbook

 

[snow bird]

Chop Hi You can use Copper or S S or brass Even Alu Use thick wall tubing and good Surgital tubing For your Ins

 

[TheRealPorkchop]

I knew the ARRL was a great place to start but Snow Bird has hit the nail on the head. That’s more of what I’m thinking about.

I want a near blow-proof gamma on my beams. I’m giving serious consideration to stacking my pair of shooting stars, absolute ridiculous overkill. And I don’t want to have to take them down over a crappy built gamma.

 

[BJ radionut]

Try one of Bill Orr's Radio Eng handbooks...many editions on-line...I think there are link's here to find several edition(versions)...
As far a insulators for the adjustment tubes...Teflon or Delrin comes to mind as holding up to the power.
All the Best
Gary

 

[TheRealPorkchop]

I like the Delrin. Thanks BJ.

 

[Shockwave]

Derlin may be easier to find and less expensive than Teflon. However, make no mistake because Teflon is the superior material to use in a high power gamma match. Teflon can handle twice the heat without melting and is also not prone to cracking over time. Because of the difficulty finding Teflon in the right diameters, this is an item I suggest most people buy if you can't find a good source for the insulator.

With respect to the Maco gamma match ratings, they must have been PEP because the early 10KW model use to fail regularly as soon as you past 7,500 average on the Bird. I believe Tom has upgraded the Maco gamma match as he mentioned this last time I spoke to him. The real bullet proof replacement for a gamma match is a ceramic vacuum variable capacitor.

 

[TheRealPorkchop]

I contacted Maco and they said the 2kw factory piece was rated as average power or continuous.

I’m having a hard time believing that, that’s why I’m looking for an alternative and I want to build it. Most likely I won’t be exceeding 4kw PEP. The tower will tilt but ain’t nobody got time for that.

 

[Shockwave]

I contacted Maco and they said the 2kw factory piece was rated as average power or continuous.

I’m having a hard time believing that, that’s why I’m looking for an alternative and I want to build it. Most likely I won’t be exceeding 4kw PEP. The tower will tilt but ain’t nobody got time for that.

You should beware that the stock UHF connectors are the weakest link on these antennas and usually short out long before the stock gamma. The stock gamma can handle 2kw continuous but, that doesn't mean it can handle more peak. The issue here is the breakdown voltage and you only have to reach it for a fraction of a second for an arc to punch through the insulator.

Replace both UHF connectors with Teflon insulated SO-239's. Solder an eye connector to the back of the SO-239's, so you can use a screw, washer and nut to attach a Maco 5kw Teflon insulated gamma match. Use GE clear silicon II, to seal the back side of the connector. This will meet your requirements.

 

[HomerBB]

I've used PEX tubing for gamma insulators, but have never run high power. What say you guys..?

 

[TheRealPorkchop]

You should beware that the stock UHF connectors are the weakest link on these antennas and usually short out long before the stock gamma. The stock gamma can handle 2kw continuous but, that doesn't mean it can handle more peak. The issue here is the breakdown voltage and you only have to reach it for a fraction of a second for an arc to punch through the insulator.

Replace both UHF connectors with Teflon insulated SO-239's. Solder an eye connector to the back of the SO-239's, so you can use a screw, washer and nut to attach a Maco 5kw Teflon insulated gamma match. Use GE clear silicon II, to seal the back side of the connector. This will meet your requirements.

So buy their 5kw gamma and mod it with Teflon, is that what you’re saying?

 

[Shockwave]

So buy their 5kw gamma and mod it with Teflon, is that what you’re saying?

The 5kw was Teflon last time I used one. So is the 10kw and Tom told me they have one even bigger now. Perhaps a 40?

The weak link is the stock antenna connectors with the stud that bolts to to gamma match. Inside the stock UHF connector there is an insulator and the gapping used here is the limiting factor. Replace those with quality Teflon insulated SO-230 connectors. The 10 kw model is supplied with a porcelain stand off insulator with a bolt that connects to "pigtails" on the cable, rather than a PL-259.

 

[Shockwave]

I've used PEX tubing for gamma insulators, but have never run high power. What say you guys..?

PEX breaks down when exposed to sunlight (UV) and has a low melting temperature. You also have to watch out for any color additive (black can be a problem) that may be conductive at RF. Test a piece you use in the microwave. If it does not melt or burn up, you know it has no conductive properties.

If you cover any exposed PEX with heat shrink tubing and run conservative power (it de-rates as frequency increases), you will probably not have any issue. How much it heats in the microwave will give an indication of its RF losses. Just because it gets warm at microwave frequencies, does not mean it will be useless at HF either.

 

[TheRealPorkchop]

The 5kw was Teflon last time I used one. So is the 10kw and Tom told me they have one even bigger now. Perhaps a 40?

The weak link is the stock antenna connectors with the stud that bolts to to gamma match. Inside the stock UHF connector there is an insulator and the gapping used here is the limiting factor. Replace those with quality Teflon insulated SO-230 connectors. The 10 kw model is supplied with a porcelain stand off insulator with a bolt that connects to "pigtails" on the cable, rather than a PL-259.

My idea of bright and shiny, you just knocked it right out of me. This is a better idea I gues and faster. Maybe I need to just pony up and get the 10kw version and be done with it.

 

[Dr_DX]

So buy their 5kw gamma and mod it with Teflon, is that what you’re saying?

https://www.gigaparts.com/so-239-bulkhead-connector-silver-teflon.html