Stock Maco gamma vs off-the-shelf beta match CHALLENGE!

[DCAVALLARO]

CHALLANGE

Has anybody taken you up on this ?? besides the bird field strength meter are you using any other equipment such as Anritsu site master or the bird version ??

One thing about the hair pin and the like is you have to split the driven element thereby giving up some physical strength. A t-match is nothing but a dual Gamma but it does balance out the input which in the real world is not worth the expense.

the whole idea of trying to squeeze out an extra point db or 1 whole db is really pointless on the lower frequencies as you do not have to concern yourself with loss in connectors or adapters as we are talkin .01db maybe. Also the good old PL259 is not an impedence constant connector. Who know what the impedence is at any given frequency. That is why commercial antennas were using N connectors and are now using Din connectors. When you start seeing a CB or Ham antenna with N connectors then I will consider the other factors.

KC6ZWH HAM and PCIA certified tech.:bdh:

 

[Shadetree Mechanic]

Back from the dead....... someone buy me a beta match. Haha! That's too funny.

 

[Shockwave]

I've experimented with all of these matches and never noticed a change in signal. On the other hand, I did notice a reduction in common mode currents and elimination of pattern skewing when switching from a gamma match to a balanced T-Match.

 

[Marconi]

I've experimented with all of these matches and never noticed a change in signal. On the other hand, I did notice a reduction in common mode currents and elimination of pattern skewing when switching from a gamma match to a balanced T-Match.

Donald are you telling us these antennas had no chokes or other devices to help eliminate CMC's on the feed lines for the Gamma Match and the other two balanced setups, the T-Match, the Beta Match, that you experimented with?

 

[Shockwave]

Donald are you telling us these antennas had no chokes or other devices to help eliminate CMC's on the feed lines for the Gamma Match and the other two balanced setups, the T-Match, the Beta Match, that you experimented with?

Hi Marconi,

All three of the matching networks were tested with a piece of LMR-400 that had a foot of 1 inch OD ferrite beads on the antenna end of the cable. I'm pretty sure the mix was type 61. Prior to switching out to the T-Match, I had been able to monitor the station signal with my scope using about 3 turns of wire around the coax in the shack. After the installation of the T-Match, my local AM radio station was placing more RF on the braid of the coax than my own transmitter.

The Beta Match seemed just as dependent on having a good balun as a directly fed element. The thing I like most about the T-Match is that it feeds both sides of the driven element with the required 180 degree phase offset through a 1/2 wavelength of coax. This allows the element to be driven perfectly symmetrical without forcing common mode currents down the coax.

These tests were done on a 2 element horizontal yagi and the results so far, were exactly what I expected. What wasn't expected was the amount of pattern skewing that was taking place with the standard Gamma Match. Without having any director elements, the pattern pulled noticeably towards the side of the gamma match. I didn't think to take the same pattern skew test with the Beta Match so I can't comment on that aspect.

Adding director elements to the Gamma fed Yagi tends to hide this pattern skewing. That is because these elements are parasitically excited and perfectly symmetrical. That does not mean the same problem doesn't exist in larger Yagi antennas that are Gamma fed. Their driven element is still not firing inline with the rest, the problem is just buried behind other elements that don't have the same asymmetrical problem.

Since experimenting with the T-Match, I'll never use another match for a Yagi when the priorities are efficiency with the least amount of CMC and the most power handling capacity. Don't use the old school T-Match that adds a second Gamma match. Use the high efficiency UHF method where you extend the small diameter T-Bars much longer than a Gamma. They end up being about 2/3 the length of the driven element they hang below.

The advantages this offers is you remove any insulators in the Gamma Matches. The only insulator used on the entire antenna is in the RF connector. This makes the antenna "DC grounded" to eliminate static buildup and reduce lightning damage. It will also handle anything your transmission line can deliver.

 

[Shockwave]

Donald are you telling us these antennas had no chokes or other devices to help eliminate CMC's on the feed lines for the Gamma Match and the other two balanced setups, the T-Match, the Beta Match, that you experimented with?

The shorter story is, the T-Match showed the least CMC. The Gamma match was next in line while the Beta Match has the most CMC without a balun. The CMC problems with a Beta Match can be drastically reduced with a balun but your results are entirely dependent on how effective that balun is. You don't even have to be concerned about that with the T-Match. All three were tested with the ferrite balun described above but the T-Match still showed the least CMC because it was not dependent on the balun to achieve that result.

 

[Marconi]

And there seemed to be a bit of confusion so let me add that the arrangement of the elements on the boom will be IDENTICAL. Front to back, rejection and forward gain is not the issue here. ONLY THE FEEDPOINT! Please keep to the subject at hand.

Donald, thanks for your comments.

When Shade Tree revived this old thread, I was reminded that I had done some models to see what modeling might suggest about MC's ideas.

About the only thing I found back then was these matching devices seem to all require different driven element lengths and maybe a difference in spacing. I also found the two balanced models seemed to need something more than just a matcher...in order to get the low value for R up closer to 50 OHMs.

Then MC revised his challenge with his comments above. So, I never posted my models when he narrowed the challenge down to the simple result, "ONLY THE FEEDPOINT!" Please keep to the subject at hand.

 

[Shadetree Mechanic]

Sounds like if the antenna came with a gamma match then there is more work needed than just putting the T match on?

 

[Shockwave]

Sounds like if the antenna came with a gamma match then there is more work needed than just putting the T match on?

Adjusting the element length is only required when going from Gamma to Beta because the Beta adds length in the center of the element. That is not required when going from Gamma to T-Match. I've installed the T-Match on both an M-104 and M-105 without having to change any stock element length or spacing.

 

[Marconi]

Don't use the old school T-Match that adds a second Gamma match. Use the high efficiency UHF method where you extend the small diameter T-Bars much longer than a Gamma. They end up being about 2/3 the length of the driven element they hang below.

Donald, I don't find much useful information on the Internet about this design and what I do find is very technical. I would like to try and model this one on my M-104C model, and then try it on this M103 noted in this thread.

If the T-Match is just wires, do you happen to have the details and dimensions? If it is frequency sensitive what was the frequency you used. I can scale my model to my frequency of choice.

 

[Shockwave]

Donald, I don't find much useful information on the Internet about this design and what I do find is very technical. I would like to try and model this one on my M-104C model, and then try it on this M103 noted in this thread.

If the T-Match is just wires, do you happen to have the details and dimensions? If it is frequency sensitive what was the frequency you used. I can scale my model to my frequency of choice.

The T-Bars are small diameter aluminum tubing. I used 3/8 and 1/4 inch so that it was telescopically adjustable. The ratio of diameter between the driven element and T-Bars effects the impedance transformation. I only saved measurements from the M-104 and it was different from the 2 element and the M-105. On the 4 element each side of the T-Bar was 67-3/8 inches long with the shorting strap placed 35 inches away from the center on both sides. The M-105 required T-Bars that were about a foot longer (from memory).

 

[Mr Clean]

I had a friend who went from a imax to a penatrator antenna and lost some gain talking to people 60 miles or so from here. The problem was there were some hills between them and the penatrator had a lower take off. This has nothing to do with matches but can tell why some antennas talk better local with less gain. There is no perfect antenna for all situations and a quarter wave may do better sometimes local.