Yagi question.

[DXman]

Ok guys here is what is happening.

I have the antenna tuned for a set freq. by using a model program.
Everything is fine until it rains...then the resonating freq will then shift up the band as much as 225 KC's
Then when the antenna dries off, it drops back down to the original resonating freq.

This is quite a jump up the band, so I am really puzzled why it's going so high.

It's a 5 Maco.

 

[Marconi]

Larry when this happens what is going on at the original setup frequency when reported via your analyzer. I guess you are seeing this change with an in line meter, right?

I also guess you believe you are getting water inside the gamma. If so, you might have to drill a small weep hole in the bottom end of the rod to let water out if that is the case. I have severl antennas with gamma and we get lots of rain here at times and I have never had such a problem. Most of my gammas are Maco.

That sure is a fine looking animal in your avatar.

Good luck.

 

[DXman]

Yes Eddie, I am reading it with the 259 and I was thinking along the same lines as you mention...water getting into the gamma match!

Just wasn't positive that this could be the problem, so I guess when it comes down in another month I will have to take a good look at it.

"Auroral activity is taking place tonight in the Northern states"

Thanks

 

[Master Chief]

One more reason why gammas are the third or forth choice for impedance matching!

 

[Marconi]

Hey MC, the problem Larry has is not a regular problem with gammas in general. You know that stuff happens from time to time. Larry has been working his stuff for some years now and I believe he is just now experiencing this problem. Even though his problem is likely related to water in the matcher, nobody including Larry really knows at this point what his problem is.

It is just like the problem I have with my I-10K when it rains. The antenna makes so much precipitation noise that you cannot hear even an S9 signal. I understand that I may be the only one with this I-10K problem, so I don't consider it a problem with Jay's tuner design or effectiveness. It is just a fluke situation for me.

All kidding aside and whether my hype about my 1/4 wave and if it will ever outperform a well designed antenna like Jay's I-10K or not, could you tell me just how much difference there is between the matching device you prefer and a good gamma device in some value we can understand, maybe in S-units.

Me too, Highlander821.

 

[Highlander_821]

I seriously doubt whether the difference between a gamma and any superior matching devices used for Yagi antennas will be measurable with S-units.

 

[Master Chief]

could you tell me just how much difference there is between the matching device you prefer and a good gamma device in some value we can understand, maybe in S-units.

No, or should I say, not at this time.

I like the beta match and have for a long time! Hy-Gain has used this for years. DX Engineering sells beta match kits for upgrading beams.

Next favorite is the T-match. While some say it is like a gamma, it's not. Its a balanced matching network and not a capacitor. Like the beta match, it makes an electrical connection to the driven element. M2 has been very successful with this matching network.

It has been proven by others that the gamma match, by design, exhibits more loss than the two listed above. The gamma match also skews the pattern of the driven element.

Someday I will do my own tests and even take near field tests. For now, I'm going with my gut based on what I've read and heard from those who know way more than me.

The major antenna manufacturers actually design antennas in the UHF band and higher to test their theorys. The antennas are small and easy to test at different wavelengths from the ground. A small test range is also manageable. Once the antenna results are consistant and repeatable they scale it down to the desired frequencies and re-test. My tests will consist of building a simple single element dipole, probably on the MURS frequencies. Then I'll build the three feedpoint matching networks above and take some near field tests.

If the gamma was the cat's meow, the majors would be using them. They are not. Even Cushcrap went from gammas to T-match networks on the VHF/UHF antennas.

The gamma works; other networks work better!

 

[Highlander_821]

could you tell me just how much difference there is between the matching device you prefer and a good gamma device in some value we can understand, maybe in S-units.

The gamma works; other networks work better!

But, all other factors being equal, would the difference at the RX end be measurable in S-units? DBm? uV?

 

[Marconi]

You know 821, MC may have a point and testing should shed some light on the subject, but it would seem to me someone would had done the definitive testing by now, doesn't it? Is it because the testing is so lacking in determining these type of results, and that manufactures do things in order to just be different, hoping to make a market with style differences in mind?

Personally I like the non-grounded antennas for the possible RX advantages they can exhibit. I tend to think balanced antennas that are not effectively attached to the earth hear a bit better than those that are effectively grounded.

 

[Master Chief]

But, all other factors being equal, would the difference at the RX end be measurable in S-units? DBm? uV?

I don't know. You should be able to measure it in uV and convert it to DB per meter and finally S-units. What I do know is that the more energy you get into the radiating element, the more energy it throws out on the air. Don't tell anyone, but this is the secret of the I-10K! The lower loss feedpoint gets more energy into the air and THIS is why it works better. 8)

.....it would seem to me someone would had done the definitive testing by now, doesn't it? Is it because the testing is so lacking in determining these type of results, and that manufactures do things in order to just be different, hoping to make a market with style differences in mind?

I think the manufacturers use what WORKS. I know Mike Staal (The brains behind M2 and "M" in KLM) has done a lot of testing on feedpoints; we've discussed them. Because they understand that a good feedpoint will make or break an antenna, I believe they keep these secrets to themselves rather than giving then away to their competition. IMHO!