directional gainmasters

[bob85]

What is going on with gainmasters directivity.

two locals have noticed that twisting the pole their gainmasters are mounted on so that the coax connector faces the other station causes signals to increase, & decrease if you twist it 180degrees,

both are mounted on poles that don't reach the ground 20ft & 10ft,

could cmc on the feedline be getting shielded by the pole ?
could the stub hung down the side of the radiator be effecting the pattern ?

i can't think of anything else that could cause the assymetry in pattern.

 

[Jay Mojave]

Hello Bob: Wow really. How many S-Units was the change when the Gain Master was rotated? If it was just a needles with no biggie, but if it was more do tell. Yeah I would vote for the matching stub radiating causing a pattern difference. But I have been proven wrong several times by hands on measurements.

Jay in the Great Mojave Desert.... "Next Gas 150 Miles"

 

[bob85]

Hello jay,
one guy said my signal went up almost 1 s-unit on his icom7600,
he twisted it one way yesterday & noticed i dropped & a station in the direction of the coax connector went up in signal, then back towards me today & the signals reversed,

the other guy also uses a ic7600 & claims his is directional too, he turns it for best signal towards a guy in bradford about 15 miles from him.

im not familiar with the 7600 meter response to know if that's significant or hardly anything,

if it was 1 s-unit on my jrc meter it would be the equivalent of doubling your tx power.


i see some directivity from the astroplane but that's explained in the lob sided pattern avanti claim and what eznec shows,

i did not expect a gainmaster to be acting the same way..

 

[sp5it]

Yes, 2 vertical antennas with proper spacing will give effect like you said.
Google for "Christman phasing". It gives very good results.
Mike

 

[bob85]

spit5,
these guys are rotating a single unmodified vertical gain-master with no other cb antennas within 1/4mile radius and noting a change in signal that favoures the direction the coax faces.

just thought i would mention it to see if anybody else has noticed the effect or has any theory other than what i posted above as a likely cause,

i have no idea how much of a change 1 s-unit is on an ic7600.

 

[sp5it]

Sorry Bob, English is not my native.
It is really weird if antenna act that way when rotated.
We can assume, that it transmits the same way it receives. I would take field strength meter and measure RF field let's say 100m from antenna during antenna rotating.
Mike

 

[314]

Last year when I put up my sirio 2016, I raise and lower depending on how the wind is that day. So my coax going into the antenna ends up in a different direction alot, I also thought I noticed something funny, but I did have a lot of beer on the menu. Might have to do some testing with no beer this time.

 

[Marconi]

if it was 1 s-unit on my jrc meter it would be the equivalent of doubling your tx power.

Bob, that sounds really unusual. Would you call that a stingy meter or is it the other way...super sensitive?

How does it compare with other radios you have?

I seldom took much note when other guys reported to me what my signal was on their end. I saw way too often that such reports were no where close to what I was seeing on my end of the contact, and I sure couldn't explain that. That is why I mostly recorded only receive signals.

i see some directivity from the astroplane but that's explained in the lob sided pattern avanti claim and what eznec shows,

I did some models that tried to see change in my A/P models when I put the radiator and top hat in the middle of the support bracket. This will be recollections however. I didn't see much difference in gain but I think the elevation pattern got skewed a bit more. I figured that was because the radiating dipole was no longer in a straight line. That surprised me.

I also eliminated the isolation at the bottom of the mast inside the radials and a 1/4 wave below. I placed a simulated choke at the same point where the isolation was. Don't exactly remember the results, but that probably did not work out so well. So, then I raised the whole antenna a few inches above the ground and isolated it at the base. I recall that made a nice improvement, albeit there was no feed line on the model. I also left the simulated choke where it was in that case. I'll have to check these ideas over and get back.

i did not expect a gainmaster to be acting the same way..

That is strange Bob.

I seldom hear anybody talking about their GM any more. I think mine was hit by a nearby lightening strike shortly before I went into the hospital the last time. I say that because it was not blown to bits, with nothing left, like my old Big Stick in a tall Pine Tree years earlier that is probably still flying around.

 

[314]

The one thing I did notice the most that I do remember is, if my coax going into the antenna was facing my direction, I'd hear a lot more noise, and I'd come thru my tv..Face it the other direction or away from me just a little and it would go away

 

[Mark Malcomb]

Wow after all this info, I ran home from work and spun my GM 180
degrees. Damn I didnt get any improvement. Damn I was excited. Thanks guys...MM

 

[Mudfoot]

I'll spin mine.

 

[bob85]

Eddie my old jrc meter is stingy vs a typical cb,

people still talk about gain-masters here but not in the same way they did when they first came out,

the game is up for 5/8 gain-masters pronounced "GAYMASTERS" in this area,
the honeymoon is over.

the last GM that went up was on a popular ch19 gateway & did not last more than a week because of vswr rising with the high duty cycle of gateway use at way below rated power,

they break in wind far too easy & won't handle more than about 200w for long overs on uk FM,

the 1/2wave version is a bit stronger & handles more power in the real world.

 

[loosecannon]

i like the stationary field strength meter idea.

put it far enough away to get a mid scale reading, then spin the antenna around while TXing.

are both of these antennas mounted on metal poles?

what if you wrap the coax around the mounting pole?
circular polarization??? JK

also Bob, which direction should the broad face of the top mounting bracket for the astroplane face for maximum east west communication?
LC

 

[Marconi]

Bob, I was always impressed with the performance of my GM and it lasted over 2 years without a problem...except for lightening taking it out of commission.

I don't recall any of the Texas operators in my area even knowing about this antenna. I also don't remember anybody ever reporting on the Internet or this forum about the 1/2 wave version either. Good ideas maybe, but apparently wasn't made to last.

I really like the Eznec pattern it made that seemed to me to improve the 5/8 wave into a full length constructive radiator instead of the bottom 1/8 wave portion being out of phase with the top portion.

IMO, it seems they're very few CB OPs that would even consider a 1/2 wave vertical antenna...with all the hype about high gain antennas being discussed as the only way to go.

 

[Mudfoot]

Mines pushing 5-6 years or more. Don't remember when I bought it. Still working great and has survived a few high wind events. Guzzles 500-600 watts NP. I'll replace it with something else when it craps.