J-pole with a gamma match ???what's that all about

[Marconi]

You have seen one before Eddie, a sigma4 is a 3 leg variant,

heres what one ex avanti employee said about the gamma fed j-pole,

"The gamma fed J pole is probably the only correct way to feed the J and
reduce (not eliminate) feed and support radiation. Avanti Antennas
patented this idea back in the 70's

Dale W4OP"

I do seem to recall Dale telling us how he was connected, in some way, with Avanti back in the days. I don't remember exactly what he said however.

I'm not doubting that a J-Pole can't be fed with a gamma, I've just not seen one, except for the one that Dave8 posted above. I'm not finding any examples on the Internet either for the gamma fed J-Pole. I do see the idea as you describe for the S4/NV4k however. Maybe that helps explain a little about why Siro described their New Vector 4K antenna as a Coaxial J-Pole.

I also remember how some folks became all triggered-up by the idea that Sirio...referred to the New Vector 4K as a coaxial J-pole of all things.

 

[davev8]

link to manufacturer
https://radio-media-system.com/epag...hOAuuUNaB5vaF4rT1-52J4Ttl_AgDqK2DZnO3ztTrqaew

 

[davev8]

better photo from that link

 

[Marconi]

better photo from that link

Now that gives the image a fair shot as seeing more of the design. And, I always thought the stub was the tuning mechanism of choice.

Thanks dave8 for the link. Here is another link showing the dimensions and specs. Now we see the radiator is about 27.6' feet tall. Looks like a folded SlimJim 3/4 wave J-Pole that is extened straight rather than folding back.

So, Bob is right, it looks like a Vector with a gamma. The stub is still there, maybe this antenna works against that stub similar to how the center conductor and the radial basket have a tuning relationship.

Just my opinion on thinking about this.

https://ita-antennas.com/fr/cb27-mhz/120-intercontinentale-27dx.html

 

[Drifter]

 

[Marconi]

Drifter, I can't tell for sure, but that J-pole matching connection looks pretty conventional...a bit above the base IMO. Does not look like a gamma, if that is what you're suggesting.

The J-Pole looks to use some smart, effective brackets to Isolate the antenna form the mast however...and I like that feature.

 

[Shadetree Mechanic]

Looks like the short part is being fed?

 

[bob85]

it does have the coax shield connected to the long leg and its tapped up the stub at an elevated voltage point,

i see nothing smart about this j-pole,
its probably the worst of the commonly seen methods of building & feeding a j-pole,

their jazzy models would likely not look great if they included the coax tapped up the stub with braid connected to the long leg, even if the mast is isolated on plastic stauff clamps.

https://www.w8ji.com/end-fed_vertical.htm

 

[sunbulls]

I’ll either continue making my own or I’ll buy from a time tested manufacture that takes pride in taking a few quality photos. This particular antenna is only interesting from a detective’s point of view, many potential buyers will shy away from their shoddy presentation. IMO they’re either deliberately trying to hide pertinent construction details or they need to at least find someone that isn’t so inept at taking photos.

 

[Marconi]

SmarTech: https://www.smar.com/en/

 

[davev8]

sooo will having the feed point viar the gamer match being in a different place change the charastics of the antenna? ..A normal j-pole i bleve is a 1/2 wave and the 1/4 wave U is used for matching and the 2 parallel 1/4 wave bits sort of cancel each other out like ladder line feeder do ..now it looks like its fed at the bottom of a 3/4 wave radiator and the remaining 1/4 stub probably does very little but with some coupling like a fan dipole or DX commander..so if its acting like a 3/4 wave the take off angel may have gone skywards so may not work as well as a J-pole fed normally

 

[Marconi]

sooo will having the feed point viar the gamer match being in a different place change the charastics of the antenna? ..A normal j-pole i bleve is a 1/2 wave and the 1/4 wave U is used for matching and the 2 parallel 1/4 wave bits sort of cancel each other out like ladder line feeder do ..now it looks like its fed at the bottom of a 3/4 wave radiator and the remaining 1/4 stub probably does very little but with some coupling like a fan dipole or DX commander..so if its acting like a 3/4 wave the take off angel may have gone skywards so may not work as well as a J-pole fed normally

Dave here is my model of the conventional J-Pole with a CMC choke that I added dimensions by the wires #'s 1-8.

I agree this antenna does tend to look like and end fed 3/4 wave radiator and that may help explain its very good performance...as long as only the antenna itself is doing the radiating and not from the feed line and conductive mast below.

I also removed the choke as an example of what can happen to the J-Ploe if the choke is left out.

The "L" inside a small black box, is the choking device sitting on the last segment of the 36' mast pipe right below the bottom of the antenna. With the choke added, the antenna performance results look remarkable good and the maximum gain and angle are among the best in the overlays I posted earlier, showing 4.45 dbi at 8* degrees maximum angle on the horizon.

Match and Bandwidth curve is also very good in this case.

The model characteristics pattern without any CMC choking is remarkably skewed...with very bad results as noted.

 

[Big Kahuna]

Technical sheet
Frequency band - Bands - Bandas 27 MHz
Elements diameter - Elements diameter 40 - 16 mm
Height - Height - Altura 8.4 m
Gain - Ganancia 4 dBi
Admissible power - Maximum power - Potencia máxima 2000 W PEP
Adjustment - Matching system - Adjustment system Gamma-match
Impedance - Impedance - Impedancia 50 ohms
Connector - Connector - Conector SO-239 (PL)
Wind resistance (without ice) - Wind survival (without ice) - Resistencia al Viento (sin hielo) 120 km / h
Weight - Weight - Peso 7 kg
Learn more


The INTERCONTINENTALE 27 is a J-pole on which a gamma-match has been grafted to facilitate the adjustment. It can be used in different ways; in high or low impedance, depending on the type of supply line: coaxial cable, twin-lead or "frog ladder". The total height of the antenna is 8.4 m and its weight is around 7 kg. The admissible power varies according to the type of supply. With the gamma-match, it accepts a power of 2000 W PEP while supplied “direct”, the maximum power will be that which the supply line can withstand at most, the tubes constituting the antenna accepting a power greater than this one. Works close to the ground.

For foolproof robustness, the tubes used have a thickness of 1.5 and 2 mm!

 

[Marconi]

Technical sheet
Frequency band - Bands - Bandas 27 MHz
Elements diameter - Elements diameter 40 - 16 mm
Height - Height - Altura 8.4 m
Gain - Ganancia 4 dBi
Admissible power - Maximum power - Potencia máxima 2000 W PEP
Adjustment - Matching system - Adjustment system Gamma-match
Impedance - Impedance - Impedancia 50 ohms
Connector - Connector - Conector SO-239 (PL)
Wind resistance (without ice) - Wind survival (without ice) - Resistencia al Viento (sin hielo) 120 km / h
Weight - Weight - Peso 7 kg
Learn more


The INTERCONTINENTALE 27 is a J-pole on which a gamma-match has been grafted to facilitate the adjustment. It can be used in different ways; in high or low impedance, depending on the type of supply line: coaxial cable, twin-lead or "frog ladder". The total height of the antenna is 8.4 m and its weight is around 7 kg. The admissible power varies according to the type of supply. With the gamma-match, it accepts a power of 2000 W PEP while supplied “direct”, the maximum power will be that which the supply line can withstand at most, the tubes constituting the antenna accepting a power greater than this one. Works close to the ground.

For foolproof robustness, the tubes used have a thickness of 1.5 and 2 mm!

Here is more details on the SmarTech J-pole.

https://www.antennas27.com/vertical-jpole

 

[Marconi]

BK, here is my J-Pole over a Perfect Earth Ground that produces a similar pattern as SmarTech shows in the link I posted for them above. I maked their poor image with a big "X".

I found nothing on the Bandas 27 MHz J-Pole antenna idea.