Vector 4000 on 15m 20m

[siltronix_man]

I was curious to know if anyone had results using the vector 4000 on 15m and 20m with a tuner and how it worked out 73s

 

[Shockwave]

Unfortunately most gamma matched antennas have poor performance when operated well below the resonant frequency. As you go lower in frequency the capacitor in the gamma looks more and more like an open circuit to the RF. Antennas that are matched with an inductor like a 5/8 wave ground plane or Imax 2000 do a better job loading up out of band.

 

[mackmobile43]

Sounds like a guy would just need to break down and tune the gama and vertical length for the band being used and adjust height accordingly.

 

[Needle Bender]

...or run multiple gammas?

 

[hookedon6]

...or run multiple gammas?

you can't make a silk purse outta a pigs ear,..... use it where it is designed to operate^^ ab v c^^

 

[Marconi]

...or run multiple gammas?

I wonder how that would work?

 

[BOOTY MONSTER]

Unfortunately most gamma matched antennas have poor performance when operated well below the resonant frequency. As you go lower in frequency the capacitor in the gamma looks more and more like an open circuit to the RF. Antennas that are matched with an inductor like a 5/8 wave ground plane or Imax 2000 do a better job loading up out of band.

what if you tune the antenna for the lowest band used and then used the tuner to match it to higher frequencies ?

the multiple gamma idea is interesting too NB

 

[Needle Bender]

Thanks, but not my idea, I first saw multiple Gammas on a copper cactus:
144/220/440 J-pole

Where he had added 2 more gammas at the point 1/2 wave down from the top for each band.

 

[W5LZ]

Could using a tuner make that antenna 'work'? Yes, more than likely. But don't expect it to work well.
Multiple gammas? I really doubt it. Why not just adjust that gamma? That's basically what you would be doing with a tuner.
Or just get one of the 'Steppir' antennas? They do all that 'adjusting' stuff. Sit down before looking at their prices !
- 'Doc

 

[siltronix_man]

thanks all for your response i expected it to not be real efficent on 20 meters i went with the gap antenna 20 m monoband

 

[Shockwave]

Siltronix did the right thing buying a 20 meter antenna. The Sigma design just does not lend itself to multi band operation this far outside its tuned bandwidth. Multiple gammas would only improve the situation if they had independent feedlines. Otherwise both gammas would have their capacitance in parallel with each other and just look like one big gamma.

Then you're still dealing with a radiator that is not going to be resonant on 20. Not so big a deal until you consider how this antenna is different than most others. It heavily relies on the proper phasing of the currents on all of the radiator surfaces. If the first 1/4 wave of the main radiator is not shielded by the coaxial cone, the antenna functions like crap. Both the cone and main radiator must be the correct wavelength for the band in use.

The bandwidth here is about 10% (+5% or -5%) of the resonant frequency for the main radiator wavelength and about 20% (+10% or -10%) of the resonant frequency for the coaxial cone wavelength. Beyond this and the loss in gain is noticeable.