Any difference in NGP kit antenna's and regular antenna's?

[WagoneerSX4]

Sorry for another question that probably seems really straight forward, but nobody can give me a straight answer. Are there any difference in the firestik antennas that come in the NGP kits compared to just a regular firestick fiberglass antenna? I'd like to swap out my 3' antenna for a 2' antenna (getting sick of smacking the thing every time I go into my garage or smacking pipes in my underground parking at work) and I'm trying to figure out if I can just replace it with a regular 2' antenna.

Here are the reasons for my confusion. The antenna that came in my NGP kit doesn't have a part number, just the entire kit has a part number. And on the kit itself it says very plainly that I cannot modify the length of the coax cable or use a different antenna with the cable. This makes sense, but the antenna part doesn't. I compared my 3' antenna with a friend's 7' firestick antenna and everything looks identical, right down to the tunable tip (and obviously the actual antenna wire isn't wound as tightly as my 3').

So is there anything stopping me from just swapping my 3' out with a 2' and retuning the SWR's and calling it a day? I've emailed firestik with no response, I haven't tried to call yet though.

I'm sure the difference in the NGP kit is only the coax cable and not the antenna's, I just want to make sure.

TIA

 

[DaveInDenver]

I assume we're talking CB.

I can't say for sure about Firestik but in general when an antenna is called ground plane independent or no ground plane it means that it's electrically 1/2λ and doesn't rely on a counterpoise to radiate.

That counterpoise on 1/4λ, 5/8λ and most other antennas is the car body, the Earth, wire radials, etc. The return of the circuit relies on a correct impedance path to work. The 1/2λ monopole antenna is a unique configuration as it radiates without needing the counterpoise. It comes with a major obstacle though, it is VERY high impedance, 2kΩ and higher. Since your radio expects 50Ω this presents a problem, so a matching network is built into the antenna to match the 50Ω to 2kΩ to keep everything happy. The reason you would chose not to use a 1/2λ is the matching network itself is lossy, so it's less efficient than other types of antennas.

The reason I caveat that Firestik might not be the same is they always tell people to use a particular length of coax. With a correctly built and tuned antenna the length of the coax will make no difference. So it's possible they are using the coax shield as the antenna's counterpoise on purpose. This can work sort of but is a poor way to make it work. When this happens to hams we usually consider it a defective installation and try to eliminate it. We deal with a lot more power and interference can cause major headaches, though. There are times when you might do it intentionally, J-poles, Zeppelin antennas, etc., but they are special cases. You generally never, ever want RF current flowing on the shield of your coax and we tend to put chokes and baluns everywhere to prevent it from happening.

But in fairness when you do this you don't technically need a true 1/2λ antenna nor would you really need a matching network. The downside is the antenna system is going to work poorly and you will likely cause a lot more interference inside the vehicle.

Short answer is that with most installations you can swap a 1/2λ for a 1/4λ or any other antenna and get a decent match. Not always ideal necessarily, but good enough. It might not be efficient but good antennas will have a matching networks built into them if the design requires one. If the antenna relies on the coax length to resonate then you cannot just swap antennas and expect it to work right.

You can't really tell that by looking at a wound fiberglass whip. The whole whip is an inductor and the spacing and the number of winds changes what the antenna appears like electrically. You could measure the feed point impedance and try to infer if it's wound to be 1/4λ, 1/2λ or 5/8λ. If you have an antenna analyzer then swap them and see what it measures. Honestly, though, my guess is Firestik is just using the shield and it probably won't work any worse.

 

[Robert Bills]

What he said ^

Short answer:

Firestik NGP and "GP" antennas are different. They cannot be interchanged. Your options are: (1) get another NGP antenna to go with your NGP coax; or (2) replace your coax with high quality RG-58, properly ground your antenna mount, use your vehicle as your ground plane, and choose any length "regular" CB antenna that works for you.

 

[WagoneerSX4]

Thanks for the awesome answers once again guys. I'll keep searching for a shorter NGP antenna!

 

[4x4junkie]

Just a FYI, 2' antennas for 27MHz are extremely inefficient (and that's if you can even get a good SWR on it, they can be a lot more difficult to tune too). If you're concerned about hitting things overhead in your garage, what I would suggest instead is to get a quick-release or fold-down antenna mount, and run a 4' or longer antenna on that, then just remove/fold it down when you pull into the garage. This way you don't compromise the range of your station so much (the 4-watt output legal limitation is limiting enough already).

And agreed, a "GP" antenna almost universally works much better than a NGP ant. NGP antennas are mainly for specific situations where there isn't a metal vehicle body available to mount it on (a boat, and some RVs, for example).

 

[WagoneerSX4]

As a follow-up I finally got in contact with Firestik USA and they confirmed that yes they do have to replaced with their specific line of NGP antennas. Only problem is that they rarely sell these antennas seperately and are always sent out in their NGP kits. So it looks like my only option is buying directly from the factory.

I'm not really concerned about range or efficiency with my setup. The only time I use my CB is to communicate with friends who I'm driving with who are rarely ever more than 100ft apart from each other. A huge range was never really my intention or else I would never have gone with an NGP setup.

I have what is basically a quick-disconnect system right now. I just have my antenna hand-tightened on my spring and get out and remove it whenever I enter my garage or my underground parking at work. But getting out of the car every day to do that gets pretty old. Sacrificing some range so I don't ever have to do that again is worth it as I never reached the limits of range of my 3ft antenna when I was wheeling with friends. Actually I've been nothing but impressed with the range of this system thus far. I was even able to get the SWR's to under 2. Not to mention the 3ft antenna just howls like a banshee at anything over 80km/h. If the 2ft antenna is a little quieter because it's smaller that's just a bonus as well.