HFU HF Underground
General Category => Amateur Radio => Topic started by: Matt285 on January 28, 2020, 1323 UTC
-
So I bought a fake 'Nagoya' HT antenna. It is approx 14.5'' long compared to my stock antenna which is approx 8'' in length. However the shorter stock antenna out performs the new longer one? I decided to dissect it this morning thinking for sure there a broken soldering joint etc. No signs of anything. One thing I noticed is that the ground is used for the radiator. I would have thought the center feed line would be used for this? I just don't understand how something this simple could be screwed up. It would seem to me that you would find a length of wire that is resonant on 2m/440 and attach it.
-
Correction. After some continuity testing I've found that the center conductor is used. Still don't know why this thing performs so terrible though.
-
Correction. After some continuity testing I've found that the center conductor is used. Still don't know why this thing performs so terrible though.
Because it is made in China?
-
Ha, yes it is made in China, but it's a very simple concept. The construction actually wasn't too bad inside. I'm thinking that it's possible a improper measurement and that High VSWR power fold-back may be a factor.
-
So, as said I dissected the antenna and broke it down to the soldering points. Everything looked OK. I soldered the connections in a couple of different new points of contact and glued back together. Did a test of 15 repeaters on 2m/440 and the stock antenna still outperformed the knock off longer antenna. Conclusion- Buy name brand from reputable sources.... Still can't quite explain though?
-
It's the wrong length.
Str.
-
Yes. I tend to agree.
-
Indeed, that wasn't too difficult to work out!
VNA's are super cheap now and anyone with the remotest interest in anything RF should buy one.
Str.
-
I've been playing with my NanoVNA and all my HT antennas (close to 50 of them). Many, even some brand name stock antennas, are not resonant where they should be. I did testing in "free space" and close to my head as it would be in normal use. Many are designed to be resonant next to your head, btw.
I took a few of the cheap Chinese knock off antennas that I picked up for 10 for $10 and most were way off. Using a heat gun I removed the top plastic cap and started trimming the whip. In almost all cases the whip was too long and the 2m antennas were resonating in the 138-142 MHz range. After trimming performance was equivalent to other whips of comparable length.
Since a $1 antenna can be made to perform as well as a $15-20 one using the NanoVNA, I am quickly recouping my investment in this test device. 😁
-
KX4O works as an antenna engineer. You may find his comments helpful.
https://www.hamradio.me/antennas/ht-antenna-comparisons.html
-
Im glad I didn't throw it in the trash yet. It will be a great first experiment for my Nano VNA that on its way.