Discussion in 'General Technical Questions and Answers' started by KI4RVY, Jan 10, 2007.
I dont know about your pick of an antenna
I did just that. got 100 foot coming. Thanks.. Now I need this antenna thing settled
Sounds like a couple of folks got factory lemons from new. It happens. Every other review there was a High 5 rave. Mine works flawlessly for years and provides the 7 mhz bandwidth as advertised.
Belden 8214 USED to be the "Hot ticket" for VHF/UHF 30 or so years ago......... It is no longer considered any good at all for VHF/UHF. Times LMR-400 series is MUCH better. As already mentioned, LMR-600 is even better, And some good used Heliax is better yet.
A good way to buy coax is to get several club members, Or buddies together and go in and buy a 500 foot roll of coax. In such a quantity buy, LMR-400 can be had for around .60 cents per foot.......... (Plus shipping)
Belden 9913 series of coax had serious problems with SEVERAL of its versions..... NOT related to improper sealing methods.........
8214 still works acceptably except for the gang that has to have nothing but the best available.
i used 8214 on fast scan tv(439.25) years ago and had no problems with it.admittedly 9913 is better but it also has the problem of being too rigid to use with a rotating antenna.
a uhf antenna fed with rg/8 u is better than no antenna at all.
use what you have and upgrade when you can afford it.
i am currently using some mini rg/8 for 2 meters, not the best in the world but it does get enough rf to the antenna to work a fairly good range of repeaters.
Yeah, I used to use Belden 8214 for 432 many years ago also. Back then it was about the best available. A quick comparison between 8214 and LMR-400 with only a 50 foot length of coax will open up anyones eyes. My Bird wattmeter tells the truth. Close to HALF my signal on 432 is eaten up in the 8214. I thought I had a bad length of coax! So I tried some brand new 8214. Same story. (I dont care what those "paper" charts show. Try it in real life with connectors, etc)
Those who use obsolete lossy crappy coax have no idea how many signals they are missing out on
There is really no point to use Belden 8214 as Times LMR-400 is actually CHEAPER!
if you happen to have a chunk of 8214 and not much available in the budget for new coax, what would you do ?
stay off the air until you could afford the new coax or use what you have until you can upgrade to the better feedline?
i would choose to go on the air.
why do you need an antenna with a 7 mhz bandwidth on a band that is only 4 mhz wide to begin with ?
an even more interesting question is how did you determine the bandwidth of the antenna ?
Although you weren't specifically directing your questions to me, I'll relate to you why I use wide-band antennas for some things on the Ham bands, and how I determine their bandwidth:
I like to have antennas with wide bandwidth simply for listening out-of-band on VHF/UHF. They usually perform better than a narrow-band antenna of similar gain & efficiency will - when listening out-of-band. For instance, my 2m/70cm mobile antenna's 1.5:1 bandwidth is 140-160/435-465 MHz. Although it isn't a high-gain antenna, it usually outperforms my higher gain, narrow-band mobile antennas on the NWS frequencies, and on Marine Band frequencies, for instance.
No mystery here - to determine bandwidth, I simply perform a simple swept-frequency s11 measurement on my antennas. No problem!
Joel - N0NCO
One must be careful when evaluating antenna bandwidth. A simple swept scattering parameter analysis, or sweeping the antenna for SWR vs. frequency, doesn't tell the whole story.
Resistive loss improves bandwidth while rendering an antenna inefficient. Sometimes, very inefficient.
For example, if you wire a 50 Ohm resistor in series with your antenna, and another 50 Ohm resistor in parallel with it, and those are perfect, non-reactive resistors, your SWR can never exceed 2:1, at any frequency. However, the antenna efficiency will stink.
The T2FD (terminated, tilted folded dipole) design commonly used by the military for HF comms is another example of a very lossy but very wide bandwidth antenna. It places a terminating resistance opposite the antenna feedpoint, so SWR can never be over 3:1 anywhere in the HF spectrum. But its efficiency can be as low as 10%.
A "rubber duckie" antenna can have enormously wide bandwidth by design, and is typically 10 dB down from a 1/4-wave resonant whip.
OTOH, a "Ringo Ranger" design has very narrow bandwidth because of the way it's matched: It's a 1/2-wave radiator (or a pair of stacked 1/2-waves) with a very high feedpoint resistance, matched down to 50 Ohms using a critically tapped autotransformer ("ring" at its base. That performs a great job of matching, but only over a very narrow bandwidth, because it's matching over 1000 Ohms down to 50 Ohms. However, although it's a narrowband match, it's very efficient and will run circles around some designs having greater bandwidth.
There's no real relationship between bandwidth and performance other than "too much" bandwidth is almost always a bad thing, and an indicator of system loss.