Antenna feedline options/advice?

[KF7QLP]

Hi everyone --

I'm a new ham, interested in improving my antenna. I'm using one of the little Wouxun HTs on 2M/440. I thought of a couple options and am soliciting advice. First, I'm thinking the antenna will be one of the Slim-Jim units. I starting down this path thinking I'd solder up a j-pole, but if Joe wants to chase down the materials and do the work for $20-25, I'm inclined to let him. http://www.n9tax.com/Slim Jim Info.html

Some options --

o My initial plan for mounting was to extend a short mast up from the peak of my roof, putting the base at about 25' elevation. That would require about 50' of feedline to get to my office. Found a chart showing RG-58 loses 12-14 dB / 100' http://www.rfcafe.com/references/ele...coax-chart.htm. Seems a shame to buy a few more dB with a better antenna and elevation, then give it back in the feedline.

o What do people typically use to avoid the losses? (Move the radio closer to the antenna, thought of that, and maybe in the future, but not now.) What's a *practical* alternative to RG-58 for lower loss?

o Another alternative was to move the antenna closer to the radio. It occurred to me I could mount the antenna in the house attic. I'd give up 15' of elevation, the antenna base being at about 10' this way, and the antenna would be hung among the wood trusses and shining through a cedar shake roof. But the feedline would be < 10' in this arrangement.

Thanks for any advice and suggestions,

Benton 24jul11
KF7QLP

[K9KJM]

Yes, Feed line loss needs to be watched at VHF/UHF. Keep whatever feedline you end up with as short as possible. A quality RG8X type like Belden can be run to 25 or so feet no problem, Full size RG8 types usually to 40 or so feet, And a good coax to get is some TIMES LMR 400. Good to 75 or so feet anyhow for normal uses, And is only .79 cents a foot from places like Texas Towers.
http://www.texastowers.com/times_lmr.htm

(If running to a small hand held radio, It is a good idea to change over to a very flexible small size coax for the final few feet so you do not have the stiff coax connected to the radio.)

Those folks who proclaim how they run lots longer coax lengths with small or crappy lossy coax also have NO IDEA how many signals they are missing out on!

[KF7QLP]

Thanks for the reply, K9KJM. Good info about the different flavors of coax available and tradeoffs.

Thought I'd re-warm this thread with a follow-up question: I've concluded I'll mount the 2M/440 j-pole mentioned previously in my attic, with the simplified mechanics of getting the job *done* trumping cost, feedline attenuation, stealth, etc. In another thread someone mentioned, for that situation, the emission was all from the fed end of the antenna, nothing was coming off the far end.

It occurred to me to wonder, is that true for all antenna types? True for the j-pole I'm planning? I'd have thought the emission would be distributed along the length of the antenna... I thought if the emission is biased towards the fed end, I could hang it "up side down" and gain a few feet of elevation at the cost of a few more feet of feedline. Thoughts?


Also, had an epiphany after reading another thread, regarding the longevity of RF connectors and went to confirm with one of the guys I work with. The issue is that the Wouxon HT has an SMA connector in the top and neither the stock, stub antenna nor their SMA-BNC adapter have provision to insert the fitting, then spin on a nut. The center pin rotates as the connector is joined. Friend confirmed that this particularly accelerates the wear on the connection, with higher frequencies hit first, but even down to the 440 MHz range, after several hundred to a thousand connections. I had been swapping antennas back and forth a couple times a day, but have backed way off and am trying to figure out how to add a base-station and/or mobile radio to the inventory, so I don't *have* to swap antennas so much.

Benton
KF7QLP

[K8JD]

In another thread someone mentioned, for that situation, the emission was all from the fed end of the antenna, nothing was coming off the far end.

It occurred to me to wonder, is that true for all antenna types? True for the j-pole I'm planning? I'd have thought the emission would be distributed along the length of the antenna...
Benton
KF7QLP

YOU SHOULD get some Antenna books or better yet get the big ARRL radio handbook and read the section on antenna theory !
It's a fact that the current and voltage varies along an antenna conductor and the low Z point, where we attach coax, has a maximum current and minimum voltage and a quarterwave away from there is the maximum voltage and minimum current (this is a high Z point). The highest radiation is from where the highest current flows.
Get that book ! Read all about radio ! It's an amazing story !

[WB2WIK]

Thanks for the reply, K9KJM. Good info about the different flavors of coax available and tradeoffs.

Thought I'd re-warm this thread with a follow-up question: I've concluded I'll mount the 2M/440 j-pole mentioned previously in my attic, with the simplified mechanics of getting the job *done* trumping cost, feedline attenuation, stealth, etc. In another thread someone mentioned, for that situation, the emission was all from the fed end of the antenna, nothing was coming off the far end.

The j-pole is an end-fed 1/2-wave with respect to its radiation pattern, and the current maximum is near the center. Most of the "radiation" occurs from that point and not either end.

It occurred to me to wonder, is that true for all antenna types? True for the j-pole I'm planning?

No, it's as described above.

I'd have thought the emission would be distributed along the length of the antenna... I thought if the emission is biased towards the fed end, I could hang it "up side down" and gain a few feet of elevation at the cost of a few more feet of feedline. Thoughts?

You have no need to do that; however for antennas that are current-fed as many are, where the current maximum as at the feedpoint, you still wouldn't want to install one upside down unless you could run the coax "straight up" and away from the antenna for a long distance, to prevent it coupling to the antenna itself. That's usually impractical, so it just isn't done.

Also, had an epiphany after reading another thread, regarding the longevity of RF connectors and went to confirm with one of the guys I work with. The issue is that the Wouxon HT has an SMA connector in the top and neither the stock, stub antenna nor their SMA-BNC adapter have provision to insert the fitting, then spin on a nut. The center pin rotates as the connector is joined. Friend confirmed that this particularly accelerates the wear on the connection, with higher frequencies hit first, but even down to the 440 MHz range, after several hundred to a thousand connections. I had been swapping antennas back and forth a couple times a day, but have backed way off and am trying to figure out how to add a base-station and/or mobile radio to the inventory, so I don't *have* to swap antennas so much.

HTs are mostly designed to be used with the small flexible whips they come with, or something very similar. Using a "bigger" antenna (in terms of performance) can cause the receivers to overload and suffer undesired intermodulation, desensitization and other bugaboos. Sometimes, not. Depends on your location and proximity to powerful sources of RF in the VHF-UHF spectrum. Hard to predict this until you try it. In any case the SMA is a poor choice for a connector to be frequently, repeatedly used and with most hand-helds the connector is actually "mounted to" a circuit board directly below the connector; straining that connection mechanically by using the connector a lot can eventually break the connection altogether.

[KD0CAC]

Steven or whoever , I had thought that maybe one could put wire , with a crimped eyelet connector under the SMA connection of the antenna , with the thought being of adding counter-poise ?
Steven could you elaborate on using a better antenna with an HT , would like not to damage a HT .
I have seen many use an HT in mobile , with mobile antenna .
Again just like to get ahead of the problems ?
Thanks John

[WB2WIK]

Steven or whoever , I had thought that maybe one could put wire , with a crimped eyelet connector under the SMA connection of the antenna , with the thought being of adding counter-poise ?
Steven could you elaborate on using a better antenna with an HT , would like not to damage a HT .
I have seen many use an HT in mobile , with mobile antenna .
Again just like to get ahead of the problems ?
Thanks John

Yes, the wire you're referring to is often called a "Tiger Tail." An example of how to build one is shown here: http://brainbender.blogspot.com/2007...und-plane.html

One made properly usually will extend the working range of a VHF hand held transceiver, without changing the original flexible whip antenna at all: This just supplements that.

HTs are use in mobile systems quite often. Some HTs have SMA connectors (some have other stuff -- in the "olden" days, most had BNC connectors and a few had TNC connectors; some had "mini-UHF" connectors, etc), and for the ones having SMAs it's strongly recommended to use a short, very flexible coax extension plugged into the hand-held's SMA and just "left there," then using that as an extension to plug in mobile whip feedlines, home station antenna feedlines, or whatever. This way, you're not stressing or repeatedly using the SMA on the hand held, at all.

[KD0CAC]

Thanks for the link .
I have a light weight small adapter coax for connecting the HT to other antennas / coax .
Also you mentioned cause damage etc.
" Using a "bigger" antenna (in terms of performance) can cause the receivers to overload and suffer undesired intermodulation, desensitization and other bugaboos. "
I would like to understand what could happen better , anything else would be appreciated .
Thanks again

[WB2WIK]

Thanks for the link .
I have a light weight small adapter coax for connecting the HT to other antennas / coax .
Also you mentioned cause damage etc.
" Using a "bigger" antenna (in terms of performance) can cause the receivers to overload and suffer undesired intermodulation, desensitization and other bugaboos. "
I would like to understand what could happen better , anything else would be appreciated .
Thanks again

Try it and see! No way to predict this.