Posted: 5/18/2010 5:44:21 AM EDT
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I'd really like to have another option for my 2-meter handheld radio concerning antennas. I've currently got a quarter wave antenna on the handheld (the rubber duck has long been lost). It works great in most cases , but some times getting the antenna up higher would be a good thing. So, I would like to build a J-Pole antenna out of twin lead (which I've known plenty of people to do). However, I was curious how long I could make the coax lead from the radio to the antenna? Ultimately, I'd like to be able to have the antenna for a survival type situation, using fishing line to be able to hoist it up in a tree or such (20-30ft high). Most of the online guides I've seen say to keep the coax lead to 6ft or less, otherwise it ads noise to the signal and becomes useless. If there was a way to have a longer line , it'd be good ,as then using the twin lead for the antenna itself, would be entirely flexible and could be stored in a small container. Thanks :) |
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your not going to notice the difference in loss between 6ft and 12ft. yeah, there is some loss but not that much. the better feed line you use the less loss there will be.
here is a loss calculator to figure out what your loss will be at any given freq. with options for the type of line as well as the length of the run. http://www.timesmicrowave.com/cgi-bin/calculate.pl |
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Every foot of additional height is worth more than the loss of the coax getting there.
Don't bother making a roll up J-pole (or it's 1st cousin, the Slim Jim). These are well made, you can't make one yourself any cheaper: Review of the N9TAX Slim Jim: http://www.hamuniverse.com/n9taxslimjimreview.html Buy here, 2 meter only, 2 m / 70 cm, with or without coax, and your choice of connectors: http://www.2wayelectronix.com/ |
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Quoted: I just bought the dual channel slim jim after I priced out everything I'd need to build just 1 freq j-pole. Really good value IMHO. Hopefully it will be here by the weekend. Every foot of additional height is worth more than the loss of the coax getting there. Don't bother making a roll up J-pole (or it's 1st cousin, the Slim Jim). These are well made, you can't make one yourself any cheaper: Review of the N9TAX Slim Jim: http://www.hamuniverse.com/n9taxslimjimreview.html Buy here, 2 meter only, 2 m / 70 cm, with or without coax, and your choice of connectors: http://www.2wayelectronix.com/ |
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Quoted: Quoted: I just bought the dual channel slim jim after I priced out everything I'd need to build just 1 freq j-pole. Really good value IMHO. Hopefully it will be here by the weekend. Every foot of additional height is worth more than the loss of the coax getting there. Don't bother making a roll up J-pole (or it's 1st cousin, the Slim Jim). These are well made, you can't make one yourself any cheaper: Review of the N9TAX Slim Jim: http://www.hamuniverse.com/n9taxslimjimreview.html Buy here, 2 meter only, 2 m / 70 cm, with or without coax, and your choice of connectors: http://www.2wayelectronix.com/ Yeah , that's a darn good price, I might go with them anyways, I had some twin lead laying around here somewhere that someone had given it to me. Thanks also for the loss calculator as well, really I want to be able to get it as high as the tallest tree I can find. I happen to have a few trees in my area that are around 50ft high , so I'm curious if the loss will be worth it. We have some hills in my area, as we're on a big east/west divide, with the east side of the county being hilly, as it sort of starts into the Appalachian foothills and only gets worse, then on the west side of the county it starts to get extremely flat. I can hit a repeater approx 50mi away w/ my current quarter-wave solution on the handheld, but would really like something more for survival type situations (As the jpole would be for.) Now if I could find a way to use a external antenna with my cell phone , or use the cell phone for packet radio ,i'd have a very neat solution :) |
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Quoted:
Quoted:
I just bought the dual channel slim jim after I priced out everything I'd need to build just 1 freq j-pole. Really good value IMHO. Hopefully it will be here by the weekend.
Every foot of additional height is worth more than the loss of the coax getting there. Don't bother making a roll up J-pole (or it's 1st cousin, the Slim Jim). These are well made, you can't make one yourself any cheaper: Review of the N9TAX Slim Jim: http://www.hamuniverse.com/n9taxslimjimreview.html Buy here, 2 meter only, 2 m / 70 cm, with or without coax, and your choice of connectors: http://www.2wayelectronix.com/ Just looking at the photos those look very well put together, and as mentioned couldn't buy the stuff and make it yourself any cheaper. The only thing I'd suggest is a specific type of RG58 coax for these kind of things... Belden 8240. Just because it's very flexible and easy to work with for this kind of application. Don't worry about coax loss for the lengths of cable involved in something like this, even RG-174 type. If you plan on 50' - 100' of cable, then we'll talk cable losses. |
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I will second the N9TAX antenna. Got one and it works great on a 16' crappie pole. Also have the copper slim jim made of 1/2" copper pipe and get full-quieting reports all the time with it 12' up in a tree.
Copper Slim Jim Antenna |
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Quoted: I will second the N9TAX antenna. Got one and it works great on a 16' crappie pole. Also have the copper slim jim made of 1/2" copper pipe and get full-quieting reports all the time with it 12' up in a tree. Copper Slim Jim Antenna I know it's hard to judge, but how much better do you feel the signal is now that you've switched to the slim jim? |
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Both slim jims are a huge improvement over the ducky. I get great signal reports and clear comms with repeaters across the county. The advantage to the copper slim jim is it will probably be a little more durable than the wire one. I leave it up all the time and keep the N9TAX anteena rolled up in a backpack in my trunk. Don't think there is much, if any difference between the N9TAX and copper in use.
I use them both with a FT-60R and a Pryme speaker/MiC. It was just a big kick to sweat some pipe together, slap some coax on it and get really good signal reports! I built mine to the dimensions in the article above, however it doesn't look like theirs- their measurements were off. If you build it to their measurements the spacing between the sides will be 2 1/2 inches CTC. If you build one just shorten the little short spacers at the top and bottom from what they say. I run mine with a 1.5 inch air gap and the adjuster up 4 1/2 inches from the bottom of the antenna. SWR is 1:1 from 145.000 to 148.000. 1:4 at 144.000. Also I used PVC Tee's with a very short piece of PVC pipe to reinforce everything. I will try to get a picture up in bit. |
+2 for the N9TAX Slim Jim. I ordered mine with a BNC to fit my EmComm box and with an adapter my FT-60R HT. 
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Here is the overall pic
Closeup of the PVC Tees (you have to open them up with a drill) http://i19.photobucket.com/albums/b163/bduffel/DSC00372.jpg This is the spacing you'll get if you follow the directions and cut the short spacers to 1 3/4" per the directions. They probably should be 1 1/4" but it all works out once adjusted for low SWR. http://i19.photobucket.com/albums/b163/bduffel/DSC00373.jpg If I ever do another one I will increase the air gap and thread a couple of bolts into the caps to adjust the gap. |
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There's no benefit that I can discern to the extra loop of copper at the top. J poles made from twin lead are often made that way for mechanical reasons or ease of construction, but there's no signal or mechanical benefit to that for a copper pipe antenna. |
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Well , I was at my parents today digging through stuff, and found a Jpole :) I totally forgot someone had given me one made out of twinlead. The one thing is though , it's not a 'standard' connection (at least for my Icom) is there a easy way to identify what kind of connector it is (it has threads to screw into the antenna out of of a radio). |
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Quoted:
Well , I was at my parents today digging through stuff, and found a Jpole :) I totally forgot someone had given me one made out of twinlead. The one thing is though , it's not a 'standard' connection (at least for my Icom) is there a easy way to identify what kind of connector it is (it has threads to screw into the antenna out of of a radio). PL-259? Does it look like it would screw into a mobile or base style radio? They do make some handy adapters that that will screw into and then a short piece of flexible cable to a sma adapter. |
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Quoted:
Well , I was at my parents today digging through stuff, and found a Jpole :) I totally forgot someone had given me one made out of twinlead. The one thing is though , it's not a 'standard' connection (at least for my Icom) is there a easy way to identify what kind of connector it is (it has threads to screw into the antenna out of of a radio). SMA? check the N9TAX antenna site for crossover pigtails. |
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I'll be using my roll up Slim-Jim from N9TAX in the morning. They will be doing some kind of tourism thing down on main street USA. The ham club will be there doing some Echolink contacts around the country, around the world. We'll be serving coffee and donuts, too.
So, a major TV station in the state will be covering the event. We wrote a guy there, one of the news guys who also is part owner of the station, to please try to get us a little coverage. Since he's an Extra (and sponsors a repeater whose antenna is on the TV station tower), we think we might get a little action on this. I'm using the PA speaker stand with three sections of the milsurp fiberglass mast. The top end of the Slim-Jim will be taped to the top of the mast. So as to not have to run any extension cords through the streets, I'll be running my FT-1802M from the RBC-6 gel cell set. Some cards, and a pen and note pad for logging. All very KISS. That's it. AFM |