|
3/8x24 2 meter mobile
Have been looking around for plans for a 1/2 or 5/8 2 meter mobile
antenna to play with. I have several Iron Horse whips I no longer use and thought id use them as a starting point for a 5/8 2 meter mobile whip I could use on my CB mount for most of the time. (I use the CB only when our RV club travels as a group). I did a ton of google/bing searches but have come up fairly empty. I know I could buy one cheap but thats not what ham radio is about :). |
3/8x24 2 meter mobile
On Monday, January 27, 2014 2:06:56 PM UTC-6, R. Scott wrote:
Have been looking around for plans for a 1/2 or 5/8 2 meter mobile antenna to play with. I have several Iron Horse whips I no longer use and thought id use them as a starting point for a 5/8 2 meter mobile whip I could use on my CB mount for most of the time. (I use the CB only when our RV club travels as a group). I did a ton of google/bing searches but have come up fairly empty. I know I could buy one cheap but thats not what ham radio is about :). The tricky part is rigging up the matching/loading coil. About the easiest way to rig up a 5/8 2m whip is to take one of those old CB antennas with the base loading coil which has a plastic sleeve over the coil. Very common back in the day.. Pull the sleeve up and redo the coil to act as a loading coil for 2m. Usually will end up maybe 4-5 turns or so, but will have to be tweaked. That's about all I can think of offhand that is easy to make, and still looks OK after it's finished.. Naturally you'll need to trim the whip, or get one the right length. I have no idea what an "iron horse" whip is, so couldn't say much about those. |
3/8x24 2 meter mobile
In article ,
"R. Scott" wrote: Have been looking around for plans for a 1/2 or 5/8 2 meter mobile antenna to play with. I have several Iron Horse whips I no longer use and thought id use them as a starting point for a 5/8 2 meter mobile whip I could use on my CB mount for most of the time. (I use the CB only when our RV club travels as a group). I did a ton of google/bing searches but have come up fairly empty. I know I could buy one cheap but thats not what ham radio is about :). It has been many years, but I recall some CB antennas that were outwardly similar to a 5/8 wave Two Meter antenna. They consisted of a base loading coil connected to the vertical whip. The Two Meter antenna had a grounded coil with whip at the top, with a connection from the connector's center conductor to a tap on the coil. The CB whip may have been a little shorter than 5/8 wave on Two Meters, but it might still be possible to rework the CB coil to match it. Fred K4DII |
3/8x24 2 meter mobile
Have been looking around for plans for a 1/2 or 5/8 2 meter mobile
antenna to play with. The tricky part is rigging up the matching/loading coil. Also, you might want to read up on actual (as opposed to simple-model) results with a 5/8-wave mobile antenna, on a typical mount. I've read a couple of reports which state that the theoretical gain advantage of a 5/8-wave antenna, over a quarter-wave monopole, depend a great deal on the 5/8-wave being mounted over a large ground plane (several wavelengths at least). Without a large ground plane, the 5/8-wave tends to "squint upwards" - its primary gain lobe takes off at an angle significantly above the horizon, rather than directly out forwards and backwards from the vehicle. This can result in poorer signal "towards the horizon" than a quarter-wave would give you - not good if you're trying to do simplex communication between vehicles, and maybe-not-good if you're using repeaters (depending how high above horizontal the direct line to the repeater antenna lies). 5/8-wave antennas are also more prone to "lean back" away from the vertical when you're driving at highway speeds as a result of air pressure, and this also can cause the pattern to squint upwards more than is true for a quarter-wave. The thin "spaghetti noodle" 5/8-wave antennas such as Radio Shack used to sell (and perhaps still does) would really have a problem with this, I think. Anyhow, here's one set of plans: http://www.vk4adc.com/web/index.php/...58th-wave-whip The article has some comments attached which make reference to plans in the ARRL Handbook (doesn't say which edition) which use a tapped loading coil for impedance matching. Most of the 5/8-wave antenna designs I've seen use this approach... it has the advantage that the whole antenna is DC-grounded through the tapped coil, and thus static buildup on the whip isn't an issue. I believe I've seen other 5/8-wave mobile plans in various of the ARRL Antenna Compendium collections. http://www.arrl.org/files/file/Techn...df/8009022.pdf has some other interesting approaches. |
3/8x24 2 meter mobile
"David Platt" wrote in message ... Also, you might want to read up on actual (as opposed to simple-model) results with a 5/8-wave mobile antenna, on a typical mount. I've read a couple of reports which state that the theoretical gain advantage of a 5/8-wave antenna, over a quarter-wave monopole, depend a great deal on the 5/8-wave being mounted over a large ground plane (several wavelengths at least). Without a large ground plane, the 5/8-wave tends to "squint upwards" - its primary gain lobe takes off at an angle significantly above the horizon, rather than directly out forwards and backwards from the vehicle. This can result in poorer signal "towards the horizon" than a quarter-wave would give you - not good if you're trying to do simplex communication between vehicles, and maybe-not-good if you're using repeaters (depending how high above horizontal the direct line to the repeater antenna lies). 5/8-wave antennas are also more prone to "lean back" away from the vertical when you're driving at highway speeds as a result of air pressure, and this also can cause the pattern to squint upwards more than is true for a quarter-wave. The thin "spaghetti noodle" 5/8-wave antennas such as Radio Shack used to sell (and perhaps still does) would really have a problem with this, I think. From years of using several kinds of 2 meter antennas I have found there is not one that will work best in every case. Several times another ham and I would swap antennas in the same mount and look at differant repeaters. One type of antenna would work good in one direction and another in a differant direction or repeater that is up higher or lower. Even a 40 meter loaded whip that had a low swr on 2 meters worked beter in some directions than the other 1/4 to 5/8 wave length antennas. The thin whip that lays back is not too good. Another one is the ones that are about 5 or 6 feet long that tend to whip around and give lots of flutter at highway speeds. While the antenna programs will show you alot about the patern of the antenna, it is difficult for them to take into account everything around them and repeaters mounted at differant heigths. The best is the roof of a car or van. For the most part if you are in the low rolling hills like around here , just put a 1/4 or 5/8 on and forget about it. If you are in an area that is very flat your results may be differant. Where I am the land is from about 600 to 1000 feet above sea level for the most part. The repeaters may be from 300 to 1000 feet above that with a few up to 4000 feet or more above that. Now that I have been using the dual band antennas there is not really a choice of what kind to use. Just try to get it stiff enough it does not lay back or whip around. All that is based on my and a couple of local hams expierance over the last 40 years. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
Dave Platt already beat me to the answer.
The bottom line is that it would be a waste of a perfectly good 10 / 11 meter antenna to modify one to work on two meters just because you already had the mount on the vehicle - even though the mount was in the wrong place. |
3/8x24 2 meter mobile
On Monday, January 27, 2014 6:03:19 PM UTC-6, Ralph Mowery wrote:
If you are in an area that is very flat your results may be differant. The area around here is real flat. The 5/8 was always the best when we compared them. They were the best at low angles at long distances, and gave less picket fencing when driving around town for some reason. Back then I was using a Larson, and it was on the center of the roof. But these days I have simple 1/4 wave whips on the trucks. I'm not as picky these days about 2m, and they hit less stuff overhead, being they are also mounted on the roof of the cabs, which sits fairly high. When comparing all the various vertical types on 10m at the house, the 5/8 ground plane always beat the 1/4 wave, and 1/2 waves I tried. And the half wave was decoupled, and did work very well. But.. The 5/8 beat it quite noticeably on distant local paths where the angles used are very low. Now, when I tried 5/8 ground planes on 2m, they were horrible if you used 1/4 wave radials. So in that case, the problems did show up. But if I used 5/8 lower elements and rigged it as a collinear, it did fine. Anyway, in the cases I tried with the whips on the vehicle roofs, the 5/8 seemed to work pretty well. But a vehicle is larger than the 1/4 wave radials which did not work well. I've always felt a 5/8 element should really be paired with another 5/8 element as a collinear. That is a very good antenna if decoupled from the feedline. So you never really know for sure about the 5/8's until you try them in each case. I've heard many prefer the shorter 1/4 wave whips if in a valley with the repeaters up on nearby mountains and such. But Houston is not really like that and the 5/8's usually won if mounted on decent metal. |
3/8x24 2 meter mobile
On Monday, January 27, 2014 6:41:34 PM UTC-6, Channel Jumper wrote:
Dave Platt already beat me to the answer. The bottom line is that it would be a waste of a perfectly good 10 / 11 meter antenna to modify one to work on two meters just because you already had the mount on the vehicle - even though the mount was in the wrong place. If he's got several, why would it be a waste if it's adding another band? He can only use one CB antenna at a time.. :/ And he hasn't mentioned where the mount is. If it's on the roof or a decent trunk, it will work OK. But mirror mounts and such, a 5/8 will usually not work too well at all. But mirror mounts are about the worst place you can mount a whip, no matter what type. But one problem about converting a base load CB antenna I forgot about.. It's not a 3/8x24 thread.. They use a different type of wider screw on mount, and would need to be modified, or use a base load mount. With a 3/8x24 thread mount, I would just use a 1/4 wave.. So much easier and better looking. Most loading/matching coil schemes are going to look fairly ugly in a case like that as you usually can't enclose them in anything. |
3/8x24 2 meter mobile
On Monday, January 27, 2014 8:01:29 PM UTC-6, wrote:
With a 3/8x24 thread mount, I would just use a 1/4 wave.. So much easier and better looking. Most loading/matching coil schemes are going to look fairly ugly in a case like that as you usually can't enclose them in anything. Pondering.. About the only other easy way to make a 5/8 whip that would screw into that mount would be to take a glass whip and then rebuild it into a 5/8 for 2m. You would need to strip the original wire, or at least partly, then wind a loading coil at the base, and then pretty much straight up to make the 5/8 element. That would work.. The reason I call the coil for the 5/8 a loading coil, rather than matching coil, is the coil is tuning the 5/8 whip to be a 3/4 wave electrically, which is resonant. Some ground the coil, and tap at the best match. But I prefer an ungrounded coil. Why? If it's ungrounded, it can also be used on other bands. IE: a 1/4 wave whip on a lower freq.. I used to use my 10m 5/8 ground planes on 30m as 1/4 waves. But you can't do that with a grounded coil. Works fine ungrounded. |
3/8x24 2 meter mobile
wrote in message ... But I prefer an ungrounded coil. Why? If it's ungrounded, it can also be used on other bands. IE: a 1/4 wave whip on a lower freq.. I used to use my 10m 5/8 ground planes on 30m as 1/4 waves. But you can't do that with a grounded coil. Works fine ungrounded. I have not tried it, but have seen where an ungrounded coil on the 5/8 2 meter antenna is good for a loaded whip on 6 meters. Suspose to match with a low swr. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
3/8x24 2 meter mobile
"R. Scott" wrote in message ... Have been looking around for plans for a 1/2 or 5/8 2 meter mobile antenna to play with. I have several Iron Horse whips I no longer use and thought id use them as a starting point for a 5/8 2 meter mobile whip I could use on my CB mount for most of the time. (I use the CB only when our RV club travels as a group). I did a ton of google/bing searches but have come up fairly empty. I know I could buy one cheap but thats not what ham radio is about :). I have used several MFJ magmounts as the start-point of antenna building. They stick on a metal car top, obviously, but they also stick on anything else ferro-magnetic, like the lid of a can full of rocks (yes, I did) or an old, discarded chassis slide (yes, again). Added counterpoise may be required. Check this before you buy ... but I think the item is the MFJ 1724B. The base I used has the 3/8 inside thread you described and the MFJ threaded insert can take a whip of any length -- just loosen the setscrew and replace the existing whip with one of your choice or your design. The base thread also accepts Hustler HF elements and maybe some others. Added physical support may be required for HF elements. BONUS: On my minivan, I often use a particular insert into which I installed a long, untuned whip. When it's connected to the built-in car radio instead of the stock vehicle antenna, that roof-mounted long whip is a dynamite AM antenna on my long trips across the western desert. "Sal" (KD6VKW) |
3/8x24 2 meter mobile
|
3/8x24 2 meter mobile
In message , Ralph
Mowery writes "R. Scott" wrote in message ... On 1/28/2014 1:25 AM, wrote: The vehicle is a 2011 F-350 and I have the Fender Mount CB. Like I said I use it only for the RV runs. Thus I would like to experiment with one of the whips to run a 2 meter. I could have easily did a 1/4 wave vertical but thought that 5/8 would be better experiment. the loaded 5/8 ungrounded as NM5K posted just might be what I need. I was looking for how many turns of wire might do the trick. Problem is I dont have a GDO to get the right turns so thats why I was hoping to find someone whom ad done it before :). I saw an antenna similar to what you are wanting to do. I think it was 47 inches long. The coil will only be a few turns. I don't recall the number of turns on the form for that antenna, but it was only about 2 or 3 turns. I would start with 3 turns and check the swr and trim the turns for a low swr. Most 5/8ths on 2m are more-or-less electrically 6/8th (=3/4) waves, but with the first 1/8th being the coil. With mine, the whip is 50" long, and the coil is 3.5 turns, 1" dia, appx 10 gauge well spread steel spring, 1.75" long. The feed impedance over a flat groundplane (7" magmount in the centre of the car roof) should be around 50 ohms, whereas a 1/4 is more like 37 ohms. In most situations, I've not found it remarkably better the a 1/4 wave (maybe a couple of dB on a good day). -- Ian |
3/8x24 2 meter mobile
On Wednesday, January 29, 2014 11:15:17 AM UTC-6, R. Scott wrote:
Anyway ... Ill start with 3/4 wave of wire and wrap the 1/2 wave section in a coil and have the last 1/4 go vertical up the fiberglass ... That will be way too much coil, and not enough vertical. I think a 5/8 for 2m is around 48-50 inches or so, depending on freq. The coil will only be a few turns. If the converted base loaded CB version is 5 turns, with the thinner glass whip form, it would take just a few more turns. Like maybe 8 or so using a thin glass whip form. You could hang a 5/8 length of wire from something, and then wind a coil on a pencil or something about the same dia as the whip to get an idea on the number of turns. The vertical section up the glass must be the correct length. IE: 48-50 inches. Otherwise it will not be a 5/8 whip. With a 1/4 wave going up the whip, it's a 1/4 wave with a loading coil at the base detuning it. :( |
3/8x24 2 meter mobile
On 1/29/2014 9:25 AM, Ralph Mowery wrote:
"R. Scott" wrote in message ... On 1/28/2014 1:25 AM, wrote: The vehicle is a 2011 F-350 and I have the Fender Mount CB. Like I said I use it only for the RV runs. Thus I would like to experiment with one of the whips to run a 2 meter. I could have easily did a 1/4 wave vertical but thought that 5/8 would be better experiment. the loaded 5/8 ungrounded as NM5K posted just might be what I need. I was looking for how many turns of wire might do the trick. Problem is I dont have a GDO to get the right turns so thats why I was hoping to find someone whom ad done it before :). I saw an antenna similar to what you are wanting to do. I think it was 47 inches long. The coil will only be a few turns. I don't recall the number of turns on the form for that antenna, but it was only about 2 or 3 turns. I would start with 3 turns and check the swr and trim the turns for a low swr. Thanks, My figuring was all wrong :). Just so everyone knows, its a standard Firestik wound loaded about 4ft long. So its not base loaded, they distributed the coil from top to bottom (tighter winding at the top). Ill experiment when I have time. W7PSK Ive experimented with many wire antennas over the years, but never loading types. Thats why I came to the experts :). |
3/8x24 2 meter mobile
"R. Scott" wrote in message ... On 1/29/2014 9:25 AM, Ralph Mowery wrote: Thanks, My figuring was all wrong :). Just so everyone knows, its a standard Firestik wound loaded about 4ft long. So its not base loaded, they distributed the coil from top to bottom (tighter winding at the top). Ill experiment when I have time. W7PSK Ive experimented with many wire antennas over the years, but never loading types. Thats why I came to the experts :). The antennas you have to start with are almost the opposit of what you want to do. The ones you have are physically too short to be a 1/4 wave on the low bands and need lots of wire to make up the differance. When used on 2 meters and above it is easy to go over 1/4 wave and still mout them on a car. You may get some gain by doing this. To use the whips that have wire wrapped around it for several feet on 2 meters, you will need to strip off all the old wire and just run a single wire up the whip and put just a few turns around the bottom to match it. Always fun to expirment with what you have. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
3/8x24 2 meter mobile
On Thursday, January 30, 2014 2:03:04 PM UTC-6, Ralph Mowery wrote:
The antennas you have to start with are almost the opposit of what you want to do. The ones you have are physically too short to be a 1/4 wave on the low bands and need lots of wire to make up the differance. When used on 2 meters and above it is easy to go over 1/4 wave and still mout them on a car. You may get some gain by doing this. To use the whips that have wire wrapped around it for several feet on 2 meters, you will need to strip off all the old wire and just run a single wire up the whip and put just a few turns around the bottom to match it. Always fun to expirment with what you have. The glass whips do make a handy platform which is light. All of my HF mobile antennas are plastic bugcatchers built from various fire sticks, ham sticks, etc. My main version is center loaded and 11 ft tall counting the 5 ft whip attached to the 6 ft glass stick. When parked, I can also add a solid 3 ft hustler mast below the glass stick to raise the coil level to 8 ft, and a total of 14 ft tall. Works all bands 80-10, and on the higher bands, I use shorter "stinger" whips with the coil bypassed with a jumper. What is handy is I get bugcatcher performance with a much lower weight, which makes it a lot easier to mount and use. I've built the exact 2m 5/8 whip that I earlier described using a glass whip. and is still around somewhere.. If I can find it, it would tell me exactly how many turns the loading coil was on the one I built. I remember on mine, the glass whip was a tad bit short, and I had to add a short stinger to the top to get the full 5/8 wave. I used it on the back of a Honda Accord for a while.. I've still been too chicken to drill any holes in my newer Toyota, and haven't run any radios from it yet. If I want to run mobile, I have to use one of my old trucks. :| |
3/8x24 2 meter mobile
wrote in message ... On Thursday, January 30, 2014 2:03:04 PM UTC-6, Ralph Mowery wrote: I've still been too chicken to drill any holes in my newer Toyota, and haven't run any radios from it yet. If I want to run mobile, I have to use one of my old trucks. I have seen some clever mounts that slide into a trailer receiver. Some home brew, some commercial. "Sal" |
3/8x24 2 meter mobile
On Friday, January 31, 2014 3:34:25 PM UTC-6, Sal M. O'Nella wrote:
wrote in message ... On Thursday, January 30, 2014 2:03:04 PM UTC-6, Ralph Mowery wrote: I've still been too chicken to drill any holes in my newer Toyota, and haven't run any radios from it yet. If I want to run mobile, I have to use one of my old trucks. I have seen some clever mounts that slide into a trailer receiver. Some home brew, some commercial. "Sal" There isn't much way to attach one of those on that car. There is no real bumper per say, and underneath is just trunk floor, which doesn't look too strong. But even if I could do it, I'm not sure I would bother. Hitch mounts are a horrible place to mount as far as performance. I've pretty much given up trying to do anything with that car. If I really had to have it, I'd drill a hole in the truck like I did the Accord. But I found with that car, after a period of using the antennas, the flexing and such sort of warped the trunk lid a bit around the hole. And that was with it reinforced underneath with a steel plate. I don't want to risk that with this one. I'd pondered maybe using a trunk lip mount, but even that makes me nervous. |
| All times are GMT +1. The time now is 01:13 AM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com