75m-80m MOBILE ANTENNA - WHAT HAVE YOU MADE?

[CDX-007]

OK, good points... So now I'm thinking a cap hat that big at the top would help eliminate corona but be a bugger to physically stabilize.

...and I thought the larger coil would have a lower Q but now you've got me preparing myself for the worst.

I guess if I needed to BBQ some skewered chicken on the way to a Ham picnic...

Actually, that corona discharge cold be fun if I build the 4-400C amp I'm thinking about for the mobile.
It could prolly take it, ...for a while.

I went to buy some 1" fiberglass rod today but they only had 3/4" so I have a paid order waiting,

then,


















CORONA, BABY! HAH HAH HAH!! :twisted:


























.

 

[Captain Kilowatt]

The purpose of a capacity hat is NOT to reduce corona. It is to provide loading to tune the antenna.A cap hat above a loading coil will reduce the number of turns required and thus increase the efficiency.

Check out the corona from this antenna.

 

[CDX-007]

The purpose of a capacity hat is NOT to reduce corona. It is to provide loading to tune the antenna.A cap hat above a loading coil will reduce the number of turns required and thus increase the efficiency.

Check out the corona from this antenna.

Sweet! I saw a bunch of that earlier tonight.

,,,and I can still tpye!

 

[C W Morse]

Fireworks around an antenna is a BAD thing. It might be exciting to look at, but it does absolutely NOTHING for your signal. The SWR goes astronomical and it puts an unacceptable strain on the finals! Getting sparks can also cause.......................POP!!! There went the finals! :shock: And remember, too, that sharp edges, angular surfaces can contribute to corona, so a cap hat such as a disk or those with "whips" or "finger-like" protrusions can cause it. It is more likely at 160 Meters.

On the "Q" of an antenna or circuit, generally speaking it is the SMALLER coils that are lower in efficiency. That's why an 80M hamstick stinks and a larger bugcatcher shines!

Like I said earlier, have a BLAST with this project!

73

CWM

 

[CollinsMan]

I've tried a lot of antennas for 75 meters mobile, but the best thing I've found for LOCAL (out to a 300-mile radius) is:

1. Two "dummy load on a stick" 75 meter hamsticks
2. 1 Dipole adapter bracket (allows you to hook two hamsticks up horizontally like a diploe and connect the whole thing to a mast pipe)
3. Attach said mast pip to heavy duty "trailor hitch" or tool box mount.
4. Keept the thing at least a couple of feet over the top of your vehicle (it will be about 14 feet/7ft per side long)
5. Have fun - mine works within 3 S-units to local stations of what my full-wave loop at 38 feet does at the home qth. Not too bad for only 100 watts mobile...
6. Yes, the hamsticks are very inefficient, but when you shoot most of the signal straight up NVIS style, it doesn't take many watts to achieve good local communications. The top of your vehicle makes an EXCELLENT reflector ;-) (the Germans invented this type mobile antenna set up back in WW2, and they only used about 3 watts AM on 6 MHz to talk all over the Russian front for example...)
7. Yep, it is ugly and weird looking, but it works...
8. You can use quick-disconnects on the antennas, and then switch in 60 and 40 meter antennas for more NVIS fun if you want to do so
9. Best of all, you don't really have to bother with all of that ground-strap bonding drudgery as your antenna is ground independent because it is a shortened dipole.

Good luck with whatever you decide to use; I hope to hear you on the bands sometime!

 

[CDX-007]

I've tried a lot of antennas for 75 meters mobile, but the best thing I've found for LOCAL (out to a 300-mile radius) is:

1. Two "dummy load on a stick" 75 meter hamsticks
2. 1 Dipole adapter bracket (allows you to hook two hamsticks up horizontally like a diploe and connect the whole thing to a mast pipe)
3. Attach said mast pip to heavy duty "trailor hitch" or tool box mount.
4. Keept the thing at least a couple of feet over the top of your vehicle (it will be about 14 feet/7ft per side long)
5. Have fun - mine works within 3 S-units to local stations of what my full-wave loop at 38 feet does at the home qth. Not too bad for only 100 watts mobile...
6. Yes, the hamsticks are very inefficient, but when you shoot most of the signal straight up NVIS style, it doesn't take many watts to achieve good local communications. The top of your vehicle makes an EXCELLENT reflector ;-) (the Germans invented this type mobile antenna set up back in WW2, and they only used about 3 watts AM on 6 MHz to talk all over the Russian front for example...)
7. Yep, it is ugly and weird looking, but it works...
8. You can use quick-disconnects on the antennas, and then switch in 60 and 40 meter antennas for more NVIS fun if you want to do so
9. Best of all, you don't really have to bother with all of that ground-strap bonding drudgery as your antenna is ground independent because it is a shortened dipole.

Good luck with whatever you decide to use; I hope to hear you on the bands sometime!

Cool idea!

Now, what if someone were to do this with a single Hi-Q or equivalent laying horizontally over the top of the vehicle as a counterpoise / reflector...?

You've got me thinking -

 

[CollinsMan]

That would probably work pretty well. Back in my military days, we would pull the rear-mounted whip over the top of our jeep and tie it to the front bumper with a non-conductive cord.

That always worked pretty well - much better that running the whip vertically on frequencies under 10 Mc or so.

If I were to go that way, I would bond all of the large metal panels (doors, hood, etc.) together as you will be using the vehicle body as the second half of your antenna (obviously).

If you've already got the antenna mounted in an area that would allow you to tilt it backward (or forward) 45 degrees or so, that would work well, too.

Henry Allen at Texas Bugcatchers dot com could probably fix you up with an adapter to allow you to tilt your antenna if you need one.

One other thing about running your antenna as horizontal as possible - Since your signal goes mostly straight up, it remains relatively constant even when driving through urban areas with tall buildings, valleys, canyons, etc. Unlike vertically polarized signals that tend to be absorbed in such situations... (At frequencies below 10 Mc or so, of course.)

I wish you luck! Have a great week.

 

[W5LZ]

I'm afraid Henry Allen no longer does the 'Texas BugCatcher'. Wish he did!
I think I'd also think twice about trying to 'bend' any 80 meter vertical, just not worth the effort at best. Polarization isn't a problem, vertical/horizontal, the efficiency of a 'shortened' radiator is, no matter what the polarization. Remember, it's all about wave length type thingys, not feet and inches. At 80 meters that efficiency just isn't gonna get much better than about 5% for a -practical- mobile antenna no matter what you do (within reason!).
Just for 'grins', if you really want to shorten an 80 meter loaded antenna, do away with the top whip and substitute a metal sphere the size of a medium 'beach-ball'. It should be on a short mast to put it a foot or two above the loading-coil. Looks weird, but it does work. Basically a huge 'top-hat', NOT very broadbanded at all, but also not a 'tree-trimmer'. You -will- have to guy it, you wouldn't believe how much it moves around in the wind!
- 'Doc

(Henry Allen = K5BUG)

 

[Captain Kilowatt]

Hey Doc,with that idea you could run QRO and have your very own mobile Van de Graf generator. Or at least something that resembles it.

 

[CDX-007]

...One other thing about running your antenna as horizontal as possible - Since your signal goes mostly straight up, it remains relatively constant even when driving through urban areas with tall buildings, valleys, canyons, etc. Unlike vertically polarized signals that tend to be absorbed in such situations... (At frequencies below 10 Mc or so, of course.)...

Now THAT is what I want to hear!!

That would be fantastic as it will help with the large (efficient?) open coil's Q which I understand will tend to wig out easily with the varying surroundings.

I'm hopefully picking up the Fiberglass rod this week and might have this thing playing by the weekend. I hope so as I have a long drive this weekend and would love some radio company.

73

 

[CollinsMan]

I hate to read that Henry isn't in the bug-catcher business any longer. He made top quality stuff.

Check out any of the pages on "NVIS Mobile" through the search engines and you will find that most government users tilt their whips in order to utilize the NVIS effect.

This is the way it works in simplified terms. Turn off all the lights in your room at night so that you have total darkness. Shine a flashlight straight up at the ceiling. See how the reflection off your white ceiling illuminates everything in the room.

The same principal exists with NVIS. If you aim your signal straight up, it will reflect off the ionosphere and penetrate practically everthing in the landscape for a couple of hundred miles.

I've turned my mobile SEA 235 HF down to 1/2 watt SSB and successfully communicated to folks out to 300 miles with no problem at night on 75 meters. During the day, you use 40 meters, of course, even though 75 meters will work most of the time. (Of course 100 watts works better.)

Don't take my word for it though. Check it out on the Internet. If it wasn't a sound method, the U.S. government wouldn't utilize it as they don't care about costs. They will pay for whatever works the best, and they've chosen this method.

Good luck, and have fun! To me that's what it's all about!

 

[CollinsMan]

CDX-007

What frequency do you plan on running this weekend? I'll give you a shout. I usually run 3.765 Mc, myself.

Oh, where will you be traveling to? I've got a vertical that I'll use if you will be pretty far away from my area.

Have a great week!

 

[CDX-007]

CDX-007

What frequency do you plan on running this weekend? I'll give you a shout. I usually run 3.765 Mc, myself.

Oh, where will you be traveling to? I've got a vertical that I'll use if you will be pretty far away from my area.

Have a great week!

Sure, I can look for you on 3.765, what time PST would you typically be on the band?

 

[CollinsMan]

Good deal - I monitor that frequency 24/7 on the weekend unless I step out to go to the store or something. During the week, I usually monitor it from about 3:30-11:00 PST.

I'll switch over to my vertical as you are probably too far away from me to reach very well with the loop.

Oh, here's a link to the U.S. Army Signal Corps' NVIS basic information page. There's a lot of good info. on it.

http://www.gordon.army.mil/AC/wintr01/HFIBCT.htm

 

[CDX-007]

Forgot that was a contest weekend.

Still gathering parts, nothing to report yet, but coming soon to a DX theater near you...