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"WHAT IS THAT ANTENNA ON TOP OF YOUR CAR!?!?"




 
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Author Topic: "WHAT IS THAT ANTENNA ON TOP OF YOUR CAR!?!?"  (Read 895 times)
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WBear2GCR
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« on: April 18, 2019, 08:00:19 PM »

"WHAT IS THAT ANTENNA ON TOP OF YOUR CAR!?!?"

So, I heard this exact thing at least ONCE every day, since I put a mobile antenna on
top of the van!

The bandspammer mobile ant dates from some time in the late 50s to early 60s afaik.
Seems to work well on receive so far.

But the thing that is most surprising to me is the interest it has attracted.
Not expected in the least.
I got to say good things about ham radio, and explain what it is to a wide range of people!

I think this is a good thing, and an interesting advent.

Seems to me that IF you are at all interested in generating and adding to the public awareness
of amateur radio, this is a good way!

The math on this is not half bad:
100 hams with HF mobile ants x 365 days = 36,500 more people who know about ham radio!

Ok, so that's a bit optimistic, but it's non-zero, and there potential this!
I hope you will join me!


                             _-_-bear

PS. I was able to copy the 3885 group in the AM all the way from smAlbunny out to the Framingham hamfester.
ok FB! Most days I can copy fine with good signals... Q5 for the most part.
                                                             _-_-


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_-_- bear WB2GCR                   http://www.bearlabs.com
KA0HCP
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« Reply #1 on: April 18, 2019, 11:03:52 PM »

Looks fast just standing still! 
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New callsign KA0HCP, ex-KB4QAA.  Relocated to Kansas in April 2019.
WB2EMS
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« Reply #2 on: April 19, 2019, 02:24:16 PM »

I've got a Hi-Q antenna on a VW Golf TDI and a tarheel MT200 on the back of the Equinox and it's been amusing.

As you say, it often generates questions that lead to discussions about ham radio to the point where I need to print up a handy handout about ham radio to point folks at the local meetings and other resources for interested parties.

It's also fun to watch heads turn as you drive by when people do double takes.

Less fun was getting pulled over by *two* police cruisers at 5 am (on the way to work for network updates), blocked in, and officers with hands on weaps and the first question was "What is that thing on your car!!" in command voice. "Um, a radio antenna officer. Why do you care?"

A surprising number of interactions with aggrieved females marching up to me in the supermarket parking lot *demanding* to know what that thing on your car is. And not happy no matter what the answer is.

I eventually printed up a sheet to tape in the window of the car of "The Top Ten answers to 'what the hell is that thing on your car?"  Several folks got good laughs off the things in that list.

Does make finding the car in a big parking lot easier though....  Grin
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73 de Kevin, WB2EMS
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« Reply #3 on: April 19, 2019, 06:57:36 PM »

Is that a full size bandspammer? I think they made a smaller one too. Do you have any cap/inductor arrangement at the bottom of it for 75? I see that you have it tied back, besides for keeping from wacking trees, wires, drivethrus, birds etc you might get some nvis effect good for local work. Have you noticed anything like that compared with it vertical?
Larry
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KK4YY
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« Reply #4 on: April 19, 2019, 07:15:25 PM »

When people ask me about the antenna on my car I tell them it's for CB radio. They probably think Smokey and the Bandit or something, but it seems to satisfy their curiosity. The last thing I want to do is engage a stranger in a conversation about Amateur Radio. Let them figure it out for themselves. I did.


Don
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W1ITT
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« Reply #5 on: April 19, 2019, 08:28:36 PM »

I have 3 or 4  Webster Bandspanners, and probably one parts unit.  The story I heard is that they were originally made for a Raytheon contract in the Sixties, then sold to the Amateur market as well.  There are brown ones and green ones, but they all work the same.  They are the original screwdriver antenna, but manually operated without the motor.  Some of them have little marks on the stainless whip that get you in the ballpark for band changes.  I used to carry an Autek RF-1 SWR meter for band changes when I ran mine.  Theoretically, a long skinny coil should be terribly inefficient but, properly mounted and matched with shunt inductance at the base, they get out quite well.  Joe, K1RQG (sk) ran one for years mounted on the  back hinge of a van.  His proudest mobile achievement was working a JA, at our sunset, in the 80m ssb DX window, while going through a toll booth on the Maine Turnpike. 
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AJ1G
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« Reply #6 on: April 19, 2019, 09:09:16 PM »

I often get asked about the 40 meter Hamstick on the back of our Tacoma, usually by members of a local CB club that hang out at the local Cumberland Farms in Westerly RI. They often think itís some sort of new CB antenna.  I show them my little K1 which is about the size of a CB radio and about the same 5 watts output.  They are usually amazed when I tell them I can work Australia and New Zealand on 40 meters with that setup.  So far, none of the CB gang were also hams.  I often will have hams come up to the car to chat, or I will find a ham waiting to chat when I come back to the car in a store parking lot.

BTW a Tacoma Mobile photo I took down at Stonington Point where I was operating in in last Novemberís CW Sweepstakes ended up in May QST in the CW SS results article.  The editor screwed up the caption saying I took 1st place QRP in the New England Division.  It was supposed to say 1st place QRP CT Section, which I won by default (no other CT QRP entries) 😁.  The caption has been corrected in the online QST article.  I only dabbled in the contest for about 8 hours, made 99 Qs in 46 sections mostly on 40 and some 20 meters, all from the truck with the K1 at less than 5 watts and Hamsticks.  No mobile in motion Qs...Iím not that crazy!


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Chris, AJ1G
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« Reply #7 on: April 20, 2019, 02:38:46 PM »

bear,

Well now, here in Orygun only an antenna mount is needed. Yes, just a Diamond K550. Just purchased a "new" Honda Passport and it is back to the dealership the third time, less than 700 miles.

Traded in a 1998 Chevy Blazer with lots of mileage and the old Icom 229H never caused a bit of trouble. The salespersons thought it was a CB, oh well.

Removed the Icom & stuff to install in the new ride. Just got to the mount and kaput. Passport will not come out of park, 10 warnings: battery, brakes, transmission, steering, suspension, etc. Technician claims it is the unknown accessory on the cross rail that is the cause of the issues. Wonder what would happen if a new Passport was taken to a fast food chain and the drive-though? Wireless head set would cause the Passport to go crazy. About 90 licensed Amateur Radio operators in and around home, L.A. Pine Orygun. Better stay away from those houses and their vehicles (if it comes out of park).

Darned antennas, electric meters.........ÖÖ.. Grin

Craig...
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kb3ouk
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« Reply #8 on: April 20, 2019, 06:13:46 PM »

You would think that the manufacturers would test vehicles to make sure rf does not mess up the electronics. At one time i was browsing the fcc part 5 experimental license database and found a license for chrysler corporation that listed frequencies in every ham band plus land mobile and broadcast too i believe, which i can only assume was for testing electronic performance during rf exposure. I believe i may have found a similar license for Ford and GM.
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n1ps
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« Reply #9 on: April 20, 2019, 08:17:56 PM »

They ask me what that THING is on the back of the car. I choose between 2 answers:
1. Its an antenna and I talk to aliens with it. (which is technically true if we include VE land)
2. Its a snorkel.

p
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WBear2GCR
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« Reply #10 on: April 21, 2019, 09:32:27 PM »

W1TTT, please 'splain that reference to the shunt inductor at the base?

N1PS, yeah, I have given the "alien" answer, but as soon as I get that "deer in headlights" look,
I take that opportunity to switch gears and delve deeper and see if there's any potential ham radio
interest...

--- Yes this is the "brown" smaller unit. It does have rings cut into the whip to mark the bands.

In the vertical position I was able to get a very good match on 75. Pulled back as it is now, I am NOT
getting the dip down into the band on 75. It's just barely at 4.000mHz. I've got the whip at max out now.
I was considering a short extension for the end of the whip... but another matching method might be
useful.

The manual for the Webster Bandspammer calls for "21 feet of RG-58" - Don't think I have "21 feet" on
there. Close maybe. But why "21 feet"?? They also ask for the shield be tied to the chassis... really? Like
where? I Imagine with a classic chain bumper mount, or with the good old ball mount to the rear fender,
sure.

Oh so many questions!

                          _-_-bear
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ka1tdq
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« Reply #11 on: April 22, 2019, 12:29:19 AM »

I had an outrageously large setup on top of my car and got lots of questions everywhere I went. One person even asked if my car was solar (I drive a 2010 Rav4).

I've since scaled it back quite a bit and things have quieted down on the question front.

Jon
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W1ITT
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« Reply #12 on: April 22, 2019, 08:10:50 AM »

In answer to WB2GCR's question, let me see if I can 'splain the concept of the shunt inductor and a mobile antenna.  First, a quick bit of theory.  Let us assume that the impedance at the top of a monopole is infinite.  It's more like 3000 ohms in the real world, but let's just play along. The impedance at the bottom, if it were shorted to ground is, you guessed it, zero ohms.  Neither is 50 ohms, which is where we'd like to be.  Wouldn't it be swell if we could slide a tap to a place where it was 50 ohms and resonant?
In pursuit of that goal, let's place an inductor between ground and the bottom of the monopole, in this case, our Webster Bandspanner.  We'll have to shorten the top whip just a skoche to stay resonant on our favorite frequency, but that's easy.  Then we connect coax, any length, as it becomes non-critical.  Tie the shield to ground at the antenna base, and tie the center conductor to the junction of the coil and the Bandspanner.  How much inductance?  I dunno.  For 75 meters I used 3 or 4 turns of #12 on a 2 inch form.  If you have one of the "antenna analyzers" you can get there in a few minutes. (Run your antenna analyzer on battery power so you don't couple into the "ground" provided by your power supply.)  In the old days, mobile hams used a little rotary inductor in a clear plastic cylinder made by the Jones Micromatch company to dial the inductor right in, but the more plebian among us cut and try with a basic coil.  I've occasionally seen the Jones coils at hamfests, in various states of repair.  They are worth getting, if only for the coolness factor, especially with the 60s genre of the Bandspanner. It's not critical, and I found that the same shunt coil could be left in place up through 20 meters.
I suppose you could do the same thing with a powdered iron toroid.  And you can skin the cat from a different angle with shunt capacitance, but that's not as easy to manage, at least the way I play.  Realize that on modern cars, what looks like ground isn't necessarily so.  Even parts of sheet metal that look connected may be insulated with plastic parts so the vehicle doesn't squeak.  The body and chassis, if it even exists, may be two different things, and the exhaust system is usually afloat.  Bond all that stuff together with sheet metal screws, braid and stainless hose clamps.  Drill it and screw it like ya stole it.  Ground is the other half of the mobile antenna, so do the best you can.  And make good connections, star-tooth washers and all that, and tighten them occasionally.  And be proud of that Bandspanner!
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WBear2GCR
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« Reply #13 on: April 22, 2019, 08:36:29 AM »

So, you're simulating a shunt fed tower. going "up" an electrical "quarter wave"?

Not fond of the idea of putting sheet metal screws through the roof of the van though... any ideas for that?

Hmmm...
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« Reply #14 on: April 22, 2019, 11:17:25 AM »



B,

Do the roof have mounts for a roof rack?

Maybe some Cu  STRAP   to lay on da roof and then screw /pop rivet/ fasten into the door recess?

KLC
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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


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« Reply #15 on: April 22, 2019, 12:44:51 PM »


That'll look simply terrific!!

The copper strap would need to both painted and glued down to the surface of the roof.
I'd sooner just wack a hole and drive some short far self tapping stainless screws into that roof.
Of course, I'd need to test to see if the roof is in fact attached to anything!

Then too, I've yet to search for a way to get two big fat power wires out from the battery
through the fiyah wall, into the cabin to power the suckAh!

Thinking seriously of a deep draw marine batt down in the hatch behind the front seats...
Or some of K1QAR's Lithium Eye-On batts that he found on epay down there...

On that Honda (?) Passpart - the guy said that a load across the BATTERY would trash the
computer? Or was it the RF getting back in??  YIKES!!
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« Reply #16 on: April 22, 2019, 12:52:40 PM »

I wish I had taken some photos of what we used for 2M transmitter hunts back in the 70's. WA2SLR's Chevy Nova had an 8 element yagi mounted on a roof rack. We would ride around and take headings. 1st time we used it, we came in 2nd. It definitely looked strange going down the highway.

Back before we could drive we had 102" whips on our bicycles. I recall the day when we took out the bottom of a low hanging neon sign at a local Chinese restaurant! Bikes got a lot of use. Had a local dealer about 5 miles from where I lived n Bergen County. He had NOS Mosley TA-33's for $90. Myself and a friend rode to his place. We each tied an end of the carton to our bikes and rode home. Took about 3 hours with all the stops we had to make!
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KK4YY
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Golí na vydumku khitra


« Reply #17 on: April 22, 2019, 07:00:13 PM »

Bear,

After resonating a hamstick on my Jeep, I added a spring at the base. To my surprise, the resonant point moved UP. I had to lengthen the whip section to get it back down where I wanted it. What I think was happening was the spring moved the base loading coil closer to the center of the antenna. Center loading requires more L than base loading. So, if you can't lengthen the whip section, shorten the spring - or ditch it.

If the manufacturer is specifying a certain length of transmission line then it's not running flat. It's part of the matching.

If you can't ground the coax at the antenna the cable shield will be hot with RF and will look to find a ground somewhere. Maybe at the radio. Maybe at the battery. It will find a path. If you can't ground the antenna at the feed point, I think you're loosing the advantage of roof-mounting. You may be better off bumper of trailer hitch mounting the antenna. That way, you can let the antenna stand up vertically. It may attract less attention that way, but Amateur Radio will survive even if you're not out proselytizing to curious onlookers. Grin


Don
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« Reply #18 on: April 23, 2019, 09:15:43 PM »

I've used shunt coils on the base of the mobile antennas for quite a few years now, they work very well. I usually have to pick a compromise that works well on 75 meters, a bit less well but good enough on 40, and by the time you get to 20 meters it's looking more like an RF choke and isn't too critical. On the occasions I've tried 160 mobile I needed a much larger base coil.

One advantage over using capacitance at the base for loading is that the coil puts the antenna at DC ground, which is helpful for snow and rain static. I've gotten a pretty good charge build up on the antenna before using the coils - caused squealing in the receiver and made me worry about the front end. Had an FT857 front end nuked by snow static once.

As far as grounding on the van roof  - I once built an arrangement with a large square aluminum plate that laid flat against the roof to capacitively couple to ground there. It was held down by wooden bars over it that were tied into large magnets. It worked very well on 40 meters and the higher bands. I didn't have anything but hamsticks to use with it, so 80 was pretty much a joke though I did make one local contact with it once on that band. The idea was to make the contact area of the mount very large to get enough capacitance to get decent coupling to ground. In that unit I had a bud box on top with a switch and various matching capacitors (I'd use shunt coil if I did it now) and a ball mount on top of the bud box. I used that arrangement very successfully for several years on a couple of different station wagons or vans until I moved on to screwdriver antennas.

As far as responding to comments on the antennas - if they are genuinely curious or just polite, I'll happily explain what's going on, if only to be a decent ambassador for the hobby. If they are snarky are nasty, they'll get a different kind of answer.  Grin

I've had several security folks at various places ask if the HiQ was one of the google street view cameras.

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73 de Kevin, WB2EMS
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« Reply #19 on: April 24, 2019, 10:18:36 PM »

  My 2016 Tacoma has a composite (non metal) bed, I put a spring mount on the side of the lock box, the initial plan was for a 6 meter or 10 meter antenna to used while stopped. I really don't want to contemplate operating mobile on any of the DPRK Kamikaze Freeways!!! The lock box is bonded with 1" braid to the metal outside of the bed and to the cab.

  Later I decided to try HF but again only while stopped, the picture was taken in March 2017 at Death Valley, the Outbacker antenna has a lot of wind area and there was a steady 20 MPH wind so the line is to keep the antenna from blowing over. I also put out a 65 foot counterpoise which does help. I was able to check into several 75 meter nets.

   The night before while in the campground I worked South Africa on 40 meters, conditions were good, the SA station was working W6's one after another. I also did not have the counter poise out  as I was afraid some one might trip on it.


* Radio Setup Pamamint Valley.JPG (2344.14 KB, 2592x1944 - viewed 30 times.)

* Bonding Strap.JPG (360.59 KB, 1024x768 - viewed 26 times.)
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