HF Mobile antenna advise/suggestions?

[Glenn NY4NC]

Hello;

I'm finally going to install a mobile HF/VHF radio in my mini van. It's been 10 years since I've had a radio in my vehicle and I'm really looking forward to getting on the air during my drive to and from work.

I've decided on the Icom 706mkIIG but I'm not sure what/who makes a good HF mobile antenna these days. I see some mfgs make all-in-one HF-6-2-440 antennas but I'm thinking it make be better to have two separate antennas, one for 6-2-440 and another for HF.

Recommendations for an efficient HF mobile antenna anyone? What about those motorized center loaded whips? Yaesu has one that works automatically with their mobile rig. I wonder if they're any good.

Or maybe a steel whip one of those remote tuner boxes located inside the vehicle?

Thoughts?

[Carl WA1KPD]

I have a KJ7U screwdriver that I used with my 706 mobile for 3 years and loved it. I bought it used and it never gave me a bit of trouble. 160 to 6 and I used it on all bands with no trouble. Even though I bought it used Larry was very helpful in getting me set up with it

Worked into England and Belgium several tines on 75SSB. I was not 40 over but we could make a contact. I would endorse it without any question.

I do not have any relationship with the seller, I am just a very happy customer

[Bill, KD0HG]

If performance is more important than looks, use a Texas or Oklahoma bugcatcher.
No question about it.

Try a Google search referencing the mobile antenna shootouts.

..

[Jeff OGM]

It all depends on how often you'll use HF in the vehicle, and whether you want to be able to stow the antenna for whatever reason (like parking in a low headroom area).

The texas bugcatcher is the best performer, mounted top center on the vehicle.
The screwdrivers are convenient for changing bands, but don't perform as well as the bugcatcher.

I use hustler resonators, only because I don't use HF mobile that often and can stow them all in the back of the Jeep.  It takes less than a minute to mount one on the ball mount with a quick-dsconnect.  If I can hear them, they can hear me.  Using a 706-MKII.

Jeff
KA1OGM

[KB2WIG]

so far, the suggestions are gud. Whatever you do, on HF its very important to establish your ground(s) carefully. You are relying on the vehicle to be the 'other' part of the ant. The vehicle body is capacitively coupled to the earth: this is the other end of the ant. Try to bond large areas of metal together. Check under the hood. In my vehicles, there are metal clips on the hood, connected to braid which is bonded to the firewall/vehicle frame.... except the clips contact the hood paint. No ground here.  I got out a Dremmel the  ground the paint away at the contact area and drilled a small pilot hole.l I got some small stainless steel washers and hardware, and bonded the clip and hood together. Spray a couple of coats over this for rust protection.  DON'T drill through the hood to the outside-- just through the inside part...

The minivan part tends to reduce your options for mounting the antenna. If you can, mount the ant. in the middle of the roof. Bumper mounting couples much of the energy into the vehicle body as the body is only inches away from the vertical. If you cant/will not mount on top, put it on the side as high up as you can.The left side gives you better "street" clearance for overhanging things... A usefull trick is to use a cheap wip for the top part that can be replaced after you smash things with it......

somewhere on the web is a picture of the Cadavarlacki with a dog log design: try the am window site

              PW little mobile-----------

    klc

10-15-20m is more forgiving than 40m; 80m is tough and 160m.....

 There is a lot of stuff to look at, such as not hitting things when you drive, pwr conductor size, auto generated  noise etc.... gud luck

[KE1GF]

Hey Glenn Here's my mobile install in my truck...

http://unix-srv.1gflabs.com/ke1gf/new_mobile/new_mobile.html

-Bill 'GF

[KA1ZGC]

Center-loading is the only way to go.

I can tell you from experience that Hustlers just plain suck. They're base-loaded, so the current node lives entirely in the reactive portion, and the pansy wire they use doesn't cut it. They get really hot really fast. The so-called "kilowatt" versions suck even more, because those large metal end-caps they put on the coils act as a signifgant amount of capacitance in parallel with the inductance, reducing your radiation resistance and making things look like they're tuning far better than they are.

The hamstick design is much better, since they wind the coils from the center down, but on the 75M version the coil goes all the way down to the feedpoint, so you run into the same RF current limitation that you do with the Hustler. They should made the 75M version with a larger diameter base. It still works better than the Hustler, but there's lots of room for improvement.

Ironhorse makes a pretty good hamstick knockoff, which I actually prefer. The top radiating element and it's collet unscrew from the base, unlike the fixed collet of the original hamstick design. Makes them quicker to assemble and disassemble, no allen wrech required.

All in all, you're probably best off with a bugcatcher design. You can do a Tron-esque dog log, but he puts his capacitance hat right down next to the coil, which I beleive has the same effect as the end caps on the large Hustler coils, but you can't argue with results.

Anything with a nice manly centerload should do the trick. Bill, KE1GF has a very good mobile signal with his particular screwdriver setup out of his Tacoma. That's certainly worth looking into.

And, while I was typing that, he posted the link. I love it when a plan comes together.

My $0.02.

--Thom
Killer Aircraft One Zero Ground Clearance

[K1JJ]

Hi Glenn,

The most important part of your comments is that you will be using a mini van. The large ground plane makes the difference. Just like Bill/GF's truck. On 75M this is the bottle neck.

Dino, Lich/ETP and I ran a lot of side-by-side fielld strength tests back in the mid 90's. We found (as well as others)  that when you hit a certain threshold, there is little difference between GOOD antennas on a given vehicle. ie, Once you get past the lossy commercial gimmick antennas, and into the Bugcatcher and even a well designed  Screwdriver, the real difference is in the size of the vehicle and how well the groundplane is to ground.

All of us built elaborate antenna configurations. I made a 20' whip with HUGE coil material for a center load coil, big capacity hats - even better than a Bugcatcher for my Blazer. Looked ridiculous.  While for a coil Dino used 3/8" copper tubing wound on a 5 gallon plastic bucket with a big whip for his pick up truck. We found that even though the losses were small for the radiator, the ground plane coupling was so lossy that it was the series component that negated our extra efforts.

So, that said, after finding how much the ground plane dominated the equation, I've decided that a standard, well made, screwdriver design is probably the best compromise. This is assuming it uses good materials and is mounted well on a big groundplane, like a truck. The reason being is that it's a dream to be able to adjust the antenna from the operating position while going down the road. The wind bending the antenna has a big affect as well as the rain, snow, etc. You need a perfectly tweaked match with such tiny bandwidth as with a short wavelength mobile vertical system.  Nothing like tooling down the highway, it starts raining and you tweak the match to compensate. Or, switching bands automatically.  My guess is that in well installed systems, the diffence between a good Bugcatcher and good Screwdriver antenna is within a db. So why give up the great convienince of a screwdriver? It's all because the radiating element is dominated by the poor groundplane of any vehicle.

Warren/K2ORS had it right when he once tied 60' wires to his bumper and drove down the highway. It work very FB until cars behind him started stepping on his wires...

T

[w1guh]

I'd dearly love to put a radio in my car but I'm afraid of what the RF'll do to all the on-board electronics.  Anyone ever have ther mobile radios screw up the computers in your car?

[W1JS]

I've decided on the Icom 706mkIIG but I'm not sure what/who makes a good HF mobile antenna these days. I see some mfgs make all-in-one HF-6-2-440 antennas but I'm thinking it make be better to have two separate antennas, one for 6-2-440 and another for HF.

I have/use a Comet all-in-one ant. that I picked up at Hosstraders a few years ago.  I would not recommend it.  I works, but not great.  Besides I don't know of any of the all-in-one ants. which covers 75.  My next install (just got new wheels) will have separate VHF - HF antennas and mounts.  Also, the 706 has two antenna connectors, VHF for 2 and 440 and HF for 160-6 meters.  Six is not on the VHF ant. connector.  To use the all-in-one ant. you need a duplexer which combines HF and VHF. 

There is a bunch of stuff in the mags, books and on the Internet about HF mobile installations, of course the FB comments you get right here.  Good luck!

[Warren]

I'd dearly love to put a radio in my car but I'm afraid of what the RF'll do to all the on-board electronics.  Anyone ever have ther mobile radios screw up the computers in your car?

Hi Paul,

    I wouldn't worry too much about wrecking the electronics in the car. The only rfi problem I ever had was when I ran several hundred watts to 1.2 KW out with a solid state linear in the car, if the swr was too high it would cause one or two of the dashboard warning lights to come on. No permanent damage, everything went back to normal as soon as I unkeyed the transmitter!

73 Warren K2ORS/WD2XGJ

[kc2ifr]

Probably one of the best if not THE best screwdriver antenna is from Tarheel. A bit on the pricy side but..........u get what u pay for.
http://www.wb0w.com/tarheel/tarheel.htm

Check out the reviews.....
I think this is one of the only products that has 120 reviews and ALL of them are a 5, the highest rating it can get.
http://www.eham.net/reviews/detail/1953

[AJ1G]

Glenn - for starters, you might want to give a Hamstick mounted on a bike carrier pedestal that bolts into your trailer hitch receiver a try - Check out my thread "Undesevered Bad Rap for Hamsticks?" in the Technical section of the AM Forum. which includes a photo of the setup on my 98 Volvo Cross Country.   Acceptable performance, low price, and low nerd factor apperance wise.  No need for guy supports.  Get out great n 40 and higher bands, marginal on 75 but still useable.

[Glenn NY4NC]

Thanks for all the great comments and suggestions from everyone! 

Yes, lots of metal on the mini van although if you look at the vehicle when all the doors are open, there isn't much left  but as mentioned, bonding will make a difference. Not sure how I will bond the sliding side doors though.

Tom said;

I've decided that a standard, well made, screwdriver design is probably the best compromise. This is assuming it uses good materials and is mounted well on a big groundplane, like a truck. The reason being is that it's a dream to be able to adjust the antenna from the operating position while going down the road.

That's what I'm thinking Tom, the screwdriver looks like the best all around choice. The bugcatcher looks good, but I don't want to pull over to change bands, especially while driving to work. There is also a multiband antenna, forget who makes it, that uses several coils mounted at the top of a mast, sticking out in different directions like tree limbs.

Now here's my dilemma ..... The three screwdriver companies I'm considering, (High Sierra, KJ7U and Tarheel) make a shorty version of the screwdriver that can mount on top of the mini van in addition to the full size bumper mounted version like Bill KE1GF has. Considering the issues of ground losses and absorption to the vehicle body with the bumper mounted antenna, would I be better off with the shorty version of the antenna mounted on top, dead center on the roof of the mini van, vs the bumper mounted full size antenna?... With the bumper mounted setup, a majority of the antenna will be inches from the van body and considering I would have to weld something like a trailer hitch to mount the antenna, the shorter rooftop mount would be easier...

Which would be more efficient? longer antenna mounted low with ground losses and vehicle body absorption? or shorter antenna mounted up top in the clear on a uniform groundplane surface?

waddya think?

[K1JJ]

Which would be more efficient? longer antenna mounted low with ground losses and vehicle body absorption? or shorter antenna mounted up top in the clear on a uniform groundplane surface?
waddya think?

Hi Glenn,

You brought up a good question. I had to think long and hard about it, but I have some answers.

Intuitively, you would think a longer whip would be the best. But you have a unique situation with that van. I can see several reasons why the shortie Tarheel ScrewDriver on the center top of the roof will be better than the longer Tarheel mounted on the bumper.

You have a height limitation when mounting a whip on the van roof, which means a shortie is needed to avoid hitting bridges, etc.

1)The bumper mounted antenna will have most of its area only inches from the van's body and will act like an open wire transmission line for that enclosed distance. The free area above the roof is your actual radiating element. The radiation will cancel below the roof. Also, the coil is only inches away from the van's body, lowering its Q.  On 75M, open wire that is spaced even 2 feet! apart works FB - I've tried it.

In contrast, with the top, center mounted whip, the entire whip and coil are in the clear to do it's thing fed against the whole van body.  If you had a truck that permitted the whip to be mounted in the clear on the rear top bed, like Bill/GF's, then then go for the longer whip.

2) Shortie whips that use heavy components are not that bad as shown by W2IHY's shortie vertical experiments. I would add a spoked capacity hat to the whip as high above the coil as possible near the top. That screwdriver will tune anything, and the capacity hat will help bring the current portion up even higher on the whip.

3) The difference between the short and longer whip is insignificant, assuming that they are both made of strapping coils and base connections, etc. As said before, the overwhelming loss is in the groundplane (van body) to ground. The whip assembly loss is small in comparison to ground losses. They are in series.

On the shortie, the overall Q will be higher and bandwidth will be smaller than the longer whip, but who cares, since you have remote tuning from the op position.


4) There is a directional tendency for whips mounted on the rear of a vehicle. A center roof mounted whip is pretty much omni. The last thing you need are pattern holes in your already PW signal when driving down a long, straight highway.  Chances are you will have guys in the holes from time to time.

The center top roof  mounted antenna is simply the cleanest pattern and best choice for a tall van like that.  Be sure to axe the TarHeel guys for the optional bigger coil and capacity hat, if offered.  I am leaning towards the Tarheel Screwdriver after reading Bill's post here  and seeing the ads and 100% testimonial posts from hams. The price seems cheap for that product compared to what is out there.

You might even consider building your own screwdriver. There are plans out there. Use the biggest coil wire possible, a capacity hat, silver plated everything...    But, because of the tremendous ground losses, it will probably work no better than the best Tarheel version.

Also, spend plenty of time bonding, strapping and bypassing to get the minimum vehicle noise. Axe the dealership for noise directives, etc. Receiving will be your biggest problem due to noise. When I was mobile, I could work anybody I could hear when parked in a good spot. But once on the road with my own vehicle noise, noise from other vehicles, powerlines, digital noise from lines, etc, it was difficult to hear. But it was a fun experience and worth it. I later added a solid state 1500W pep linear. Talk about being an alligator. Now Warren/ORS owns that amp and uses it mobile when needed..

73,
T

[Glenn NY4NC]

Hi Tom;

Glad to hear you agree with what I was thinking.   

You said;

The center top roof mounted antenna is simply the cleanest pattern and best choice for a tall van like that.  Be sure to axe the TarHeel guys for the optional bigger coil and capacity hat, if offered.  I am leaning towards the Tarheel Screwdriver after reading Bill's post here  and seeing the ads and 100% testimonial posts from hams. The price seems cheap for that product compared to what is out there.

After looking at all the screwdrivers, reading comments, I've decided to go with the Tarheel II. I'll mount it dead center on top of the mini van.

There is a capacity hat available but it's designed to mount where the top of the coil meets the bottom of the whip. My experience tells me this is not the best place for a capacity hat. I guess placing it on top of the whip (ideal location) creates a stability problem? 

Also, spend plenty of time bonding, strapping and bypassing to get the minimum vehicle noise. Axe the dealership for noise directives, etc. Receiving will be your biggest problem due to noise. When I was mobile, I could work anybody I could hear when parked in a good spot. But once on the road with my own vehicle noise, noise from other vehicles, powerlines, digital noise from lines, etc, it was difficult to hear. But it was a fun experience and worth it.

You brought-up a bad memory for me.... my mobile installation from 10 years ago... bad noise problems,   mostly from the vehicle.... computer birdies, engine noise... I'm going to have to address those problems again with this installation...

If I tune my AM broadcast radio in the van to an empty freq when I'm driving, I hear a loud "bizzzzzzzzz, bizzzzzz bizzzzz," a pulse type noise where the rate is changing depending on my RPM's. I'm sure this will also be heard when I install the HF rig. The car dealer has some sort of noise reduction kit?

Here's the ant,,,

[K1JJ]

That looks like a FB installation, Glenn. The large mag mounts work just fine.. no need to cut holes. Looking forward to seeing yours. It will be quite the system sitting up centered high on the van's roof, in the clear like that... esp on the higher bands.

I'll bet that installation will do everything you want and more.

I would use a bigger diameter wire for the little matching coil at the bottom. Lots of current there at ~10 ohms. Can't hurt.

The capacity hat can sit as high as possible on the whip above the coil.  Even if it is only a few inches above the coil, it will be better than not. Yes, the cap hat will bother the coil if sitting close, right above it. The best place is at the very top, but mechanical considerations are the problem, as you said.  You might guy the whip with 90 lb test monofilament clear fishing line to help.

73,
T

[K1JJ]

As a follow up, Glenn....

I've been mentioning the importance of putting a capacity hat on the short whip. Maybe this will help make up youir mind....

If you add a capacity hat to that short whip, you can raise its input impedance to the point of being just as efficent (or more) than the longer whip you talked about putting down lower on the rear bumper. Actual length means very little - it's the losses that count. 

There will come a day when a 75M Yagi will be a few feet long using room temperature super conductors. The antenna pattern will be the same as a full sized one in the far field... it doesn't matter how the pattern gets formed, just that the losses are held in check.

ie, You can have your cake and eat it too by adding a capacity hat to that shortie whip on top of the roof! Just depends how big you can make it...

73,
T

[WB2EMS]

If you add a capacity hat to that short whip, you can raise its input impedance to the point of being just as efficent (or more) than the longer whip you talked about putting down lower on the rear bumper. Actual length means very little - it's the losses that count.

One thing I've wondered about - aside from adding a capacity hat, how about just bending the whip over, or adding a right angle to it some how, and trailing more conductor off behind or in front of you. My screwdriver is on a mount attached to a rear hitch mounted bike rack, which gets it up and away from ground as well as spacing it a couple of feet behind the body of the vehicle (and behind the window instead of the metal body). If I were to go up 4 feet from the top of the coil, then bend forward, I could get another 10-12 feet of conductor in the air going forward to the front bumper. Supporting it might be interesting, but doable. It would be 2-3 feet or more above the roofline. Would that be better, or worse, than a capacity hat?

Another antenna option that looks worth considering is a small transmitting loop. There is an australian company that makes HF gear for interior travellers in that country and they offer an antenna that is a combo roof rack and loop antenna for 3-30 mhz. They claim 10 db improvement over a whip. Running some of the loop design programs, the efficiency of a loop of practical dimensions (say a 4 foot wide, 8 foot long rectangle) seems to compare favorably with some of the numbers I've heard quoted for whip antenna efficiencies, especially if the loop conductor diameter is large. Anyone have any experience with that? Check out k6hpx on qrz.com to see an example mounted vertically. The owner claims it's the best mobile antenna he's ever used. 

[WU2D]

All of the "high efficiency" mobile antennas presented are going to give great results. Even so they are still fairly low efficiency devices compared to a high dipole or full size vertical with a million radials.

I have run a couple of less than ideal setups that worked fine on 75M AM mobile.

The first was to combat vandalism in college. A Hustler whip was the typical Ham mobile antenna back then. I came out of my dorm to see my antenna tied in a knot - actually I laughed too - it was amazing. The answer was to join the CB craze and mount a 102 ich stainless whip on a ball mount. Don't forget to put it on the passenger side (that is another story).

This antenna was tough and it could be tied down in a half loop. The whip was resonated at the base inside the trunk with an autotransformer match. I seem to remember 30 or so turns of copper tubing on insulators. The bottom of the coil was grounded and you simply tapped up to the 50 Ohm point. This was a quiet antenna beacuse it was a DC short and it was a good performer on 75 Meters. This antenna produced high voltage.

The second antenna was a small early mag mount which I stuck on may compact car in 1992. It is shown below. It consists of a small 75M Hustler tip on top of a PVC pipe helically wound with #12 enamelled wire to acheive resonanace. the whole deal was 5 feet long. I used a ground strap to the trunk and two fishline stays. That is about a simple and small as you can go. This was no Bugcatcher. It worked well with a command set transmitter.

Mike WU2D

[K1JJ]

I've wondered about - aside from adding a capacity hat, how about just bending the whip over, or adding a right angle to it some how, and trailing more conductor off behind or in front of you.

Hi Mike,

Yes, making the whip longer and bending it over so that it forms a curve over the vehicle will give you the "avaerage" of a whip and a capacity hat. It will tend to give more horizontal polarization, too.

I tried that once with a 20' whip on my Blazer. After running lots of field strength tests against other "Bugcatcher" type homebrew antennas, I came to the conclusion that it wasn't worth it. The ground losses are so high with the vehicle that you reach the point of diminishing returns quickly with any mobile ant config..

I even tried a 30' whip in a stationary position and it made no difference against a "Bugcatcher" style antenna. (Filed strength tests)

The bottom line is this:  I once parked my Blazer outside in the field, in the clear. I had an antenna switch to go from a full sized dipole to the "Bugcatcher" on the Blazer. I ran an AM KW into each. The difference was 15db at best and sometimes 20db. Very consistent. That's not bad when you think about it.  Trying to squeze a differential of less than 15 db is probably fantasy.

I think the average Hamstick type ant is down about -25 db from a standard dipole, where the BEST Bugcatcher is about 8db better. (-17db) Going to anything more elaborate is a waste on a car. Heck, even full sized verticals with a radial field are down 15-20db for local high angles signals on 75M right?

The low angle signals seem to be favored around one hour before sunset on 75M. That's when 75M mobiles kick ass locally.

73,
T

[Glenn NY4NC]

Hi Tom;

The only problem with adding a capacity hat on the shorty Tarheel is it may no longer resonate on the 6 meter band. The whip length on top of the coil is 32". A quarter wave on 6mtrs is roughly 4.5ft so the stock antenna setup probably uses only a few coils turns to achive resonance on 6. If I add a capacity hat, the electrical length may become too long to resonate on 6 meters. I could probably add a cap in series at the feedpoint but that would have to be switched out when using the other bands.

I was thinking I could use the capacity hat at the top of the whip by replacing the stock 32" Tarheel whip with a cut down 8ft CB whip whip. The top would then be thick enough to mount a capacity hat. Of course like you said, it would still need to be guyed with fishing line....

High Sierra makes two types of capacity hats. The flat one is designed to mount right on top of the coil, the other one (45 deg elements) can be mounted above the coil on the whip.

As a follow up, Glenn....

I've been mentioning the importance of putting a capacity hat on the short whip. Maybe this will help make up youir mind....

If you add a capacity hat to that short whip, you can raise its input impedance to the point of being just as efficent (or more) than the longer whip you talked about putting down lower on the rear bumper. Actual length means very little - it's the losses that count. 

There will come a day when a 75M Yagi will be a few feet long using room temperature super conductors. The antenna pattern will be the same as a full sized one in the far field... it doesn't matter how the pattern gets formed, just that the losses are held in check.

ie, You can have your cake and eat it too by adding a capacity hat to that shortie whip on top of the roof! Just depends how big you can make it...

73,
T

[K1JJ]

Yes, the stronger whip would be FB with the capacity hat.  The cap hat is probably easy to take on and off.... or if not, just drill and tap a 3/16" threaded hole and use a knob/bolt to quickly take it off.   The time you spend on 6M may be rare, so it will be worth it on the lower bands to have it on all the time.

T