Tall 20-80m antenna on bumper or short single band hf antenna on roof?

[K7POC]

I live in a low brush area but have a 50' cobra whip for 10m that survives ok. Just got another 706 for the mobile. I can ether mount say a MFJ 36' short mobile whip on the roof or something like a opek hvt-400b on the back bumper. Witch would be better? Oh and I've got a 99 jeep cherokee.



R

[N9AAT]

I have asked myself the same question many times. In my case, I'm usually driving (with time to talk on the radio) during daylight hours when 10-15-20 meters are the only bands open. My trip to work is 45 min each way and I use a 10-meter Wilson mag-mount because I hate pileups and also I just like the mystique of 10-meters.

Obviously at night the opposite would be true, so regular night drivers would probably want something for 40 or 80.

If I were a long-haul trucker I'd want multiband capability.

:cool: My advise is to get the multi-band, go for a year and see what your favorite frequencies are, and keep a single-band mag-mount around for when you have to go somewhere in another car.

[N9AAT]

And oh, here's a quick story. A couple of friends and I do RFI chasing from time to time, and we're usually looking for something interfering with VHF aircraft frequencies. To simulate a real-world antenna, my buddy Jeff bolted a real four-foot VHF aircraft antenna which we call a donkey-dong (I don't elaborate further) onto five feet of SCH-80 galvanized pipe welded onto a trailer hitch. By driving along behind him in another vehicle, I did a quick survey and discovered that he can break low-hanging branches up to 1.25 in. thick, and throw them on the hood of my car!!! I would NOT try this experiment with the Opek antenna! :D

[K0BG]

Without knowing a lot more than we do, it is a conundrum. Typically, length matters more than mounting location, as radiation resistance is a function of the square of the length. Ground losses (the reason to mount antennas as high as you can) do decrease with height, but not that drastically.

[KD8NPB]

I live in a low brush area but have a 50' cobra whip for 10m that survives ok. Just got another 706 for the mobile. I can ether mount say a MFJ 36' short mobile whip on the roof or something like a opek hvt-400b on the back bumper. Witch would be better? Oh and I've got a 99 jeep cherokee.



R

Trying to do 75m/80m on the go is a losing battle. Even with the most efficient of antennas, you'd be lucky to put out 5w, and your receive sensitivity is going to be terrible.

Either go my route,

Option A: 102" whip with an auto-tuner right at the feed point
or
Option B: Screwdriver antenna

[W0LPQ]

7POC you said a 50 FOOT whip?? How does that work .. driving down the road??
I use an N9JMX screwdriver.

[AC4RD]

I've been trying a bunch of different antennas on my car, over the last few months. I tried the "Shark mini whip" on my roofline, and found it worked better than I really expected. I don't have hard data, but I decided the mini was an S unit or two down from a full-sized Hamstick on my bumper. For me, the extra length provided better performance than the higher mounting. No guarantees about whether it would be the same for you, of course. HTH!

[W0LPQ]

7POC I don't know if you meant inches or feet ..

" = inches
' = feet .

[K7POC]

I meant inches that Wilson 5k is about 53" inches long. I'm really looking for a solution that dose not involved a $3-$400 antenna. Thinking about that 102" whip on the bumper with a tuner.

[K9STH]

If you look in the old mobile manuals (ARRL, CQ, etc.) you can find instructions on making some pretty good all band mobile antennas that don't cost a fortune. Nowadays most people just go out and purchase an antenna. But, don't sell short what you can do yourself.

Glen, K9STH

[WA7PRC]

I've run modified Hustler/New-Tronics (http://www.new-tronics.com/) stuff, starting with the 54" tall MO-1 mast:


75m = RM75 w/ inductance removed + 56" whip (129" OAL)
40m = RM40 w/ inductance removed + 40" whip (111" OAL)
20m = RM15 + 39" whip (108" OAL)
15m = RM12 + 25.5" whip (91" OAL)
10m = NO resonator (MO-1 mast + 40" whip & homebrew adapter)*

The 20m setup has worked well enough to work into Europe and Maylasia from NW USA. I s'pose I could use a longer whip with less loading coil. I haven't tried that... yet.

All whip lengths are only the part that protrudes above the resonator. You'll need a whip at least a few inches longer than that. The RM75 uses the Larsen W640 (64") whip. Others are either Larsen W490 (49") or Hustler/New-Tronics.

* The adapter is made from a 3/8"-24 coupling nut + 1/4"-28 socket head screw (stainless steel). The old but still available Hustler locknut + split ferrule is used with it. A 1/8" hole is drilled through the stud at the top of the mast tubing to allow the whip to pass through.

Photo of 10m adapter:
http://farm5.static.flickr.com/4118/4903254975_cfc59fdfee_m.jpg

I had to buy enough material to make 10 of these, just to have one for myself. I still have 9 available (w/ locknut & ferrule) around here somewhere.

[N0JA]

I am using a Hustler 30 meter coil with a long whip, 56" or more to operate on 40 meters mobile, and a 15 meter resonator with long whip for 20 meters. In addition to an S unit or two additional signal, you get broader bandwidth. On 40 the bandwidth is about double the stock Hustler 40 meter set up. I can operate over 60 or 70 kc with a SWR of under 2 to 1. My 54 inch mast is mounted on a bracket approx. 4 feet above ground on the rear of a mini-van. On 40 meters, the antenna gets a little tall, but I generally only use it on long trips on the interstate, and keeping schedules with friends when visiting my daughter, grand sons, and son in law in Louisiana. I view the mini screwdriver antennas as a bad joke. The big screwdrivers are well BIG, and would be a problem for my mounting arrangement because of size windloading, and weight. Also have a 40 meter Ham Stick, and it seems to work about the same as the stock Hustler on 40 meters with my mounting arrangement. A good solid grounded to the body mounting arrangement and clean connections for the coax is the secret. I have to disassemble the mounting and clean/renew the connections every few months. It still amazes me that you can work anybody mobile on 40 meters running 100 watts or less with a dummy load on a stick!

[WA7KKP]

HF antennas are very inefficient -- the more loading you have (need) the less efficient they are. In a nutshell, size is everything.

You'll want as long an antenna as practical, without slamming into those low flying trees and other flora along our roads and highways. So my vote goes for a bumper mounted tall antenna. I had great results with the Hustler mast and separate loading coils/whips for all of the bands. Use the KW rated loads, even though they're all the diameter of a beer can -- the efficiency of the load is much better than the smaller versions.

I even worked Russia mobile from Jasper AB -- that should say it all -- with aformentioned skyhook.

Gary WA7KKP

[K0BG]

Here a truth about Hustler coils. The smaller ones have a slightly higher Q than the bigger ones (read that as less lossy). The reason this is so, it due to the rather large end caps the bigger ones have.

I still wonder, however, why everyone uses the ability to work DX as a measurable antenna parameter?

[KG6UTS]

K0BA and the group..
The new QST has a good piece on a home built 75/80 meter antenna, nice piece of work and the details are on "QST in Depth". VE6AB has a pickup/campershell arrangement so the coil and lower mast are above the metal truck body. The antenna is mounted on a steel tube that appears to be bolted to the bumper. Is this in violation of "far removed grounds???
I've collected all the parts including the 3"X10"@8TPI coil stock to build the bugcatcher detailed in the December '80 QST and plan to build an antenna based on that article, the N1LO piece, and VE6AB. My lower mast is a used hustler tilt model with an old heavy duty spring and ball. The vehicle is a 94 Jeep Grand Cherokee so I have no problem drilling a mounting hole. I'd like to put the antenna on the right rear with the coil above the roof and the bend joint in the lower mast near the roof line so I can forward drop the antenna when loading kayaks and fishing rod tubes. That puts my feed inside the Jeep rear quarter panel inches from the radio. Any problem with this? I have another antenna for the left side and use a metal mast in a trailer hitch tip-up tube for VHF antennas. The VHF gear is used parked.

[KA5S]

I have experimented with low mounted masts vs rooftop mounts, and on 80 and 160 meters I saw comparable results with bottom-loading, coil and whip on a roof mount, versus center loading with the coil and whip on a frame-mounted 5 foot mast. Best results were center loading in the middle of the car roof -- and a big top-hat. Not good for low-hanging branches, though!

Cortland
KA5S

[KA5S]

Here a truth about Hustler coils. The smaller ones have a slightly higher Q than the bigger ones (read that as less lossy). The reason this is so, it due to the rather large end caps the bigger ones have...

IIRC, Sevick noted that with the poor ground under most cars, even the better Hustler coils weren't noticeably worse than high-Q coils. 3 dB more radiated power when the system was only 0.5% efficient to start with is still only 1%.

Cortland
KA5S

[WA7PRC]

Best results were center loading in the middle of the car roof -- and a big top-hat. Not good for low-hanging branches, though!
With my modified Hustler setup mounted around 36" above ground, the tip of my 75m antenna (RM-75 + Larsen 64" whip) is something like 13' 6" above ground. It's hit a few low hanging branches. Years ago, I did 2-way radio (mostly CB) mobile installations. Motorhomes usually got Larsen NMO-27s (48" tall) mounted on the roof. Now, THOSE were tall setups! ;)

The good news: they're easy to spot in a crowded parking lot! :D

[K0BG]

Yes it is. The article was written some three years ago,and just recently published. He has since fixed that problem. He also designed a much better all band antenna. it is unique, in that it uses a linear actuator. Photos of it are in the Photo Gallery, Others Install album on my web site.

As for Sevick's comments...

As a general rule, that might be true as ground loss dominates the efficiency equation. However, as you decrease ground losses, the difference is much more apparent, and can be as high as 10 dB, perhaps a bit more depending on the antennas in question.

If you really want to see a big difference, use an aluminum mast instead of a stainless steel whip, along with a big cap hat.

[M0GVZ]

I still wonder, however, why everyone uses the ability to work DX as a measurable antenna parameter?

Because without $10,000's of professional test equipment, what other method can you use?

[K0BG]

My point is, that using you're log book as a measuring tool is a bit inane, and a little self-serving. I personally never, ever mention my DX count, or grid square totals, even on my web site, albeit I know what they are. I don't, because they really don't mean much. People have worked DXCC with little more than a Tuna can QRP transmitter, and a 40 watt light bulb. So what does near legal limit mobile relate to?

You're correct about the equipment, except you need to add a zero or two to be able to measure field strengths accurately. Except for the military, the last privately-owned antenna test site was the one HyGain had back in the 70s. The University of Nebraska's field house sits on the site now.

You can, however, measure relative strengths, and compare one antenna set up with another. That can be done with several hundred feet of coax, and a dual port VNA. The way I do it is in the same fashion Rudy Severns, N6LF, used for his series of articles (http://www.antennasbyn6lf.com/) for QEX. All told, I suspect I've spent about $1,500USD. But even then, you have to be rather careful. As Rudy pointed out, he could see real-time the changes caused by local weather conditions. This is also the reason antenna shootouts are suspect at best.

All of this boils down to a few hard facts. If you want to get the best out of your mobile installation, all you have to do is follow a few basic rules.

1). The antenna must be as physically long as you can make it, consistent with as much metal mass under it, and local conditions allow.
2). RF conducting elements shouldn't be any form of steel, especially 17-7 stainless steel. Its permeability is about 240, while aluminum is about 2! Here is some food for thought (http://vk1od.net/antenna/conductors/loss.htm).
3). Cap hats are a given. The efficiency of any vertical antenna is a function of the effective electrical length, and the current flow along that length. Properly installed cap hats (not at the coil, but as far away from the coil as possible) will increase the radiation resistance by as much as four times! When the radiation resistance is a few tenths of an ohm as it is on 160 meters, or a ohm or two on 80 meters, four times is a very significant increase!
4). Coil Qs must be kept above 250 or so, but anything over 350 is all but a waste of time. This means there cannot be any significant metal within the field of the coil. This includes large end caps, metal shorting plungers, the body of the vehicle, etc.
5). As alluded to above, it is the metal mass directly under the antenna, not what is along side, that counts. This eliminates low mounting (trailer hitch mounts for example), and almost always requires holes to be drilled.

Anything less, is exactly that, less! If you're satisfied with whatever you have, good for you! As for me, I'll continue to put my best foot forward.

[G7DIE]

2). RF conducting elements shouldn't be any form of steel, especially 17-7 stainless steel. Its permeability is about 240, while aluminum is about 2! Here is some food for thought.


OMG 102" ss whip :-0 opened my eyes somewhat!

[KG6UTS]

. Except for the military, the last privately-owned antenna test site was the one HyGain had back in the 70s. The University of Nebraska's field house sits on the site now.


All of this boils down to a few hard facts. If you want to get the best out of your mobile installation, all you have to do is follow a few basic rules.

1). The antenna must be as physically long as you can make it, consistent with as much metal mass under it, and local conditions allow.
2). RF conducting elements shouldn't be any form of steel, especially 17-7 stainless steel. Its permeability is about 240, while aluminum is about 2! [URL="http://vk1od.net/antenna/conductors/[/QUOTE]

I'm lucky enough to work next to the Navy antenna test range on Pt. Loma, my friend N6TYF runs it. They did extensive tests on the military version of the Hi-Q antennas here and I've used the range to test some of my homebrew 6 meter antennas. When the bugcatcher is done and on the Jeep I'll drive it out there on the weekend. Thanks for the reminder on materials! The whip here is a fiberglass model with embedded conductor. I have not measured the Airdux coil yet, 3"X10"@8TPI, and still have to pick up some delrin and poly to machine for end caps and coil cover. The center strength member is 1" fiberglass rod sort of like the VE6AB coil support. This turning into a fun project and seeing input and comments here makes it even more interesting.

EdZ KG6UTS

[K0BG]

Just don't be surprised at the outcome of the HiQ measurements. Anytime you introduce large metal end caps, and an aluminum shorting plunger to the mix, the Q drops drastically. They just introduced a new shorting bar, with spring-loaded ball bearings to replace the beryllium copper contact assembly. I just can't wait to see the results!

[KA5S]

OMG 102" ss whip :-0 opened my eyes somewhat!

When I lived South of Fort Worth, and worked at the Tandy Center, I frame mounted (Icom AH3A mount) a five foot mast with Bugcatcher and steel CB whip on my Chevy Sprint, then drove back and forth to work on IH35W. Every so often it'd hit an overpass; CLANG! And after it did, I'd grind off the part curled in a circle and readjust the coil tap. I had not yet done roof versus mast tests, but it consistently had the best 75m morning commute signal crossing the (IIRC) 4th St bridge, steel whip or not.

For 160 I did use base loading, a coil wound on a piece of 4 inch sewer pipe with a fiberglass CB whip (that didn't sway so much) and a pair of tuning arms just above the coil to QSY with. It was a terrible design, wound with about #20 wire to boot, but I did work 90 stations in 30 states (and both coasts) during a 160m CW sweepstakes. Eh. Good old days.

Left there in '93 for Irvine,CA. FWIW, I had a lot of fun yakking with JA's on 80 CW from the car. REALLY strong signals coming off the ocean.


Cortland
KA5S

[W5LDA]

699046990569906

Never tried to attach a file with this new computer. Hope you can see my antenna install