Mobile antennas - What is there these days

[VK1DX]

Hi all. Been a long time off the air. We just got a 4WD and I am wondering from experience what antennas to add. Forget the phone and computers. Don't want any. I will be installing UHF CB as a natural because everyone seems to have one in the "outback".

Because of mounting restrictions the HF rig will be one of my trusty FT707's. But what's the latest in antennas? While moving, what should I use and then at night what is there these days for a whip that would go on the same mount. I would prefer not to use an ATU. Again where does the ATU get mounted! Just simple setup. Don't need DXCC or contesting.

These modern 4WD's do not have a lot of places to put anything other than a CB. Not even enough room under the drivers seat for a box of matches. Thats why my choice of radio. Just small enough to be mounted on the sides of the center floor console.

Hi again to all from a voice from the past (vk1dx and vk1pj)

[VK3DJ]

Hi Frank, there is lots of stuff around for mobile/portable operation. But like it has always been, all these types of antennas are a compromise. The most popular seem to be the tapped whips and the screw driver types. Depending on the freq, they can be little more than a dummy load.

As I do a lot of portable operating (too much noise at home) I have taken to building my own antennas. For mobile use I have made top loaded verticals on the longest practical whip blank I could find. I have seperate whips for each band - less of a comprimise that way.

For portable operation when I am parked, I use a squidpole as a support for a variety of vertical and dipole antennas. If you dig up a copy of AR for Jan-Feb 2008 you will see an article I wrote and all the dimensions required to build a 'squidpole 1/4 wave antenna'. I and others have been using them for a couple of years now and always with excellent reports. They are very easy and inexpensive to make.

Good luck with whatever you decide to do. And welcome back to AR.

Dallas
VK3DJ

[VK1DX]

Thanks Dallas

I will check it out.

Since you did not high;ight any particular model it sounds like commercially built mobile HF antennas haven't gone anywhere since I went off the air. I used to be fine making beams and wire based antennas (as applicable) for most bands. Whips - a dead loss. Could never figure out what I did wrong.

I have a couple of old whips the spiders have been using under the house somewhere and maybe I will use them.

Best for 2009

Phil

[VK7HDX]

I use HF in the ute and recommend from first hand experience using monoband antennas by Diamond antennas. I use the HF20FX..HF40FX and HF10FX series around $99 AUD each from Andrews (VK2) and Strictly ham (VK3) . Sure there is 3 separate antennas but monoband antennas just work better due to that is what they where designed for and as for SWR issues with these mono's....nothing at all... in fact with a antenna analyzer less than 1 minute and they are fairly flat on each band depending on which part of the spectrum you wish to TX on but I have found the higher band antennas example 14MHz and beyond they have a larger SWR window to play with. But then if you have limited space on your mobile maybe a trapped stick maybe the other answer. It basically depends what you really want and what kind of condition you have to work with (space on car/ute or 4WD) but for me monoband antenna are the true way to TX.

73...Karl
VK7HDX

[VK2OMD]

... and as for SWR issues with these mono's....nothing at all...

Karl,

It helps to understand the operation of direct fed short loaded whips.

By direct fed, I mean the configuration where a 50 ohm coax attaches directly to the base of the whip and vehicle body with NO matching circuit.

The feedpoint impedance consists of reactance and resistance. A loading coil, or continuous loading (AKA helical) can be used to 'tune out' the reactance component.

The remaining feedpoint resistance (Rt) can be thought of as comprising three main series components, radiation resistance (Rr), earth resistance (Re), and radiator+loading loss resistance (Rl),

The VSWR gives a clue to the total feedpoint resistance. If the VSWRmax is say 2:1, then Rt=50/2=25.

Rr is really important, it can be thought of as the ONLY component of Rt that results in radiation, current flowing in the other components of Rt, ie Re and Rl is converted to heat. As a whip becomes progressively shorter wrt frequency, Rr becomes smaller... approaching just a couple of ohms for a short whip on 80m.

Re might typically be 15 to 20 ohms. Lets use a value of 15 ohms to illustrate what happens.

If a certain short loaded 80m whip has VSWRmax=2, and Re=15, Rr=2, then what is Rl? Rl=50/VSWR-Re=50/2-15=10. Efficiency=Rr/Rt=2/25=8%. Of course, there are additional losses in the feedline and the radio might not deliver 100% of rated power into a VSWR=2 load, so SYSTEM efficiency might be somewhat less than 8%. In dB terms, the antenna has an average gain of WORSE than -11dBi. (Efficiency means PowerRadiated/PowerInput.)

But, what about such an antenna advertised with a VSWRmax=1.5... is it 'better' (whatever that means)?

I hear you say "show me the numbers".

If a same height 80m whip has VSWRmax=1.5, and Re=15, Rr=2, then what is Rl? Rl=50/VSWR-Re=50/1.5-15=18.33. Efficiency=Rr/Rt=2/33=6%. Of course, there are additional losses in the feedline and the radio might not deliver 100% of rated power into a VSWR=1.5 load, so SYSTEM efficiency might be somewhat less than 6%. In dB terms, the antenna has an average gain of WORSE than -12dBi.

The manufacturer builds out the feedpoint resistance with loss resistance to achieve the specification VSWR, for two such antennas with equal height, the lower VSWRmax, the LESS efficient the antenna. It that seems counter intuitive, go back and reread the above explanation of the design of these type of antennas.

There are three competing factors that are of interest, VSWR, bandwidth and efficiency. It is challenging to optimise all three, usual practice is to hand up one and optimise the other two. Hams usually focus on VSWR and bandwidth at the expense of efficiency.

Owen

[VK4QB]

Many Happy Returns.
The antenna problems are still the same . I look on the short antennas as getting close to a dummy load. and so the bigger the better, which gives more capture area , with mobile antennas. As the bottom of the antenna is the part that radiates the most the top loading is the most efficient, but its all a compromise. Nothings changed. I have a 12 foot bottom loaded whip on my motor home and it works well. I don't use it mobile though, due to the base being 8 foot off the ground. I tuned it using 3 methods, resonance with GDO, noise bridge, and SWR.
Welcome back
Brian 4QB

[VK7HDX]

Hello Owen,

All that you have written above is so TRUE about many factors of antennas theory. But I was "generally "speaking only. All I was trying to say without going into great lengths was..... 28MHz (loaded coil) antenna plus a antenna analyzer set @ 28.490MHz shows close to 50ohm with a SWR of 1:3:1 on the meter. So I'm happy enough. Yes there a lot of factors to take in to account but I was looking for the.."load up-tune up and drive away" answer only at the time..

73 Karl
VK7HDX

[VK2OMD]

... I look on the short antennas as getting close to a dummy load....

Brian, it is interesting that you say that.

There are three competing factors that are of interest, VSWR, bandwidth and efficiency. It is challenging to optimise all three, usual practice is to hand up one and optimise the other two. Hams usually focus on VSWR and bandwidth at the expense of efficiency.

It may not occur to readers that if you take this to the extreme, good VSWR and bandwidth and zero efficiency are the characteristics of a good dummy load!

Efficiency in short antennas is a challenge, but the design of direct fed short mobile whips is consciously an inefficient one in favour of simplified 'matching' to the transmitter. A conscious design decision even if buyers are unaware.

Owen

[VK2OMD]

Hello Owen,

All that you have written above is so TRUE about many factors of antennas theory. But I was "generally "speaking only. All I was trying to say without going into great lengths was..... 28MHz (loaded coil) antenna plus a antenna analyzer set @ 28.490MHz shows close to 50ohm with a SWR of 1:3:1 on the meter. So I'm happy enough. Yes there a lot of factors to take in to account but I was looking for the.."load up-tune up and drive away" answer only at the time..

73 Karl
VK7HDX

Karl,

The 28MHz example you discuss is probably not such a short antenna in terms of electrical length, meaning that Rr is higher, Re is probably lower, and Rl doesn't need to be as high for good VSWR, and efficiency is higher (though efficiency is not important to most hams).

The intent of my post was to explain how manufacturers appeal to a VSWR focused buyer, rather than to criticise a particular antenna. The interesting things is that for such designs, lower VSWR indicates lower efficiency... not intuitive to a VSWR focused buyer perhaps.

Owen

[VK3XIL]

Hi

I have been using 2 Terlin tapped whips for HF on my previous Toyota Troopie (front bullbar mounted) and my current Ford ute (centre of front ladder bar mounted)

I have an Outbacker reach - 3m tall and works a treat - bandwidth is narrow on lower bands - but that is to be expected

for mobile/city work I have an Outbaker Perth - at 1.8m its a bit more managable.

Both work fine - within their limitations

cheers

matt
VK3XIL

[VK1DX]

Thanks all

Sorry but not only have I been away on a couple of trips, I was also in bed for 7 weeks with a huge big bad super bug. Five weeks at home and then when I finally went to see the doctor, two more weeks in hospital. I was admitted as soon as I sat down in his consultation room. Bloody quickly onto drips and so on. Some kind of strefacolpolous. Two days to find it. The specialist who eventually found it said I should have been kicking up daisies. Lucky man and the lottery ticket did not win anything. I now have to be at the hospital every four weeks for IV infusions. NO EXEMPTION. So the trips will be restricted.

I believe my solution will be three whips. One each for 40, 20 and 10. They are easy to carry and can be used on the move if I so choose. No setting up wires and so on. Just put the desired antenna on the front and turn the radio on. That will do me. Most likely just the 40 for the travellers net checking though.

Cheers and again thanks all.

Phil

[VK5KLV]

Hi Phil, I have been using monobanders for HF on my 4wd but am about to try a Codan 9350 as the separate whips are a pain to store when mobile & not in use. I use a 2 piece whip about 3 metres long on my Camry & feed it with a Yaesu FC40 auto coupler. That works very well! By the way, the travellers net is on 20 M & is great when on the road. Cheers, Les, VK5KLV.

[VK3GDM]

I can also vouch for the Diamond antennas. I also have the HF20FX, HF40FX and HF10FX models.
Using this combination, I've worked just over 80 countries from the car during the winter this year.

I also have the Terlin Perth Plus and on air comparisons with the Diamond have shown no notable difference in S meter readings.
The height range is about 1.2 to 1.5 meters depending on band.
The things I like about the Diamond HF antenna range are:
- Light weight and low profile/slim line.
- Look really good relative to many of the other big ugly sticks.
- Easy to mount. You don't need heavy duty mounting arrangements. I use a hatch mount.
- Easy to store in the boot.
- Work really well!

Mobile whips may not be as efficient as full sized antenna, but why let that stop you from having a great time.

Go to this link: http://www.clublog.org/charts/?c=T32C# and enter my call VK3GDM/M.
The proof is in the pudding!

73
David

[VK2FXXX]

Hi all.
For anyone interested in mobile operation, here is what I would consider the best web site on the subject.
Many hours of reading here.
http://www.k0bg.com/
Enjoy
Brendan
VK2FXXX
Gday Owen!

[VK4CRO]

I use a FAMPARC WHIP from VIC. , I use the 40m tap and it tunes flat swr on
40m - 15m and 6 m
I bought one these as I listened on 30m with delta loop at home almost
all the contacts I had were mobiles and all with Famparc antennae
FAMPARC Frankston and Morning Peninsular Radio Club make the whips
Build quality TOPS!

[VK8DOD]

Hi all.
For anyone interested in mobile operation, here is what I would consider the best web site on the subject.
Many hours of reading here.
http://www.k0bg.com/
Enjoy
Brendan
VK2FXXX
Gday Owen!

Your link is worth its weight....... As DJ mentioned in one of the very early postings, too much emphasis is placed on SWR and no one appears to care about efficiency. When I got back into AR a few years ago after having bought my own place and not having to worry about what the landlord would say, I began experimenting with antennas again, long wire and mobile. And now that I have access to excellent test equipment I can confirm what k0bg says about efficiency. I still have a yaesu mobile antenna set from when I bought my first FT-101Z and also tried some well known commercial manufactures antennas. The monoband verticals I've built are as good as any commercials I've tested.