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Car Vehicle Static Deployed HF Antenna


#1

Does anyone use car-mounted HF antennas that work and would recommend them? I’d be interested only in 20m and 40m currently. I’m not thinking about mobile here only static operation.
I’ve heard /M stations operating on 20m - it would be useful if I want to do some 20m SOTA chasing for example.

I have an FT-817 + MiNiPA50 amp - I don’t have an HF antenna at home and sometimes it’s not practical (either due to weather or time constraints) to set up a /P station so was wondering what my options would be for a /M station - quick setup and operation from within a car - the antenna could be deployed near to the car if required, but speed and ease would be key.

Many thanks, Mark.
M0NOM


#2

Hi With Sota, no operations allowed from with in or connected to a motorized vehicle.
Must be fully portable. So Mobile Sota ops not allowed or the norm. if drive on, nothing stopping you chucking the gear out and moving car way from the PORTABLE station set up.

Karl


#3

Hi Mark, I’m assuming you’re not talking SOTA here, but rather how to get around the lack of a home HF station.
I have very limited experience, however I hear that the crucial element is to get a good earth/ground plane. I’ve done a bit of 6 & 10m work from the car but tended to always do it stationary with an earth wire direct to the ground (actually a jump lead connected to a spike in the ground) to avoid having to scrape off paint or some such.
There’s loads of advice on the web if you search. Try contacting Peter (MM3PDM) who always works /M on 40m.


#4

Hi Karl

Not SOTA activating but chasing. The Lake District is great for hills to walk up but I can’t think of many places where mobile would work well with take off in all directions (thinking here of 2m FM chasing for example).

Regards, Mark. M0NOM


#5

Over the last 4-5 years I’ve had very good results with the MFJ HF Sticks (similar to the old Hamsticks) on multiple vehicles. The mini versions work OK if conditions are right, but the full size versions work quite well.
I will say they are a bit narrow banded, and their structural weak point is near the base. Many of mine have broken there, even when using a large spring, so I have beefed up all mine (they make them from 6-80M) at the base with fiberglass. There are a couple other style HF mobile antennas I’d like to try, and may get a screwdriver type at some point, but the HF sticks are a pretty good bang for the buck antenna, and can quickly swap out when changing bands.

As others have stated, good grounding goes a long way in mobile performance. Many articles online about this. 73, Mark/K6MTS


#6

Hi Mark,
I have done this while living in a holiday flat - I just drove away from the Metro EMI and chased in the RF quiet. My approach was to take a fibre glass pole and an inverted V dipole. After parking, strap the mast to the side of the car (door handle plus roof rack bar) - run out the wires and away we go.

Not as quick as using a whip of some kind that is permanently on the car and you need some space but the dipole at 5 metres or so high works better than a car mounted whip.

73 Ed.


#7

Chasing hmm

Why not indeed. Have good look around you for big wide open spaces up on drive able hills or even go to coast line and go toe dipping when the tide is high pref above 5m, 1hour prior and 1 hour afterwards.

Got couple places around me in Rame head on the coast and Kitt Hill on where noise levels are LOW and reaching out is good and plenty room to slap up big antenna off the car CW80 being one of them.

Have good explore around you will find somewhere.

karl


#8

Thanks for the suggestions, much appreciated. I may well just give using my 8m fishing pole and sotabeam quad bander (inverted V wire dipole) a go to start with. I like the idea of either a V or inverted V hamstick dipole, there seems to be very favourable reports with that configuration and it removes the need for good grounding. I was also toying with the idea of a 20m half-wave dipole wire supported by 2x8m masts in a V configuration, but I haven’t done the math on that so not sure that is going to give at least 0.25 wavelength above the ground (gut feeling is it will).

The other option of course is a drive on mast support and winch if going the whole hog, although I don’t think that would support even the most lightweight 20m yagi. Was just watching the video for http://www.m0cvoantennas.com/apps/webstore/

I do have an very unused motorbike trailer. That would make a good antenna platform, but that’s getting quite serious. I’m general not that organised.

Oh and noted Mark/K6MTS about the hamsticks. I bought one very early on for 80m (probably the worst compromised out of the lot) and it broke first time at that very place when I was laying out radials and the tripod got pulled over having carted it up a hill. It is good they are cheap, but not cheap enough for zero use.

Cheers, Mark.


#9

Hi Mark,

If you have a tow bar you can maker up a bit of hardware to take a piece of plumbing pvc tube. About 1 m long with one end sitting close to the ground and mounted vertically. Needs to be big enough so you can slide your sota mast (8m + recommended) into it. Wind a quarter wave of wire on the mast and use an ATU to match this against the car body. Mobile whips are fine if you don’t mind an efficiency of less than 10%. A wire vertical that is equal or nearly equal to a quarter wave will be near 50% using the car as the counterpoise. If you run a real counterpoise you can pick up more efficiency.

I have used the standard inverted vee dipole on a squid pole tied to a nearby fence post to chase when the mobile whip failed to make the grade.

With an FT817 you need the higher efficiency options.

73
Ron
VK3AFW


#10

Mark, you might find this PDF useful if you consider using a mobile antenna on your car. It’s by the late Terry Graves K7FE.

http://www.moosedata.com/K7FE_antenna_myths.pdf


#11

Many thanks - I should probably buy a book or two too.
It’s a lifetime of learning this antenna lark!


#12

And then some.


#13

Thanks for the link Andy, an interesting read. It is easy to become complacent with what we “know”.

Specifically, I’m going to remove the coax choke balun from my ladder line J Pole. I only added it because it seemed like a good idea - based on flawed understanding…

That will shorten the feeder length, saving a little weight; reduce the feeder loss a little; take up less space in the rucksack, and probably radiate more efficiently. What’s not to like :smile:

Sorry for going OT from vehicle antennas!

73
Adrian
G4AZS


#14

Is it really true that a J Pole/Slim Jim needs radials? I think it’s a myth that it’s a myth.


#15

Well, a J Pole is essentially an end fed half wave, with a transmission line matching transformer. Without much thought, I had assumed that all necessary current flow occured within the matching section.

However, in an EFHW as used at HF, with a matching transformer, there would be current flowing in a counterpoise / radial, albeit small, and often relying on the coax braid / radio / operator.

So, it sounds plausible to me that the J Pole could have the same requirement…

As Mark observes up the thread, I need to read a bit more about antennas. Advice from a retired BBC engineer when I was first licenced was “you need to keep your current up” which is good, but not comprehensive :smile:


#16

My naive view is that an EFHW is just a single wire and so you need a ground or counterpoise but a Slim Jim is a folded dipole, just fed from the end, and so doesn’t need a ground. I’m not sure about the J Pole, but I can’t find any other reference that says you need radials.


#17

Curre(a)nts is Watts. Not sure what raisins will give you though? Maybe good for erecting aerials :smile:

(;>J


#18

Or to put that another way, an EFHW is just a wire “dipole” fed at one end, and a slim jim is a “folded dipole” fed at one end.
In each case it is the “fed at one end” which implies current flowing into one end, and so, according to Terry’s logic, some sort of counterpoise is required to mirror this current flow.

Jack - yes, maybe I need to revise dried fruit too… :smile:


#19

[quote=“G4AZS, post:18, topic:15910, full:true”]Or to put that another way, an EFHW is just a wire “dipole” fed at one end, and a slim jim is a “folded dipole” fed at one end.
[/quote]

But the folded dipole has two wires at its end. Another way to look at it is that the ground of the coax is connected to a quarter wave of wire, which is just the right length for a counterpoise or radial. I could be talking rubbish here, but I’d like to see more than one source before I dismiss the Slim Jim which has been very widely used for years.


#20

The lower “U” is a quarter wave matching section. The upper section is a half wave, and in the case of a slim jim, it is a half wave consisting of two conductors, shorted at the top.
EDIT: With my pedant’s hat on, it isn’t a folded dipole, rather a folded half-wave monopole.
The feed point is at the lower end of one of the conductors.

I wouldn’t dismiss the design either, as you say, it is widely used and is well suited to “roll up” wire construction for portable work. Significantly better than a rubber duck on a handheld.

Currently, though (dried fruit again), I’m inclined to think that it won’t be improved by the addition of a common mode choke on the feeder, and might actually work better without one.

I might try some comparison tests, though I suspect the difference will be difficult to measure, and likely to vary in practice.