dirty 'balun' (choke) for mobile?

[Back_Crick_Hobbies]

i have a Wilson 1000 installed on the hood of our Honda CRV.
noticed that moving the cable around in the car affects the SWR.

before i trim/tune it, should i put a dirty choke on it? like a piece of PVC.

appreciate your thoughts on this.
/thanks and 73

 

[9C1Driver]

Never heard of anyone running one mobile. Is this a mag mount antenna or bolt in mount?

 

[Back_Crick_Hobbies]

Never heard of anyone running one mobile. Is this a mag mount antenna or bolt in mount?

that is a great question. it's a bolt mount.

 

[loosecannon]

yes you should add a choke to the feedpoint of the antenna, and no you should not use the "wrap coax around a form" method.

go on ebay, and look for a place called palomar engineers.
they sell snap on ferrite chokes that are made for this purpose and they work better than the coax method. they are also WAY less bulky and obtrusive.

the kit comes with 5 or 6 chokes and you just snap them on the coax right at the feedpoint.

now, as for the larger point of "should mobile installations use feedpoint chokes?"

the answer is a resounding YES!

in a mobile installation the vehicle body acts as the counterpoise to your antenna, and as is pretty obvious, no vehicle makes a perfect counterpoise.

putting the chokes on the coax at the feedpoint of the antenna will force those currents that are swirling around on the shield off of the coax shield and back out to the antenna and vehicle body.

I put those chokes on every mobile setup i do, and have ever since reading this:

Antenna Efficiency

and this:

Common Mode Currents

LC

 

[Back_Crick_Hobbies]

@loosecannon many thanks! i have been researching fighting Common Mode Currents with chokes for the inverted V i plan on building, and it got me thinking of my mobile.

i'll pick some up for sure. looking on ebay for 'Palomar Engineers' i only found a seller called 'bobsezshop'.

cheers and 73
/max

 

[TM86]

Go direct: https://palomar-engineers.com/

 

[Back_Crick_Hobbies]

Go direct: https://palomar-engineers.com/

right on. thank you

 

[Crawdad]

A great site for all things mobile:

Www.k0bg.com

7 3

 

[M0GVZ]

i have a Wilson 1000 installed on the hood of our Honda CRV.
noticed that moving the cable around in the car affects the SWR.

before i trim/tune it, should i put a dirty choke on it? like a piece of PVC.

appreciate your thoughts on this.
/thanks and 73

Tuning it is not going to cure the problem, putting in a RF choke is just going to hide the symptoms. A dirty choke is coil of your coax made of 5 turns with 4.25" diameter for 27MHz and it needs to be at the antenna which clearly isn't really realistic in a mobile install. As mentioned you need toroids. Get a Mix 43, not the small ones that clip on the coax, get a larger clip on one you can put a couple of turns of coax through. That'll do more choking than 5 or 6 of those clip ons put back to back. You'll get around 250 Ohms of choking putting a clip on one on. Put a turn or two of coax through just one of them and you'll get over 1KOhm. Just remember when doing this that coax has a minimum bend radius. Do it too tight and it'll damage the coax.

Do this:

Bonding

In particular do the one across the hinges.

 

[sp5it]

If antenna is bolted to car chassis and waving the coax changes SWR it means bad antenna installation. I would rather diagose and remove the cause of the problem.
Mike