eHam Forums => Mobile Ham => Topic started by: KG4OXP on April 17, 2002, 08:53:35 AM

Title: AH-4 tuner to a mobile whip question
Post by: KG4OXP on April 17, 2002, 08:53:35 AM
I have a large mag mount with a whip I'd like to use with an AH-4 tuner (located in the trunk). Trouble is that the mag mount whip is coax fed and the tuner only takes a single feed.

Could I run a short lead of coax to the tuner, cut the coax and just use the center lead. What about the braid at the tuner end? It is certainly in use at the antenna end, as a ground? Just wondering if I have any options here.



Title: AH-4 tuner to a mobile whip question
Post by: N8EMR on April 17, 2002, 09:39:01 AM
FIrst you may find that a magmount will not be hard pressed to support and large enough antenna tune above 20m. a 40m whip needs to be 9ft min, longer for 80m

If you need 20m and down then just strip back the ground on the coax or better yet run a wire from the ah4 to the center connection of the antenna.

Title: AH-4 tuner to a mobile whip question
Post by: WB2WIK on April 17, 2002, 02:14:34 PM
The AH-4 needs an antenna about 8' long to work properly.  If you've got an 8' long antenna on a magnetic mount, wow, that's a lot.

I've used the AH-4, trunk mounted, with a ball-mounted (through a hole in the fender wall) 3/8-24 CB whip (102" long), using no coax at all but a short length, about 8", of high voltage wire between the center post of the ball mount and the antenna terminal of the AH-4.  It worked very well on 40-10, with some quirks and foibles, but overall not bad.

One interesting thing I found is that the 102" whip actually worked better on most bands when "folded over" and clipped to the rain gutter up near the windshield, making the whip mostly horizontal.  This would be nearly impossible to do with a mag mount, as folding the whip over like this places a lot of strain on the mount.  The heavy-duty ball mount handles it just fine.  A mag mount would probably pull right off the car.

When the whip is clipped up front using an insulated whip clip (Radio Shack sells them, a couple of bucks) I found the tuner could match the whip better and faster on almost every band.


Title: AH-4 tuner to a mobile whip question
Post by: K0BG on April 21, 2002, 08:16:17 PM
The max inductance of the AH4 is about 12 uH. This limits its use to a 8 or 9 foot whip if you want to cover 40 thru 10, and it's iffy on 40. So if you're going to use a magmount, you'll need one of those fancy 6 magnet jobs. And yes, you can use coax from the tuner to the antenna, but realize, this will add to the losses, and make 40 meter matching almost impossible with a short 8 foot whip. I use a 12 foot whip with a loading coil four feet from the base, and tuned to 20 meters, and a 4 to 1 unun at the base. With this set up, I can cover 40 thru 6 meters with no problems. The antenna is properly ball mounted on the left quarter panel. And, every thing on the car that has been bolted on is grounded. If you REALLY want to be heard, do things right and forget the magmount.

Title: AH-4 tuner to a mobile whip question
Post by: N3JWN on June 10, 2002, 09:37:30 AM
Well I read all this and many other articles on the AH-4. Your all right when it comes to HARDLY Any documentation that will help!!......... Well I finally bit the bullet I ran approx 9FT of RG/8x form the tuner. Mounted(under the back seat) in a 98 Jeep Cherokee. First of all I have the R.S. troid cores on the power leads, on the coax feeding the tuner ferite beads on the control cable inside the AH-4 torid's on the control head cable, speaker..... The radio is seperately grounded to the body (used a seat belt holddown bolt under the back seat next to where the tuner is mounted. The Ground on the tuner is the common point for all 3 gnd's, the radio, the gnd to the body and the RG/8x coax... The Icom 706 is sitting under the front seat..I ran the coax hidden under the plastic trim and comes out the left rear tail light where another toroid wrapped approx 5-6 turns........ Hooked to a 3/8-24 thread to SO-239 mount insulated with spacer/nylon washer on the top the bumper mt. I was going to use Ham sticks and probably still will... With the 102" stainless whip cost $19.95 at a local fest!!all hooked up the tuner did the following:
6 meters 52.525 mhz swr 2.5-1 at best antenna toolnog?
          50.400 am  swr 1.1-1.2 changes with mod.??
          50.150 usb swr 1.0-1.2 mod no change..
10 meters 29.200 AM  swr 1.1/aok
          29.010 am  swr 1.1/aok
          28.500 mhz - 28.050 swr 1.1
12 meters 24.950 mhz swr 1.1
15 meters 21.280 mhz swr 1.2/ with mod jump to 1.3??
          21.425 mhz swr 1.2/ with mod jump to 1.7??
17 meters 18.165-18.385 swr 1.1 same wiht out tuner
20 meters 14.450 mhz swr 1.1/with mod jumps to 1.5
          14.300-14.100mhz swr 1.1/with modjumpsto 1.2
40 meters  7.390-7.150 mhz swr1.1 mod no effect

I would Imagine the mod change is due to lead length Haven't figured it out YET!! Good to great signal report on all bands 40-10 nothing on 6 ssb yet!!I haven't used ant Hamsticks yet!! that's about it very little road noise and HF works great ... I couldn't belive it thanks 73's good luck works great for 102" whip!! Dick / n3jwn