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Author Topic: Fixed Mobile Setup Advice  (Read 1261 times)
VA7CAB
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Posts: 3




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« on: February 06, 2006, 10:41:17 PM »

Hi Folks,

I'm currently operating a lot of fixed mobile (Mazda Protege parked at really nice quiet location) with a TS 570 and some hamsticks and a small MFJ magmount on my roof. Sometimes I setup my Buddipole near the car too. I have no desire to move the car since I operate mostly CW and digital.

All is A-OK and am working great DX but I think I can do better especially on 40M and below.

I'm thinking of getting a big Hi-Q antenna (4-160) with a caphat and one of the MFJ telescoping whips. I emailed Charlie and he thinks the mag mount will be FB with maybe some fishing line to guy the antenna on windy days. The mag mount is tiny though (only 4") so that would have to be upgraded.

Sounds good to me, but I just thought I'd float this idea here and see what you folks think.

Here are my other choices:

A K400 3/8 mount on the trunk.

Fabricate something for the tow hook and afix a proper mount.

I know the last one is probably the best, but I really don't want to change the car's appearance ...


Thanks for any advice!

73 Chris
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AC2RC
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Posts: 114




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« Reply #1 on: February 07, 2006, 06:38:43 AM »

Any trees near the portable location ? I had two locations one had a 80m half wave dipole ,the other a 20m dipole fed with ladder line ,using a 706 and AH-4 tuner .I left the antenna s in place.If that can't be done the Hi-Q with papacity hat will work though you still have to see that your vehicle is all properly grounded for maximum ground plane.
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K0BG
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« Reply #2 on: February 07, 2006, 07:50:47 AM »

One of the misconceptions associated with the use of a capacity hat is where it should be mounted. The answer is, at the very top of the whip (your description would indicate otherwise).

This is a little difficult to do, so most amateurs mount it closer to the coil. Problem is, TOO close to the coil. Doing so, reduces efficiency rather than increasing it. Properly placed, it will be at least 2 coil lengths ABOVE the coil. The photo on HiQ's site shows it much closer unfortunately. Further, the cap hat needs to be fairly large in size to be truly effective. About the only one that is, is the one sold by DX Engineering when the longest rods are installed.

The HiQ is a very good antenna (I use one myself), but using a proper cap hat with it, all but negates its use on bands higher then 20 meters. The reason is, even when the coil is set to its least reactance, there are open turns remaining. To exemplify this, a four foot diameter cap hat, mounted three feet above the coil on a HiQ 580RT limits its resonance to 20 meters and below. With just an eight foot whip, you can work 17 meters, but you'll be on the last turn.

Alan, KØBG
www.k0bg.com
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VA7CAB
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« Reply #3 on: February 07, 2006, 12:43:30 PM »

FB on the cap hat. The intention of getting the 4/160 is to try and get a few CW QSOs on 160M now and then. I wouldn't normally be using the cap hat as my main band is 20M and, hopefully, be QRV on 40M which I am missing with the current setup. I'd put the cap hat on top of the Hi-Q extension rod.

The dipole idea is cool, but unfortunately I can't do it. The little spot I found is near a university research farm and they have "special" trees with little tags on them. Could be dangerous!

Any recommendations for a beefier mag mount that would still be easy to remove?

PS

Been reading your site Alan and it's got so much information! Will be redoing my wiring with THHN in the very near future.
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K0BG
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« Reply #4 on: February 07, 2006, 12:55:40 PM »

Chris, you need to find yourself an old GE Master ballmount. They are not easy to find, but they are worth the search. If MFJ wants a new product to make, this would be it. That is to say, if they make it as rugged as the old GE ones were (which I doubt they would).

Alan, KØBG
www.k0bg.com
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VA7CAB
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« Reply #5 on: June 03, 2006, 10:30:10 PM »

Hi Folks,

Here's an update. Shortly after I posted this, I bought a TS 480 HX and permanently mounted it to the rear of the back fold down seat on the Mazda Protege. From there I run the coax to an MFJ 910 matching unit. The matching unit is then connected to a Diamnond K-400C 3/8 mounted on the trunk.

For an antenna I settled on modifying my Buddipole. I use one 22" arm, the larger Buddipole coil, and then a 10' MFJ telescoping whip.

The electrical connections are two AGU 60 AMP fused 8 guage T90 (THHN) wires running from the battery to a distribution block. From there, there's a breakout to the radio and an extra PowerPole wire to run accessories (Microham USB Interface).

For grounding I dug the K400C's set screws deep into the Mazda's trunk and have braided coax running from the radio to the car's body.

For operating I drive to the location and mount the antenna adjust the MFJ 910 for the band I'm interested in and adjust the whip until I get a match. I use my RF Analyzer to save my finals. I keep all the accessories in the trunk including the control head.

The whole setup takes about 15 minutes from parking to get on the air and pound out CW or RTTY. 5 minutes to break everything down. When I fold the seat back up, no one would know I have a radio (unless they knew what a K400C was for).

I normally always run 200 watts from the rig. Using RTTY I will run the car every 15 minutes or so for about 5 minutes, for CW I will run the car every half hour for 5 minutes.

Results are absolutely outstanding. I've put over 1000 HF contacts on this setup since late February (90% contesting). And have worked a lot of DX. The best was some 40M EU on RTTY and a couple of new entities on 20M Phone (9M, VK9).

I hear better than I ever had at my noisey home QTH, but I can't always be heard.

Future experiments will be with a cap hat. Over the summer I'll also look into a larger coil for 160M this winter.

I'm still thinking about a small Hi-Q or Tarheel so I can drive around, but I doubt either antenna will exceed what I have now.

73 Chris
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