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Author Topic: Temporary Mobile HF Setup  (Read 2742 times)
NS8Q
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Posts: 139




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« on: July 30, 2013, 01:48:16 PM »

I am debating on whether or not to try a temporary mobile HF operation.  I don't have one of the new HF mobile radios, but I have a Yaesu FT-757GX2, which according to the manual, can be installed in any negative grounded vehicle.  My car is a 2000 Grand Prix SE if it matters.  Does anyone have some suggestions on what I should do in addition to connecting it to the battery?  From what I've read, I SHOULD NOT connect it to a DC source with more than 15V flowing out of it, as that would damage the radio.  I'll have to check that with my multi-meter.  The antenna will be a 20m hamstick with a mag mount on top of the car.  I will have a tuner with me as well.  Keep in mind, this is only temporary and not a permanent installation.

Tu 73,
Chris, NS8Q
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K5LXP
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« Reply #1 on: July 30, 2013, 02:48:15 PM »

I've done a temporary installation like that in the past too.  Great way to get your feet wet before you start buying radios and drilling holes.

You should never see more than about 14.4-14.6V worst case at the battery terminals with a properly operating vehicle charging system.  Any higher than that and you'd end up with a roasted battery much less a roasted rig.

A 20M hamstick will work OK, A tri-mag mount will help with ground coupling.  It should be tuned for the band segment you want (CW or SSB).  You won't need, and shouldn't use a tuner.  If the hamstick won't tune in you need to resolve the problem and not force feed it with a tuner.  One less thing to futz with going down the road anyway.


Mark K5LXP
Albuquerque, NM
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M6GOM
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« Reply #2 on: July 31, 2013, 02:36:56 AM »

Unless the alternator has a fault it should end up settling around 14.4V.

Magmounts are a poor way of mounting but for getting your feet wet will give you an idea. I certainly wouldn't want to be driving down the road with hamstick on one though. 20m is a good band to get going with.

Once you decide you want to make it more permanent the best to worst methods of mounting are:

Drill hole in roof
Lip Mount
Magmount.

www.k0bg.com has all the resources you could ever need.

HF mobile gets addictive.
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NS8Q
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« Reply #3 on: July 31, 2013, 11:45:22 AM »

Thanks guys.  I've also played with the idea of taking out two or three painter poles and throw up a dipole, which would beat the pants off a ham-stick anyway!  Grin  I think I would need more time to play in that case. 

Well I'm connecting the radio directly to the battery, would I need any kind of filter on it?  There is an in-line fuse on the power cable.  Of course, the car will have to be running to operate, unless I drop it down to QRP levels.  The last thing I want to do is ruin the battery and have to rip it out of there and replace it.
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K5LXP
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« Reply #4 on: July 31, 2013, 01:09:47 PM »

Well I'm connecting the radio directly to the battery, would I need any kind of filter on it?

If it's so bad you'd need a filter, then your charging system probably needs repair.  As long as you use adequate cabling and make a solid connection at or near the battery you should be fine.


Quote
Of course, the car will have to be running to operate, unless I drop it down to QRP levels. 

Depends on the power, mode you use and what your operating duty cycle is.  You should easily be able to operate for several hours of casual contacts with a 100W radio and have plenty left over to start the car.  The average power draw isn't as much as you might think.  Car batteries aren't meant to be deeply cycled very often but once in a while shouldn't be a problem.  I would conservatively rate a typical car battery at 40Ah, and at 50% duty cycle running SSB with a "typical" 100W radio you will require less than 2Ah.  This is less average power than the headlights.


Mark K5LXP
Albuquerque, NM
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WX7G
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« Reply #5 on: July 31, 2013, 03:01:34 PM »

A 20 meter Hamstick will work quite well, however a mag mount will not provide a good RF connection to the car body. The last time I used a short 20 meter antenna on a mag mount I ran a 4" ground wire from the mag mount to a self taping screw just inside the trunk. The mag mount sat on the trunk near top edge.

The antenna I used was an MFJ-2320T and at only 36" tall it held on at 75 mph with a single magnet.

I have used the car cigarette lighter plug to power a 100 watt radio with no problem. The 20 amp draw of such a radio is intermittent and the average current during transmit is less than 10 amps and only two amps during receive.
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AC4RD
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« Reply #6 on: July 31, 2013, 03:14:54 PM »

Chris, good advice from everybody so far!  One point I'll add:  if you don't already HAVE a mag-mount, you might do well to get a lip mount instead.  It'll be cheaper than a mag mount, and it's easier to do as WX7G said and run a little ground braid from the mount to a bolt inside the trunk or wherever you put the antenna mount.   I started with a mag mount but found a big increase in signal strength going to a lip mount--though it was the braid that made the big difference, and you could stilll do that with a mag mount, I guess.  My lip mount was on a '96 Bonneville (back when it was fairly new) and it held hamsticks perfectly well at highway speeds.  It never warped the trunk sheet metal, though I don't know if that would be true with my newest car. :-)

What you've got in mind is a fine way to get a taste of mobile HF at a bargain price.  And if you find it fun (I sure do) then you can start experimenting and upgrading and fiddling.  :-)   Have fun and GL!   --ken
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N6AJR
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« Reply #7 on: August 01, 2013, 02:47:23 PM »

go for it. just don't drive and try this  tem setup. park and use it.  this is how I started, and now I have  radios in all my vehicles.  check out my call sign at qrz.com
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