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Author Topic: Mounting radios with detachable heads  (Read 483 times)
KE7FD
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« on: July 09, 2008, 01:25:54 PM »

I offer this comment to those who like myself need to mount mobile radios that separate into two parts. Furthermore, those who have seen my arrangement have been impressed with the install even though I do not yet consider it quite finished.

I have both a TS-480SAT and a TM-D700A, Both of these radios have removable heads. I drive a Grand Cherokee and I wanted to keep the coax runs as short as possible and decided to place the main radio units as close to the rear hatch as possible. Once I determined how I would mount the control heads on the dash, I arranged the cables (CAT-5 and speaker outputs) from front to rear. Next I ran dedicated power lines (+ and -) from the battery to the rear of the cargo area for the radios, using a 40 amp circuit breaker in a plastic box near the battery. The bodies of these two radios just fit inside a 50-cal ammo box. I modified the ammo box to allow ventilation from one end to the other; front to rear, and it is at the rear of the ammo box where a large 12v fan is mounted. There is an "old fashioned" house type thermostat that controls the external fan inside the ammo box sharing the space with the radios. I can set the thermostat anywhere from 60 to 95 degrees F. The fan works quite well and the radios have not overheated. I made sure to use a fan with plenty of draft; it is mounted external to the ammo box but attached to make sure the seal is solid. There's also a 5 volt regulator attached to one side to power the GPS unit for the APRS side of the D700.

The VHF/UHF antenna has a homemade mount to the body that complements the look of the Jeep, and the HF antenna is mounted to a homemade mount affixed to the hitch. In all cases, the mounts ground to the frame. What's more, I have provided additional braid-grounding elsewhere such as on the rear hatch. The radios also go a short distance to chassis ground. The idea was to keep the coax, and ground runs short and solid. Following this approach has allowed my Hustler resonators to perform at 10 to 20 over on 20 meters. The importance of grounding the radios and the antennas using best practices for environmental considerations cannot be overstated. In my opinion, the more flaky the grounding considerations, the weaker the radiated signal.

There are still other things I can do to improve and enhance the install, the overall grounding and I'm sure the antenna would like to grow up to be a Tarheel or Scorpion some day. Until then, I'll have to settle for my 10 to 20 over.
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K0BG
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« Reply #1 on: July 09, 2008, 03:24:24 PM »

What ever signals you get (10 over, 20 over, whatever) have no bearing on efficiency, grounding, or anything else. It only means there is enough S+N/N ratio for you to carry on a conversation.

The most important aspect, is putting as much metal mass under the antenna as possible. Just remember, every HF installation is a compromise. It's how big a compromise you're willing to settle for that is the crux of the matter.

I admire your thoughtfulness about hiding the radios from prying eyes, and making sure the radios are fan cooled. However, I never recommend using boxes or other cramped areas, fan or no fan. While you'll more than likely get by with this, keeping them free and clear is also important attribute.

You might e-mail me some photos of the install, and I'll post them in my photo gallery.

Alan, KØBG
www.k0bg.com
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