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"Beating the heat for older radios."

Add a cooling fan!

By Ian J. Turner

It is true that I am just a newly licensed ham, but I have been doing work on my elder father's ham shack equipment that was left to me after he pasted away. I have been under his license for many years and I worked with communications while serving in the military. I work from a practical but experimental approach.

In this case I found that several of my older Kenwood 7800 /7950 two-meter radios did not like the heat and lack of airflow in my shack. When the inside temperature of one of the radios hit 120 degrees Fahrenheit on transmit, the led screen on the radio started to flash and generally act up.
I was not dismayed; I had more than one of these radios which I use as base stations so it was time to experiment a little to see if I could cure the heat problem that builds up in the radio.

As I have the radios hooked up to larger external speakers, the tiny little speaker inside one was redundant so I unbolted the top of the case and just removed it in hopes of installing an internal cooling fan. I surveyed the size of the space created by the removal and came up with the next part of the plan.
I placed one of those thin, low draw, high speed, quite, little computer CPU fans like the example picture below, over the vacant space.

Example of CPU cooling fan
{Note that is should be 12 volts DC rated.}

It fit and it covered the speaker grill work on the underside of the top cover so well I figured I was on to something here.
After bolting it up to the case top and running the leads out through the small hole in the back of the finned case, I hooked the leads to the same 12vdc source the radio used and I was impressed. It works and the temperature dropped. The project could have ended happily there but would that be the amateur radio way.

I went further with the project. I wanted a way to turn the fan on and off. I then found a small little hole in the back of the radio case on the flat spot next to the fins that appeared to have nothing much next to it, so I CAREFULLY drilled it out  just a little bit to a more usable size in which to mount the switch.

Sub-miniature toggle switch - not to scale

Then I inserted a micro flip switch similar to the picture above and it looked like it should have been made that way.

On further inspection inside the rear of the radio while looking at the power section, I saw a good location point off of the power main lead connector before it reached any electronics inside the unit, so the soldering kit came out, and I soldered one side of the switch connector to the DC power input (positive side) and the other switch connector to the (hot fan wire), then I found a suitable case ground for the other end of the circuit. See photo below for final installation.

Va7fsm fan modification
Location of fan switch on rear of radio at end of white "arrow".

You can use your choice for the style and size of the switch that will fit your radio.
When the radio gets too hot, I flip the switch, when it is cool enough, I just turn it off.
You may forget that the fan is running due to their very quiet operatiion....no problem!

Va7fsm radio cover exposed
Cooling fan shown installed in top cover. Notice 4 mounting bolt/nuts.

Now I am not going to recommend that everybody go ripping out the speakers of all their radios, especially since many newer radios already had internal fans hooked to the transmit side of their boards these days. Also many radios may not be as troubled by the heat build up in the case as the older radios, however for my money I think this fix is hard to beat in the heat we have been having of late. Onward to the next radio, it will get a thermistor controller to turn it on automatically, so what do you think?

What a concept! A twenty year old 2-meter radio saved from the hottest summer weather in years by a $1.95 used CPU fan! Canadian Radio Shack part number 273-248.

Not so bad for guy who has not even had his ticket for a month.

Parts used 1 ea Canadian Radio Shack 273-248A fan.

1 ea Switch (on/off) of your choosing that will fit your particular location in your radio.
Enjoy and 73.......

Ian J. Turner
"Just your Basic ham"

Editors note:
Many radios will suffer heat related problems in hot weather that causes all kinds of problems to show their ugly face. Most all transceivers have a temperature range specification that they are designed to work in. Excessive heat beyond the specifications will quickly destroy solid state devices if not properly cooled or operated within their temperature range. Some components are more sensitive than others.

It is advisable to insure that if you do want to install an internal cooling fan that you do not use a fan rated at other than 12-15 volts DC. Many "CPU' fans may be rated at much less voltage than your radio's supply voltage which will usually burn them out quickly.

So be wise and check the "specs" on the fan you intend to use! Remember, if you plan to use the DC power that supplies your radio, use the same voltage fan.
In some cases, you may not have room for an internal fan so the only other option you have is to install an external cooling fan.

Another location option for the fan is the back of the radio attached to the cooling fins provided for most radios. These fins act as a heat sink and the additional air movement across them will certainly help to dissipate more heat. The "forced air" from the fan should move between the fins if possible. Use your own ham ingenuity in the mounting process and location and provide a way to shield fingers from the fan blades for safety if they are external!



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