Before I start this discussion, I want it known that I do not know a whole lot about radios and electronics but the good news for me is that I know folks who do... My continuing mission, as an office Captain was to evaluate a new repeater that was placed along side an existing one to keep traffic off our command channel in areas that can only receive our primary channel. But how do you subjectively test your radios?

The first attempt was to simply go out in the field and do radio checks with the dispatch center. What you get with this are terms such as:

- sounds scratchy
- can barely copy you
- loud and clear

I met up with our counties radio shop folks and once again was oriented to their world and a myriad of devices used to calibrate, tune, and put into service radios for ems, fire and law enforcement agencies. From my prior discussions, it is obvious that we all have to do the same thing. You can't do our job without a radio and cell phones. We have to be able to communicate, and clearly. So how do we take the subjectivity out of radio testing? I know there are a lot of ways to do this but for the sake of this discussion, assuming that there are others who are clueless like me... So with that spirit, and hoping that those of you out there will once again share your insight and advise for us less informed folks... I share with you what I learned and put into motion to identify and document our new radio repeater.

To accomplish this, an Aeroflex IFR Marconi COM-120B Mobile Radio Test Set was used to facilitate the testing of the fire department land mobile transceivers. Everytime someone talked on the frequency, both input and output were displayed on a screen, giving an absolute number instead of subjective terminology.

Prior to starting the testing process, two portable radios were analyzed to ensure correct operability and battery strength. This is important to ensure that the reason the radio did not work wasn't because of reception but mechanical / battery issues.

When radio transmissions were received from the dispatch center or when the we keyed the transmit button on the portable radio, a numeric value was displayed in a graph format indicating signal strength using dBm as the reference standard.

What's a dBm? (sometimes dBmW) is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW). It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form. Compare dBW, which is referenced to one watt (1000 mW).

Here's what I learned about using dBm data as a reference...

Rule of Thumb: The closer the negative number for the dBm is to zero, the better the reception.

General dBm Guidelines:

> -82 dBm Receive Only
-75 dBm to -82 dBm Unreliable Breaking Transmissions
-65 dBm to -75 dBm Scratchy or Popping Noises
-65 dBm to -30 dBm Good Transmission
> -30 dBm Loud & Clear Transmission

Note: Atmospheric conditions, terrain, structure shadowing and other factors affect the quality of the mobile radio transmissions. The above General Guidelines are subjective and are provided to enable an easy way to evaluate the research data

An added benefit was being able to get to know the radio technician and work together as a team. Plus the scenery wasn't all that bad either...

Here's the rough map I put together to document our findings:

Hope this helps anyone out there out. Just be sure to make friends with your radio shop folks!

TCSS, Santa Barbara Mike