Last night the Spokane County ARES group asked me to come out and give a presentation on FM voice repeaters and to talk about their repeater system.


It was a great talk with a lot of good questions!


Here is a copy of the side show I used for the talk.

Below are images of the propagation predictions I’ve done for both the RX and TX for the ARES system. As well as a link the a zip file that has everything you need to look at the propagation map on google earth.



Spokane ARES RX Coverage


ARES TX Covrage

ARES TX Coverage

Google earth file.

Google earth file instructions:

1:Download and install google earth, you can get it from here.

2:Unzip the file some place you can find it. It will include, SRECS.kmz(this is the file with all the site locations), srecs-krell.ppm(This is the transmit coverage file), and srecs-mica.ppm(This is the receive coverage file.) All of these files must be in the same directory for it to work.

3:Open SRECS.kmz in Google earth.

4:Pick a layer. When you open this in google earth it will open in your temporary places, Like this:


Scroll down to the bottom of this list and you will find the coverage layers.


ARES-RX is the receive coverage and ARES TX is the Transmit.

For some reason Google earth turns them both on at the same time. So turn off the one you don’t want, or both if you just want to see the SRECS microwave map.



Notes on propagation map:

This map was made using SPLAT set to it’s basic settings. That means this map will get close to real life, but not match it. I did not set this up to account for reflections, or double diffraction(signals bending around things twice.) SPLAT also has no data about builds, so in down town it will not be right.

That being said it is a good guide to get an idea of where the repeater should cover.


Audio Examples:

Here are the audio examples I used during the presentation in .WAV format.(This will help prevent compression losses.)

I will make example audio clips using voice in the coming week(Thanks to Dan NV2Z for the suggestion) and Post them in this post.



In this clip I slowly turn the signal level up going into my Yaesu FT-875, We start out with 0dB quieting, and end at 40dB quieting.



Off Frequency:

In this clip I have a 300Hz tone 3kHz deviation. I then lower the frequency to drop out of the bandpass of the radio, then raise and go above frequency.


Over Deviation:

Here I start with a 300Hz tone at 3kHz deviation and slowly turn up the deviation to 10kHz. Then drop it back down to 0kHz.


Sub-audible tone high deviation:You may need to turn your volume up for this one

Here I start out with a 100Hz tone at 300Hz deviation and slowly turn it up to 5kHz deviation.



Questions about radio repair:

I had a some folks come up and ask me about repairing their radios, if you want to contact me about that you can head over to my work website, and fill out the contact us form to get a hold of me for more info on that.