How to Figure out your transmit range

How many watts your radio puts out does not necessarily dictate the range.

What does dictate the range however, are several factors:

* How tall or short your antenna is...the taller the better ( a 102 whip is the best CB antenna)
* How high or low your SWR is....the lower the better (1.5:1 or lower you want for optimal results)
* What kind of terrain you are transmitting in...if you are in the mountains you will not be able to get out as well as the transmitter in the dead middle of flat wheat field Kansas

However a few extra watts does help, especially in the modulation department which is where AM radios can shine. I decided one day to do some comparing and contrasting between two different radios, one being an actual CB radio and the other being an "illegal" export radio set up to run on the CB frequencies. I wanted to find out how far both could get out when used in the same vehicle with the same antenna and with the same "opposite end" to pick up both signals.

My "receiving end" was my pick up truck with a 102 whip set up running into a typical Cobra 25/Uniden 66 chassis style radio built before 1985. I set up a video camera inside aimed at the radio's TX/RX meter. I set it to record. I then tested the two radios by transmitting on channel 20 at certain mile markers in the road. I chose channel 20 as to not to interfere with any truckers that might be using 19. (around here all but 19 is dead) I also did both tests in the middle of country bumpkin Missouri where's plenty of trees and curvy roads, a few houses and farms.

The first radio I tested was a Uniden PC68LTW that was running 6 watts deadkey and I think somewhere between 20-24 watts of modulation, or "swing". The PC68LTW is a typical 40 channel radio that happens to have a built in weather radio feature.

Results: From where my receiving end was up until .75 mile away, the PC68LTW pegged the needle in the truck's radio. At about the 2 mile mark from where the receiving was, the road made a 90 degree right curve to the west. After the curve in the road where it hit the 2 mile mark, the PC68LTW came up as a 9 with light static on the RX meter. Then at 2.5 miles it came up as a 7 with moderate static on the RX meter, as the road made another 90 degree curve to the left going south again. Another mile down from the curve at 3.5 miles the RX meter read off a 6. After this the static started getting bad to where it was hard to understand.

Now the antenna I used for this test on the PC68LTW was a Wilson 1000 with a 1.5:1 SWR.

The next radio I tested was a Superstar SS-158EDX. This radio puts out 10 watts dead key and modulates to around 50 watts. The SS-158EDX is not an FCC certified radio; it is an export radio set up by a CB shop to work on the CB frequencies. The SS-158EDX also has single side band (SSB) as well as the ability to get onto the 24 mHz to 29 mHz band. (not recommended unless you are licensed to transmit there)

On this test I used the same Wilson 1000 antenna set up as before. I even tested the SS-158EDX in the same vehicle I tested the PC68LTW in.

All the way up until the first 90 degree turn the SS-158EDX buried the needle on the truck's RX meter. At the 2 mile mark just past the 90 degree to the west, the SS-158EDX was coming in the red portion of the TX/RX meter whereas the PC68LTW came in as a 9. No static that I could detect. Then at the 2.5 mile mark where the road makes the 90 degree curve to the left going south the SS-158EDX was coming in at a 9 whereas the PC68LTW was only coming in at a 7. Again no static that I could tell. Then again at the 3.5 mile mark, the SS-158EDX came in between a 7-9 on the meter as opposed to the PC68LTW which came in at a 6. I think by this time I might have encountered a little static but not to where you couldn't understand me.

So in all reality, the SS-158EDX, which is also known for it's punchy modulation and similarity to the famous Connex 3300 minus the SSB (yes people have actually thought I was on a Connex 3300), the SS-158EDX was able to be heard more clearer at a greater distance than the PC68LTW.

However, if you have a crappy antenna, crappy coax or high SWR, a powerful radio or running some heat with your radio is not really going to help you much. That's the importance of the antenna. And if more and more people would take time to learn how a CB radio really works and how the antenna makes or breaks a CB transmission, they'd realize it's not necessary to run a lot of power to get out.

As you can see, both of my antenna were pretty good, although the Wilson 1000 certainly is not the best, but it's not bad for a magnet mount. Now I just need to get myself another 102 whip and do my tests again. I'll probably be heard even further.

Hopefully this helps you some.

 

Ok here is how it REALLY WORKS

Now lets take your 60 watts that is about +48 DBM .....
Now your normal AM CB set can hear .5 UV about -113 DBM

SO you have about 161 DBM to work with ......


Loss is about ....


Path loss is usually expressed in dB:
where L is the path loss in decibels, λ is the wavelength (for instance meter), d is the distance between the transmitter and the receiver (for instance meter).

Now its easy all you have to do is find the point that equals -161 DB and your all set .......

Class over .....

 

AND .......

Remember the earth is curving away too so no matter how much power you run when you go behind the earth your gone .....

On 2 meters with 150 watts ( 600 watts ERP ) and a 40 foot high antenna you looking at again 20 - 30 miles real range .....

 

Hit and Miss ...... and you can work skip up to 432 MHZ !

BTW .....

EME ...... To the moon and back .....

About 250 DB SO the moonbounce guys build big antennas with 20 or more DB of gain on both ends with 1,000 watts on each end running CW or digital and very narrow bandwidth .

I got one echo off the moon with my 4 17 elm beams and 70+ watts back in 1971 ....... part of the station is in the photo but the big boys hold CONTESTS

http://images.google.com/images?hl=...esult_group&ct=title&resnum=4&ved=0CBgQsAQwAw

Check out w5un web site if you really want to see how crazy some people get ......

 

Do you still have any of the RL Drake gear?