Off Roading

[gortex2]

Dixie Run at Windrock this weekend if anyone is looking for something to do. We have repairs from Uhwarrier JJ last weekend so can't make it to this one. Fun weekend in Uhwarrie again even with a little breakage..litterly lost the brake line on left rear (steel line near frame) on Dicki Bell and limped to Troy for parts. Then the other half backed into a tree on sunday and we broke a ujoint. Pile of parts at home so busy weekend. next trip is Cumberlands in October. 

 

[nokones]

About a month or two ago, there was a discussion on that the CB Radio FM Mode may be something that should be looked at to consider bringing back the use of the CB radio for uses such as Off-Road Trail Comms.  I stated that the CB FM Mode would probably propagate or provide better communications than the CB with AM modulation, and even better than FRS.

Some Forum members disagreed but no one could cite any facts or back up their statements.  I related that I think the CB FM modulation would have a better signal-to-noise ratio thus, better communication Farz.

I also stated that as time permits, I would conduct a radio comparison test.  Well, that day came, and I conducted the subject test comparing the communications with FRS, CB AM, and CB FM.  I kept the test simple, and I did not record any RSSI (Radio Signal Strength Indicator) readings.  I just did the ol’ hoot & howler type test to see if you can hear the communication and determine the usable distance and audio quality between the three subject radio transmissions.

The test was conducted essentially in a desert environment on flat terrain, with a slight dip in elevation for a dry creek bed and a test point was conducted in that dip, consisting a few cacti, pucker bushes, and giggly weeds, with no other obstacles.

A 2007 Chevrolet Avalanche was the Stationary Transmitting Point using a Cobra 29 LTD Classic Nightwatch AM/FM CB Radio with a Firestik II 4 Ft. Antenna in the center of the roof.  CB Ch. 16 was used for both the AM & FM modes and the antenna was tuned at less than 1.1:1 VSWR.  The CB Radio operated in the AM Mode with a Dead Carrier, no modulation, at 3.5 RF watts and was drawing 14.01 DC volts at 1.12 amps; and 3.9 RF watts with modulation, at 14.00 DC Volts and was drawing 1.46 amps.  In FM mode, the radio was emitting 3.7 RF watts with essentially no difference in power draw.

The data collection vehicle was a 2023 Jeep Wrangler Rubicon using a Cobra 25 LTD Classic CB AM/FM radio with a Firestik II 5 Ft. Antenna tuned to less than 1.1:1 VSWR and the antenna located on the rear Spare Tire Carrier Bracket near the passenger side of the vehicle.

The data collection consisted of collecting test data every ¼ mile driving away from the stationary vehicle.  The test concluded at the 3.25 mile checkpoint.  The data collection vehicle operated the radio squelch level at the threshold of squelching out the noise.

The FRS radios were two Midland LXT radios with fully charged batteries.  The stationary vehicle transmitted on the FRS radio from inside the vehicle as a user would be doing on an actual off-road trail run and the test collection vehicle was receiving the communication transmission from inside the vehicle as an user would be doing on an off-road trail run.

The RF output power was not checked due to the inability to measure.

The FRS became non-existent passed the ¾ mile mark.

The CB AM signal was good and quiet up to the 1 mile mark.  The next ½ mile, the signal was readable but RF noisy.  At the 2 & 2 ¼ mile marks the signal was barely readable.  At the 2 ½ mile mark the signal was non-existent and covered by possible skip interference.

In the FM mode, the signal was very good essentially full quieting for the first 1 ½ miles.  From the 1 ¾ mile mark to the 2 ¾ mile mark, the signal was readable with some RF noise.  At the 3-mile mark, the signal was very noisy but readable.  At the 3 ¼ mile mark, the signal was very noisy and unreadable.

In conclusion, the FM signal transmissions outperformed the AM signal transmissions.

Based on these results on what would be the best Off-Road Trail Comm., I think the FM CB transmission has a good chance of being a very good trail comm.  I think a test on an actual off-road trail with trees/foliage would be warranted to see what would be best under trail conditions. 

There is no doubt that any VHF or UHF mobile radio with RF output power higher than an FRS would perform better.  I think that I just may conduct that test once I get my XTL VHF radio installed in my Jeep which will occur in the near future so I can conduct a comparison radio test between the VHF & UHF radios on the trail.

[marcspaz]

@nokones i have said many times that there is a huge advantage with CB over FRS or GMRS, because HF has LOS propagation, like GMRS, but also has the advantage of Ground Wave and Sky Wave propagation as well. However, very few people I have met in my entire life, have a properly installed CB. Even fewer have SSB to take advantage of the extra power and sideband performance characteristics. I only know one person (personally) that has an FM CB.  Bad performance of poorly installed factory stock AM radios that only put out 1 or 2 watts and 75%-80% modulation on a good day, and the lack of operators with compatible gear for SSB led me to recommend the much more powerful and installation forgiving GMRS.

 

I have an AM / FM CB. Ive done a test similar to what you mentioned, comparing AM CB to FM VHF and UHF. While I didn't compare CB AM to CB FM, my results showed a dramatic range improvement with a 50w GMRS radio compared to my well performing AM CB. Living here in VA, I should try to find some time to duplicate your test, to see how terrain and woods impact performance. I'll have to see if I can get the one person I know with an FM CB to run some tests with me.

[WRQC527]

50 minutes ago, marcspaz said:

there is a huge advantage with CB over FRS or GMRS

CB has better slang, too. In fact, I think that's one thing missing from GMRS. 

[nokones]

1 hour ago, marcspaz said:

@nokones i have said many times that there is a huge advantage with CB over FRS or GMRS, because HF has LOS propagation, like GMRS, but also has the advantage of Ground Wave and Sky Wave propagation as well. However, very few people I have met in my entire life, have a properly installed CB. Even fewer have SSB to take advantage of the extra power and sideband performance characteristics. I only know one person (personally) that has an FM CB.  Bad performance of poorly installed factory stock AM radios that only put out 1 or 2 watts and 75%-80% modulation on a good day, and the lack of operators with compatible gear for SSB led me to recommend the much more powerful and installation forgiving GMRS.

 

I have an AM / FM CB. Ive done a test similar to what you mentioned, comparing AM CB to FM VHF and UHF. While I didn't compare CB AM to CB FM, my results showed a dramatic range improvement with a 50w GMRS radio compared to my well performing AM CB. Living here in VA, I should try to find some time to duplicate your test, to see how terrain and woods impact performance. I'll have to see if I can get the one person I know with an FM CB to run some tests with me.

Today was my first opportunity to try out the CB FM mode. I had a friend help me with my own CB radio, I took out of my Dually Diesel, and put it in his Avalanche. He was the transmitting source. I actually like the audio quality of the CB FM radio mode.

If I remember correctly, my modulation peaked at 85% and my CB radios are not modified.

[nokones]

@Marcspaz Too bad we live many States apart. I would love to join you in your test.

[marcspaz]

 

Since several of you are somewhat local to Uwharrie, I figured I would share this little gem with you.  Its a video of the gatekeeper and v-notch of 390 / Daniel.  There are some fairly funny parts; especially the last 2 minutes.