The future of CB radio

[nocomradio]

Over in West VA, there used to be a guy "Nailbender" was his handle. He could melt down sets miles away with the power he was running. This was back in the late 70's early 80's. I wonder if he's still around. He must have been in the Kw range as far as output power. You could hear him all up and down the East coast and well into the West, even with all those mountains in the way.

 

[Darth_vader]

Maybe his signal was powerful enough to bend nails? ;o)

The couple guys I mentioned in my last post could probably do that, if one was close enough......

 

[ok walters]

He was most likely running more power than you think. My mobile rig would push 4000 watts on the swing and would dead key 2500 watts, and my rig wasn't considered that big. One guy I knew ran a 20,000 watt mobile rig on Channel 6, so there are some absurdly large operators out there (or were out there).

 

[w9wi]

How, pray tell, did you power a 20kw mobile?!

 

[nocomradio]

How, pray tell, did you power a 20kw mobile?!

I'm thinkin' a whole lotta alternators....... ;D

 

[K4WRF]

How, pray tell, did you power a 20kw mobile?!

1 5/8" transmission line only rated for about 18kw average in the MF band IIRC... I'd like to see that thing, from a safe distance.

 

[crainbebo]

Never heard any 10kw+ Super Bowl truckers melting down my Grundig G5 portable yet...

-crainbebo

 

[ok walters]

Most are powered by large deep cycle batteries and a high output alternator or two. Some of the battery banks consist of several D8 batteries, which weigh almost 150 lbs each. It is a bizarre setup to say the least, but those boys have some serious heat.

One trick several of them used to do was to hold a flourescent tube several inches from the antenna and key up the mike - the light would light up like it was in a fixture. Pretty good indicator of how much RF was baking those boys brains.

I usually ran my rig on just the driver amp, or at about 250 watts. My rig consisted of a small 2 pill linear amp of about 250 watts driving a large 8 pill linear. It was one loud rig, and would clearly carry 25-30 miles, peaking at almost 4000 watts. I had one D8 battery for when the big box was on - the truck's system would power the small box no problem. I ran that through a Wilson 5000 mag mount antenna and had good success, at least until my hair started falling out. Just kidding.....

 

[Darth_vader]

Aren't the D8 batteries what they used to run phone exchanges off of?

 

[ok walters]

Maybe - they are large deep cycle batteries. Mine had a peak of 1300 cranking amps and would supply a 25 amp draw for almost 8 hours. Put several of those together and you have one large power supply, Most guys upgraded the alternator and the batteries would stay pretty well charged unless you were a "ratchet jaw" - there is an old CB term for you.

 

[w9wi]

Let's see the math here.

20,000 watts RF output, let's say we get 50% efficiency, requiring 40,000 watts DC input.

40,000 watts DC input, at 12 volts, is 3,300 amps. (+/- 35 amps or so)

I found a spec sheet for an "8Dd" battery. 12V at 240 amp-hours. As a deep-cycle battery the cranking amps aren't specified, but the same spec sheet shows a similar 8Dc starting battery rated at 1,250 cranking amps. Probably pretty similar to what "ok walters" was using.

A 25-amp drain would be a discharge rate of about 0.1C, which is not unreasonable - it's along the order of what much smaller batteries in portable ham applications do.

Delivery of 3,300 amps would require 133 of these batteries. Now, since you're only transmitting half the time, you can get away with a bit less, although the storage capacity drops when you discharge faster. Let's be optimistic and say we can get away with 65 8Dd batteries to run our 20kw rig.

According to the spec sheet, each 8Dd weighs 66kg. 65 of them would weigh nearly 4,300kg. That's about five tons.

Other articles suggest these batteries can be recharged in as little as ten hours, which suggests (I'm pushing my knowledge of battery technology here) a required charging current of 24 amps per battery for the 8Dd. 24 amps times 65 batteries = 1,560 amps.

According to Wikipedia, common heavy-duty alternators deliver as much as 300 amps. So you'd need five to keep this system charged.

===============

So, I guess a 20kw mobile is not entirely outside the realm of possibility.

- It's going to require a truck. Not a typical pickup truck, but an actual *truck*. Something that can haul around five tons of batteries.
- I'm thinking you're going to have to have an auxiliary engine to keep the batteries charged -- I don't see any way you're going to fit five alternators under the hood. Unless you charge the system from utility power while stationary & just let the thing run down while driving.
- This calculation doesn't consider the cooling system. If the 20kw transmitter is 50% efficient, you're going to have to get rid of 20,000 watts of heat somehow. And you're going to have to power that cooling system.

A quick check suggests this system will have peak currents on the order of 40 amps at 2,000 volts on the coax. You're certainly not going to run that through RG-8, nor are you going to feed it to an off-the-shelf antenna.

I think your 20kw mobile is going to require a semi; the semi is not going to have room for a payload (it's going to be all transmitter, batteries, and cooling); and I'm not at all sure you're going to have room for an antenna capable of taking the power.

It would sure be interesting to see.

 

[ok walters]

Not much on that type of math, but I have seen a Chevy van with 12 of these batteries installed, with three alternators. Have heard claims of 20 kw, and have personally seen the Chevy van rig swing almost 12 KW on a meter. Any way you look at it, that is some brain cooking power. And it can probably bend nails as well. ;D

 

[w9wi]

The other thing I suspect may be going on here... is that CB operators may not measure transmitter power in the same way broadcasters do.

In the regulations for ham radio, power is measured as "peak envelope power" -- the power at the peak of the modulating envelope. For 100%-modulated regular AM (not SSB) that's 4 times the carrier power.

AM broadcast stations are regulated at carrier power.

So 20,000 watts PEP is 5,000 watts carrier. That brings us down to something on the order of what you're describing (12 batteries), and with the heavy-duty alternators one might be enough to keep it charged. (you're going to need another one for the battery that starts the vehicle itself) I'm still thinking you're looking at about a ton of batteries, but you could probably haul that in a Chevy van. (I was surprised just how small these batteries are -- I mean, they're big, but they're not *that* big..)

That's also 10 amps on the coax, and if you use a full quarter-wave antenna* (and don't need a matching network) the antenna might be something you could install on something smaller than a semi.

* and IMHO it would be simply stupid to go to all the trouble to build a 20kw transmitter & then use a sub-par antenna.....

 

[Bill Betten]

These are 10 second key downs max during a shootout.

 

[ok walters]

My D8 was about 12 x 12 x 20 inches and weighed about 150 pounds. It is a fabulous battery for an electric motor on a boat as it has super long draw down time at 25 amps.

 

[nocomradio]

If one were to delve into a rig like that, I'd think a portable gas powered generator would be more in line with supplying the needed power for something making that sort of output.

Many portable generators are capable of up to 15K watts now in a pretty compact unit.

 

[Basnya]

Many of the big boys are running AC boxes in their Suburbans and vans. Very common to see four or five Leece-Neville locomotive alternators mounted under the hood. Some people install nitrous to provide extra HP to turn those alts. Not at all uncommon to see a serpentine belt thrown during the keydown.

 

[nocomradio]

Many of the big boys are running AC boxes in their Suburbans and vans. Very common to see four or five Leece-Neville locomotive alternators mounted under the hood. Some people install nitrous to provide extra HP to turn those alts. Not at all uncommon to see a serpentine belt thrown during the keydown.

If anyone uses nitrous oxide just to provide the horsepower needed to power extra alternators, for their mobile rat shack then chances are, they are picking up extra engine parts from the road behind them. Stock engines don't like nitrous, especially with cast pistons as most come from the factory equipped with.

Besides, a shot of nitrous is only a boost for a few seconds.

 

[WPHA]

Many of the big boys are running AC boxes in their Suburbans and vans. Very common to see four or five Leece-Neville locomotive alternators mounted under the hood. Some people install nitrous to provide extra HP to turn those alts. Not at all uncommon to see a serpentine belt thrown during the keydown.

If anyone uses nitrous oxide just to provide the horsepower needed to power extra alternators, for their mobile rat shack then chances are, they are picking up extra engine parts from the road behind them. Stock engines don't like nitrous, especially with cast pistons as most come from the factory equipped with.

Besides, a shot of nitrous is only a boost for a few seconds.

They only need to transmit for a few seconds... what do they "win"? Is it even worth spending all that money? I doubt it. What a waste.

 

[Mikey Radio]

While this thread is nearly a decade old, I found it interesting and the first few comments (before they started chatting about high powered rigs) certainly brought back memories...Many engineers got their start in CB or shortwave and continued on with those hobbies. For me, my dad always had CBs (usually portable rigs with magnetic antennas that he'd toss in the car when needed) and when vacationing with friends and relatives, we used CB radios to keep contact between our vehicles, to track speed traps and it also offered some peace of mind in case we'd ever break down or needed help (LONG before the days of cell phones and even 911 service).

I really got my start when our family bought a motorhome that had a JC Penney 23 channel mobile in it. I used to go out to the camper each night to talk, and eventually moved it into my bedroom. I had a portable clamp-on antenna that I clipped onto the rain gutter outside my window, ran a power cable down through the very edge of my bedroom floor to a car battery in our garage that I'd trickle charge during the day and use to power the radio at night (hey, I was about 13 or 14, so my engineering chops were limited) and talked on that thing for hours! A few of my friends in the neighborhood ended up with similar setups and we put colored lights in our windows that we'd illuminate if we were "on the air". Eventually I bought a used Realistic base and also a second-hand ground plane antenna (our neighborhood just got cable about a year prior, so I was able to remove our old TV antenna and install my ground plane in its place). Later I traded that Realistic base and some $$ for a Realistic Navajo TRC-458 with sideband, extra channels and extra power. A few years on and someone gave me a really excellent Royce base, so I sold the TRC-458 since I really only used the 40 channel CB and never really farted with the SSB or extra channels. Once I started working full-time, the CB hobby kind of fell by the wayside.

A few years ago when visiting my parents, I looked in a closet and the Royce base is still there along with various mics and mobile units and antennas I'd collected over the years, though none of it's been touched in decades. The ground plane was taken down years ago. Still, seeing all that stuff made me smile as I have fond memories of tinkering with all of it. It really was our form of 'social media' and 'chat rooms' long before computers became a thing!