Radios that work

Radios that work

Postby grebs » Sat Jun 13, 2009 11:24 pm

I have tried the handheld FRS/GMRS radio thing, and the clutter was terrible, too many mouths talking, make them go away!

What option exists for radios that actually work? We are building a sand worm MV and "thumper(s)" with embedded radios. The Mv and camp could have antennas up high, which I think might be critical for range.

One thing that comes to mind is MURS radios. Any experience out there?
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Postby Captain Goddammit » Sun Jun 14, 2009 6:04 am

CB radios work quite well on the playa, particularly between mutant vehicles and camps where handheld portability isn't a concern. The 4-watt output is much more effective than the fraction-of-a-watt GMRS or FRS walkie-talkies.
They're pretty cheap new and ultra cheap used. Use the biggest longest antenna you can.
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Postby motskyroonmatick » Sun Jun 14, 2009 11:10 am

I am going with CB communication this year in my mutant vehicle and with a base station at camp. For mutant vehicles be aware of Ground Plane concerns. If you can not install your antenna on or directly next to a large somewhat flat well grounded metal area then you may have an insufficient ground plane which would eventually burn out the crystals in your CB radio. I have just spent a bit of time figuring this out with installing a CB on the golf cart that I loan out to a camp mate so she can have mobility on the playa.

The best location for an antenna is in the middle of a large grounded flat sheet metal plane. The top of a school bus would be ideal. Mirror mounts come close in my experience.

I ended up getting 3 no ground plane kits to solve my ground plane issues with the golf cart and my mostly plywood mutant vehicle. Now if my SWR meeter is what is causing the problem then that is all for naught.

This has some good tips that started me on the way to understanding some good practices with CB's.

http://www.firestik.com/Tech_Docs/63Things.htm
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Postby Simon of the Playa » Sun Jun 14, 2009 12:56 pm

i'm with the capt on this one having used both...you can pick up at garage sales, good will etc etc hand held portable cbs that are like walkie talks on steroids.

they work great, and it's easy to bump up the signal, but not needed.

you will need like 10 C or D batteries, but i found if you retrofit a lithium with the same voltage you can recharge them again and again and they last a while if on stand-by mode.
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Postby Sail Man » Sun Jun 14, 2009 1:06 pm

motskyroonmatick wrote:I am going with CB communication this year in my mutant vehicle and with a base station at camp. For mutant vehicles be aware of Ground Plane concerns. If you can not install your antenna on or directly next to a large somewhat flat well grounded metal area then you may have an insufficient ground plane which would eventually burn out the crystals in your CB radio. I have just spent a bit of time figuring this out with installing a CB on the golf cart that I loan out to a camp mate so she can have mobility on the playa.

The best location for an antenna is in the middle of a large grounded flat sheet metal plane. The top of a school bus would be ideal. Mirror mounts come close in my experience.

I ended up getting 3 no ground plane kits to solve my ground plane issues with the golf cart and my mostly plywood mutant vehicle. Now if my SWR meeter is what is causing the problem then that is all for naught.

This has some good tips that started me on the way to understanding some good practices with CB's.

http://www.firestik.com/Tech_Docs/63Things.htm



What about the cb antenna's that mount to glass? I know that they arent the greatest for range etc but I did not want to put a hole in the top of my nice shiny new rv.

I also have a pair of k30's that I could stick (mag. mount) to the roof. Opinions?
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Postby theseus » Sat Jul 25, 2009 6:09 pm

The Motorola Talkabout 280 offers 38 privacy codes for the 14 channels which effectively expands the number of lines to nearly 500. It shouldn't be too difficult finding a clear line if you play with the privacy codes.
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Postby Ugly Dougly » Sun Jul 26, 2009 9:54 am

It's fun to hear the chatter.
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Postby Token » Sun Jul 26, 2009 10:29 am

If you need comms from main vehicle to spotters and walkers or what not, one of them cordless phone systems with a half dozen handsets will work like a charm in intercom mode.

Cheap, rechargable and guaranteed private.

This however will not work for long range to base camp. CB or MURS would be better for that purpose.
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Postby oneeyeddick » Sun Jul 26, 2009 11:14 am

What that Token hippy above me said will work, as will cheap ass kids walkie-talkies for the purpose he described.
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Cross talk

Postby tangerinehuge » Tue Jul 28, 2009 1:28 pm

What about crosstalk on the CB spectrum? Are there a lot of art cars out there using CBs? Do the channels get jammed? What are people's experiences with this?

As far as ground planes are concerned, will a magnetic mount to the roof of a school bus work? Does it need to be bolted down?

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Postby motskyroonmatick » Tue Jul 28, 2009 6:02 pm

A magnet mount should work if the top of the bus is steel. Checking the SWR with the system fully installed will allow you to tune the antenna for the best performance and also check to see if there are ground plane issues. If the SWR is off the charts you either have a short or insufficient ground plane. Any CB shop would be able to check your SWR and give good advice possibly involving some sales to get your set up working well. I bought a SWR meeter on ebay and learned how to use it over a period of time and number of attempts. Now I can use it without directions.
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Postby Captain Goddammit » Tue Jul 28, 2009 7:47 pm

motskyroonmatick wrote: For mutant vehicles be aware of Ground Plane concerns. If you can not install your antenna on or directly next to a large somewhat flat well grounded metal area then you may have an insufficient ground plane which would eventually burn out the crystals in your CB radio.
The best location for an antenna is in the middle of a large grounded flat sheet metal plane. The top of a school bus would be ideal. Mirror mounts come close in my experience.

I ended up getting 3 no ground plane kits to solve my ground plane issues with the golf cart and my mostly plywood mutant vehicle. Now if my SWR meeter is what is causing the problem then that is all for naught.




OK gotta clear up some misinformation.
CBs haven't had crystals in them for decades, and when they did, they were for frequency control and had nothing to do with the transmitter's "final stage" amplifier, which is usually transistors.

The lack of a groundplane also has absolutely zero to do with whether your radio will fry. You can properly tune an antenna without a groundplane the same as with one. Thousands of boats have radios, both VHF and CB, and are fiberglass, no groundplane.
A groundplane is for is modifying the radiation or signal pattern of the antenna. Without a groundplane, it will radiate much of it's signal upward instead of down lower to the ground and outward, where it's more useable.

The groundplane simulates the other half of a half-wave length antenna, sort of similar to putting half of something on a mirror, making it act like a full-wave antenna. Full-wave length antennas do not need groundplanes. On CB frequencies, a full wavelengh is about 36 feet, too long for practical antenna size, so "half-wave" antennas are popular. Antennas can be made any physical length by coiling some of the length... that's the "loading coil" you see on shorter antennas.

A groundplane will make a less-than-full-wave antenna more effective by concentrating more of it's signal pattern closer to the ground rather than wasting it skyward.

If the "K30" antennas Sail Man mentioned are actually "K40" CB antennas, yes, use them, those are some of the best CB antennas ever made. Years ago some friends and I did a lot of field testing, the K40 was hard to beat.

Twin mirror-mount antennas are another way to modify the radiation pattern. To work properly they should be at least 8 feet apart. What happens is the signal pattern resembles a figure 8 as viewed from above, stronger to the front and rear, weaker to the sides. Truckers originally did this to maximize performance up and down the highway and reduce interference from whatever city they were passing through.

When I've used CB on the playa, channel clogging was zero issue. Very few people are on CB out there. The vast majority of people are on foot or bikes and not carrying a CB.

No, the antenna doesn't need to be bolted down to it's groundplane. It's not being "grounded" the way a power circuit is. A magnet mount is fine.
You can change your antenna's radiation pattern by moving it around relative to the groundplane, or metal surface, it's sitting on. The signal strength will be greatest toward the bulk of your groundplane surface; if you mount the antenna toward the rear of the bus, it's signal will be strongest toward the front.

We used to hang an antenna straight off the back of cars and drive in tight circles while watching a large signal-strength meter to track people down. The signal would be strongest toward the front of the car because of the groundplane effect, so when we got the highest reading we knew we were pointing in the direction of the signal. It works transmitting as well as receiving.
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Postby motskyroonmatick » Tue Jul 28, 2009 8:35 pm

Great information Captain Goddamit. I am still learning on the subject.
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Postby Captain Goddammit » Wed Jul 29, 2009 7:15 am

So about tuning a CB antenna...
When an antenna is tuned to the same physical length (or an exact multiple) of the wavelength of the frequency it's being used for, it resonates almost all the power into the air. When it isn't tuned, it doesn't resonate well, and a lot of the power is wasted. That un-radiated power is what can damage the transmitter - those are the "standing waves" that you measure with an SWR, or Standing Wave Ratio meter.
An SWR of 1/1 is perfect but anything less than about 1.5/1 is good.
To tune the antenna you usually loosen a hex set screw and adjust the length. On some fixed-length antennas, they are (hopefully) a bit long and you trim them down to tune.
CB is a pretty narrow band (26.965 MHz to 27.405 MHz) but it's big enough to see a difference in antenna tuning from channel 1 to channel 40. Higher frequency = shorter wavelength, and vice-versa. If you tune on channel 1, the antenna will be slightly longer than ideal for channel 40... tune on 40 and it will be slightly short for channel 1. It's best to tune on a channel around 20-ish, and compare your "match" or SWR between 1 and 40 to try to get them about even.

So, if your SWR is higher on channel 40 and lower on channel 1, you need to trim the antenna shorter. If SWR is higher on channel 1 than on channel 40, it's too short.

If there's no way to physically adjust the antenna, there are adjustable devices that go inline with your antenna cable informally called "match boxes" that artificially tune it. It's not as efficient but it works.
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Postby Token » Wed Jul 29, 2009 9:00 am

Oh I get so aroused when you guys talk dirty like that!

So Cap'n, since you did a bit if field trial stuff on this...

1/4 vs. 1/2 wave antenna length (102 vs. 204 inch). Both can fit the carrier sine wave on the whip with minimal power reflected back to the amp.

Did you observe any tangible gain in signal strength with the longer whip?

I would guess that the long whip would only be marginally better since it's peak power is still located at quarter height and the diminishing signal power beyond the quarter length peak would not gratly benefit from the added elevation.

Thoughts?
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Postby Captain Goddammit » Wed Jul 29, 2009 4:04 pm

I had a half-wave (a Shakespear "Big Stick") and a 9-foot fiberglass whip and the 18-foot "Big Stick" does perform better.
One of the antennas sticking up from the Land Yacht is that 18-foot half-wave. If nothing else, it's up higher and that helps.









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Postby oneeyeddick » Wed Jul 29, 2009 8:24 pm

Long antennas, big sticks, long whips......I enjoy all the rhetoric, but where does that leave those of us who are using a hand-held CB ?

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FRS Radios

Postby theseus » Thu Jul 30, 2009 7:58 am

So to correct my early numbskull remarks about FRS radios: a friend explained to me last night that all the Motorola privacy codes do is make the conversations of other people using other codes inaudible. If you are both on the same channel, and key at the same time, who can hear who depends on distance, radio power, and conditions, regardless of privacy codes.

He explained that on the playa both at the beginning and end of the week, the FRS radios can be useful. But once real numbers begin to show up, fergetaboutit.

They would still be useful for a caravan. We use them that way.
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Postby Captain Goddammit » Thu Jul 30, 2009 4:37 pm

That's all true, but I've never found them to have adequate range for caravanning. CB works a hell of a lot better for that too. I've wired a cigarette lighter plug to a CB's power cable and handed that and a magnet-mount antenna to people I caravanned with and it was a lot better than those underpowered crappy-ass FRS or GMRS things.
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