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bxgirten
01-08-2006, 10:50 AM
After cleaning out the basement, I found a 27mHz radio transmitter. I think it was to a RC car my son had some years ago. Can't find the RC car, so it must have been trashed.

Can someone suggest what would be needed to interface this with the BS2? Can I buy/build a receiver? Thanks.

ChrisP
01-09-2006, 12:01 AM
There are either 3 or 4 <too lazy to find the chart and check> 27 MHZ AM frequencies reserved for general radio use hidden in between citizen band radio channels. If this is a single channel unit, then yes its for an RC toy and the easiest way to get a matched set would be to purchase a cheap RC toy. The range and transmit power are both very low so keep that in mind when working on an application. Sorry I cant help with the actual interface though that should be simple enough, coming up with the communications protocol would probably be the most difficult. Possibly you could use low speed serial directly over such a link with no error correction. If memory serves 27.0850 and 27.1950 are two of them.


Hope that helps some,
Chris

mm
01-09-2006, 12:08 AM
It's cheaper to buy a new receiver than build it if you don't have the equiment.

Look on the back for a frequency number then go over to this link,www.towerhobbies.com and look for receiver modules which will drive a number of servos depending on which receiver you purchase. 27 Meg R/C comes in channels A1 thru A6 and they are AM or FM transmitters so look for a corresponding 27 Meg receiver. If yours is a 27 Meg FM transmitter then you need to look for the same frequency FM receiver.

Look for any of the FUTABA series 27 MHz AM or FM receivers model numbers and then let your imagination run wild.

I'm working on a BS2 controller for a home made 14 inch NITRO hydroplane and buy my motors from th above link.

I'm using my own 50 MHZ FM receiver but always thought that towers receivers were a nice deal if you don't have the test equipment like I do. I have a ham license SO I can use this band. I'm using a home made transmitter.

I'm a RF Power amp/transceiver Engineer by profession so I hava lot of Transmitter/Receiver modules sitting around doing nothing but they do take some work and encoders/decoders to integrate for RC use.

The stamp will be controlling motor speed and rudder control. Very simple to start with but later on I'm sure I'll add other items to the radio end. like a video link at either 900 or 1200 Megs.




Mike

Post Edited (mm) : 1/8/2006 4:20:08 PM GMT

bxgirten
01-09-2006, 05:22 AM
Thanks for your responses Chris and mm. It's funny - I just mastered IR control with the BS2 and I thought I'd get creative with an RC transmitter.

I never considered that I'd have to get a license to make a bot move a couple of inches.

http://forums.parallax.com/images/smilies/smile.gif

Paul Baker
01-09-2006, 06:00 AM
You can look for one of the zip-zap cars, they are very cheap (~$10) and someone posted how to hack them over in the projects forum.

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ChrisP
01-09-2006, 12:07 PM
As long as your using prepackaged transmitters and receivers like those out of a zip zaps, I dont think you'll have any trouble with needing·licensing. If you start experimenting outside of those bandwidths there could be issues.

mm
01-11-2006, 10:19 PM
What you cannot do with an OEM product like the zip zaps is remove the antenna from them and add another aftermarket one. You need to use the stock antennas that come with them, especially with the transmitter as they are also part of the certification process. They go thru whats called MPE testing for Maximum permissable emissions to ensure they are not radiating out of there part 15 certification limits.

Of course this is all nit picking as I seriously doubt the FCC is searching for rouge R/C enthusiast hacking remotes. Just food for thought as it's a good idea to keep the antenna that came with the OEM product as it's also one less item you need to interface.


Mike

Tronic (Greece)
01-11-2006, 10:44 PM
I took an product·simular to zip zaps and used on my BS2 robot.

I desoldered the tiny curly type antena from the receiver an soldered a new (longer in length) that I made from a thick wire. Is this illegal? I don't think so since the receiver·doesn't emmit any signal...! After all the transmiters range is less than 20 meters at its best http://forums.parallax.com/images/smilies/tongue.gif



http://img520.imageshack.us/img520/3528/rfmodulecompare6cr.jpg

The phone in the picture·is for comparison reasons only!

http://img508.imageshack.us/img508/513/rfremakeback5ty.jpg

Thanos
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Tom Walker
01-11-2006, 10:51 PM
As far as I know, modifying the antenna on a receiver is not illegal...but remember that antenna design can be a fairly involved process...as a matter of fact, there have been whole books written about it.

In short, in order to get the best reception, the antenna needs to be of a length appropriate to the desired reception frequency (i.e. quarter-wave, half-wave, full-wave). This will gve the maximum transferrence of power.

Google is your friend...

KG4TQW

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Truly Understand the Fundamentals and the Path will be so much easier...

PJ Allen
01-11-2006, 10:55 PM
Tronic (Greece) said...
Is this illegal?
Only your "controlling legal authority" knows for sure.·
But, anyway, it's only illegal if you get caught.

Beau Schwabe
01-12-2006, 12:54 AM
Tronic(Greece) said...

I don't think so since the receiver doesn't emmit any signal



Contrary to popular belief.... If the receiver is a regenerative type receiver, then it most certainly CAN emit a signal.

...but you are probably ok with this. As Tom Walker says, "in order to get the best reception, the antenna needs to be of a length appropriate to the desired reception frequency (i.e. quarter-wave, half-wave, full-wave)." ...This is absolutely correct, anything outside of an optimal antenna length will de-tune your receiver or transmitter.

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Paul Baker
01-12-2006, 02:02 AM
A half wave antenna for 27mHz is 208 inches, quarter length is 104 in. So you'll have to employ a helix design if you want the proper length. RC forums talk about it a little (proper antenna length) and for 27mHz the standard length is 22in which corresponds to a 1/19th wave antenna, don't ask me to explain why its 1/19th wave.

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Robert Kubichek
01-12-2006, 03:00 AM
Paul Baker said...
A half wave antenna for 27mHz is 208 inches, quarter length is 104 in. So you'll have to employ a helix design if you want the proper length. RC forums talk about it a little (proper antenna length) and for 27mHz the standard length is 22in which corresponds to a 1/19th wave antenna, don't ask me to explain why its 1/19th wave.


What you see is 22" on the controller, but electrically with a loading coil inside, it would be the 104" of a quarter wave.... If you look at "some" older hand held
cb's, you will notice that on the antenna there is a larger barrel section in the middle, this is the matching/loading coil...

Bob N9LVU http://forums.parallax.com/images/smilies/scool.gif

mm
01-13-2006, 03:13 AM
Yes technically it is illegal since every receiver also emits a signal and the receiver is also part of the entire system certification process. Receivers go thru the same type 15 cert process as do transmitters as they both have Local Oscillators in them which emit signals back out thru the antenna system.

The efficency of the antenna or lack of, in most R/C installations is a integral part of meeting the minimal permissable radiation specifications of the FCC certification process. Altering the antenna of either the transmitter or the receiver by improving its efficency is what creates interference issues since all of the bands in which R/C models operate are shared frequencies with other Licensed services.

Most R/C systems operating at 27 and 49 Mhz have antennas with efficencies in the 10% or less range and they use some form of L/C matching to try and come close to 50 ohms which they never truly achieve, hence their short range of operation as compare to some of the newer systems which operate at 900 Mhz or 2.4 Ghz which are starting to appear on the market.

Getting back to the antennas, the same goes for items such as Bubble pack/FRS radios. The transceiver ( transmitter and receiver in one module) are one complete system and certified as such with one antenna which cannot be removed and replaced with one of higher efficiency.

A good example are the OEM receiver antennas found on high quality R/C planes and boats, the receiver module typically comes with a short length of wire coming out of the receiver/motor controller module. This wire is actually part of the antenna system after which it is typically attached to a rigid protruding whip section which most people think is the real antenna. All of these parts, the wire leaving the module and the outboard rigid whip are part of the Manufacturers antenna system.

But with other issues such as the increasing number of people hacking into Public safety comm. systems to try and use a high qty transceivers as a scanner, I seriously doubt that the FCC will be coming after you for your wire antenna attached to the Zip Zaps.


Mike

Post Edited (mm) : 1/12/2006 7:18:34 PM GMT