RF Transmitter/Reciver

[Fredrick]

The legal limits are on the radiated power not distance. Distance is heavily influenced by environment. It's impossible to say whether you are within the legal limits without some sophisticated and expensive test equipment. The tests required by the FCC for the USA cost about $US3000.

You can see the limits here...

• http://www.radiometrix.co.uk/apps/apnt102.htm

Of course, whether the authorities will catch you and punish you if you exceed the limits is another matter.

Ok... but in teori (legel or not) i only have to bypass or change the resistor R5 to another value.... or?

In the doc i find the limit is Max 25 mW in sweden not 10mW.
http://www.scanner.nu/pdf/riks.pdf (it´s i swedish)

[mackrackit]

Ok... but in teori (legel or not) i only have to bypass or change the resistor R5 to another value.... or?

In the doc i find the limit is Max 25 mW in sweden not 10mW.
http://www.scanner.nu/pdf/riks.pdf (it´s i swedish)

If R5 is connected to LADJ then you may be right. Just remember the max voltage of 3 any place on the LINX.

Another way to get maximum distance from any radio is to use a good antenna. I doubt the , as we call them here "duckie" that is on the Parallax is very good. Most duckies are not very good for for distance.

A quarter wave with ground plane or a half wave will work the best for distance at any power.

I think dhouston has antenna info on his web site. Or google for a ham radio site for more info. The antenna is half of the radio in terms of performance.

[dhouston]

I've never used the Parallax receiver and transmitter so there may be reasons why the things I've learned with the simpler (and order of magnitude cheaper) TWS transmitters and receivers may not all be applicable.

From the LADJ excerpt that was quoted, shorting the resistor so that Vcc is applied to LADJ will give maximum output power from the transmitter.

The distance above the ground will also have a big effect on range. Reflections/refractions from the ground, buildings, trees, etc. degrade the signal. Most of the range estimates that accompany these devices are outdoor, line-of-sight figures. Indoors, my rule of thumb estimate is 20-25% of the outdoor figure.

An efficient, directional antenna (e.g. a yagi) on both the transmitter and receiver can give you large increases in range by concentrating the power in one direction rather than spreading it equally in all directions. The stubby antennas on the Parallax modules are not very efficient and are omni-directional. There are some yagi antennas for this frequency that are printed on circuit boards (or even mylar). Here's an example...

• http://www.wa5vjb.com/products1.html

A wideband preamp between antenna and receiver can also give a big increase in range but this may not work with all receiver designs. In some cases, the increased signal can overwhelm a receiver but I've used them successfully with the TWS receivers and have even tested with 2-3 of them cascaded. This has one major advantage - it does not violate any of the legal limits on transmitted power levels.

[Fredrick]

Ok thanx for the information.

I agree that Parallax is expensive but i need the LINX module on an PCB becouse i don´t have the things needed to make my on PCB´s.

[mackrackit]

Ok thanx for the information.

I agree that Parallax is expensive but i need the LINX module on an PCB becouse i don´t have the things needed to make my on PCB´s.

http://www.rentron.com/remote_control/TXLC-XXX-LR.htm

[Fredrick]

Yes i have lookt at Rentron but 2 transmitter and 2 recivers + 2 anntena coast $111 and at parallax $109,95 with antenna.

[mackrackit]

Yes i have lookt at Rentron but 2 transmitter and 2 recivers + 2 anntena coast $111 and at parallax $109,95 with antenna.

OK, but the antennas from parallax do not look very good (very short ), the ones from rentron are 1/4 wave.

As I said before, the antenna will make all the difference for long range.

Let us know how it goes.