Radio

Hi,
Can someone please tell me which component to adjust/change to
increase the range of my 40 MHz transmitter for my remote control car?
I want to know which BIT inside the transmitter to tamper with...
(Don't tell me to use a signal booster or better antenna at the
receiving end, I don't want to do this - I want to boost the
transmitter.)

Thanks
AA
http://uk.geocities.com/aa_spaceagent/

 

Before you consider doing this, you should do some research.
Specifically, you need to check with whichever agency in the UK performs
the same function as the FCC. Specifically, check what the power limits
are for RC stuff. You could easily end up in deep kimchee if you exceed
that limit and you get caught.

 

According to the Radiocommunications Agency,
http://www.radio.gov.uk/topics/spectrum-strat/uk-fat/annex-b2002.doc

The limit is 100mW (ERP), which is probably what you're outputting.
Plus the primary user of the frequency is the Ministry of Defence.

Simon

 

O.K. I appreciate the legalities and restrictions on transmitter power
imposed by government thanks for your information. But I am a "space"
man with many un-Earthly applications in mind! What if... you were
stranded on the Moon or on a space station hundreds of miles out in
space and your life depended on boosting the transmission power of
your "local" radio - designed for communications only with your
immediate space/moon based colleagues - so that you could send a
message to ground control on Earth for a rescue mission? In that
situation, I doubt if anyone would give a toss about the FCC or other
bodies!?

I just want to know: do you adjust the CRYSTAL, do you change the
FERRITE ROD or COIL or do you change another component that dictates
the output power and the ultimate range of the transmitted signal?

RSVP - I'm stranded on the lunar surface...!
AA
http://uk.geocities.com/aa_spaceagent/

 

Sometimes on transmitters, there are resistors which connect to the the
antenna to cut down the signal, maybe changing those might do something. (I
have no idea)
Just don't blame me if something goes bad...

Andrew Howard

 

The _power density_ (watts per square meter) decreases as the square of
the distance, but the _field strength_ (volts per meter) decreases as the
first power of the distance.

It's volts per meter at the receiving antenna that matters.

 

Thanks Fred. I had some dimly half remembered formula that it had
something to do with the square of the distance; many things it
seems have to do with the square or sq. root of things! Also I
was too lazy to even remember where to look it up!
What I was trying to help Abdul with was the idea that even IF he
was able to successfully double the output power of his RCC
transmitter it would probably have little effect! If his plane or
model, whatever, went a few yards further away the signal would
be just as weak as before the power increase. etc.
Also; in these suspicious times it might be wise, especially if
one is not an 'electronically skilled person' to NOT tamper with
something that may have regulatory authority (FCC in the US)
approval? Terry.

 

Yes, I think I understand the technical intricacies involved here...
but just one more question: If the radio signals from my 40 MHz model
transmitter are expected to stay weak no matter how much the power
amplification, then how do we expect the alien recepients (if any) of
the 1974 Arecibo Radio Telescope message to respond back???

For those of us not familiar with this, an interstellar radio message
was sent to Messier 13, a globular star cluster in the constellation
of Hercules, on November 16, 1974, from the Arecibo Radio Observatory
in Puerto Rico. As M13 is 24,000 light years from Earth, and radio
signals travel at the speed of light, it will take 24,000 years for
the message to reach the star cluster.

Abdul Ahad
http://uk.geocities.com/aa_spaceagent/