70Mhz FM amplifier circuits..

Hi,

does anyone have a link to a circuit for building a 20W RF amplifier
(FM) for my RF plane?I'd like to fly with the live cam on beyond my line of sight, but the
transmitter has only about 0,8W power, so the range is about 1000 metres.
I'd like to extend it to about 5000 metres.
Most FM amplifiers use the radio frequencies of 88-108MHz...

Any links, tips are welcome!

A merry christmas and a happy new year to you all!

 

There are other users of that frequency band out there. Imagine everyone
else with such power/range, it would be a mess (knowing there is a limited
number of channels available).



SioL

 

[/QUOTE]

 

The FM amplifiers should work at that lower freq with lower output, of
if you retune it or pad the capacitors, it should put out more power
than in the FM band. Remember, you may be violating the power limits
for the band.

 

Ground-to-air 20W will get you *much* further than you either need nor
want! Your 800mW should be plenty; you simply need a more efficient
antenna system! Take out the telescopic whip and loading coil and make
up a simple half wave dipole. That should get the job done. Also check
out your receiver/antenna set up in the plane isn't 'deaf' - that's
the other side of the story that's equally important!

 

Ok, thanks!
I'll try that!
Will be more legal too I suppose ;.)
I also thought of replacing the antenna of the transmitter with a sort
of dish, pointed towards the plane.
Don't know if 70MHz can be directed with a dish, as sattelites use GHz
frequencies...

 

The higher the frequency, the more radio signals start to behave more
like light, which can be reflected and directed with mirrors.

At 70 MHz the radio signal are basically sent out in all directions and
you cannot use dishes to create a beam like you can at 10 GHz.

 

Sure you can. The wavelength and reflector size just have to remain
in the same proportions.

 

Alright, let's say we build a parabolic reflector for 70 MHz, a kilometer
or so in diameter, do you say we can create a 70 MHz beam which can
travel to Saturnus and it still keeps together as a beam?

Won't it diffract a lot worse than a 10 GHz beam?

What kind of feed horn would you recommend for such a kilometer size
parabolic dish?

 

That is what I understand to be the case.
Any beam of plane waves that is launched at X wavelengths wide will
have the same divergence angle.

Not if the beam width is proportional to the wavelength.

One sized proportionately to wavelength, of course.

 

I have always had the impression that electromagnetic waves change
behavior and characteristics with the frequency, because I had heard that
radio waves become more particle-like at higher frequencies.

At visible light frequencies we talk about wave-particle duality.

So the waves would have to be more directive at higher frequencies, and
behave more and more like particles.

Now I realize these photons can very big, so the long wave radio
signals consist of kilometer sized photons.

Okay, you are probably right, it is just a question of scale.

 

You can, but a dish would be the size of the palomar radio telescope...

SioL

 

Yeah, but the diameter of the horn would have to be _enormous_ at
70Mhz. He could always try a multi-element Yagi, of course, and just
point it towards the plane.

 

Now we get to the practical intersection of physics and the range of
materials available versus the size of our opposable thumbs. For some
wavelengths, in the range of of centimeters to hundreds of nano
meters, we have tools and materials to create efficient and reasonably
expensive reflectors and launch mechanisms to form plane wave beams
many wavelengths wide. For bigger wavelengths, the size of the
mechanism becomes large and expensive and for smaller wavelengths, the
materials that reflect well and the difficulty in making a reflector
that is smooth on the scale of wavelengths is difficult and launching
organized waves gets tough.