Oscillator power!!!!

[mikebg]

Imagine the receiver to 100MHz ,that receives a radio signal over natural obstacles and the transmitter power 20w ,he will be heard but very little, however, if the transmitter power increase at 150w, This I have personally tried on doing RF transmitters.With 20w I barely caught a signal while I was with 150 w same signal caught mint.

Orbit, my hobby was to design antennas and transceivers (TX and RX) used in QRP amateur radio. TX power is limited to 5W and even less:
http://en.wikipedia.org/wiki/QRP_operation
The sensitivity of RX used in QRP ham radio is limited by interference and noise in input. To increase sensitivity they receive very narrow band and operate with AGC.

Sensitivity of RX used for metal detecting is limited by AIR&GND signal in input. It is generated by its own TX. To increase depth of detecting Vaino Ronka uses ABC (Automatic Balance Control) to suppress AIR&GND signal in input of RX. I reinvented his ABC using in addition an AGC (operating also as automatic bandwidth control).
http://www.geotech1.com/forums/showt...eferrerid=2910
In this case TX power can be reduced to a level when sensitivity is limited by EMI and thermal noise. The depth of detecting is increased because preamp of RX operates with maximal gain and because synchronous demodulator in principle has immunity against EMI and noise.

[taliesin]

i hope you didn't tx on 100 mhz at 150 watts orbit

[allan.au]

re. magnetic fields and radio frequency radiation.

re magnetic fields and radio frequency radiation...after a lifetime as a broadcasting tech, RF transmitters, recievers, and audio, and many years study of metal detectors, i think i know the differences regarding signal propagation.
40 years ago it was not uncommon for a 1 watt handheld 27MHz AM tranciever with a 1 to 2 metre (3-6 ft) whip antenna, to get a perfectly readable signal across the pacific ocean from california to sydney australia.....(on these occasions the "skip" was open and there was a fortuitous path through and reflected by the layers of the ionosphere.) this was with a tx antenna only about an eighth of the wavelength, (get much less than this and efficiency soon drops off)....communications like this are possible because of the very narrow bandwidth of the transmitted signal, and the very narrow bandwidth and the very high gain of the reciever.....thats what radio is all about, well ever since the early spark transmitters dissapeared about 100 years ago..
a pulse induction metal detector is like a spark transmitter, rich in harmonics of the fundamental, but decreasing in energy with frequency, with some spurious emmissions as well, with some of the energy up in the MHz region....BUT, the coil is not very big in terms of the wavelength of the energy, so it makes a lousy transmitting antenna, AND, it is almost on the ground, (not where you usually locate VHF antennas), AND, the coil/s are usually sheilded to prevent the metal detector's reciever susceptability to radio frequency broadcast signals etc, and ground capacitance effects....so the resulting "radiation" from the tx coil is largely magnetic only, and bugger all electric field escapes, hence little electro-magnetic radiation.....i suspect the magnetic field would be hard to find 20 metres away ,except with a reciever optimized to find a faint echo of it.( ie, a similar metal detector)
similar principles apply to continuous wave VLF type machines regarding emmissions.

regarding the virtues of more power: more power has more costs and other issues, but it seems to workto some extent,,,, getting smarter is often the way to go, ie being able to sample earlier with a pi.

al

[Orbit]

If the transmitter uses 100 MHz frequency of 100hz or if there is no power that we get in range, and as we all know the best low-frequency pass through the country.As for noise I agree with the fact that it is higher the greater the power and electromagnetic interference,But I personally experimented with smaller and more power with greater strength I got certain results, despite elektomagnetnih and other disturbances and with less force,with greater strength I had some kind of admission and with less power I had no signal.

[Aziz]

Hint

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