AM transmitter antenna problem..

[wiwi]

I have built an AM transmitter using colpitts oscillator in the following link:

https://commons.wikimedia.org/wiki/File:NPN_Colpitts_oscillator_base_coil.png

and i was applying the decoupled audio signal to the base of Q1 and the values for C1, C2 and L were 1n , 10n , and 50uH respectively to get about 700 KHz carrier frequency. i could see the AM signal clearly displayed on the oscilloscope , but when i tried to receive it in a radio i could not hear the audio signal sound unless i touch the antenna with my hand , when i do touch the antenna i hear a very clear and loud voice and it has a high range . when i leave the antenna i cant hear anything .
Is there anything i can do to handle that problem ?

the antenna i use is one from an old radio and i connected it to about 30 cm of wire directly to the emitter of Q1

thanks

 

[E-design]

To transmit at this low frequency you need a long antenna and a good earth connection. For shorter antenna's you need a loading coil to compensate. Without this you will not transmit further than your bench.

http://charliethompson.50megs.com/1610khz.htm

http://www.antennex.com/shack/Dec06/cps.html

 

[wiwi]

please take a look at the following AM tr :

http://english.cxem.net/radiomic/bug15.php

as said in the last row it does not need an antenna or using just 30 cm will increase the range . does this imply that the output signal power in this circuit is larger than that of my circuit ? what do u expect the range of this circuit be ?

 

[jeffrey samuel]

True the power of this design is higher than your transmitter's design

Bit range can't be altered drastically a little improvement is very much likely to happen

 

[wiwi]

True the power of this design is higher than your transmitter's design

How did you decide that this circuit's power is better ?

 

[jeffrey samuel]

Every Circuit uses DC power input to increase the power of AC signal

Here the second ckt uses a 9V supply and considerable dissipation by the resistors is not of great impact and so The power of the second Transmitter Ckt is higher than the previous one which uses just a 6V DC margin for amplification and enhancement

 

[wiwi]

oh sorry i forgot to say that i used 9V battery instead of 6 V in my circuit and i got around 6v p-p in the oscillator output. may be it has something to do with the resistors ?

 

[jeffrey samuel]

The second amplifier is a multi stage amplifier

If the gain of the first system is A and the gain of second stage is B then the effective gain of the second system is AB

Thus the second one has higher gain cause of multi staging

the first one is a simple single stage amplifier and in general the power op of them is lesser than cascaded versions

 

[wiwi]

actually the audio signal i used was amplified in a first stage CE amplifier and the decoupled output was applied to Q1 base hence it's also a multistage amplifier . i wonder if the problem is related to the position of the tank circuit or to the oscillator type .. ?