neazoi
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I wonder, for KHz emmissions (LF or VLF) can one record these somehow and play them in very slow speed, in order to hear their audio ?
Hi, a normal radio mixer would mix the LO with the RF to produce audio (assumming direct conversion)...
Replaying the record with respective low rate will produce audible signals. But what is it good for? What do you expect to hear?
Morse yes, it drops the pitch and the dot/dash speed of the carrier, bringing it into the audio range.Hm... would that be possible for voice? would that be possible for morse code?
Morse yes, it drops the pitch and the dot/dash speed of the carrier, bringing it into the audio range.
Voice no, it drops the carrier so you hear a tone but the modulation rate is also dropped so in most cases the voice would go sub-sonic.
Brian.
Under normal circumstances, no. Very few transmissions use AM with a keyed audio tone, the whole carrier is keyed on and off. If you slow the carrier frequency down so it is audible, the Morse speed is also reduced of course so it would probably be far too slow to read without needing bathroom visits and sleep breaks between words!Wouldn't the morse tone also decrease in the subsonic range in frequency?
Under normal circumstances, no. Very few transmissions use AM with a keyed audio tone, the whole carrier is keyed on and off. If you slow the carrier frequency down so it is audible, the Morse speed is also reduced of course so it would probably be far too slow to read without needing bathroom visits and sleep breaks between words!
For example 12 words per minute on 1.8MHz dropped to say 1KHz audio would play at about one word per 3 minutes! Even I, with rusty ears can read Morse at that speed :lol:
Brian.
Some astronomical bodies emit radiation which can be treated as AM and recovered through a simple diode detector. Pulsars for example can emit signals pulsed at quite low frequencies.
The principle used these days to 'slow down' a signal is to digitize it at a fast rate and store the samples in RAM then read the RAM back through a DAC at slower speed. The only practical use for such a system over normal radio I can think of is to recover high speed Morse bursts used in meteor scatter experiments. For that, a Morse message is recorded and transmitted at high speed as the radio link may only be open for a second or two. A receiver records it and slows it down so the message can be recovered at normal speed. It isn't the same as actually slowing the carrier itself to make it audible though.
A similar system is used on some telecoms protocols. The phone continuously digitizes the microphone output but sends it periodically as high speed data bursts. It's a method of increasing the channel capacity by sharing time slots with other users. The bursts are slowed down and stitched together at the receiving end so they sound uninterrupted. Look up "Time Compression Multiplexing" for more info.
Brian.
... Pulsars for example can emit signals pulsed at quite low frequencies. ...
The sun also emits radio waves and that also can be seen in a radio telescope (I do not know whether it can be seen in a regular radio).
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