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Old March 18th 04, 07:38 AM
Pete KE9OA
 
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Xtal stands for crystal. As Tony said, a superheterodyne receiver is one
where the input signal is combined in a mixer with a local oscillator
signal. The local oscillator signal is separated from the input signal by a
difference in frequency that is referred to as the intermediate frequency
(I.F.) Either high or low side injection can be used, although most of the
time, high side injection yields better response in terms of in-band spurs.
This refers to whether the local oscillator (LO) runs either above or below
the received frequency.
The reason that this scheme is used is because high gain can be achieved
without the need to have several stages tracking at the received signal
frequency. This is a good deal, since most of the amplification is done at
the I.F. Typical intermediate frequencies are 455kHz, 10.7MHz, 45MHz, etc.

Pete

"S R" wrote in message
...
Hi Tony: The bubbling sound I hear, only happens on the 10 & 11 meter

band.
(Analog). It is at random.

Someone once refer to this bubbling as a whale fart.

Now, I am not sure if we are talking about the same sound? Marti or

Havana,
Cuba is usually on 49 meters. 6.000 mhz (I think).

Please tell me which FREQ. & UTC you hear that jamming. And jamming at
which station? Thank you.

Last night (Tue) at 0200 UTC I was listening to 7415 Hour of the time.

The
station came in very clear and after maybe 15 minutes, a lot of

interference
came in. I wonder?

73


"Tony Meloche" wrote in message
...


S R wrote:

(snip)

Another strange sound is like a bubbles exploiting. I hear this only

on
analog.



This is part and pracel of listening to Radio Marti, which broadcasts
from this country to Cuba. The bubbling sound is Cuban jamming. Not
very effective here, but we're close to the signal and far from the
jamming. Wonder how it sounds there?





Hey, what is AFC, X-TAL & Superheterodne???


AFC is Automatic Frequency Control. It "locks" the station freqency
to prevent drift, in theory. Sometimes it's a great help. Sometimes,
it's a hindrance. Most effective in FM radio.

I honestly don't know what X-Tal is.

Superheterodyne means "above heterodyne". Heterodyning involves
using two carrier waves at different frequencies. The sound created
between the two is a whistle or sine wave tone that rises or drops in
frequeny as you approach the "center" of the station's signal. Have you
seen old movies or cartons where someone is tuning a radio statin in,
and those swooping "weeeeeohhhhwaaahh"
tones until they get to the station? Those are heterodynes.
Superheterodybe circuitry eliminates it by using carrier waves above
audible frequencies, but they are still clearly heard in any SSB mode,
and are a great aid to tuning precisely.

Tony


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