T.E.M. A07B500S Manual - About  Fm  Syncronous

A07B500S   manual 

Pag. 57 

in circuit and adjust the output of the noise generator , so that 

the noise meter gives the same reading. The peak-dev. is now 

correct.     

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For stereophonic operation 

Check that the appropriate pre and de-emphasis are in circuit 

Adjust the output of the LF generator at <1KHz to a level  

corresponding to a frequency deviation of 40 KHz including  

pilot tone. 

Measure the peak value in channel B after the demodulator  

and stereo encoder by means of the noise meter (without the 

weighting network ). 

For the remaining procedure , see the method used for 

monophonic operation 

In case of stereophonic broadcast in accordance to the IEC 244-13 rule the reference power is 

moved highwards of 1.9 dB in relation to the corresponding REC. ITU-R BS.412-7. 

ABOUT  FM  SYNCRONOUS 

7.5 

There are many people who would like to resolve over-crowding of the frequencies by synchronizing 

two or more FM transmitters on the same frequency to cover ever-expanding zones in case of diffusion on 

the same program.  The idea in itself isn’t bad, but there are many technical-theoretical difficulties which in 

our opinion advise against the creation of such a system except in extreme and exceptional situations such as 

those described below. 

Most importantly, FM modulation, unlike AM, cannot be synchronized on an analogue-type transmitter.  As 

such, the creation of an FM-synchronous system on all traditional transmitters is invalid even if input for 

external synchronization via GPS or reference to rubidium or caesium is taken into account.  This category 

of transmitters also includes the 500W TX, upon which, for the reason previously described, input for external 

synchronism has not been implemented.  (The internal reference has a level of stability which more than 

satisfies all regulations, and the frequency can also be fine-tuned by remote).  If two analogue FM 

transmitters are synchronized with a common reference, the two transmitters will have the same carrier 

frequency.  The modulations won’t ever be in phase for theoretical problems, however, and as such won’t 

ever be able to verify the synchronous vector sum of the two signals overlapping at the listening point.  This 

could cause unsatisfactory results on the listening end in the area of reciprocal interference. 

Recently, digital transmitters have been introduced to the market which many say should resolve the 

problem.  These devices have the generation of a modulated carrier with a digital synthesis which resolves 

all previous theoretical problems but which, apart from the difficulty of respecting the most rigorous 

regulations regarding spurious emissions from the digital process, must also be confronted with other 

irresolvable difficulties.  The velocity of the light propagation (approx. 300 meters per microsecond) creates 

insurmountable limits on the creation of a synchronous system.  Having multiple synchronized transmitters 

over a distance of a few kilometers which serve intersecting areas (which occurs in most documented cases), 

it is theoretically impossible for signals to overlap at the same point and not have reciprocal delays.  To reach 

the user, starting from the transmitting antenna, the radio signal takes 100 microseconds if the distance is 

between two and 30km.  A few microseconds of delay reduces listening quality.  Resolving this problem is 

often attempted by artificially delaying the radio signal by adding adjustable digital delay lines in the