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Lectro mW power: Digital vs analog


GNinja
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I remember reading somewhere here on this forum regarding the difference between digital and analog power output and why digital does not need a 250mW option, specifically on lectro transmitters. Can someone please point me in the right direction of what reading material or educate me on the difference?

Reason I'm asking is Lectro just released the new DBSM and DBSMD transmitters and their power output settings differ from their SM counterparts.

 

Thanks!

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7 hours ago, GNinja said:

I remember reading somewhere here on this forum regarding the difference between digital and analog power output and why digital does not need a 250mW option, specifically on lectro transmitters. Can someone please point me in the right direction of what reading material or educate me on the difference?

Reason I'm asking is Lectro just released the new DBSM and DBSMD transmitters and their power output settings differ from their SM counterparts.

 

Thanks!

Several things have driven the differences:

One- Rules and laws (FCC and CE) have changed since the SM was designed. This has affected both usable frequencies, power levels and FM deviation for Parts 74 and  15 in the US.

Two- Full digital transmission requires both FM and AM components in the RF signal. To stay within the bandwidth rules, neither component can be distorted by the output stage. The FM component of the RF signal is no problem but to keep from clipping (compressing) the AM component it is necessary to use an output stage that is not overloaded, i.e., has headroom. This means  a digital 50 mW signal needs an output capable of 150 mW or more. A 250 mW digital signal would require an output that consumes more power than a 750 mW FM design. Battery life and heat become a big concerns. Hence, lower power levels.

Best Regards,

Larry Fisher 

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Thanks for weighing in Larry.  Is there any useful apples to oranges comparison with the analog to digital power level?  I've noticed that 125mw in my (non Lectro) digital wireless does not seem to have as good range as my Lectros at 100mw, so I get a bit worried when I see the new Lectro digital radios at such low power outputs.   I trust that you guys are creating new digital units that compete with the digital hybrid units effectively, but can you shed any light on range differences at the different power levels, and how the distance failure mode changes?

Cheers,

Brent Calkin

 

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Hi Brent,

In our extensive walk tests with and without many reflective metal surfaces, the digital systems had as good or better range than the older higher power, digital hybrid units. That was one of the other reasons the newer units have been able to trade increased battery life for reduced power. A good bit of the range improvement is due to  different diversity techniques; even more improvement is due to the type of error checking in the modulation, i.e., how missing bits are restored in weak signal conditions. As with all full digital, the audio is either perfectly on or totally off. In my walk tests several years ago, I was very impressed with the softness of the digital dropouts. At NAB, the indication of a digital dropout, was a brief cessation of crowd noise. Since speech has a lot of dead periods, the digital dropouts can go by unnoticed. I assume (that word) they still work that way. Keeping in mind that I am a Lectro Fanatic, my recommendation is try them out for range and see if they meet your expectations.

Best Regards,

Larry Fisher 

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