Pre-emphasis or Not for VHF digital modem tones


ad7i
 

Greetings --

I posted this a while back in winfldigi@groups.io  but didn't get much of a response, so I'm reposting it in this group.

I'm somewhat new to using fldigi at VHF.  In doing testing and observing on the air signals, I see that some VHF stations are using pre-emphasis in their transmissions and others are not, often with some of those VHF stations not aware that they either are or are-not transmitting with pre-emphasis.

The difference appears to come about because some operators inject their fldigi TX audio into the microphone jack of their VHF transceiver, because that's the only option available to them (so their signals are transmitted with pre-emphasis).  And other operators inject their fldigi TX audio into the 6 pin (or 8 pin) mini-DIN jack on the back of their VHF radio when their radio has such a jack, because it's convenient way to connect to the transceiver, and those transmissions in most cases appear to be without pre-emphasis.

For high-speed wide-bandwidth operation at VHF is there any consensus among experienced VHF fldigi operators as to whether it's better to make those transmissions with or without pre-emphasis?  I would presume it's best for everyone to do the same thing (pre-emphasis or no-emphasis), but is it better for everyone to do it one way or the other?  If no pre-emphasis is the best option, should those who are forced to inject fldigi audio into the VHF transceiver's mic jack add some sort of external de-emphasis circuit before the mic jack, so that their transmitted audio spectrum has a flat frequency response?

thanks,

Paul, ad7i

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