[GreenKeys] 850 Stream

[Ralph Mowery]

In the early days the hams used what was called shift pot keying or tuning.
A capacitor was switched across the tuned circuit of the VFO so it shifted
the frequency lower.
Then it became 'ham standard'.  It does not really make much difference
which way the tones are shifted .  You can either tell the demodulator to
reverse or normal and switch sidebands to match.  For hams it was normal to
use LSB so the demodulator could be use in the normal position.  Way back
most of the commercial went the other way so to demodulate those the
receiver was switched to USB.  For some reason many years ago lots of
demodulators did not have a reversing switch.

If using a receiver it only matters the amount of shift.  The receiver if
SSB can be tuned to match the demodulator filters. Usually you want both
tones to be between about 1500 to 2400 Hz.  The low limit is so the ssb
filter will help eliminate the second and higher harmonics and the upper
limit is so the filter will pass it.

Ralph ku4pt
 


-----Original Message-----
From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Alf Fisher
Sent: Sunday, February 05, 2023 5:09 PM
To: Greenkeys
Subject: Re: [GreenKeys] 850 Stream

On 05/02/2023 18:30, Harold Hallikainen via GreenKeys wrote:
> I agree with 1575 (mark)-2425 (space). With military radios, I think this
> results in space being on the higher frequency since they generally run
> USB.
>
> 50 years ago, when I ran 2125, 2975, I was directly FSK keying a Viking
> Ranger and receiving with a National NC-300. I could get the 2975 Hz that
> way. Most SSB transceivers will not, of course, pass 2975 Hz.
>
> Harold
>

As I understand it, this is audio streaming via the internet so it wont 
have the bandwidth restrictions of a SSB Tx/Rx so there will be no 
problems sending 2975 Hz or higher frequencies.
Please correct me if I've got it wrong.

Also please can someone explain the rationale behind downshift on mark 
or downshift on space or is it just a convention.

73,
Alf
G3WSD