[amsat-bb] Question about PL/CTCSS on uplink

[R.T.Liddy]

The FM SATs decode discreet frequencies. The PL Tone goes up as 67 Hz
and is detected only at that particular freq.

The Linear SATs receive a wide bandpass and the incoming signals are
beat against the SAT local oscillator and the resultant freq is the
differential. Therefore, the resultant freqs are different based upon
that differential. With multiple signals coming up to the SAT on their
different freqs within the bandpass, which one would only have exactly
67 Hz? Tune across any HF Band with CW/SSB signals and you'll hear the
result of multiple signals/freqs.

Bob  K8BL


> On 2/3/2018 09:45, Philip Jenkins wrote:

> > I understand why FM satellites need an PL tone on uplink (to keep out

> > land-mobile services, like taxi-cabs, etc), but why is a PL not required

> > for the linear sats utilizing the same frequencies? A linear transponder is

> > certainly capable of receiving/transmitting an FM signal (albeit not

> > successfully demodulating that signal).

> >

> > This question came up at a satellite presentation I did, and I had never

> > thought about it. ( Moreover, will radios even transmit a PL on SSB/CW

> > transmissions?)

> >

> > Philip N4HF

> > _______________________________________________