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

[Philip Jenkins]

Thank you, Stefan! You answered the question that I was really trying to
ask...and didn't express very well.

 What I meant to ask initially is why unwanted FM signals on the uplink of
a linear bird didn't pose (much of) a problem while unwanted FM signals on
an FM sat did; I understood the latter, but not the former...and now I know!

Thanks to everyone who responded

73 de Philip N4HF

On Sat, Feb 3, 2018 at 10:25 PM, Stefan Wagener <wageners at gmail.com> wrote:

> I guess there might be a very simple answer:
>
> On FM (one channel) satellites without the PL tone, any unwanted signal can
> mess it up for everyone; on linear satellites any unwanted signal (uplink)
> will mess up only a small portion (specific downlink frequency) and the
> rest is still available. Bottom line PL tones on FM sats helps all of us.
> No PL tones on linear sats will not be a significant problem.
>
> My simple mind :-)
>
> 73 Stefan, VE4NSA
>
> On Sat, Feb 3, 2018 at 9:11 PM, R.T.Liddy <k8bl at ameritech.net> wrote:
>
> > 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
> >
> > > > _______________________________________________
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> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
> to all interested persons worldwide without requiring membership. Opinions
> expressed
> are solely those of the author, and do not reflect the official views of
> AMSAT-NA.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
>