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 [email protected] 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 [email protected] 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 [email protected]. 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