[amsat-bb] Making the transponder sats as easy as the fm birds

Sun Apr 15 23:14:49 UTC 2018

You are correct that a full power carrier is not needed, but still the
whole exercise, while interesting to contemplate, is unnecessary for the
task at hand.  My opinion is that computer control is plenty good
enough.  Even full manual control is good enough in the hands of an
experienced operator.  Neither method is going to be as easy as chatting
on simplex or the local repeater "out of the box";, nor do I think they
need to be.  Both require some knowledge, learning (which is different
than book knowledge), and practice.  That learning is a big part of what
the hobby is all about. 

Then it will be easy.  It took me weeks of work and elmering to make my
first satellite contact, and a lot of that success was due to the skill
of the operator on the other end (Mel, KW7E).  That was on RS-10, which
was considered the ultimate "Easy Sat".  The second contact took a lot
less time, and pretty soon I could fire up the rigs, find myself, and be
in business in seconds, all on a lash-up of equipment that I can only
smile at today.

There is certainly a place for automation.  Those repeater contacts we
have all made are aided by the rig's automatic offset shift on
transmit.  That makes sense, as it ties in with the band plan, repeater
construction standards, physics of narrow bandwidth filtering, etc.  We
have no such structure on the transponder satellites, nor for a linear
transponder do we really need one.  In the future the communications
channel will be much more complex in the services that it supplies, so
yes, there will be automation there too.  But for simple transponders,
there is no need for complex handling techniques.

And, don't forget Engineer Scott's observation, or perhaps it was a
warning:  "The more they overthink the plumbing, the easier it is to
stop up the drain." 

Oscar-7 still works.

Greg  KO6TH

Eric Fort wrote:
> Yes, a zero hertz tone would be ideal if one were going to insert a tone for tracking. Not sure you’d need full carrier though. The advantage of a zero hertz tone is not having to notch it on rx, a ctcss tone is probably easier to generate on modern transceivers though. Having a (reduced) “carrier” to measure and track would seem to be an aid to automated tuning of the receiver though. Sound card listens for the tone and adjusts rx frequency according to the offset from a known and agreed upon transmit tone. What I’m hearing here in the comments though and I’ll ask if this is correct.... is that the computational approach of adjustment based upon published elements is good enough. Can and does the computer frequency control get us close enough for hands off operating when both stations us it?
>
> Also if computer control and tracking is “good enough” why is it not almost universal on the transponder sats?  For the cost of a Raspberry pi or similar sbc and the proper ci-v / cat cable you have computer control of frequency.  As cheap as this is compared to the cost of an all mode radio why is it not more often put to use?
>
> If computer control is not good enough for hands free operation, how can we make it so?
>
> Af6ep 
>
> Sent using SMTP.
>
>> On Apr 13, 2018, at 10:23 PM, Greg D <ko6th.greg at gmail.com> wrote:
>>
>> "subaudible" is only sub audible when you're dead on frequency if you're
>> using SSB.  For FM, where we are familiar with the technique, that's
>> fine.  But instead of a tone, you'd perhaps be better off running Single
>> Sideband AM (i.e. a sub audible tone of zero hertz); there was a
>> satellite recently that was in that sort of mode (I forget which bird),
>> and it was really interesting to work.
>>
>> BUT, one huge problem with sending up a "beacon tone" for aligning
>> stations to, is that you're sending a 100% duty cycle carrier (though
>> perhaps reduced power) to a transponder that really hates having 100%
>> carriers run through it.  That's one of the big reasons why they don't
>> allow FM on the SSB / CW birds (the other being the extra bandwidth that
>> it takes).
>>
>> Bottom line is that, yes, one can construct methods to aid in frequency
>> tracking.  But One True Rule software-assisted operation works really
>> well already, for those who can use it, and can be backed all the way
>> down to manual for those who can't.  And, manual operation of an SSB
>> station through a satellite is quite an interesting exercise.  I often
>> find it more satisfying than having to deal with starting up and fussing
>> with all the computer automation "help".  Just takes a bit of practice.
>>
>> Greg  KO6TH
>>
>>
>> Eric Fort wrote:
>>> Computer control or actually a variation of such *IS* what I’m considering and proposing.  Yes I have read “the one true way”. I understand this manual tweaking is how it’s currently done.  Why however are we adjusting only one frequency?  It seems that we can adjust the transmit frequency so that it is always the same distance from the beacon as seen by the satellite and the receiver can automatically track the subduable tone transmitted. This means that you need not drift across the transponder and the rx station automatically tracks. What am I missing in this being hands off and always on frequency?
>>>
>>> AF6EP 
>>>
>>> Sent using SMTP.
>>>
>>>> On Apr 13, 2018, at 7:49 PM, Andy <w5acm at swbell.net> wrote:
>>>>
>>>> So VERY true!
>>>> Thanks Bruce,
>>>> ANDY w5acm
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Bruce
>>>> Sent: Friday, April 13, 2018 9:40 PM
>>>> To: amsat-bb at amsat.org
>>>> Subject: Re: [amsat-bb] Making the transponder sats as easy as the fm birds
>>>>
>>>> Sorry, this theory of thought is incorrect. You must adjust the higher of the two frequencies as it is most affected by Doppler. The true way to adjust is really to adjust both frequencies, however in the absence of computer control of both frequencies, you adjust the higher. Thus, if it is the receive frequency, then you adjust the receive, if it is the transmit, then you adjust the transmit. Holding the transmit frequency on the wrong band will cause you to walk across all the other QSO's taking place which is not a good practice.
>>>>
>>>> 73...bruce
>>>>
>>>>> On 4/13/2018 8:41 PM, Eric Fort wrote:
>>>>> I’ve had an idea for a long time as to making the satellites with linear transponders as easy to use as the FM “easy sats “.  Consider the following:
>>>>>
>>>>> As I understand it, the goal is to adjust your transmitter such that your frequency at the satellite is constant.
>>>>>
>>>>> Our tracking program gives us range to the satellite and its velocity relative to us given our location and the orbital parameters. From this we should have computed Doppler for both transmit and receive.
>>>>>
>>>>> We also know the frequency at the satellite of the various beacons 
>>>>> onboard. From this we can measure the doppler and work the other 
>>>>> direction
>>>>>
>>>>> If we transmit a subaudable tone of known frequency we should be able 
>>>>> to adjust the rx automatically by tracking the tone. (Acssb)
>>>>>
>>>>> Given these multiple ways of setting our tx/rx frequencies for our location can this not simply be automated to such a degree as to simply specify an offset from the beacon and operate as if it were a regular predictable opening on hf?
>>>>>
>>>>> Af6ep
>>>>>
>>>>> Sent using SMTP.
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>>>> -- 
>>>>
>>>> Bruce Paige, KK5DO
>>>>
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>>>> _______________________________________________
>>>> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
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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