[amsat-bb] EO-80 FM Transponder Tested (noise floor?)

Wed Jun 17 17:05:13 UTC 2015

Mode A would be fun, but equipment to work VHF/UHF is so common these
days, I'm not sure there's much point in a 10m downlink. Mode B and
Mode J are really not that much more difficult than working Mode A and
have advantages (noise floor and antenna size, especially).

The real problem is deploying a good 10m antenna from a cubesat to
produce a decent signal on the ground. 10m uplinks, on the other hand,
are something to look into (as W2RS has presented in numerous forums).
With NO-84, we now have a good experimental 10m uplink to test out.
Since ground stations can usually increase power to compensate from a
loaded antenna on the satellite, the use of a short antenna from a
cubesat for an uplink receiver isn't as much of a problem.

73,

Paul, N8HM

On Wed, Jun 17, 2015 at 12:43 PM, Joe <nss at mwt.net> wrote:
> why can we not get an old skool mode "A" back?
>
> Joe WB9SBD
> Sig
> The Original Rolling Ball Clock
> Idle Tyme
> Idle-Tyme.com
> http://www.idle-tyme.com
>
> On 6/17/2015 11:26 AM, Robert Bruninga wrote:
>>
>> I also am a proponent ot using 2m for weak downlinks because of the 9 dB
>> advantage.  But it has been pointed out to me that there is a higher
>> background noise component that needs to be considered.  I have not done
>> this.  My assumption is that the noise floor at 2m is maybe about 3 dB
>> worse than at 70cm?
>>
>> So 2m still wins, but I'm not sure of what the real noise floor is.
>>
>> Bob, WB4aPR
>>
>> -----Original Message-----
>> From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Zach
>> Leffke
>> Sent: Wednesday, June 17, 2015 11:23 AM
>> To: amsat-bb at amsat.org
>> Subject: Re: [amsat-bb] EO-80 FM Transponder Tested
>>
>> Paul beat me to the punch as I was typing up my response, but I'm sending
>> it anyway:
>>
>> Path Loss.  ->  function of lambda (wavelength) squared.
>> So all other things being equal (antenna gains, power levels, range,
>> etc.), you can look at the power ratio of the two.
>>
>> Rough calculation (going from 2m to 70cm):
>> 10log[(0.70/2)^2] = -9.1 dB
>> OR
>> Rough calculation (going from 70cm to 2m):
>> 10log[(2/0.7)^2] = +9.1 dB
>>
>> The thing to watch out for is antenna gains on the ground.  The arrow for
>> example has more gain on 70cm (7el) than it does on 2m (3el).  So while 2m
>> has a 9-ish dB improvement over 70cm in terms of path loss, the receiver
>> may not see the full 9dB because of the difference in gains on the antenna
>> between the two bands.
>>
>> Again VERY rough approximation (for demonstration purposes only):
>> 3el yagi -> call it 7.5 ish dB of gain
>> 7el yagi -> call it 11.5 ish dB of gain
>> so, about 4 dB of LOST gain (going from 70cm to 2m using the arrow
>> example).
>>
>> So net gain going from 70cm to 2m (all other things equal except the gains
>> on the arrow antenna) 9dB - 4dB = 5dB
>>
>> so your typo was actually fairly close :-) for those planning to use their
>> existing setup for the new birds.
>>
>> -Zach, KJ4QLP
>>
>> On 6/17/2015 10:43 AM, Andrew Koenig wrote:
>>>
>>> *9dB (typo)
>>>
>>> On Wed, Jun 17, 2015 at 9:42 AM, Andrew Koenig <ke5gdb at gmail.com> wrote:
>>>
>>>> Can you explain the 6dB advantage 2m has over 70cm? I've seen it here
>>>> on the amsat-bb, and in the mesh realm when comparing 2.4GHz and
>>>> 5.8GHz WiFi gear, but it still hasn't "clicked."
>>>>
>>>> 73 de KE5GDB
>>>>
>>>> On Tue, Jun 16, 2015 at 6:56 PM, Paul Stoetzer <n8hm at arrl.net> wrote:
>>>>
>>>>> Nick,
>>>>>
>>>>> It should be even stronger than AO-27's 500 mW, AO-27 had a 70cm
>>>>> downlink, the EO-80 downlink is on 2 meters, so EO-80's signal
>>>>> should be up to 9 dB stronger than AO-27 (12 dB stronger if they run
>>>>> it at 1 watt).
>>>>>
>>>>> 73,
>>>>>
>>>>> Paul, N8HM
>>>>>
>>>>> On Tue, Jun 16, 2015 at 7:49 PM, Nicholas Mahr
>>>>> <nicholasmahr1 at gmail.com>
>>>>> wrote:
>>>>>>
>>>>>> Thats very good news, Hopefully the two get activated before field
>>
>> day?
>>>>>
>>>>> Im
>>>>>>
>>>>>> most looking forward to EO-80, It should be like AO-27 with 500Mw or
>>
>> 1W.
>>>>>>
>>>>>> Good to know both are working well and wish a long life to them.
>>>>>>
>>>>>> 73 KE8AKW
>>>>>> _______________________________________________
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>>>>>>
>>>>>> are solely those of the author, and do not reflect the official
>>>>>> views
>>>>>
>>>>> of AMSAT-NA.
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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.
>>>>>
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>>>>> are solely those of the author, and do not reflect the official
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>>>>
>>>> --
>>>> Andrew Koenig
>>>>
>>>
>>
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>
> _______________________________________________
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