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

[Robert Bruninga]

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
>>>> _______________________________________________
>>>> 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
>>> _______________________________________________
>>> 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
>>>
>>
>>
>> --
>> Andrew Koenig
>>
>
>


_______________________________________________
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