[DSP-10] 2nd EME2 Test, also nil, more questions.

[Bob Larkin]

Hi Courtney,


At 08:48 PM 5/10/2006 -0700, Courtney Duncan wrote:
>The improvements for today's moonrise:
>
>- A better idea of where north is for rotator calibration, yesterday I was 
>20 degrees off (about half power right there).
>
>- A boost from 6 W to 29 W.
>
>- Looked for a "quieter" frequency, finally settled on 144.079300 
>indicated, which is about 144.079150 correcting for my TCXO.
>
>Other info:
>
>- Local topography.  I'm not even sure I'm seeing the moon from here due 
>to a nearby hillside to the east and lots of tree obscuration between here 
>and there.  By the time the moon is high enough to see through all this, 
>it's out of the vertical beamwidth of the antenna. Moonrises for the next 
>few days are further south and later in the evening so that helps.  I 
>also, potentially, have a better view towards moonsets.  I'll try one of 
>those in a few days when it happens at a "reachable" hour.
>
>Result:
>
>Still nil, in fact the "central bin" spends most of its time < 0.000 so it 
>doesn't even report a Cntr Sig value.  I'm clearly not seeing any return, 
>not even an ambiguous one.
Yes, if the (S+N)/N is very low, errors can cause it to appear <0 which is 
of course not true! So doing the best it can, no signal level can be 
calculated.


>New Questions:
>
>- Are there gains or losses from operating near the horizon like 
>this?  I'm trying to avoid antenna work, like fixing at some higher 
>elevation than zero or, heaven forbid, an elevation rotator.

In some locations, it is possible to get extra gain from the round 
reflection. For most of us though, the big effect is increased noise. in my 
suburban QTH, I must elevate to get away from the noise.  And stay away 
from the Sun  for the same reason.



>- What about the noise temperature?  This is a straight DSP-10 without 
>pre-amp.  I seem to remember Bob saying somewhere that it was about 
>600K.  Should I be using that for Te?  Would it help?  Or, conversely, 
>should I not even consider attempting this without a 100K mast-mounted 
>preamp?  (Seems like that could be 8 dB right there.)
  Make sure that connecting to the antenna causes an increase in noise 
relative to a load. This assumes a reasonable VSWR on the antenna. Along 
the horizon, my local white noise, in most directions is well above 600K 
and a low noise preamp has no benefit, especially towards the "industrial" 
part of town.  If I elevate, the preamp is of considerable benefit.




>- The frequency seems too quiet, actually.  The number in the lower right 
>was around 5.75dB during the EME2 run and a subsequent noise measuring LTI 
>run.  When I hooked the Brickette back to the antenna directly it's more 
>like 7.75dB.  Is the amplifier passthrough or the cabling making me deaf?

The brickette loss for receive should be small.


>In the "Oh Great" category:
>
>- Well, in fact, recall all the trouble I was having getting my Brickette 
>to show more than 5.0 - 5.5 watts on the Bird 10C?  Well, reconnecting 
>with a different cable, I'm seeing 7.2 - 7.5.  Yep, that's 1.6 dB or so 
>right there.  So never mind about the deaf thing. I have some cables to 
>label "bad" now.
>
>But let me just say that it is _so_ great to be using a radio where you 
>can just do some built in measurement and figure out stuff like 
>that!  When I originally did the "U15 Mixer Ground Modification" and was 
>just able to diagnose and fix an important problem using measurements that 
>the box would just take itself I was very impressed by what we've got to 
>work with here.  What a great architecture!


Have fun and stay with measuring things. I am going to be away for a few 
days, but will await your results.

73, Bob


>73, Courtney, n5bf/6
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