[Moon] [Moon-Net] UADC4 Review

[Serge Szpilfogel]

Wow! one the most interesting email RE: the use of sound cards.
Most of it was above my ability to understand it.
However as it was mentioned first improving  your antenna system  will make
a big difference then worry about your sound card. Regardless of which sound
cards you use
It will not improve the readings of signals which have not been received to
start with. I see it here every day on 144mhz.
However it is important to experiment as Les is doing & please continue it
makes for fascinating readings from you & the great one Leif
Serge VE1KG

-----Original Message----- 
From: Moon-net [mailto:moon-net-bounces at mailman.pe1itr.com] On Behalf Of
Leif Asbrink via Moon-net
Sent: March 15, 2019 00:15
To: moon-net at mailman.pe1itr.com
Cc: Les Listwa
Subject: Re: [Moon-Net] UADC4 Review

Hello Les,


> My setup is  the IQ+ ( now Rev C),  WA2ODO 28db preamps, bandpass 
> filters, and a 4x9 LFA.  I initially used the Delta 44 ( partly 
> modified) and moved on to the the EMU1616, which was just replaced 
> with the UADC4.  I use Linrad to drive Map-65, but have also tested 
> with Map-65 direct mode. I use a 10 year old HP , 4 core processor with an
early version of Windows 10.
>  
> When I replaced the Delta 44 with the EMU1616, I was able to perform 
> A/B comparisons as the  IQ+ Rev A was compatible with both but now that my
IQ+
> is a Rev C and no longer compatible with the EME1616,   I was not able to
> do so.
"not compatible" That is not the way I would put it. When you compare you
should simply find that the noise floor with the Delta44 is much lower than
before and that a large fraction of the noise comes from the EMU1616 visible
as a small change of the noise floor when you switch your LNA on/off. As a
consequence you should find that the EMU1616 reports a worse S/N.

> There was a night and day difference between moving from the Delta to 
> the EMU1616, lower " visual" noise and less birdies and deeper 
> decodes.  Yes, deeper decodes.
"deeper decodes" What is that? Do you mean that MAP65 reports decodes at a
lower level?

Assuming that your noise floor change is 16 dB (or more) in both cases there
should be no difference at all. You should know, however, that there are no
proper drive routines for the Delta44 above the 32 bit version of WinXP. I
was once able to install the XP driver on a 32 bit version of Win 10.
No 64bit Windows version works correctly with the Delta44.


> The UDC4
> 
> But I noticed on Map-64 direct mode that  the noise figure  readings ( 
> the
> bars) were about 10db lower then usual ( with the 10db added via the 
> Map-65 I/O setup).  It was under 20db?  So I searched high and low for 
> away  to adjust the " volume" as I did with the EMU1616.... there was no
option.
There are jumpers inside the box that can set the gain. Presumably they are
by default set to fit the output level of your IQ+.

The procedure for setting the ADC gain in a direct conversion SDR is to
first set a very low gain. Place a signal near the center, perhaps
5 kHz offset. Bring the signal up until the signals ±10 and/or ±15 kHz get a
too high level. That would be the strongest signal level acceptable for the
output amplifier of the SDR hardware. Then increase the AGC gain until the
ADC saturates close to the level you have established.

> also noticed that when I switched off the preamps, the noise level dropped
> to zero.  Meaning I was over 20db,   The golden rule was a minimum of 14db
> and a max of 20db.
> 
> So I switched to Linrad, with my previous setting of the First FFT 
> amplitude (2000),  and saw my noise was now  about 10db higher then 
> with
> Map-65 in direct mode, but still lower then I expected to see. When I 
> killed the preamps the noise  dropped  24dbs  !!  Thats a problem.  
> You Linrard experts have already figured it out by now,  but not me.  
> So in Linrad,  I checked the RMS value of the floor ( Press "A")  and 
> it indicated it was at  33 !!!
That is perfectly fine!

> According to the  Linrad Instructions; optimal  is an RMS  voltage of 
> 10.
There is a misunderstanding here. The floor level affects Linrad only when
you have selected to use the 16 bit integer routines for FFT. At a sampling
rate of 96 kHz this was good on a Pentium 3 computer, but with Pentium 4 and
above you should use floating point arithmetics and then the floor level
should not be set so low. 

> To bring it down to down to 10, I needed to set the FFT to 500.
> But that damages the dynamic range .
In what way? It should not make any difference in S/N within Linrad. It
would affect the level of the signal you send to MAP65 but it should not
affect S/N as long as you do not use 16 bit integers. In the event that the
level actually matters for MAP
65 you can bring it up by decreasing the "FFT att N" parameters.


> 1) The noise as shown on Map-65 and linrad  with the combo of the 
> UAD4C and
> IQ+ Rev C is really lower !!!  We have all been self trained to expect 
> IQ+ to
> see 20++ of noise, when everything is set right  ( in my case 26db on 
> a good low noise day), but Alex explained  it is not necessary to be 
> so high, you just need to see a minimum of 14db to less then 20db drop 
> in noise when the preamps are off and pointed to cold sky.
YES!!!
>
>  2) I had too much preamp gain !!!   That was my problem.   The IQ+ ( Rev
A
> and B which most of us have)  requires a high gain 26db  preamp ( in 
> my case I had 28db to overcome cable  and filter losses) .  After some 
> emails with Alex ( who gives excellent support) it appears the new and 
> modified version  C requires only about 20dB.
But only when you have an UADC4 to use with it;-)

> So how well does it perform?  The screen looks cleaner with less 
> birdies and ghosts when my antenna is at lower elevations,  that is a
plus.
And it is highly unexpected. It indicates that "spurs and ghosts"
were caused by out-of-band signals. Lower gain makes out-of-band signals
less harmful, but since you have bandpass filters, presumably after the
WA2ODO amplifiers the out-of-band signals would have to be within the range
of those filters because signals outside would saturate in the WA2ODO
amplifiers before they (attenuated by the filters) could saturate the IQ+.


> I am decoding stations,  as I did with the EMU1616.  At this point, I can
not
> say if its  better then my  EMU1616, it may just be,    When I get the
> attenuators  and can play more, I will report back.
You should not see any difference at all in decodes. The BIG difference will
be that strong local signals that would have saturated your old system will
be far less likely to saturate your new system.


> Bottom line is if you dont have an EMU1616  ( and cant get one any 
> more ) and still using a Delta, this is a great improvement,  besides 
> the fact that its USB based and compatible with modern computers and 
> notebooks.  And if you are just starting out, this has the additional 
> benefit of not needing  a lower more standard gain preamp at the antenna.
BUT, if you are the lucky owner of a 32 bit XP platform with the proper
drive routine for the Delta44 and if you do not ever run into
overload/saturation problems because of strong signals there should be a
very small difference, if any. In an older computer the internal spurs of
the Delta44 should be very low.

> Is it worth the money? I would suggest investing the funds into bigger 
> and better antennas first, but after you do that then the UADC4  and 
> the modified IQ+ will let you get the most from that weak signal 
> buried underneath the noise.
I think the improved dynamic range of IQ+ with the UADC4 is most important
for terrestrial operators. I have not made any measurements on the combo but
I would think it is significantly better than conventional analog radios -
and terrestrial stations now and then point antennas towards one-another....
EME-ers tend to have overload problems only at moonset and moonrise. 
Working without problems at moonset and moonrise is of course an advantage,
and alternative 4-channel souncards often have issues and are typically not
really cheap.

73

Leif


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