[AK-VHF] [Moon-Net] IQ+ MAP 65 TEST & CONCLUSION

Sun Nov 6 22:43:37 EST 2016

Roger,

There is no AGC applied to the K3 1st IF.  First stage is fixed gain 
preamp and mixer tuned by digital VFO.  I do not use any part of the 
2nd IF including the roofing filters.
The K3 applies AGC only to the 2nd IF gain stages

I select F3 which is an open  filter slot and take off the 8.215 MHz 
1st IF to two SDR (LP-Pan) which generate IQ baseband for a Delta44 
soundcard.  I'm not sure if MAP65 applies sw AGC to the digital signal level.

.

73, Ed

At 03:15 PM 11/6/2016, Roger Shultz wrote:
>Ed, do you run with agc off?
>73, Roger, NJ2R
>
>Sent from my iPhone
>
> > On Nov 6, 2016, at 6:13 PM, Edward R Cole <kl7uw at acsalaska.net> wrote:
> >
> > Comments inserted, below:
> >
> > At 01:30 PM 11/6/2016, Leif Asbrink wrote:
> >> Hello Serge,
> >>
> >>
> >>> 1)  50 ohms dummy load on the IQ+ INPUT
> >>>    FLOOR NOISE 5DB ON  MAP65
> >>>
> >>> 2)  ANTENNA CONNECTED   (IQ+ TO SPLITTER LNA ON) 22DB WITH ELEVATION
> >>>    OF 15 DEGREES IN THE CLEAR OVER THE OCEAN
> >>>
> >>> 3)  ANTENNA CONNECTED   (IQ+ to SPLITTER LNA OFF)
> >>>    FLOOR NOISE  5DB  ON MAP65
> >>>
> >>> CONCLUSIONS: THE 16DB required are barley enough 22db -5db floor
> >>> noise =16db RF GAIN & very often depending on the AZ/EL it can go
> >>> down to -19db -5db = 14db RF GAIN well below of what is required.
> >>
> >> What you measure is the right thing, but it is not RF gain.
> >> It is how much the noise floor changes when you switch on/off the
> >> LNA. As expected your #1 and #3 gives the same noise floor.
> >>
> >> 22-5=17 and that is OK, but you note that this difference can go
> >> down to 14 dB and that is a bit low. If you add a LNA in front of
> >> the IQ+ you can expect to gain 0.10 dB. That will be hard to notice
> >> but your detect rate in map65 should improve by about 10% at
> >> the detect limit with the FT decoder which shows the steepest
> >> dependence on S/N. A station that detects with a rate of 50% would
> >> improve to about 56% if you add a LNA - but that would happen only
> >> when your antenna points in a direction where your noise floor
> >> is at 19 dB. The DS decoder is less steep and if you use that you
> >> can only expect an improvement from 50 to 53%.
> >>
> >> Maybe, if you look at a time when Leo (quiet sky) is in the clear
> >> over the ocean you might see an even lower noise floor.....
> >>
> >> Anyway, your system is very good (provided your LNA NF is low)
> >> I suggest you consider how often you work stations at the detect
> >> limit in a quiet direction. If you make 10 such contacts per year,
> >> improving detect by 10% from 50% to 55% would make QSOs faster
> >> but not often.
> >>
> >> On the other hand, if you have a sked and detect only 10% of
> >> the transmissions with DS, a 0.1 dB improvement on S/N should
> >> give a detect rate of 11.5%. Instead of detecting one in 10
> >> transmissions you would detect one in 8.5 transmissions.
> >>
> >> The advantage of adding more gain is small. There is a risk that
> >> there are strong out of band transmitters that saturate your
> >> system if you add too much gain.
> >
> > Serge stated he has a quiet location - not sure if that also
> > eliminates strong signals out of band like TV or commercial FM.  But
> > understanding is he is remote from all those problems
> >
> >
> >> There is no such thing as "the required gain" Gain is always
> >> a compromise. In a very quiet location (like mine was when
> >> I was QRV) it is satisfying to use very high gain to know that
> >> one has squeezed the last fraction of a dB from the system.
> >
> > This topic started with Serge noting a difference in decoding
> > threshold between using MAP65 and WSJT.  So maybe this will provide
> > that small improvement to have both Rx systems equally
> > effective.  This in the -28 to -30 signal range.
> >
> >
> >> By the way, even if you can not hear it you probably have some
> >> impulse noise that lifts your noise floor. There is a blanker
> >> inside map65, but I do not know how good it is.
> >
> > Not very good from my perspective.  If you apply it lightly to noise
> > that runs 6-10 dB higher than your quiet noise floor it helps.  But
> > if faced by major noise running 20 to over 30-dB then applying the
> > MAP NB aggressively does lower noise but also lowers signal.  The
> > effect is raising the decoding threshold from --28 to -5 or worse.  I
> > cannot decode HB9Q on 2m when noise is running S8/9 (>30
> > dB).  Normally HB9Q is -10 to -4 on JT65.
> >
> > I have more success using the DSP NB and/or NR in my K3, but only
> > usable with WSJT as there is no IQ output from the K3, only monaural
> > audio on the data line out.  To use K3/KRX3 dual Rx I have to tap
> > into the 1st IF which is sent to two ext SDR which are phase-locked
> > which provide two IQ inputs to the delta44.  K3 DSP is located in the
> > 15-KHz 2nd IF of the radio.  So I can only use the K3 NB/NR with
> > single-pol WSJT which works with simple soundcard input.
> >
> > This is what makes the IQ+ and recent other dual-channel SDR's better
> > choices (simpler/cheaper) approaches for using MAP65.
> >
> >> You might use
> >> a sound recorder to make a .wav file from your Delta44 while
> >> rotating the antenna 360 degrees in azimuth. Noise pulses would
> >> be visible with an audio editor such as audacity. If you make
> >> such a recording I would be happy to look at it - and if you do,
> >> switch off the LNA for 10 seconds at the end.
> >
> > I sent Leif a wav recording of my noise interference which he was
> > able to analyze, saying the NR in Linrad would not be effective 
> for my noise.
> > I have to locate the source and eliminate it (if legally
> > possible).  Using my shotgun as noise blanker is not an option <smile>
> >
> > 73, Ed - KL7UW
> >
> >
> >
> > 73, Ed - KL7UW
> > http://www.kl7uw.com
> >     "Kits made by KL7UW"
> > Dubus Mag Business e-mail:
> >     dubususa at gmail.com
> >
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> >
>
>
>
>
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73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
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