Thanks Gerald. Your explanation should be added to the Knowledge Base.
Regards,
Edwin MarzanAB2VW> From: [EMAIL PROTECTED]> To: [EMAIL PROTECTED]; [EMAIL
PROTECTED]> Date: Fri, 25 Jan 2008 19:57:27 -0600> CC:
FlexRadio@flex-radio.biz> Subject: Re: [Flexradio] gain on the sdr1000> >
Hopefully, I can shed a little light on this subject. Here are a few facts:> >
1) Traditional "legacy" radios measure the AGC gain and convert the gain to> S
Units. I remember my old 706 that showed a higher S Meter reading if I> turned
the RF gain down, rendering the meter totally useless. The S meter> readings
would change if I turned the attenuator or preamp on/off. That> means that the
S meter was totally meaningless for measuring signal strength> at the antenna
terminals.> 2) The FlexRadio products measure the signal strength at the
antenna> terminals in the same way that a spectrum analyzer does. If you change
the> preamp settings, the noise floor goes DOWN and the signal level stays the>
same. Remember that when you change the preamp setting, you have not> changed
the signal level at the antenna terminal. You have, however;> improved the
signal to noise ratio with the preamp and therefore the noise> should go down
in reference to a fixed signal level. > 3) If you are using a SDR-1000 you must
calibrate the radio using an> external signal generator. If you move to a new
version of the software> with a new database, you must recalibrate on the 1000
unless you import your> old database.> 4) If you are using a FLEX-5000, it is
fully calibrated at the factory and> the data is stored to EEPROM inside the
radio. We you run the radio for the> first time; it pulls the data from EEPROM
into the PowerSDR database. If> you delete the PowerSDR.mdb database, it will
start fresh and pull the data> in again.> 5) The FLEX-5000 with PowerSDR has
built in test equipment (BITE) that> allows everything in the radio except for
the power/SWR bridge to be> calibrated without external test equipment. In fact
it is the same method> used to calibrate in the factory. > > In summary, an
accurate S Meter will give the same reading no matter the> preamp, attenuator,
or gain settings in the radio. If the preamp is turned> on, the spectral noise
floor should go down while the signal stays the same> on the panadapter.> >
Hope that helps,> Gerald> President> FlexRadio Systems> > -----Original
Message-----> From: [EMAIL PROTECTED]> [mailto:[EMAIL PROTECTED] On Behalf Of
Robert Dennison> Sent: Friday, January 25, 2008 1:31 PM> To: [EMAIL PROTECTED]>
Cc: FlexRadio@flex-radio.biz> Subject: Re: [Flexradio] gain on the sdr1000> >
Hi Scott,> > Your numbers are certainly very different than mine. I think I
have a> calibration problem and perhaps a problem with the 10db preamp. >
However, in switching to PowerSDR versions along the way I almost> certainly
have lost my Level calibration. This evening I'll haul the> trusty HP signal
generator in and do a calibration. Then we should see> clearly what's up. I do
fear the 10db preamp is dead. The risk taken in> buying a used 1K.> > vy 73>
Rob> AB7CF> > > On Fri, 25 Jan 2008 12:35:06 -0500 "KQ8RP" <[EMAIL PROTECTED]>
writes:> > > > My readings from 20 CW into dummy loadat 1K> > > > RX Meter Pan
Display> > Preamp Off -109 dBm. -109 dBm> > Preamp Low -118 dBm -117 dBm> >
Preamp Med -132 dBm -131 dBm> > Preamp High - 132 dBm -140 dBm> > > > at 25 HZ>
> > > RX Meter Pan Display> > Preamp Off -99 dBm. -110 dBm> > Preamp Low -109
dBm -117 dBm> > Preamp Med -122 dBm -131 dBm> > Preamp High - 142 dBm -140 dBm>
> > > > > Scott Gordon> > http://www.kq8rp.us> > > > ----- Original Message
----- > > From: "Robert Dennison" <[EMAIL PROTECTED]>> > To: <[EMAIL
PROTECTED]>> > Cc: <flexradio@flex-radio.biz>; <[EMAIL PROTECTED]>> > Sent:
Friday, January 25, 2008 12:13 PM> > Subject: Re: [Flexradio] gain on the
sdr1000> > > > > > > Hi Eric,> > >> > > Well, I'm sure with antenna on the
preamp output is noise floor > > +> > > amplified (atmospheric noise +
signal.)> > >> > > With the dummy load while on 20M CW, I get the following RX
Meter > > and> > > Panadapter noise readings. (Panadapter readings are eyeball
of > > course.)> > > Also I'm taking the RX readings on noise with the 25 Hz CW
> > filter.> > >> > > RX Meter Pan Display> > > Preamp Off -117 dBm. -115 dBm>
> > Preamp Low -117 dBm -117 dBm> > > Preamp Med -125 dBm -123 dBm> > > Preamp
High - 125 dBm -125 dBm> > >> > > Readings would be constant except for that
step between Low and > > Medium...> > >> > > vy 73> > > Rob> > > AB7CF> > >> >
>> > >> > >> > >> > > On Fri, 25 Jan 2008 10:41:56 -0600 "Eric Wachsmann" > >
<[EMAIL PROTECTED]>> > > writes:> > >> Could this be due to atmospheric noise?
Have you tried this on > > a> > >> dummy> > >> load?> > >>> > >>> > >> Eric
Wachsmann> > >> FlexRadio Systems> > >>> > >> > -----Original Message-----> >
>> > From: [EMAIL PROTECTED]> > >> [mailto:[EMAIL PROTECTED]> > >> > radio.biz]
On Behalf Of Robert Dennison> > >> > Sent: Friday, January 25, 2008 10:29 AM> >
>> > To: [EMAIL PROTECTED]> > >> > Cc: [EMAIL PROTECTED];
flexradio@flex-radio.biz> > >> > Subject: Re: [Flexradio] gain on the sdr1000>
> >> >> > >> > Hi Jim,> > >> >> > >> > Well, yes t'would be nice to have the
panadapter display the > > input> > >> to the> > >> > preamp, but mine displays
the output from the preamp.> > >> >> > >> > Clearly the signal is amplified by
the same gain as the > > noise...> > >> In my> > >> > case as I increase the
preamp gain a notch the noise level is> > >> amplified> > >> > by say 5db and
the signal magnitude floating on top of the > > noise> > >> is> > >> >
amplified by the same amount. RX Meter with Sig Avg shows the> > >> same> > >>
> result. Also, near as I can tell by ear and eye the preamp is > > not> > >>
adding> > >> > additional noise.> > >> >> > >> > Near as I can tell from the
panadapter and RX Meter, my preamp > > is> > >> working> > >> > like a near
perfect linear amp.> > >> >> > >> > Yes, powerSDR, having some idea what the
preamp gain, is can > > back> > >> it out> > >> > of the display, but I've run
every version of PowerSDR from 1.8 > > to> > >> 1.10.3> > >> > and they work
exactly the same as I've described and measured. > > I'm> > >> now> > >> >
running SVN: 1917 and it's behaving as I described.> > >> >> > >> > Have I
found a weird display mode? I'm too good at that for > > my> > >> own> > >> >
good...> > >> >> > >> > vy 73> > >> > Rob> > >> > AB7CF> > >> >> > >> >> > >> >
On Fri, 25 Jan 2008 06:40:48 -0800 Jim Lux> > >> <[EMAIL PROTECTED]>> > >> >
writes:> > >> > > Quoting Robert Dennison <[EMAIL PROTECTED]>, on Thu 24 Jan
2008> > >> 09:08:37> > >> > > PM PST:> > >> > >> > >> > > > Hi Ken,> > >> > >
>> > >> > > > Now I'm confused. Must have something calibrated wrong or > > a>
> >> bad> > >> > > 1K.> > >> > > >> > >> > > > My SDR1K is sitting on 7.010.
Nothing but noise. Keeping> > >> AGC-T> > >> > > > constant: with Preamp Off
the noise level reads -105dBm > > peak.> > >> Now> > >> > > if I> > >> > > >
put the Preamp on Low the noise level jumps to -94dBm and > > when> > >> I> >
>> > > put the> > >> > > > Preamp on Med the noise level jumps to -88dBm.
Finally> > >> putting> > >> > > the> > >> > > > preamp on High the noise level
jumps to -80dBm.> > >> > > >> > >> > > > To me that's what I would expect from
a preamp. In fact> > >> first> > >> > > time I saw> > >> > > > it, I said to
myself "now that's the way a preamp should> > >> work!"> > >> > >> > >> > > Not
really... As you say, you're thinking in terms of the> > >> display> > >> > >
reading what comes out of the analog section. But, really,> > >> you> > >> > >
want> > >> > > the display to be reading what's at the antenna terminals > >
(just> > >> like> > >> > > a> > >> > > lab spectrum analyzer). So, you adjust
the scale according > > to> > >> how> > >> > >> > >> > > much gain there is.> >
>> > >> > >> > > That way, an input signal of a fixed amplitude (e.g. at > >
-100dBm)> > >> is> > >> > >> > >> > > always displayed at the same amplitude.
The behavior you> > >> describe> > >> > >> > >> > > (measured noise floor
getting bigger as amplifier gain is> > >> increased)> > >> > >> > >> > > is
sort of upside down (Unless the amplifier is really > > noisy?)> > >> > >> > >>
> > Is there something else going on?> > >> > >> > >> > > With a fixed level
input signal, does the SNR stay the same?> > >> (i.e.> > >> > > the> > >> > >
preamp isn't contributing significant noise)> > >> > >> > >> > >> > >> > >> >
>> > >> > >> >> > >> > _______________________________________________> > >> >
FlexRadio Systems Mailing List> > >> > FlexRadio@flex-radio.biz> > >> >> > >> >
> http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz> > >> >
Archives: > > http://www.mail-archive.com/flexradio%40flex-radio.biz/> > >> >
Knowledge Base: http://kb.flex-radio.com/ Homepage:> > >> http://www.flex-> >
>> > radio.com/> > >>> > >>> > >>> > >>> > >> > >> > >
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