Re: Pluto:: Spurious Emissions


The basic problem with the transmit side and really the receive side as well is the math involved requires small fractions of a degree and small fractions of a dB precision in setting the nulling conditions. You can setup 50 dB to 60 dB with modest effort. But the components involved are slightly  temperature sensitive. So your 50 dB balance can decay to 40 dB or 30 dB fairly quickly. This was expected and shown in the Built In Test Equipment in the  prelaunch test equipment for the first set of GPS Phase 2B satellites. The signal is a pair of PN sequence modulated signals sent at exact quadrature on the carrier frequencies. The test equipment was required to be within something like a quarter of a degree of each other and the amplitudes had to be a fraction of a dB of correct. While aligning the BITE transmitter I noticed I could fall out of specification by simply moving one of the 3" or so long double shielded 1/4 inch cables connected to the quadrature modulators. It required pretty much lab conditions to keep full accuracy. The 1/4 degree is significantly worse than the 50 dB conditions as I recall the math.

On top of that you have received signals to consider. The isolation between TX and RX on Lime or Pluto is not very exciting. It is at a level that the settings for TX can mess with RX and vice versa. At least in the satellite case you folks get to play with the TX and RX local oscillators are frequencies that are not directly harmonically related. So the cross effects will be minimum except for the temperature increase when transmitting.


On 20220128 06:48:10, Jacques RAMBAUD wrote:
Hello all,

Thank you Sigi for the help,

The spurious I reported before was due to the fact that I used the XIT (Receive side)  to align my RX and TX frequency . I understand now that it as to be done with RIT, please confirm.

The spurious I see now are about -56 dBc up to a Drive level of 50% on the TX control which correspond to about - 16dBm  CW carrier (Tune mode) .

Reducing the  Drive level down tp 10% does not help much, about -58 dBc. At 70% Drive level I measure -55dBc in Tune mode (CW) .

On Tune mode (CW) the spurious are slightly lower if Bandwith is set at 1.2 MHz (select radio)  rather than  set at 750 KHz.

I do not know if the spurious can be lowered further , for QO-100 operation it is very acceptable but for terestrial I doubt .

73 jacques F6BKI

Le 27/01/2022 à 23:10, Siegfried Jackstien a écrit :
NEVER NEVER NEVER USE OFFSET ON THE BIRD!!! not with lime and not with the pluto

otherwise a spurii may cause trouble on another ones frequency!!

offset is ONLY used in local terrestrical contacts (that the carriers rest does not block your rx signal) but then you maybe would not use fullduplex but halfduplex

fullduplex may work with local contacts on a repeater but then also no offset is needed (repeater gives the offset so rx and tx are already not on same qrg)

Simon .. in my view you could/should complete delete the offset setting in radio setup and set it fixed to 0kc

if you have not found a good iq calibration (lime is a good example) then that carrier rest is at your 0hz spot and does not hurt other qsos (and you see it in if view and press tx calibration till it is gone) ... if you use an offset of say plus or minus 50 or 100 kc (or whatever) you may send out that carrier rest on another spot and do not see it (in first view)

you even may transmit outside the band (and thats for sure not ok!!)

so repeat ... NEVER NEVER EVER use offset tuning!!!!

greetz sigi dg9bfc

Am 27.01.2022 um 23:02 schrieb Simon Brown:
Don't forget optional offset tuning.

Simon Brown, G4ELI

-----Original Message-----
From: <> On Behalf Of Siegfried Jackstien
Sent: 27 January 2022 21:56
Subject: Re: [SDR-Radio] Pluto:: Spurious Emissions

bonjour jacques

at first ... do not use tune tone at that high level (leila is already crying outcause you are way over beacon level!!)

second ... your pluto setup is NOT tuned correct (you should not have an xit setting of -10kc)

and third ... your lnb setting should be (after tuning xo correction) set that you get the beacon closer to 750 ;-)

dg9bfc sigi

ps if you do not know how to set up ... just ask .. i will help you

Am 27.01.2022 um 13:08 schrieb Jacques RAMBAUD:
taken transmiting a Tune

jacques F6BKI

Le 27/01/2022 à 11:40, Simon Brown a écrit :

May I have a screenshot taken while generating the signal shown in
the spectrum analyser please.

Simon Brown, G4ELI

-----Original Message-----
From: <> On Behalf
Of Jacques RAMBAUD
Sent: 27 January 2022 11:38
Subject: Re: [SDR-Radio] Pluto:: Spurious Emissions

Hi Simon,

Here is the screen shot

73 jacques F6BKI

Le 27/01/2022 à 11:17, Simon Brown a écrit :

You MUST add a proper screenshot of Console, I have no idea what
settings you are using.

Simon Brown, G4ELI

-----Original Message-----
From: <> On Behalf
Of Jacques RAMBAUD
Sent: 27 January 2022 10:58
Subject: Re: [SDR-Radio] Pluto:: Spurious Emissions

Hello Simon and all,

Using now the SDR Console v3.1 build 2496 and still have the same RF
spurious as before out of my Pluto , see attached picture.

Is it normal ?

73 jacques F6BKI

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