using TSA for Chinese S-LNB down converter observation

Messagede F6DZP » Mer 8 Jan 2014 17:13

Hello,
Using TSA (Tiny Spectrum Analyser) I have made some measure with my Chinese down converter (2,4 GHz --> 1,25 GHz) I will use for HamTV project.
S-band LNB5.jpg
S-band LNB5.jpg (42.9 Kio) Vu 4651 fois

Input Frequency 2.3 to 2.7GHz
L.O. Frequency 3650MHz
Output Frequency 950 to 1350MHz
L.O. Stability ±1.5MHz(-40to+70°C)
Noise Figure <0.4dB
Conversion Gain >55dB
Input VSWR 2.0:1
Output VSWR 2.0:1
Image Rejection 45dB
Phase Noise -95dBc/Hz@100kHz(max) -75dBc/Hz@10kHz(max)
Supply Voltage 12 to 24V


Receiver : TT S2-1600 using STV6110 satellite tuner IC, 65 dB gain (can be reduced by AGC voltage or by soft, as I do, and possibility to add 16 dB using BBgain)

Software: Tiny Spectrum Analyser v0.2 (can be downloaded here :http://www.vivadatv.org/viewtopic.php?f=60&t=271 )


I plug a 50 ohm dummy load.
scan with TSA without power supply:
dummy load-1GHz scan-no attenuation-2460MHz-no Volt.jpg
dummy load-1GHz scan-no attenuation-2460MHz-no Volt.jpg (159.5 Kio) Vu 4651 fois


I set power supply to 13v :
dummy load-1GHz scan-no attenuation-2460MHz-13Volt.jpg
dummy load-1GHz scan-no attenuation-2460MHz-13Volt.jpg (165.07 Kio) Vu 4651 fois


We can see that S2-1600 card is saturated by a stronger signal.
S2-1600 is set to run without AGC so its gain is at maximum (65dB), it cannot get signal higher than -40 dBm if BBgain is at 0dB, -56dBm if BBgain is at 16dB.
if we add the S-LNB gain : 55 dB , we get the noise at a very high level, so we saturate.

We must use attenuation :
dummy load-1GHz scan-14dB attenuation-2460MHz.jpg
dummy load-1GHz scan-14dB attenuation-2460MHz.jpg (172.53 Kio) Vu 4651 fois


We can see that noise is at maximum level at about 2460 MHz.
I change scanwidth :
dummy load-500MHz scan-14dB attenuation-2460MHz.jpg
dummy load-500MHz scan-14dB attenuation-2460MHz.jpg (171.09 Kio) Vu 4651 fois

again
dummy load-250MHz scan-17dB attenuation-2460MHz.jpg
dummy load-250MHz scan-17dB attenuation-2460MHz.jpg (170.45 Kio) Vu 4651 fois

and again
dummy load-125MHz scan-17dB attenuation-2422MHz.jpg
dummy load-125MHz scan-17dB attenuation-2422MHz.jpg (169.13 Kio) Vu 4651 fois


I have change also center frequency to 2422 MHz, one frequency used by HamTV.

Now I will put a little omnidirectional Wifi antenna.
wifi antenna-125MHz scan-17dB attenuation-2422MHz.jpg
wifi antenna-125MHz scan-17dB attenuation-2422MHz.jpg (174.3 Kio) Vu 4650 fois


we can see Wifi signal at the upper frequencies.
( I want to test if Wifi signal are not too strong and will impeach me to receive HamTV)

Another frequency used by HamTV is 1237MHz. I think it will be more difficult...
wifi antenna-125MHz scan-17dB attenuation-2437MHz.jpg
wifi antenna-125MHz scan-17dB attenuation-2437MHz.jpg (178.41 Kio) Vu 4650 fois


after 5 mn recording signal scanned :
wifi antenna-125MHz scan-17dB attenuation-2437MHz after 5mn.jpg
wifi antenna-125MHz scan-17dB attenuation-2437MHz after 5mn.jpg (178.24 Kio) Vu 4650 fois


Now I will try my 2.4GHz dish. just put on the floor of my shack. I will try different direction...
dish2-4GHz 24dB -125MHz scan-21dB attenuation-2422MHz.jpg
dish2-4GHz 24dB -125MHz scan-21dB attenuation-2422MHz.jpg (170.87 Kio) Vu 4649 fois

after 5 mn
dish2-4GHz 24dB -125MHz scan-21dB attenuation-2422MHzafter 5 mn changing polarity and direction.jpg
dish2-4GHz 24dB -125MHz scan-21dB attenuation-2422MHzafter 5 mn changing polarity and direction.jpg (202.95 Kio) Vu 4649 fois


changing scan-width and attenuator value:
dish2-4GHz 24dB -62.5MHz scan-24dB attenuation-2422MHz.jpg
dish2-4GHz 24dB -62.5MHz scan-24dB attenuation-2422MHz.jpg (191.13 Kio) Vu 4649 fois


Conclusions:
-2422 MHz seems to be not too much "wifi-QRM" but 2437MHz will be very difficult to use.
- lowest frequencies below 2.4 GHz will be more quiet.

TT S2-1600 works the best for signal at about -40 dBm.
If we use an 2.4 GHz pre-amplifier + 55 dB gain of this LNB we will get a chance to put too much signal inside S2-1600.
analyse all your equipment including coax and plug lost..
use this software to observe directly what kind of signal you bring to S2-1600.


Jean Pierre F6DZP
F6DZP
 
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