Lnb with 25 MHz dds Input goes bad.

PA3FBX the output is squarewave and so harmonics will appear. I did the same expierence with setting up 10 MHz out of SI5351 then I build a filtler out of 5 pcs 10MHz crystals and some capasitors. After that the waveform is very near to a sinewave. Maybe my expierence will help you.

PA3FBX Keep me updated Benno

Hi, as I see there are 800 Hz left and right from the carrier right? If so except xtal filter try to see if exist ampltituted modulation of your 25 MHz signal with 800 Hz. Did the gpsdo has a DAC with 800 Hz sampling rate?

It is not because it is a square wave. You need to look at the source on an analiser and on the input and output of the on-chip oscillator gate.

73's

Dave

Hi, can you measure the voltage that controls the frequency of the gpsdo oscillator with the scope to verify that it does not have 800 Hz ? Also with an HF receiver and an RTL stick see if the 25 MHz has sidebands of 800 Hz? Also for 10 MHz of gpsdo. Also check with the scope the power supply line that is clean.

Don't waste your time with si5351.

I started with the same begin this year and wasted weeks for getting it work.

As George and Dave already said : The internal frequencygeneration is the problem.

The si5351 produces sideband signals.

In the regular use, for examle on shortwave, they are not a problem.

But we multipy this refecence signal X 390 in the LNB.

This together builds the problem.

You should take a look on my solution with the indoor TCXO :

https://elektronik-muenster.de/viewtopic.php?f=17&t=12

This is how all my LNBs work stable and clean now.

73s

Armin DF1QE

Hi, if you have 10 MHz from GPSDO you can divide by 2 with 74HC390 (at C decoupled input use one 10K for pull up and one 10K pull down in order to bias it at middle) and then a XTAL filter (see here) and if you need more level I use a MAV11 MMIC.

2 years ago i spend my time for Si-series to get stable signal. is true, Don't waste your time, take OCXO 13~15MHz, inject reference into ADF4351 or AD9851 to set clock 25MHz.

https://www.analog.com/designt…rder=7&fc=26M&fRipple=0.5

If the spurs are separated by 800Hz at X band, does that suggeat they are 2Hz apart at 25MHz?

9750/25 = multiplication factor of 390. So 800Hz/390 = 2.05Hz

Or are they really 390 x 2 = 780Hz apart?

David

The spurs can be from bad shield or grounding.

Hi David G0MRF - the spurs are also 800 Hz apart on 25 MHz. But they are 20 x log(390) = 52 dB weaker and therefore not (easily) seen on the 25 MHz spectrum.

73 Ole

Just replaced the original 25MHz quarts by this one:

https://www.digikey.com/produc…P-T/887-2495-1-ND/5222446

25MHz/5.5V/0.2ppm

After several tries this is the best result I got for a "stand alone" stabilized LNB. Still 0.28ppm but very satisfactory.

Currently installed and running here:

http://177.20.168.179:8902/

73 de Ed PY2RN

Quote from PY2RN

Just replaced the original 25MHz quarts by this one:

https://www.digikey.com/produc…P-T/887-2495-1-ND/5222446

25MHz/5.5V/0.2ppm

A

73 de Ed PY2RN

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How long time change frequency is take to final stabilization ? How is weather affect to freq stability please?

Can you send a picture of your connection to X1/X2 ports with TCXO? Whats going with xtal, C-load and other?

Quote from 4Z4LS

How long time change frequency is take to final stabilization ? How is weather affect to freq stability please?

Can you send a picture of your connection to X1/X2 ports with TCXO? Whats going with xtal, C-load and other?

Hi, there is no final stabilization, it will keep varying freq but +/- few Hz only while external temperature goes up or down but that will not cause much trouble, mainly if you protect the LNB from the wind with a radome. Regarding x1/x2 ports it will depend on the type of PLL the LNB has but in general it will work in either one, the other goes to a 1-10nF capacitor then ground.

ok, i see. thank you for your answer. i don't want to open new theme for issues like nightmare stabilizing xtal in LNB or so...., but my testing time is very long and nothing to say,bacause only 1 of 6 LNB under test was working with external source.

about PLL is regular from RDA, 3566xx.

Quote from 4Z4LS

ok, i see. thank you for your answer. i don't want to open new theme for issues like nightmare stabilizing xtal in LNB or so...., but my testing time is very long and nothing to say,bacause only 1 of 6 LNB under test was working with external source.

about PLL is regular from RDA, 3566xx.

You should see something similar to this in the pic.

Both X1 and X2 pins will work, input at the corner pin (of the OS) is the low sensitive but better performance, -6 to +6 dBm input, the second pin is the sensitive input (-30 to +_6 dBm) but more phase noise.

Thank you!