• Official Post

    Hello all,

    I've got my both 0.5ppm RTL-SDR dongles from China but compared to my AirSpy they seem to be quite insensitive. When I turn my LNB power on/off (or when I unplug the AirSpy) I see a huge noise floor coming up. Nothing like that with the new RTL-SDR's.. also the EB is much weaker.. I think there is some 20dB or so missing? Or do I miss a gain setting somewhere in the RTL-SDR configuration?

  • I use the same RTL SDR sticks and never encountered such problems.

    When i shut off the LNB voltage the noisefloor drops as expected.

    For the RX sensitivity i can only say with an 130cm offset dish pointed at 26° after 20m cable the (lower) EB is at 39-40dB over noise.

    73 DB8TF

  • Yes, when you first use RTL-SDR sticks in software you should search for the gain setting that can be set to something between 0 and 50dB or "automatic" and make sure it is either on "automatic" or you change the setting to something reasonable for your setup. Try 20dB or so.

    • Official Post

    Hi Lucio,

    I have not made any real measurements with Lab equipment, but I must say I'm very impressed by this NEWGEN.RTL2832SDR in particular for that price. At least behind the LNB for P4-A usage it seems to be ideal and for SSB no need to worry about modifying the LNB's (with PLL).... I may try some VHF reception later and compare it with my Funcube Dongle..

    pe1chl no Serial numbers on my NEWGEN-RTL-SDR's ;)

  • pe1chl no Serial numbers on my NEWGEN-RTL-SDR's ;)

    RTL-SDR sticks have an electronically readable serial number. On most if not all devices I have seen the number is 00000001 :)

    (also on those NEWGEN-RTL-SDR sticks that I recently ordered)

    So even more exclusive than your Funcube dongle :)

    But you can change it. E.g. on Linux do this (with a single stick plugged in):

    rtl_eeprom -d 0 -s 12345678

    You will see the current serial number and the proposed new one, and answer y to the question if you want to write it.

    Then unplug and re-insert the stick and it will be serial number 12345678 now.

    When you have several sticks you can use this to know which one you are accessing in your program (at least when it supports the serial number).

  • I have been thinking about the problem of digital latency in my receiving equipment as this will make it hard to listen to one's own signal. However, it has occurred to me that there may also be in-built latency in the satellite transponder, which we can do nothing about. Please can anyone throw any light on this matter?

  • Yes, I agree with you. In itself that may be manageable. I guess we will find out. However, I have tried to speak on a local club top band net whilst listening on our web sdr (high local noise) and I just cannot get my brain to function! I was just curious in case anyone knows (and is allowed to say) whether the transponder is sdr based. Exciting times ahead!

  • The transponder itself is not SDR based and should cause no appreciable extra delay. The delays you will see are the path delay of ~240ms and the delay of your own receiver (when it is SDR).

    They typical local SDR program has less delay than WebSDR, but there still is some delay.

    It requires some experience to be able to talk while hearing yourself delayed, and when you cannot manage to do that you could add a facility to (partially) mute your receive audio while you are transmitting.

    That can be as simple as a small relay in series with your headphones which engages while transmitting and switches an adjustable series resistor in the path.

  • Listening to my own transmissions I have estimated latency on an RTL dongle using HDSDR to around 600 ms. Playing around with sample rates and buffer size doesn't seem to change this. Any idea on how to reduce latency on this type of RX??

    73 Ole