Homebrew paddles “Serrafusta”

Today i gave it a shot to build my own CW key. I still have the intention to learn CW one day and i thought having a key could be handy.

First step is to find the materials for the paddles. Looking around in my shed i found the almost perfect paddles.

WP_20150421_001Yes, it is what it looks like. I just took a hacksaw blade (serra in catalan) and broke them in two. The advantage of the blades is that they are conductive (at least when you remove the paint, that is) and they are just sturdy enough to bend with a fair resistance. The nuts and bolts at the end will be used to connect the dash and dot wires.


WP_20150421_002Next is the base. I created the base out of wood (fusta in catalan). The elevated part is where the paddles will be fixed, the ground connection will be made to a big bolt i screwed in the centre of the base.  On the base of the that elevated part i created a small cable guide.


WP_20150421_003The cable i am going to use is an old cable i found in the shed as well. I found out that it’s pretty difficult to find a cable with a stereo jack and some decent wire connected to it. This is a cable with one side a 3,5″ stereo jack and the other side a serial connector. Don’t ask me what this cable was for.


WP_20150421_004Here is where i connected the ground connection to the centre bolt. This image also shows the use of the small cable guide i mentioned before.




The paddles are now fixed to the base. I use a connecting bridge which puts enough pressure on the paddles to keep the firmly in place. As you can see the gap between the paddles and the nut is pretty small. You can adjust the gap by turning the bolt.


WP_20150421_006Here is a view from the back side of the paddles so you can see the bridge more clearly. The dash and dot cables are connected to the paddles now.



This is the finalised key connected to the radio. You can see that the key is pretty small. I found out that the base is way too light to work with one hand, so eventually the key needs to be fixed to the table with sucking naps, velcro or whatever. But in any case it was a fun thing to build, cost $0 and works fairly well. Now it’s time to start morse lessons!!

Noise canceling with RTL-SDR adapters

Yesterday someone pointed me to this video where G7CNF Nige uses two receivers and the Diversity feature in PowerSDR to phase out noise from the receiving signal. Now, cross-phasing has caught my interest when i came back to the radio almost two years ago because of the PLC noise i have in my shack. Nige is using the two receivers in his ANAN-100D, i don’t have a device like that. Also i think it’s much “cooler” to try to do this with RTL-SDR adapters.

PowerSDR is made for the Flex receivers, but there is an OpenHPSDR version of PowerSDR. Then N1GP wrote a bridge from SDR_RTL to the HPSDR platform. So using this bridge i should be able to access my RTL-SDR adapters using PowerSDR. Let’s see if that works.

  1. Get a separate Linux machine to run the bridge on.
  2. Get your dependencies installed to compile the bridge. In my case (fresh Ubuntu 12.04) i needed to install build-essential, git, cmake, libusb-1.0-0-dev, libasound-dev
  3. Clone the sources for the bridge. Do not use the branch mentioned above, if you read the README there you see that you need to use:
    #git clone https://github.com/n1gp/librtlsdr.git
  4. Then:
    #mkdir build
    #cd build
    #cmake ..
    #sudo make install
  5. You should now get something like this:
    rtl_adsb rtl_eeprom rtl_fm rtl_hpsdr rtl_power rtl_sdr rtl_tcp rtl_test

    rtl_hpsdr is the one you want!

  6. Connect your RTL adapters to the computer and test rtl_hpsdr:
    Found 2 RTL device(s), using 2.
    RTL base sample rate: 1536000 hz
    Global settings:
    config file: none
    ip address:
    length of fir: 32
    number of rcvrs: 2
    hpsdr output rate: 48000 hz
    sound device: none
    Rcvr 1 (ordered as 1) settings...
    freq offset 0 hz
    signal multiplier 1
    Found Rafael Micro R820T tuner
    tuner gain auto
    Disabled direct sampling mode
    direct sampling off
    agc mode off
    Rcvr 2 (ordered as 2) settings...
    freq offset 0 hz
    signal multiplier 1
    Found Rafael Micro R820T tuner
    tuner gain auto
    Disabled direct sampling mode
    direct sampling off
    agc mode off
    Revealing myself as a Hermes version 2.6 rcvr.
    My IP Address:
    My MAC Address: 00:00:00:00:00:00

    Nice, rtl_hpsdr is running and we found two RTL devices. Notice the last lines, they are important. “Revealing myself as a Hermes version 2.6 receiver” and the IP and MAC address of the server. Remember those two.

  7. We are almost done on the server side. The only thing that is left if to start rtl_hpsdr listening on an IP address that we can access from outside. We use the -i option for this. I suggest you enter at least once “rtl_hpsdr -h” to understand which options there are and what they do.
    #rtl_hpsdr -i
  8. We are done on the server side. Now let’s install PowerSDR on your Windows workstation. Download PowerSDR from http://openhpsdr.org/download.php and install it. Nothing special, just a standard Next, next, Finish.
  9. Remember that rtl_hpsdr told you it presented itself as a Hermes receiver? So in PowerSDR make sure that you select the Hermes receiver. Leave the Connection type to Hermes and Full Network Discovery.

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Now you are ready to start PowerSDR and connect to the Hermes/RTL-SDR server. When you are connected the IP address of the server should be displayed in the Hardware config screen.



There are a couple more things to take care of. The Hermes transceiver board covers a frequency range of 50kHz-55MHz. The RTL adapter covers, without up-converter, 24-1800MHz. So the only usable frequency range with this combination is 24MHz (lower side of the adapter) till 55MHz (upper side of the Hermes). You can extend that range a bit by using the HPSDR cinfig panel, but more than 150MHz it will not do.

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If all is working fine you should see someting like this on your console:

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You can now activate the second receiver as well by clicking on the RX2 button next to the power button and then select the Diversity menu item.

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Personally i found PowerSDR highly unreliable. I don’t know if it’s my PC, the communication between the PC and the server or the quality of the server, but in my install PowerSDR locked up every time i wanted to use it. It’s partner software cuSDR turned out to be more reliable, better looking as a panadapter, but lacks the Diversity function.

Let me know what you think of this article and let me know if you have more success than me setting this up.