Spur Reduction

This has been discussed here and on net. Here's a simple way to reduce spurious from your shack going back up the feedline and into the antenna. I used a CATV lightning block and mix-31 ferrites. That point is about mid-point on my feedline to active magnetic loop



  • edited March 2019
    I run my coax feeds underground, and have a similar grounding block set up at each end of the underground run. How much improvement do you note from the addition of the ferrite?
  • it can be hard to quantify but my wspr ranking (number of uniqs) went up several spots since implementating that 2nd ferrite scheme
  • The ground spike and ferrites method is certainly better than just using ferrites alone.

    But I think you may need more turns through the ferrite, or more ferrite, to get the best performance on the LF bands.

    Steve, G3TXQ's (SK) website gives good guidance.



    Martin - G8JNJ
  • that was implemented when there was snow on the ground.... more to follow!
  • This is one reason why I love the Kiwi, take a laptop/tablet/phone out to the feed line and try stuff while watching the waterfall, harder to do with other receivers.
    I ran one channel on a PC set to slow waterfall and then an Android tablet right at the change I was testing, that way when I got back to the PC I could see if my perceived improvements actually showed up on the slow one. Just had to do it when the local QRM was out shopping.
  • Yes! The ability to do modifications to antennas/cables/grounding/etc in the field and see the effect in real time using the Kiwi is worth the price of admission by itself! It is a huge timesaver, vs running inside/outside continuously.

    Your comment about the slow waterfall speed made me think of something... we can record audio to a file via the browser, what about being able to record the waterfall to a JPG or PNG file? Or even a simple bitmap file if that would be easier to implement? Then it would be possible to look at the entire history of our tinkering, and see the effect(s).
  • Chris... things like kiwirecorder.py and gr-kiwisdr can do some of this stuff
  • Good point, WA2ZKD. I may try that today, I want to install some ferrite cores outside and note the effects, if any.
  • I do manually save the waterfall from the right click feature but the spectrum needs a screen dump.
    It would be nice if the right click to save option could be set to include the date/time in the filename.

    I did just test a screen recording program to take interval snapshots but for me it's better to do snapshots just before a change and as quickly as possible after, to avoid condition changes or other QRM blurring any affect.
    I do look at the SNR and noise plots on http://sibamanna.duckdns.org/sdr_map.html too, that is good for picking up changes over the week though some terrible noise can just look like a drop in the SNR but only a small increase on the noise plot.
    That week of results is half the reason mine is still public even when struggling.

    One thing that I found speeded up power supply comparisons is leaving a channel running when the Beagle is powered down, once the PSU is swapped and the Kiwi is back online we can launch a new browser tab by control clicking the green arrow, we should then have a frozen "before" and active "after" tab, keep doing that at each boot/PSU to quickly compare PSU's in the browser.
  • If you can go through the tedium of installing gnuradio and gr-kiwisdr there's a tool that allows you to measure the magnitude of signals and their SNR. It is helpful. As is walking around your house with something like a Sony ICF7600 of equiv.
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