On 11/26/2025 5:46 AM, Jeff (W4DD) wrote:
We can see the BW change as we command the antenna to tune so the narrow BW is
due to the antenna. Flex BW (front end) is set to wide which I think is 14MHz.
There is a HUGE difference between SWR bandwidth and the bandwidth of an
antenna for receive. An antenna may have matching networks and
components that affect its response.
There is HUGE value in a very wide (at least 10 MHz) waterfall. Look at
what NK7Z posted almost ten years ago as a method to chase RFI. He used
an inexpensive (about $125) SDR RX to make 24 hour waterfalls that show
multiple noise sources turning on and off. The importance of this is
knowing more about what we're looking for and when to look for it. I
have one of those RX, and W6GJB and I used it to chase noise at his QTH
when we were evaluating a spot on his property to do 6M EME.
https://www.nk7z.net/i-have-rfi-now-what-locating-it/
Perhaps you can set up a simple vertical feeding one of those receivers.
Ham Radio Outlet was selling them. Don't know if they're still available.
We need to re-think instrumentation. I've been doing this sort of
instrumentation since 1982 in the world of pro audio with hardware that
cost what it took to be the down payment on my first house ($12k in
1982). $125 for an SDR that blows away the capabilities of $10K HP
spectrum analysis gear is a no-brainer! About 10 years ago,
then-neighbor NR0V, who gave us Pure Signal and did software for ANAN,
showed me even better capabilities of the QRP ANAN rig that then sold
for less than $1K. It had frequency resolution of fractional Hz and
about 120 dB of dynamic range.
To use these inexpensive solutions, all we need to do is keep them out
of overload and understand aliasing.
73, Jim K9YC
We can hear it on other bands, but much weaker, although it adds to the noise
floor.
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