SDRPlay RSP1b as an Antenna Analyzer Experiment

[sunwave]

This is really a rough way for antenna analysis but it does somewhat tell you something. I have two wires cut for 27.185MHz which is 276cm. I cut both wires to exactly 276cm then connected them to my Nooelec balun one nine v2. I hung it vertical.

In this case I use the noise floor. I see a dip in the noise floor at 27.185MHz in between two peaks in the noise floor. Don't do this for actual transmitting antennas. This was just for reception experimentation. I enclosed an image showing it. That dip is there regardless of whether a signal is there or not. I positioned the squelch yellow line as a point of reference. It still receives signals on the entire HF band but it's hottest on the CB band.

 

[merlin]

Not the greatest method to test antennas at all. The HF band is constantly changing.
One of the cheapest ways around this is getting a NANO VNA H4. under $100
276 Cm is a good reasonant length for 11 Meter CB.

 

[Ubbe]

I get the opposite to that, a peak with more noise in the spectrum sweep where the antenna resonates. When listening in AM mode I can clearly hear where the noise increases and that happens to be the frequency I have cut my wire to. I use a 9:1 balun and the bandwidth of a wire seems to be something like 10% of the frequency.

Why would you get a higher RF signal outside of a tuned antennas bandwidth? Is it some sort of automatic gain involved while using the spectrum sweep? I haven't managed to found such a setting in my SDRuno program. But I also prefer to use SDRConsole as it seems to work better for me with clearer audio in shortwave bands.

/Ubbe

 

[prcguy]

Most antennas will show more signal level or noise floor in the VLF through HF range and therefore a noise peak on a spectral display at resonance, so nothing special here. For tuning some antennas like VLF or MW ferrite rod antennas, using a spectrum analyzer and noise peak is a common way to tune them.

 

[merlin]

I dont know how this setup is configured. somthing generating a signal at 27 MHz could show a dip at reasonance, Much like a grid dip meter from the old school days.
I have a temp 15 meter long wire and show a higher noise floor just above 21 Mhz. A bit of increase at 10 MHz.