Diamond D3000N VNA Sweep

[devicelab]

Here's a sweep of my Diamond D3000N discone antenna. The antenna uses 75FT of LMR400 at approximately 30FT above ground level. In this sweep, I'm using only a RTL-SDR FM notch filter.

 

[prcguy]

It would be nice to see more detail, like limit return loss to 30dB or maybe 40dB and SWR to 3:1 or 4:1 max.

 

[Ubbe]

Start at 100MHz and end at 900MHz. Do an impedance sweep. The 2.0 SWR are either 25 ohm or 100 ohm but you'll soon realize that 50 or 75 ohm coax hardly makes a difference. Set your scanner to a fixed 160MHz frequency and sweep it's impedance between 137-170MHz. Then set to 450MHz and sweep 400-500MHz. Do the same at 700-900Mhz.

/Ubbe

 

[prcguy]

Also, the 75ft of LMR400 at 1GHz is going to have about a 6dB return loss without an antenna connected, so at the higher frequencies whatever the antenna is doing is being masked by at least several dB.

 

[devicelab]

It would be nice to see more detail, like limit return loss to 30dB or maybe 40dB and SWR to 3:1 or 4:1 max.

Updated screenshot.

 

[prcguy]

Oh, thank you! Now if we only had cursers on some popular freqs like 125, 146, 155, 225, 300, 400, 445, 460, 470, 512, 800, 900MHz, etc, it would be even more useful.

Since the actual Discone doesn't work below 100MHz, if your frequency range was 100MHz to 1GHz you would have 200MHz/div and that would be a little easier to estimate SWR at various frequencies. Don't mind me said the guy who used to teach classes on spectrum analyzers and VNAs.

Updated screenshot.

 

[devicelab]

Don't mind me said the guy who used to teach classes on spectrum analyzers and VNAs.

No I appreciate it... it's making me learn how to use the NanoVNA. This is much easier on a SA as (some) of it's done for you.

The display gets cluttered very quickly though with multiple markers. I'd probably have to use the desktop application.

 

[Ubbe]

...so at the higher frequencies whatever the antenna is doing is being masked by at least several dB.

When my workplace got a new drum of RG58, maybe 1000ft, I measured its SWR when nothing where connected to the other end. It was a perfect 1.0

Any antenna analyzer measurements will be off by the amount of attenuation, both ways, in the coax.

/Ubbe

 

[vagrant]

Thank you for the plot with the markers. It is informative along with the other details.

 

[devicelab]

Figured out more features of the VNA and PC application... here's a better screenshot of the antenna sweep. And yes I purposely set the S11 to those values so I had a clear view of the marker data.