Introduction
In previous posts I tested the various HF/VHF/Microwave antennas that I have using the versatile NanoVNA (Ref.1/5). For the past six months my apartment balcony has been under construction and finally it’s finished. Unfortunately when I setup my HF Buddipole antenna there was no reception, so I suspected that the transmission line which was left on the balcony during this time had some problems. So I decided to test the line and sweep it with the NanoVNA. A quick short circuit test measured 20 ohms which was obviously a problem.
Test Procedure
Figure 1 shows the test setup to check the cable. Using a digital volt meter at the receiver end of the cable, I measured the DC open circuit and short circuit resistance of the cable. When I first shorted the cable at the antenna end, I measured 20ohms. The RG-58 cable has a centre conductor resistance for AWG20 of about 10ohms/1000ft, so for 40ft this should amount to about 0.8ohms (2x.01x40ohms). Clearly there was a problem. I then used an emery board to sand the centre pin of the PL259 and the collar (they were caked with construction dust).
Test Results
| Test | Result |
| Resistance of DC Short at Antenna | 0.8 ohms |
| Resistance of DC Open Circuit at Antenna | >20Mohm |
| SWR 100KHz – 30MHz | <1.25 |
After sanding off the PL259, the DC short was reasonable and the DC open was infinite so that was good. I then placed a 50ohm termination at the antenna end of the cable and swept with the NanoVNA. Figure 3 shows the SWR which was <1.25 from 100KHz to 30MHz. My 20 year old balcony cable consists of 3xPL259 + 1xSO239Thru + 1BNC so not exactly precision 50ohms, but adequate for receive only for now.
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References
#1. – “L Band Dish Antenna Testing with NanoVNA”
https://jeremyclark.ca/wp/telecom/l-band-dish-antenna-testing-with-nanovna/
#2. – “Inmarsast Patch Antenna Testing with NanoVNA”
https://jeremyclark.ca/wp/telecom/inmarsat-patch-antenna-testing-with-nanovna/
#3. – “Radio Astronomy LNA/BPF Testing with NanoVNA”,
https://jeremyclark.ca/wp/telecom/radio-astronomy-lna-bpf-testing-with-nanovna/
#4. – “HF Loop Antenna Testing with NanoVNA”
https://jeremyclark.ca/wp/telecom/hf-loop-antenna-testing-with-nanovna/
#5. – “VHF Marine Antenna Testing with NanoVNA”,
https://jeremyclark.ca/wp/telecom/vhf-marine-antenna-testing-with-nanovna/
#6. – “HF Antenna Testing with NanoVNA”
https://jeremyclark.ca/wp/telecom/hf-antenna-testing-with-nanovna/
