XC70-Antenna-Tuning

Documenting the installation and tuning of a Nagoya 200A 2m/70cm antenna on my 2015 Volvo XC70.

Equipment

• Nagoya 200A 2m/70cm 39" antenna Amazon 

• NMO Mount Amazon 

• Supercat 15' RG58/U cable with right angle PL-259 connectors Amazon 

• RadioShack 21-524 SWR meter

• NanoVNA-H4 Amazon 

Initial Readings

After installation I did some SWR testing with a borrowed RadioShack 21-524 SWR meter which showed very high SWR readings when using my VR-N7500 radio.  The higher the power, the higher the SWR readings.  This meter seems to have been designed for CB and HF amateur radio and not for VHF/UHF so it is unclear if the readings are correct.

I used the following frequencies for my testing:

VHF frequency: 146.000MHz (right in the middle of the band)

UHF Frequency 446.000MHz (appropriate frequency from the ARRL band plan).

Here is a video of an SWR test with the meter into a dummy load on VHF (146.000 MHz).  This appears to indicate that the problem is with the SWR meter giving bogus readings in VHF and UHF.

NanoVNA readings

I purchased a NanoVNA-H4 and calibrated it for the VHF (144.0-148.0 MHz) and UHF (420-460 MHz) Amatuer radio bands).

Then I ran analysis in the following configurations.

Direct to Antenna

I connected the NanoVNA directly to the antenna with an RP-SMA to PL259 adapter.  

Transmission Line and Antenna

These readings are from the end of the transmission line (15' Supercat RG58 with right angle PL-259 connectors on each end.

Transmission Line and Dummy Load

These readings are from the end of the transmission line (15' Supercat RG58) with right angle PL-259 connectors into a 50 Ohm dummy load.

Dummy Load

These readings are the NanoVNA directly into the 50 Ohm dummy load.

SWR Readings with VHF/UHF Meters

MFJ

Mike (N2VR) offered for me to come over so he could measure SWR with his MFJ SWR Analyzer which showed less than 2:1 across the VHF band (we didn't measure UHF).

Moonraker SWR-300

I ordered a Moonraker SWR-300 and tested it at full power (50W VHF, 40W UHF) and measured less than 2:1 in the middle of both bands.

Conclusion

The antenna installation is adequate (2:1 across the band).  I might be able to improve it by flipping the mount so that the antenna is closer to the roof (i.e. ground plane).

The Radio Shack SWR meter that I first tried must be only for the CB (27MHz) band.