Using Rig Expert antenna analyzer to tune the multiband low band antenna


RigExpert AA-55 ZOOM antenna analyzer is the perfect tool to tune HF  antennas. It covers all bands eligible for the DXCC Challenge Award – 160,  80, 40, 30, 20, 17, 15, 12, 10, and 6 meters. 

Therefore DX-ers worldwide call AA-55 ZOOM antenna analyzer  “DXCC Challenge Champion”. 

This article shows that it is a necessary tool to make the homemade 160 to 30m work. 

The 27.5-meter-high vertical antenna was designed using the MMANA  antenna modeling software and built. 

To increase antenna efficiency the special counterpoise called FCP, or  “5/16 Wave Single Wire Folded CounterPoise” designed by Guy Olinger K2AV, is used.

The self-resonance of the top loaded vertical + FCP was around 2.6 MHz. 

This was found to be a “magic” frequency that allowed us to design low-impedance LC matching circuits for the desired bands and avoid high-voltage arching. 

The next step was to make the matching box that had independent circuits for all 4 bands switched remotely 

from the shack by vacuum B1B and B2B relays rated 3 and 5 kV correspondingly. 

Two B1B vacuum relays connected in series are used to short between the FCP feed point and the middle of the third wire to “flip” the FCP to 80 to 30m operation.  

To tune the matching circuits, several different antenna analyzers, including the nanoVNA kit, were tried to use. 

All but one, RigExpert AA-55 ZOOM, have failed not being able to handle high-level RF fields induced at the vertical antenna. 

RigExpert AA-55 ZOOM is immune to high levels of RF fields and is ideal for this kind of measurement. 

Tuning started on the lowest band -160 meters.  

Nowadays the activity there is concentrated around the main FT8 frequency of 1840 kHz. 

Therefore the matching circuit was tuned close to it. 

The matching circuits for the remaining three bands were tuned as well. 

The SWR on 80 meters was 1.25 on 3590 kHz.

The SWR on 30 meters was even better 1.15 on 10125 kHz. The worst of the three was 40 meters with SWR 1.54 on  7100 kHz.  

Anyway, PI-networks of tube linear amplifiers and most transistor transceiver finals can handle up to SWR=2 with ease. 

Once again, RigExpert AA-55 ZOOM antenna analyzer makes tuning antennas easy and pleasant.