ON7MV – Miguel Verbanck

Nine element coaxial cables for the YCCC/VE6WZ 9RX circle array

Independent comparison: Rohde & Schwarz FSH8 and DG8SAQ VNWA V2

Main objective "The relative phase spread"

 Test equipment

DG8SAQ VNWA V2 

Calibrated  RTC1002 digital oscilloscope.

Calibrated Rohde & Schwarz FSH8

Calibrated Fluke multimeter for supply-voltage verification.

Technical Report

1. Purpose and background

This report documents the calibration procedure, the complete phase measurements of all nine coaxial cables, the independent comparison between the Rohde & Schwarz FSH8 and the DG8SAQ VNWA V2, and the resulting cable placement recommendation for the RX9 array.

The purpose of this measurement campaign was to verify the electrical length and phase matching of nine coaxial cables used in a 9RX circle array. The array operates as a set of active three-element combinations: one centre element and one diametrically opposed pair selected from the eight outer elements. Therefore, both the overall nine-cable spread and the spread within each active three-element group are important.

Main objective "The relative phase spread"

The cables were first measured with a calibrated Rohde & Schwarz FSH8 and then independently remeasured with a DG8SAQ VNWA V2. The same procedure, test leads and connectors were used for all nine cables. The cross-instrument comparison covers 160, 80 and 40 metres.

2. Instruments and method

• Rohde & Schwarz FSH8 in Transmission S21 Vector phase mode.
• DG8SAQ VNWA V2 in transmission phase mode.
• All nine cables were measured using the same fixture, adapters and connectors.
• After calibration, the setup was left unchanged except for replacing the cable under test.
• The relative phase spread is more important than the absolute phase offset between two different instruments.

3. FSH8 calibration and results

The FSH8 calibration reference was practically 0° over the relevant receiving bands. The displayed residual phase was approximately 0.03° at 1.809 MHz, 0.03° at 3.8 MHz and 0.10° at 7.1 MHz.

The total spread is only 0.29° on 160 metres, 1.08° on 80 metres and 1.62° on 40 metres. Cable 4 is consistently the electrically shortest cable, while cable 1 is among the electrically longest.

4. DG8SAQ VNWA V2 “measurement 1”

The independent DG8SAQ series is designated “measurement 1”. Its calibrated reference was also practically 0°, with approximately -0.06° at 1.8 MHz, 0.00° at 3.8 MHz and -0.12° at 7.1 MHz.

The DG8SAQ independently confirms a total spread of 0.29° on 160 metres, 1.05° on 80 metres and 1.53° on 40 metres. It also identifies cable 4 as the electrically shortest cable and cable 1 as one of the longest.

5. Cross-instrument comparison

The absolute phase values differ because of a nearly constant instrument and reference-plane offset. However, the relative spreads agree exceptionally well: identical on 160 metres and within 0.03° and 0.09° on 80 and 40 metres respectively. The DG8SAQ therefore independently validates the FSH8 result.

6. Effect on array performance

The maximum equivalent timing error remains below approximately 0.8 ns. This produces essentially no measurable loss in coherent forward summation. Deep nulls are more sensitive to phase error, but the cable matching remains sufficiently accurate that cable phase is unlikely to be the dominant limitation. Element geometry, soil, preamplifiers, relays, delay lines and the local environment will normally dominate first.

7. Three-element group matching

Two candidate layouts were assessed. The FSH8-only optimisation selected cable 9 for the centre and pairs 1-2, 3-6, 4-7 and 5-8. The DG8SAQ-only optimisation selected cable 8 for the centre and pairs 1-2, 3-6, 4-5 and 7-9. Both layouts were then checked against both datasets.

8. Final placement recommendation

CENTRE CABLE: 9

OPPOSITE PAIRS: 1-2, 3-6, 4-7 and 5-8

This layout is marginally more robust on the priority bands of 160 and 80 metres. The worst active-group spread remains approximately 0.55-0.57° on 80 metres and no more than about 0.90° on 40 metres when checked with both instruments.

9. Final conclusion

All nine coaxial cables are exceptionally well matched. Two independent instruments confirm almost identical relative phase spreads. The cables require no shortening or modification. Re-terminating or mechanically altering them would carry a greater risk of introducing new error than the possible improvement would justify.

FINAL ASSESSMENT: all nine cables are approved for the RX9 array.