nanovna-H – supplied cables

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

I reported issues with the cables supplied with my nanovna-H at nanovna-H – Chinese junk?

Kurt Poulsen reported some cable measurements, including measurement of a cable supplied with a nanovna. In this case, the cable is a little longer than mine, and although his report does not identify the cable type, it seems that RG174 type cable is reported by most users.

Above is Poulsen’s measurement of s11 of an open circuit 33cm cable of presumably RG174 type.

Let’s compare that with what we might expect of Belden 8216, a RG174 cable.

Lets consider the loss at a frequency where the line is about λ/2 as the matched line loss (MLL) is approximately half -|s11|dB.

Poulsen measured |s11|=0.57dB (scaling from the graph), whereas we might expect closer to 0.35dB. The inferred MLL is 0.285 and 0.175dB respectively.

The measured |s11| is 63% higher than expected, and implies MLL 63% higher than expected for 8216.

The measurement is probably closer to correct than to specification value, the cable is probably Chinese Quality (ie junk).

Curiously, Hugen, the designer / marketer of the nanovna-H posted:

In addition, the newly released NanoVNA-H reduced the RG174 cable from 30cm to 20cm to reduce the loss. If I make a VNA with a frequency higher than 1GHz, I will use the RG316 cable. On large VNAs in the lab, it is common to use RG402 cables.
This is the cable parameter provided by China’s cable manufacturer:
http://www.kingsignal.com/index.php?ac=article&at=read&did=188

That reference specifies the inner conductor as:

1. Inner Conductor

  Copper Clad Steel

  7X0.17

In fact, plated or clad conductors are likely to have insufficient skin depth to have copper like performance at frequencies below say 100MHz, and would be IMHO a poor choice. It is no accident that the referenced data sheet does not give attenuation figures below 100MHz. I note though that the cables are short and loss at those frequencies is very low anyway and corrected by the VNA correction algorithms.