Month: July 2016

At Ratings of coax antenna switches I showed characteristics of a home made switch which has very low InsertionVSWR, but poor isolation.

A couple of correspondents have offered an explanation that the unused port must be shorted to get good isolation.

If that was the case, then we would expect all coax switches that leave the unused port open to have poor isolation.

Let us look at a very good coaxial relay

Above is a Dowkey 402 series relay which has good performance to GHz. It does not short the unused port.
Continue reading Coax switches – is shorting unused port necessary for isolation?

In a recent article I discussed how InsertionLoss implies InsertionVSWR in lossless devices.

This article looks at measurements of a few antenna switches at hand.

Daiwa CS-201G II

It is difficult to find comprehensive data on the very popular Daiwa CS-201 series switches.

Above is the data from the packet of one of these switches, a CS-201G II. The specifications are pretty loose, and one must depend on one’s own measurements.

Above, the CS-201G II, a basic CS-201 series switch with N connectors, advertised as useful to 2000MHz where InsertionLoss is given as 1.2dB (or better?). If there were no TransmissionLoss in the switch, that would imply InsertionVSWR=3.6, but there is probably some significant TransmissionLoss and InsertionVSWR would be somewhat less. Nevertheless, IMHO InsertionLoss=1.2dB indicates it as unsuitable such frequencies. Continue reading Ratings of coax antenna switches

Devices inserted in transmission lines often characterised by one or more of:

1. Insertion VSWR (the input VSWR when terminated with a matched load);
2. Return Loss (RL) in dB (20 times the log of the magnitude of the complex reflection coefficient); and
3. Insertion Loss.

Practitioners often find Insertion VSWR (1) of most use as it indicates whether the device is worse than other system devices, the weak link in the chain if you like. You might see a coax antenna switch specified to have InsertionVSWR<1.2 to 60MHz.

Return Loss (2) is a function of VSWR and vice versa, so it appeals when the designer thinks in terms of Return Loss rather than VSWR (and it is a better metric for VSWR<1.2). You might see a coaxial relay specified to have ReturnLoss>30dB to 500MHz.

Insertion Loss (3) is not so readily compared to the other two which are measures of input reflection with a matched termination. It often yields some numbers that appear very acceptable, but might be deceptively so. You might see a coaxial relay specified to have ReturnLoss>30dB to 500MHz. You might see a coax antenna switch specified to have InsertionLoss<0.2dB to 100MHz. Continue reading InsertionLoss implies InsertionVSWR in lossless devices