Friday, August 11, 2017

The MS-S7-Web Remote Antenna Switch

You can either have one radio for each antenna, or use an antenna switch. Antenna switches are found in any HAM store, but if you run remote, you need to be able to switch antennas remote as well.

Enter the MS-S7-Web Remote Antenna Switch. I first heard about it when it was introduced as an extension to the KiwiSDR. I had no plans to use it with my KiwiSDR, but the KONG crew has plans of erecting another beverage antenna in Kongsfjord, and I didn't really want to add another SDR + PC to the shack.

I bought the MS-S7 from Bulgaria in the beginning of June, but haven't had the opportunity to test it until now. If memory serves me right, I paid around EUR 170.

The package consists of an in-house antenna selector, which can be controlled via web, or manually. It is connected to an outdoor (which can of course be used indoor) antenna switching box with seven antenna connector in additon to one connector for the receiver. The antenna selector connects to your router or switch (or PC I presume, not tested), and it needs 12 VDC.
From the eBay ad

The antenna selector has green LEDs for each antenna. Also there's a blue power indicator LED. The green LEDs are quite dim and easy on the eyes. The blue LED is anything but! I feel tempted to replace this one, if not I do need to cover it somehow.

The device works via an Internet browser (Firefox and Chrome are recommended). It can be set up with a static IP (which is better than DHCP in this case), and the Device Settings will look similar to that below.

There are two tabs in the user interface, and the other is the contol panel, on which you're supposed to click on the "ON" labels to change antenna. You will hear two clicks, one to disconnect from one antenna, and one to connect to the other. Or so it's supposed to work.
Web based control panel

Web based config panel

But I often need to click an extra time to get the second relay to connect. This may make problems if you are running a script-based automated antenna switching schedule. If you do, it may be wise to program double-click instead of single-click. I've always managed to change antenna when I double-click.

So what about signal leakage from one antenna connector to the other? The short answer is: There isn't any. I was rather taken aback by this. I connected a signal generator to one port, and a longwire antenna to the other. I set the signal generator up to maximum (99 dBu which equals -6 dBm), and there wasn't a trace of a carrier on the frequency I had chosen to monitor on the longwire antenna port. So was the case with the other connectors - although I admit I didn't put a 50 ohm load on them.

I also checked for insertion loss. It must be close to zero, because I wasn't able to detect any difference.

I did however notice that the switch makes its own noise, despite being fed from a linear power supply. It raises the noise floor of our super-quiet 500 meter beverage from around -135 dBm to more than -130 dBm. It also produces spikes every 8 kHz at levels around -120 dBm to -110 dBm. Admittedly, most DX-ers won't notice this, and only we will notice on certain parts of the day. But those certain parts happen to coincide with super-weak signals from the Pacific coming in. So this is not good.
Via antenna selector

Bypassing antenna selector

So, apart from the gruelling blue lazer-like LED and the somewhat unpredictable antenna selector procedure, this is indeed a good product for many DX-ers.

1 comment:

Mike said...

The noise that you are seeing may be some common mode noise, injected from the other antennas. I use a different variety of remote switch (changing to an MS-S7 switch) and found that when I connected my 160m dipole, that the noise on the 80m came up considerably. Consider that the 160m is disconnected and center pin grounded, but the other side of the dipole from the shield side is still connected. The only thing I could do to quiet the noise initially, was to disconnect the 160m dipole completely. I later put common mode chokes on both the 80 and 160m dipoles (as well as the 60m) and the noise went down considerably.
Mike, W0IH