Antenna switch - wiring query

beamrider66

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Thanks for adding me to the forum.

I am building a Wifi receive-only 2-way Antenna Switch using an ESP8266 and relays. It's going to switch between an MLA-30 and my existing long-wire.

I have a query regarding the unused antenna feed that is not switched in:

Should this be:
  1. Left floating (not connected to anything)
  2. Connected to the RF ground (shielding of the output coax going to the set)
  3. Connected to electrical ground (-ve power supply to switch/relay).
It's going to be in the loft, so difficult for me to experiment.

Thanks in advance.
 

Ubbe

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Isn't easier to use the 12v in the coax and have a 12v relay that switches the antennas? I know that if you have an amplifier at the antenna you feed that with a bridge recitfier so it always has the +12v regardless of polaity from the coax and have a diod in series with the relay and then reverse polarity to engage the relay. You only have to supply your own 12v 0,5A and insert in the MLA-30 USB power box at the DC choke. Schematic at bottom of this page: MARTIN - G8JNJ

Radio wise you only need a high ohm resistor, maybe 100k, over the antenna terminals to bleed off any static voltages for the unconnected antenna, that should be the longwire. But you must have a balun for that so it is already taken care off in the balun. The shield, ground, of an antenna or balun should always be connected. Then your local lightning protection regulations comes into play that might require much more grounding rules for antennas.


Isn't ESP8266 just a WiFi device that outputs network data, and you will need soemthing to handle IP adresses and controls an external relay in some way. Seems very complex and needs a lot of development?

/Ubbe
 

beamrider66

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Hi, thanks for the reply.

The radio (AFEDRI network SDR) and antennas are both in the loft and I listen on the PC using HDSDR, so I don't have access to the coax and also lightning isn't a concern. I've already built the switch and it works fine [in terms of switching two different voltage batteries to a light bulb]. It was very cheap, about $15 all in, plus I enjoy messing with that kind of stuff.

So the antenna that is on standby will be terminated in the switch box very close to the other antenna and output connector; I was concerned that it will affect it being so close? I didn't know whether it (the centre core) should be grounded and if so to what.

The feed from the switched-out antenna will be present on the "Normally Open" pin on the relay, which of [1-3] in the OP is best or something else?, I already have a balun for the long-wire, yes, so sounds like I don't need the resistor?

Thanks again..
 

Ubbe

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I would be interested in the schematic and connection principals of such a cheap WiFi based controller. Is it only that kit that is needed or do it require some sort of CPU with software as well?

No need to do anything with the center pin on either antenna. Just have the braid or metal chassi of the balun grounded in the box. A distance of 1mm (1/24 inch) maybe has a capcitance of 0,5pF and can be ignored.

/Ubbe
 

beamrider66

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Thanks, will give that a try.

This is the item I bought.


As you see, there are many similar products as well with more channels etc.

There are no schematics as such. I guess I can produce a write-up with photos and a simple wiring diagram if/when I know it works.

I'm currently working on the software side as it comes without any, and you need to use a couple of obscure mobile phone apps which are a bit fiddly to say the least.
 

Ubbe

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That's incedible! Just £5 for a complete kit! Just the two relays would cost more than that. It can be used both as standalone acces point or connected to a router. When you have that connected to a router you also can have internet acces remotly, if that APP will allow it.
Very interesting. Thank you so much for the info.

/Ubbe
 

beamrider66

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Yes, it's pretty cheap for what you get.

I have it working now without requiring any phone apps. You initially connect with a mobile phone or laptop to its Wifi AP in order to configure the main house Wifi/pasword, after that you can access it from any web-browser in order to switch antennas. I've wired it with one Antenna "normally closed", so there is a default antenna when un-powered.
 

Ubbe

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I have my satellite dishes a fairly long distance from my house and I have set up a VHF and a shortwave wire antenna with a diplexer connected to the sat dish coax. A LNB takes maybe 100mA and a sat box can maybe power 500mA at 12-18volts. So it should be power enough for that WiFi module and I could then add more antennas that are switchable.

/Ubbe
 

beamrider66

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Just tested, seems to work great. The MLA-30 provides a much cleaner signal than the indoor long-wire.


 
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