Remote Coaxial A/B Switch

[lilimike]

I have something like this to switch between a Digital antenna and Satellite system:

I want to build a remote switch. I'm ok with the remote part of it but not sure about the switch itself. Can I just use a simple relay?

Mike

 

[Brevor]

This is usually done using PIN diodes to do the switching. If you are OK at building RF circuits you might check out this link.

https://electroschematics.com/3002/pin-diode-rf-switch/

 

[lilimike]

Thanks for the link.
This is not clear to me, my manual switch does not have any power inputs, does this mean it is not using PIN diodes?
or if I don't need any LEDs like indicated in the link and modify for 2 inputs and replace s1 with a standard relay can I omit the power source other than for the relay coil?

Mike

 

[KeepItSimpleStupid]

Just buy one: https://www.amazon.com/Remote-Control-Satellite-Selector-Switcher/dp/B0042QCLQ4

Radio Shack used to sell them. Used terms like "Remote Antenna Switch"

Simple relay? Maybe. An RF relay is most appropriate.

 

[mbarazeen]

this is how different LNBs are switched in single antenna, no matter you have a single antenna or two antennas the switching is done by two different level of DC voltages applied on the line by the receiver. normally 4 LNB input switches are handled by commercially available receivers.

Eidt: see the example product - https://www.alibaba.com/product-gs/357650003/DiSEqC_4X1_satellite_dish_switch_to.html

 

[lilimike]

Just buy one: https://www.amazon.com/Remote-Control-Satellite-Selector-Switcher/dp/B0042QCLQ4

I already have the circuit for the remote I just need a way to switch, this thing is over $30, I don't understand why the manual switch is under $3. So much difference just for the remote?

this is how different LNBs are switched in single antenna, no matter you have a single antenna or two antennas the switching is done by two different level of DC voltages applied on the line by the receiver. normally 4 LNB input switches are handled by commercially available receivers.

Eidt: see the example product - https://www.alibaba.com/product-gs/357650003/DiSEqC_4X1_satellite_dish_switch_to.html

This is not good for my application, I don't want to switch between two satelllite antennas, I want to select between satellite receiver and digital antenna.

I think I will just try a standard relay and see what happens.

 

[KeepItSimpleStupid]

Go here: http://search.digikey.com/scripts/DkSearch/dksus.dll?x=0&y=0&lang=en&site=us&KeyWords=RF+relay

and then Select Relay/Signal

Then select RF in the selector column

Beware, the latching relay style usually comes in two varieties:
1) Single coil - pulse and polarity changes state
2) Dual coil - pulse of correct polarity to a set or reset coil

Probably used moreso in RF applications, so coil EMF doesn't get induced into the signal.

 

[davenn]

I already have the circuit for the remote I just need a way to switch, this thing is over $30, I don't understand why the manual switch is under $3. So much difference just for the remote?

its cheaper because you do the work and its just an el cheapo slide switch ! for a remote operated relay there are more components involved and the RF relay costs significant money

not too difficut to understand the reasons

Dave

 

[KeepItSimpleStupid]

Lets just use:
$1.50 for 3 F connectors
$5.00 for metal case
$8.00 for relay
$3.00 for perf board (might not be needed)
$6.00 for 5V wall wart
$0.50 for DC in jack
$0.50 for two back EMF suppression diodes
$1.00 for two push buttons

Time to put it together
Postage

Now make it automatic: Detect significant current for each system draw and pulse appropriate relay. Now that makes it useful.


prices are low

 

[BrownOut]

Lets just use:
$1.50 for 3 F connectors
$5.00 for metal case
$8.00 for relay
$3.00 for perf board (might not be needed)
$6.00 for 5V wall wart
$0.50 for DC in jack
$0.50 for two back EMF suppression diodes
$1.00 for two push buttons

Time to put it together
Postage

Not having to get your lazy a** of the sofa....priceless!

 

[lilimike]

In my case I have to go down 2 floors to switch systems and the problem is my wife is always watching Spanish on the satellite and I am always watching local French or English on the digital antenna.

I am working on it and will report back with my results and costs.

Mike

 

[lilimike]

I started off testing with what I have on hand. I have an OMRON G5AK-237P-27 relay.
View attachment G5A.pdf
My setup is 6 feet of coax from satellite receiver and digital antenna receiver going to the switch and from the switch I have a 75 feet coax going to the TV.
On the electronics side I've only soldered 2 F connectors and the relay on a PCB all within 3/4 inch traces apart with the relay latched to connect those two F connectors.

With this setup the signal from the digital antenna is crystal clear and I see no difference between using my relay or manual A/B switch. Switching to the satellite however I get some garbage lines on the TV, I would say the picture is degraded by 2% due to those lines. Bringing the TV at 6 feet from the switch (6 feet cable) it is all clear with satellite and digital antenna.

What does an RF relay have that regular relays don't have? can I add filters to my regular relay to improve the signal at the longer distance?

I need a latching relay with low coil voltage because I want battery operated switch (these relays are quite expensive)

Now make it automatic: Detect significant current for each system draw and pulse appropriate relay. Now that makes it useful.

This would be ideal but the satellite receiver and Digital antenna receiver are on at all time so how can I detect which one I am using? when in Satellite mode I set my TV to channel 3 and I use the satellite remote to cycle through channels and on the Digital side I just cycle the TV remote to the other available channels listed as x-x.

After writing this I am thinking why not just use a Y splitter? I am tempted to try it but would like to get any comments on this. Not sure if it can damage the Satellite receiver or Antenna receiver.

PS: what I call Antenna receiver:
My antenna is in the attic with a coax running to a small box which supplies current to the antenna's rotor and the signal at the same time. From this box is 2 TV outputs, one of them is going to my switch.

Mike

 

[mbarazeen]

what are the frequency ranges of both system, i have no idea about the digital antennas frequency, i hope you can use a signal combiner (not a splitter) to combine both signals, but the problem is channel selection that sends a switching signal to satellite antenna for LNB change over.

you better find a way to modulate the video from satellite receiver and combine with digital antenna signal so that a particular channel can be allocated for satellite channels on your TV.

 

[KeepItSimpleStupid]

Look up diplexer: https://en.wikipedia.org/wiki/Diplexer

they may be the device you want.

As for what's different in a RF relay. What comes initially to mind are:
1. Shielding
2. A contact wiping motion
3. Precious metal contacts such as gold or mercury wetted

Here is the deal. There is a specification for any switch called wetting current. This current is the minimum that has to flow in order to remove the oxide from the contacts. For a typical switch, it is on the order of 1-10 mA. A sliding motion will ensure that the oxide is removed.

your relay isn't a bad start, but notice its states 10 mV and 0.1 mA. These are orders of magnatude above what you need to switch.

Suppose you had a 100 uV signal into 75 ohms. The amount of current is 100 uv/75 Amps. This is pretty small.

Shielding removes the effects of RFI (Electromagnetic interference). Twisting, which isn't typicaly done in an RF environment removes EMI (Electro Magnetic Interference).

I suppose that with your setup, and just for a test, you replaced the relay connection with a short wire, it would work fine even with the effects of the relay being energized.

 

[KeepItSimpleStupid]

See: https://www.antennasdirect.com/store/diplexers.html

Use in pairs, but it only passes power on the satelite side.

What you may have to do is run an RG-6 as the rotor control cable. The model Eagle Aspen ROTR-100 works this way. You don't have to pass the TV signal down this coax, you can use a separate line. The ROTR-100 can also supply power to an antenna pre-amp if the voltages and currents are correct.

So, what you might consider is to run the rotator with one coax and bring a separate lead down from the antenna to connect to the diplexor.
If your antenna requires a pre-amp, then that has to be injected so that the diplexer doesn't see the pre-amp power.

 

[lilimike]

Thanks for the information.
I am not sure I can split the rotor power from the signal but I will open the box and take a look. I have this unit

I will also try to insert the relay switch I made into a small metal box and see if it makes a change, it really doesn't take much to get a good picture. The funny thing is, using my relay switch I get a clear picture in HD from antenna above and noise from a standard non HD Direct TV satellite receiver!

Mike

 

[BrownOut]

Deleated