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Cable TV switch box circuit - RF Cafe Forums

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dmac

Post subject: Cable TV switch box circuit Posted: Thu Nov 13, 2008 2:57 pm

Lieutenant

Joined: Thu Nov 13, 2008 2:48 pm

Posts: 2

I have a control circuit that has TTL electrical levels (I can change it to some other electrical interface as well if needed) that I want to drive a switch circuit of some sort to turn "on" and "off" a simple, inexpensive switch, relay, or whatever makes sense to use for Cable TV signal. Basically, picture the cable TV signal coming in to a house (standard RG59 F type connector), going into this box and the cable going out of the box to my house cabling for the TV sets. So, the big question is what do you suggest I use for a switch that I can put on a PCB. I will do the PCB design myself, but should I use an analog switch, RF switch, Relay, or what? What makes sense. I can put the F type connectors on the PCB that route traces to this switch, relay or whatever makes sense.

Thanks,

Dmac

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markapexwireless

Post subject: Posted: Tue Nov 18, 2008 3:42 pm

Captain

Joined: Tue Jul 08, 2008 7:15 pm

Posts: 11

Location: Boulder Colorado

DMAC,

I would try high power RF switch such as UPG-2010 from NEC/CEL. You can probably get eval board from NEC to test this out using SMA/F adapters. Only concern is if your cable company is running DC through the cable to power up amplifiers upstream. You can probably test this by putting a DC block (broadband capacitor) in your cable and see if you still get the signal. If DC is present, you will have to make bypass, which will be more complex.

Good Luck!!

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dmac

Post subject: Posted: Wed Nov 19, 2008 9:55 am

Lieutenant

Joined: Thu Nov 13, 2008 2:48 pm

Posts: 2

Understood, but what about just using an electro-mechanical relay that will handle the bandwidth of the cable?

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markapexwireless

Post subject: Posted: Wed Nov 19, 2008 2:05 pm

Captain

Joined: Tue Jul 08, 2008 7:15 pm

Posts: 11

Location: Boulder Colorado

DMAC,

Relay should work fine, as long as it is "coaxial" RF relay. You will probably need a power supply of some sort to supply current to coil, whereas with FET switch, a battery would last for quite some time.

You might check on e-bay to see if someone has used RF relay, possibly extracted from a piece of RF test equipment.

Good Luck!!

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IR

Post subject: Posted: Sat Nov 22, 2008 2:47 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Hello dmac,

Concerning DC which might appear on the cable: You can use a Bias-T device, which will pass both the AC (RF) component and the DC component. The Bias-T is made of a capacitor and an inductor.

You can find one a suitable one by companies like Minicircuits etc.

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