dip type reed relays as video switch

Hi Group,

Can I use a common dip reed relay to switch in/out video signals?

I would use two per channel, one would be in serial and the other used as a shunt to ground. To enable the video, I would turn on the series reed and open the shunt reed.

To turn off the channel, I would open the series reed and turn on the shunt reed.

The input would be terminated into 75 ohms.

Being that video is 6MHz BW, I would expect a reed relay to work but I would like the advice of the group.

Thanks,

PDRUNEN

Reply to
pdrunen
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Reeds are horrible. Just use a single small relay, like an Aromat TQ or something. There are lots of similar parts in Mouser and Digikey.

John

Reply to
John Larkin

I dont think that there is any problem, just look at the capacitance of the open contacts, and you can work out the crosstalk/breakthrough. My favorite relay company (Pickering)make VHF reed relays that are quite adequate for video.

The only prob would be that if you try to switch during syncs, they may not be fast enough, and the on time is generally faster than the switch off time, a potential shorting problem, but the overlap shouldnt cause any significant problem for a 75R system

martin

"An eye for an eye makes the whole world blind" Gandhi

Reply to
martin griffith

Relays work ok, but there are nice ICs made to select video. Maxim and others provide a wide range of input to output combinations, including ones with built in buffers. Board layout is simpler, and a failure is quickly fixed by replacing a chip or two instead of a handful of relays.

One word of warning about using relays. Over time they will become erratic and are a pain in the ass to troubleshoot when you get different faults at different times. I worked on products that used dip relays for video to 10 Mhz and they were a pain. In this case they were used to select the input and output of 10 bandpass filters.

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Michael A. Terrell
Central Florida
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Reply to
Michael A. Terrell

Many years ago I designed a TV line grabber for use in a lab. I could select one of the lines of video and display it on an oscilloscope. I did the switching using CMOS 4051 chips. Worked great. I suppose they are no longer available. Yes, and I did it like the suggestion above, one in series with the line and one shunt to ground. Open series, ground input line. Open ground, close series.

Al

Reply to
Al

Not only are 4051 chips still available, they're quite popular and are available in perhaps a dozen different technologies, each with various aspects to recommend them, such as 18 to 20V signal range (CD4051, MC14051), or 30-ohm Ron, 12 to 15V range (74HC4051), or supply-operation down to 2.5V (74LVXT4051) or 2V (74AHC4051). The lower Ron parts tend to have higher capacitance.

I'm a big fan of another member of the family, the '4053 series of triple single-throw switches.

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 Thanks,
    - Win
Reply to
Winfield Hill

Caution. The high voltage versions operated with large VDD-VSS and relatively small signals will yield the best distortion. (Observe the data sheet Ron versus signal voltage.)

My preference is toward tri-stated buffer amplifiers.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

the 4051 is still available, but I prefer using the matrix chips with buffers. 8 * 8 with buffered outputs in one chip makes a clean layout and reduces the assembly time. My preferences come from a background in TV broadcast where 32 in, 24 out and larger switcher / routers are common. Phase shift, noise and distortion are critical in a studio setting as well.

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Michael A. Terrell
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Michael A. Terrell

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