What is "video output"?

[fs6591]

Hello folks,

I have noticed that many HF and VHF receivers (especially vintage receivers such as Watkins-Johnson receivers) have a "video output" that appears to be a baseband output. Can anyone explain what's the purpose of this output and why it is called "video" since we are talking about receivers for narrow band AM and FM, and not for television?

Thanks in advance
FS

 

[a417]

are you referring to the ones on the back of the WJ units marked as "SMO" / service monitor outs?

 

[AB5ID]

It may be the detector output.

 

[fs6591]

are you referring to the ones on the back of the WJ units marked as "SMO" / service monitor outs?

There are many different WJ receivers. For example, the 8615 has a "selected video output":

http://watkins-johnson.terryo.org/documents/manuals/WJ-8615/external-connections.pdf

The WJ 904 and 906 have a BNC "video output jack J2" (see page 11 of the PDF):

http://watkins-johnson.terryo.org/documents/manuals/904A-906A-&-906A-4-receiver-manual.pdf

This one is not a WJ, but the manual also mentions a "video" (see page 13 of the PDF):

http://blackradios.terryo.org/documents/manufacturers/Nems-Clarke/manuals/Nems-Clarke-1301-1302-manual.pdf

All of them are receivers for AM, FM, CW.

 

[fs6591]

It may be the detector output.

Do you mean the one usually called "discriminator output"? If so, then why is it called "video"?

 

[a417]

Reading the functional descriptions in those PDFs you linked to, it certainly seems that they could recieve a television signal OTA.

It sounds very much like it is a video output if the signal contains a video component. The various manuals describe what the output characteristics are... I don't think there's that much more to it.

 

[fs6591]

Reading the functional descriptions in those PDFs you linked to, it certainly seems that they could recieve a television signal OTA.

It sounds very much like it is a video output if the signal contains a video component. The various manuals describe what the output characteristics are... I don't think there's that much more to it.

In the last of the links above there is a more detailed description of the video output (on page 23):

http://blackradios.terryo.org/documents/manufacturers/Nems-Clarke/manuals/Nems-Clarke-1301-1302-manual.pdf

 

[AB5ID]

It appears to be a detector/discriminator output for telemetry.

PPM

Nems Clarke page

PCM/FM telemetry

 

[AK9R]

Reading the functional descriptions in those PDFs you linked to, it certainly seems that they could recieve a television signal OTA.

But, it's probably an analog TV signal, not the digital TV signals being used today.

 

[kc0kp]

As someone already mentioned, it is baseband output. It is a throwback term used by the microwave industry to indicate unfiltered, wide band output. It was used for video or for subcarriers. I have seen it used on RCA microwave output that connected to the MUX to decode subchannels on the microwave. In this case, it was audio on subcarriers that were suppressed and one sideband was filtered off, much like single sideband.

 

[wtp]

i had seem some stuff with video output and an octal jack on the back.

and i 'assumed' it was for an oscilloscope hookup. never got the specs on the radios so it was only an idea.

 

[merlin]

I scoped the video output on my 4711 and it is a baseband video output.
Thing is, there is no NTSC-PAL-RAW video transmissions below 30 MHZ.
Signal in = video out and looks up to 21 Mhz wide.
The 9026 however will tune north American TV channels, but with ATSC, this output is useless.

 

[merlin]

But, it's probably an analog TV signal, not the digital TV signals being used today.

It is. And thats what makes these outputs near useless.
In special cases, sub-carriers can make use of them.

 

[merlin]

Hello folks,

I have noticed that many HF and VHF receivers (especially vintage receivers such as Watkins-Johnson receivers) have a "video output" that appears to be a baseband output. Can anyone explain what's the purpose of this output and why it is called "video" since we are talking about receivers for narrow band AM and FM, and not for television?

Thanks in advance
FS

Most WJ receivers can do far more modes than AM, FM, and CW. IE: SSB, ISB, PCM.....

 

[wtp]

Stromberg-Carlson 440M console:
there it is on an oldie.
it does not say video out, but like i said some did, so it could just be a remnant of that.

 

[Token]

Hello folks,

I have noticed that many HF and VHF receivers (especially vintage receivers such as Watkins-Johnson receivers) have a "video output" that appears to be a baseband output. Can anyone explain what's the purpose of this output and why it is called "video" since we are talking about receivers for narrow band AM and FM, and not for television?

Thanks in advance
FS

When used in certain applications, such as military spectrum monitoring or ESM applications, you want to take the detector output to an o'scope or other specialized display. You want this output unfiltered (no IF filter) to see the entire bandwidth of the signal (for example a pulsed signal with a 1 usec pulse width will have 1 MHz of bandwidth at the 3 dB points, and you want the signal far beyond the 3 dB points). This unfiltered, detector output, is often called "Video" regardless of the signal that is presented.

The use of the term "video" for this type of signal goes back to WW II when the detected returns of a radar receiver were first called "video" (as it would be visually displayed), and that term started being applied to many types of baseband detected signals. If you take a look at the WW II AN/APR-1, AN/APR-4, and the Navy AN/SPR-x versions you will see a "Video" output on the front.

I have operated many ESM stacks that included WJ gear.

T!

 

[WI8X]

Hello folks,

I have noticed that many HF and VHF receivers (especially vintage receivers such as Watkins-Johnson receivers) have a "video output" that appears to be a baseband output. Can anyone explain what's the purpose of this output and why it is called "video" since we are talking about receivers for narrow band AM and FM, and not for television?

Thanks in advance
FS

In the 432-434MHz spectrum, there is a thing called Fast Scan Television. Also, on the HF Amateur Radio bands, there are segments of the spectrum for the reception of Slow Scan Television. The FSTV and SSTV can be viewed on a separate B&W or color monitor. The receiver or transceiver has the circuitry to isolate these FSTV/SSTV signals and allow you to view these signals as they are being sent over the air. Google FSTV or SSTV.

 

[Token]

When used in certain applications, such as military spectrum monitoring or ESM applications, you want to take the detector output to an o'scope or other specialized display. You want this output unfiltered (no IF filter) to see the entire bandwidth of the signal (for example a pulsed signal with a 1 usec pulse width will have 1 MHz of bandwidth at the 3 dB points, and you want the signal far beyond the 3 dB points). This unfiltered, detector output, is often called "Video" regardless of the signal that is presented.

My bad in the above. I was thinking the video was unfiltered, but the more I searched my muscle memory the more I thought "no, you could select different filter widths". And so I pulled up some manuals and pictures, and the video typically was filtered. The video stage was after the discriminator (in FM mode) or detector (in AM mode), both of which were after the IF filter stage. On some hardware you could select "Wide" which might be very broadly filtered depending on the equipment. Looking at the manual for my CEI 906, for example, the selections are 20 or 300 kHz widths only, while the WJ 205-2 (Field opt 2) is 10, 50, 300, kHz, or 1 MHz. I also remember some equipment that had/has very wide filter settings, like 5 or 10 MHz+. The AN/APR-4 is certainly at least 2 MHz, and probably wider than that (it has a wide and narrow setting, but I don't remember the details).

T!