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Modern multiplexers with any VCR?

Q I have noticed that modern multiplexers allow the connection of any VCR. How is this achieved?

A To allow operation with any VCR, the multiplexer must have three distinct capabilities.

1 To be able to accept head step pulse signals from the VCR. This is generally known as Vext mode.

Most VCRs have the ability to generate a pulse for each head step. In this scenario, a 2-core cable is connected between the VCR head step output and the relevant terminals for head step in on the multiplexer. Whenever the VCR is ready to capture a field or frame a pulse is sent to the multiplexer. When the multiplexer receives the pulse it sends the next image to the VCR.

2 To have a means of loading the details for common VCRs.

If the VCR to be used does not have head step pulse output then the multiplexer must be able to send images to the VCR at the correct rate.

Most multiplexers hold a database of common VCR types and when loaded as the installed VCR the correct field delays are set up for each available timelapse mode.

Having the database alone is not enough to allow connection to any VCR unless, of course, you have every VCR available in the database.

3 To have means of manually setting field delays and their associated timelapse modes.

Some multiplexers use generic field delay settings for given timelapse modes in an across-the-board type of manner. In most cases this works fine unless you have an unusual VCR. If you have a new VCR or rarely used machine you need a means of setting custom field delays and possibly timelapse modes.

A good example here is that some VCRs, when set to 24-hour timelapse use a 9-field delay, a real-time 24-hour VCR when set to 24-hour mode will typically use a 2- or 3- field delay.

FROZEN IMAGES

Q I have noticed that my multiplexer suffers from erratic updates when playing back from tape, and sometimes the images will freeze for many seconds.

A There can be a number of reasons for this happening.

1 The VCR is not correctly matched to the multiplexer. If the unit is connected via a Vext connection, check to see if the wiring is OK. If the VCR is set up using menus on the multiplexer, check that the correct model is set up.

2 Check to see that the recording timelapse mode matches the timelapse mode set on the multiplexer.

3 Check to see if alarms are attached to the multiplexer and an alarm program is active.

If alarms are programmed to alter the encode pattern or exclusively record alarm cameras, this can cause non-alarm cameras to freeze on playback. Remember, if alarms are recording then this is often at the expense of non-alarm cameras, so they are not recorded for alarm periods or are recorded less frequently.

4 Check to see if activity or motion detection is active on the multiplexer. If it is, then check to see if it is programmed to affect the encode pattern.

Activity or motion detection can also record cameras at the expense of non-motion or activity cameras.

If all the above are OK, check playback directly from the VCR into a test monitor to check that the recordings are good. Any signs of noise or tearing on playback point to problems on the VCR or possibly the tapes.