Some Hints, personal opinion that will save you some headaches:
Search for a motion activated DVR.
Search for a high resolution recording capability,The bigger the better.
Pay little attention to Display resolution which means Live monitoring resolution.
Minimum acceptable 360X240 (all depends on the compression)
640X240 is better and 720X480 is even better.
On Compression, I would search for MPEG2 which is good if you don't need remote IP access. Some newer MPEG4 are good as well.
Prefer units with a removable media, something that will allow you to backup easily a clip of video evidence, USB, memory stick, compact flash or removable HD.
Be carefull with DVRs that record in Quad format. This is a trick some low cost unit machines uses to record four channels. Internally it may be a 1 channel DVR with a Quad builtin.... not good.
Prefer backups in popular formats such AVI files to allow a regular PC user to see your evidence.
Prefer watermark recording
On pictures per second capability, the bigger the better, but to keep yor budget in good health you have to know that a tape VCR in "real time" records, in average, five picture per second when programmed to record 24hrs in a T-120 tape (this may vary a little among brands). You might find that 7 or 8 ips is enough for some applications.
Remember some high speed machines are using too much processing power and you might not notice the difference.
Ask for disk usage, more than 3-4 Gig per hour when fully loaded at maximum resolution may be too much.
Most important is the source of your video. If the source is bad, the DVR will do very little to clean your picture. Remember, GIGO Garbage In, Garbage Out.Use a high resolution camera with the biggest S/N ratio possible.
Use good coax Cable, good connectors and a good lens.
Aways avoid aiming your camera to sunrise and sunset as much as possible.
Brand? well there are lots of DVRs in the market, shop around and you will find a good one.
You will like them because they are very convenient. Prefer units with looping output because you may need them for future added technologies, such as web transmitters or local monitoring.
Regards
