Posts Tagged ‘ Passive Video Balun ’

Passive Video Balun

Friday, July 8th, 2011

If you would rather use Cat5E instead of RG59 cable, it’s likely that somewhere along the way you will need a passive video balun.  Security Camera King carries a full line of baluns both active and passive.  Passive video baluns help prevent the degradation of the radio frequency signal over cable.

A balun is really a specific type of transformer that can convert electrical signals that are balance about ground (also known as differential) to signals that are unbalanced (single ended) and vice versa.  The name “Balun” comes from two words, BAL(ance) and UN(balance).

For those of us that are not electrical engineers, another way to put it is that passive video baluns can boost signal strength and help your system make a transition to one type of cable to another.  For example, most cable used in the digital video security industry is RG59 coaxial cable.   This is an excellent cable for the job, however RG59 only has a working distance of about 600 feet before the signal starts to degrade causing poor video quality.

Using a passive video balun, the signal can be changed at the connection source from RG59 to CaT5E.  This is done because Cat5E is less expensive for one thing, secondly it’s easy to pull when installing it, it’s generally less expensive than RG59, and a passive video balun and Cat5E can carry a signal further than RG59 cable, usually about 1,000 to 1,200 feet.

In addition, if you do use Cat5E cable instead or RG59 you will have multiple pairs of wires at your disposal.  RG59 basically has a solid copper core wire insulated with plastic and then a metal shield (in essences the second wire) which is then covered by the cable cover (usually some type of plastic).  A digital video camera uses both of those wires the copper core and the outer shield to transmit its signals.

However, by using a passive video balun with Cat5E cable you have access to 8 (4 pairs) of (usually) 22 gauge wire.  This allows you to use just one Cat5E cable instead of 4 RG59 cables for 4 security cameras.

Many people would say they’ve never seen a balun before, but chances are they have.  Some older model TVs came equipped with a cable TV type plug and no antenna connection.  Usually, the RG59 type cable has 75 ohms of impedance.  An antenna was often 300 ohms of impedance.  An “adapter” often came with the TV with a male cable TV type plug on one end, and two screw connections on the other end to connect to an antenna.  That adapter is actually a balun, and it’s used to balance the impedance differential between the TV outlet and the antenna.

Before going any further, now would be a good time to address the “passive” in passive video balun.   Baluns may be passive or active.  An active video balun is much like the passive video balun with one distinction:  The active video balun requires power.  Usually, most active baluns use 12 VDC, the same type of power that the digital video system uses for the cameras.

Active video baluns, depending on the type, etc. like the one used in our example above of the passive balun that got 1,000 – 1,200 foot range, would be capable of boosting the signal on Cat5E upwards to a length of up to 4,000 – 5,000 feet.

Security Camera King offers a wide variety of passive video baluns to suit your needs.  Below is a partial list of our available baluns and a short description of each:

  • Product# BALUN-P.  Passive video balun with BNC connector on one side and Cat5E connector (RJ45) on the other;
  • Product# SVU-PR8.  8 channel passive CCTV receiver hub with female BNC outputs.
  • Product# BALUN-V.  Single channel passive video balun with video and power.  This balun is not powered, it truly is passive.  The power connection provided is for continuing your power supply past the balun by using one pair of wires from the Cat5E cable.  Saves time so you don’t have to cable separate power supply wires.

This should give you a good idea of what passive video baluns are and what they do.  If you have any additional questions please contact one of our security experts.


4 Channel Passive Video Balun

Wednesday, May 4th, 2011

A 4 channel passive video balun is defined as a specialized electrical transformer that converts electrical signals that are balance about ground (differential) to signals that are unbalanced (or single-ended) and or converts signals that are unbalanced to balanced.  In that manner they are used as devices that are used to connect lines of different impedance.  Balun is derived from two separate words; BALance and UNbalance (BAL+UN).

Wow!  That was quite a mouthful.  Let’s redefine the definition without the overly technical phrases.  Simply put, any wire or cable has a natural resistance when electricity is applied.  Consider this, what if you took a typical AAA dry-cell battery and connected a wire to each end of the battery.  Now, what if the wire you attached was 5 miles long.

Would the end of the line still produce the same voltage or power as it does when the wire is only 1 foot long?  The answer is “No” and the reason for it can be attributed to impedance.  In other words, any wire, cable, or other metal electrical transmitting device has a natural resistance to electricity and electronic signals, even though it may be a great conductor.  Since impedance is a type of resistance, the impedance of a cable or wire is expressed in ohms (Ώ).

When dealing with radio frequencies, a loss of the signal means the difference between a video image being transmitted to a Digital Video Receiver (DVR) or monitor or not.  This can happen when the length of the cable is too long, unshielded, or mismatched in impedance.  This is where the 4 channel passive video balun comes in.

The majority of digital video security and surveillance cameras today still use coaxial cable, specifically RG-59.  RG-59 is a shielded cable that has an impedance of 75 ohms.  A shielded cable is one that is wrapped in some sort of material (often aluminum, mesh wires, or even plastic for example) that keeps the desired radio frequency in, but more importantly prevents external noise from reaching the cable.

The 75 ohm impedance is no arbitrary accident.  Video signals happen to have 75 ohm impedance, so the coaxial cable works well as the impedance of the coaxial cable and the impedance of the video signals are equal.  As a matter of fact, not only does the coaxial cable and radio frequency have an impedance of 75 ohms but the in impedance for displays is usually 75 ohms as well.  If you haven’t figured it out by now, for ideal quality video, it is important that the impedance of the objects involved in transmitting the signal have the same impedance, in this case 75 ohms.

Now, let’s switch gears for a moment.  With the arrival of the computer age, so became the familiarity of CAT5 or Ethernet cable.  Ethernet cable has twisted pairs of wires.  By twisting the pairs of wires electromagnetic interference from external sources can be canceled out.  However, for radio frequency applications, CAT5 twisted pair is not necessarily ideal because it contains no shielding to prevent outside noise (in the form of electromagnetic radiation).  As a result of its configuration, CAT5 cable is often called UTP or Unshielded Twisted Pair cable.

Although CAT5 cable can be used for video transmission lines for digital video security cameras, it has one other undesirable characteristic:  CAT5 UTP cable normally has an impedance of about 100 ohms.  Since the camera is transmitting its video data at an impedance of 75 ohms and the DVR intends to receive it at 75 ohms there is a mismatch between the CAT5 cable and everything else.

How can we work around this mismatch?  Use a 4 channel passive video balun.  The video balun will correct for the mismatch of ohms going to and from the cable and may also correct for noise, white balance and other video signal attributes.  Security Camera King offers a 4 channel passive video balun designed specifically for this purpose.

Product# Balun-4 not only matches the impedance factor to eliminate noise or distortion problems, but it allows you to send 4 different video signals over one CAT5 cable up to 1200 feet in length.  Please be advised that when using a 4 channel passive video balun you will need to purchase two units.  The first unit converts the signal from BNC to CAT5 and the second unit is need to convert the CAT5 back to BNC for use by the DVR.