How to avoid a bad wireless installation
In over twenty years at Radcomm UK it never ceases to amaze me the workmanship of other contractors we are called out to see & ‘fix.’ On arrival at site sometimes the problems become apparent to us as engineers but have understandably been missed by the customer. We aim to provide a brief insight into spotting ‘tradesmen’ cutting corners by possibly not understanding what they are doing themselves!
At a glance the camera and aerial installation to the right may seem ok but let’s examine this and see what is wrong and how this could affect you and your reputation.
If we look closely at the image below, the camera bracket itself has been attached correctly and securely with two metal banding clamps. Unfortunately, this is where any sign of correct workmanship ends on this installation. The other bracket in the picture has been shoved under the bottom banding and then taped with blue insulation tape at the top to hold in place! This bracket should have two lots of banding like the camera bracket (maybe they ran out)!
A 1¼ inch pole has then been attached to this bracket
but instead of using two "U" bolts they have simply used a few cable
ties and this time black insulation tape (they probably ran out of the
blue tape as well)!
Now the dish style aerial at the top needs to keep pointing at the
collection point and any wobble of this can cause the wireless signal to
break up. This was not an issue here though; as another set of five
cable ties and a little more insulation tape should do the trick! On a
serious note; this is not the case as "U" bolts would have not only
secured the pole but also prevented any twist and rotation.
I am sure I do not have to spell out the dangers of this installation as it is obvious in high winds the whole bracket and pole could easily detach and fall causing serious injury & damage below.
You may think this is the end to a very sad tale of poor workmanship; unfortunately we have only just begun....
As this particular install is an Analogue System it uses
the dish aerial on the top to relay the picture back to the CCTV Control
Room. The Pan, Tilt & Zoom (PTZ) controls which move the camera are sent
out via a separate low power UHF radio signal. To try to maximise the
reception of this signal a beam aerial has been used on this
installation. The beam aerial works exactly the same as your TV aerial
at home and needs to point to the transmitter. The beam aerial cannot be
within at least one wavelength of any metal objects. These installers
cannot be trained to practice such basic principles as they have cable
tied it directly to the "Metal" light bracket! This action will have a
massive impact on the performance of the beam aerial. What you probably
don't realise is that aerial selection is crucial for any installation.
When selecting an aerial we get very detailed plans called "planes"
which accurately predict how the signals leave and arrive at the aerial.
In this case such predictions would be useless as the lamp column itself
is interacting with the aerial and reducing the signal greatly.
If you look to the left of the aerial you can see the square plate still attached. This plate should have been used to mount the aerial ‘end on’ just like a TV aerial. Again, cable ties seem an acceptable solution (maybe they were late for tea)!
If you look closer at the previous image you will see a shiny plug (a close up is provided to the left). This is the UHF aerial connection and is an "N" type plug used predominantly for this type of connection. Such connections are in no way water proof and must be covered with a waterproof membrane. Normal insulation tape is not suitable as again this is not waterproof; a special tape known as "amalgamating tape" has to be used for this purpose.
One final point to consider which we cannot tell from the photograph is quality of aerial cables. The quality, specification & subsequent price difference with aerial cable is again massive. The choice of aerial cable is vitally important to the performance of any wireless installation. Firstly some background information; aerials have "gain" and usually the larger the aerial the more gain. If an aerial has 3dB of "gain" this effectively doubles the signal being received or transmitted. If we have a ten watt transmitter and an aerial with 3dB of gain it is the equivalent of having a twenty watt transmitter with an aerial with no gain.
Cables are opposite as they have "loss.” Again, if a cable has 3dB of loss in this case it will mean the signal being received or transmitted is halved! Yes, only 50% of the signal will pass through the cable. Each cable comes with a table giving "Loss" figures at different frequencies, the higher the frequency the higher the loss!
We have been to numerous installations where either the wrong cable is used or a cable is too long (not cut to the correct length) resulting in the external aerial being unable to relaying a correct signal (the loss/gains from the cable cancelling out any possible performance onsite).
Hopefully, this article has given you a little insight into some of the "mysteries" of wireless but more importantly enabled you to spot some of the bad workmanship which is out there being practiced every day. Our ultimate aim is to save either yourself or your organisation from a disaster, should something go wrong once the installers have moved on.
Thanks for reading
Ian Davidson
Managing Director
Radcomm UK Ltd
Footnote
The photographs used to illustrate this were not found on the internet but taken by myself just a couple of weeks ago whilst driving back home from a visit to the hospital. It is not acceptable to say were it is and any clues within the photographs have been cropped out, suffice to say that it is probably best to get your installations checked sooner rather than later.