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the toss

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Posts posted by the toss

  2. Posted

    I think you should get a better working knowledge of Ohms Law. Voltage drop does indeed depend (to a degree) on supply voltage. Lets look at two examples.

    A) DC resistance of a cable run = 2 ohm (this is a fixed value in this example)

    DC load (ie camera) = 100 ohm (this is a fixed value for this example)

    Total DC resistance = 102 ohm

    If DC supply voltage = 12V then current will be 12v/102^ = 117.64 mA

    Therefore the voltage drop over the cable will be 117.64 mA X 2^ = 0.235V

     

    NOW keeping everything the same but reducing the supply voltage to 5V we get -

     

    DC current now will be 5v/ 102^ = 49 mA

    therefore the voltage drop over the cable will be 49 mA X 2^ = 0.098V

     

    All three operators ( supply voltage , load resistance and current ) will affect the transmission line voltage drop.

  4. Posted

    Only if it IS an earth loop. As I've posted many times in this forum , noise issues can be a nightmare to solve but the first two things you can do to minimise the chance of it happening is to use a good regulated power supply AND good proffessional quality coax. Most pre-made cables are nothing more than shielded audio cables and this is your most likely source of noise

  6. Posted

    I'm not sure if you are worried about the electrical safety aspect or the potential for induced interference. The country you are in would have some bearing on the answer as well. In Australia if each cable is in their own conduit than as far as electrical safety compliance goes they can be side by side. For noise immunity I would have them as far apart as possible. EMI is a fairly inexact science.

  8. Posted

    How about STP or FTP - shielded "UTP". You ground the shielding at one end only, allows it to work as shield but prevents earth loops. Only use one pair for signal, there is no benefit in doubling up. But that does leave you spare pairs to carry camera power - you've not mentioned where that fits in.

     

    However, most national wiring codes insist on physically segregating signal cables from mains power wiring. No possibility of adding a partition in your conduit? Using weatherproof cable cable-tied to the outside of the conduit?

     

     

    A few points -

    ** there is no such thing as shielded UTP. UTP stands for UNSHIELDED twisted pair. You cannot have shielded unshielded twisted pair.

    **Earth loops are not a consideration. The signal is of a balanced configuration and does not use the shield to carry the signal. The shield can be earthed at each end.

    ** There is no benefit in doubling up the pairs for signal transmission because it WONT WORK if you do

     

    @ Darren - from your first post it is plain to see that you understand the relationship between current and EMI. If I had to choose I would use Shielded twisted pair. This will give you the benefit of the EMI shielding as well as the common mode rejection benefits of the twisted pair. Good luck!

  11. Posted

    Well at some stage your going to have to bite the bullet and upgrade. One thing in your favour is that alalogue cameras are very cheap now but they wont be around forever. So you have a choice as to your future direction - IP or HD analogue (AHD , CVI ,TVI). I am NOT convinced that IP is the way to go for domestic installations considering the potential networking problems and the current prices for the gear. Unless you are going >5Mp then HD analogue will give comparable results at half the cost.

    Personally I would perservere with what you have until the DVR fails or you cant get (cheap) analogue cameras anymore which is the least likely of the two scenarios. Then you make your decision about your future direction.

  12. Posted

    And this is the problem with neighbour disputes. As you have realised a camers have limited coverage (make that very limited if you want detailed footage) and there are probably another 300 areas on your perimeter for entry. The other main issue is that this is likely to escalate things rather than solve them. There is not a camera invented that will get past a hoodie & sungalsses. I wish you luck but your best option would be to give him a beer and have a talk.

  14. Posted

     

    @ IdahoMan - I have NEVER been able to measure radiated signal from a CCTV baseband transmission line. The shielding is primarily to prevent ingress of radiation to the coax. If you are that worried about interference then DONT use RG6 use RG59 with 0.9mm centre & 95% copper braid

     

    Interference to the CCTV system is a concern too, that's why I figured coax would be better.

     

    Thanks for the info. And RG6 can work just as well or better than RG59 as long as the requirements (materials(BC), braid coverage(95%), and impedance(75ohms)) are met, yes? They make R6 that has the same specs as RG59 but with, IIRC, larger gauge center wire.Toss, How do measure radio interference? Spectrum analyzer?

     

     

    I have had this discussion many times and have heard many people say this about the specs. Since most people have little concept of coax cable design/construction I usually put this question to them. IF this RG6 they make does in fact have the same characteristics as RG59 (but with larger centre) then why isn't it just called "heavy duty RG59". Why would a manufacturer confuse things when they already make a RG6 which is spec'd for digital TV. When you say this RG6 has the same specs as RG59 what specs are you referring to. Are you looking at things like transconductance, slew rate & velocity factor or just limiting yourself to the "salesmans" specs of braid coverage , dc impedance & centre conductor. There is SOOoo much more to coax cable design. It is a bit like thinking an engine management computer from a BMW is going to work in a Toyota. It wont - the parameters are completely different.

     

    Measuring RF interference ? Well in a previous life I had access to Refractive Interference Spectrometers & tuned cavity resonators. In many cases it is not a matter of measuring unwanted RF power (interference) as measuring the EFFECT of that interference on a know test signal in a transmission line.

     

    Now days alas all I have is a humble spec analyser.

  18. Posted

    Can you see the side entrance AND your garage with one camera. If not then two cameras fixed to the points of interest will be best. If you think that a ptz camera running on "tour" will do the job then just make sure you allow for the "HUGE" storage space that will be required

  19. Posted

    Hello back from Australia.

     

    1) If you have a reason to install CCTV then stay away from wireless cameras. They are completely unreliable in terms of connectivity.

     

    2) What seems to be the problem with a Hebel clad house ? I would assume it is constructed the same as a brick veneer house. Hebel outer wall then timber frame & gyprock. Being two storey you WILL have restrictions/limitations on where things can be mounted and cabled.

  20. Posted

    The "box" aka DVR has nothing to do with lack of night vision. If they worked before and you haven't changed the power supply then they will work now. I bet you have ONE power supply running both the DVR AND the cameras. You have put in the new Power supply that came with your new "box" and it cannot run the IR at night. If this is the case then use your old power supply for the cameras and the new one for the DVR

  22. Posted

    I'm glad this thread was brought back to life....I have been told by Liftmaster Garage Door openers that my only solution is to chose which item is more important for me to use....My security cameras or my garage doors. We have had a 4 unit security CCTV system for 5 years, which is also the age of our garage door openers, and just recently added four more cameras (two that are near the garage doors. If the two new cameras, that are next to the two garage doors are plugged in and active, the garage doors open from the wall button, the remote control, and the Homelink car button IF you are directly underneath the motor...However, the remote control and the Homelink car system will not work if you are 15 feet away in the driveway. The company that sold us the Liftmaster unit has stated he saw this same issue with a fire station in town, but they are still looking for a solution. Once you unplug the two cameras that are next to the garage doors, everything works normally again.

    The camera installer (15+ years with a major company in town) moved the security camera wires to the two new cameras away from the garage door opener wires and behind our spray foam insulation and attached 19 magnetic ferrite cores/chokes, but the problem is still occurring. However, he did not install a ferrite core to the garage door wall button wires. On the previous threads, I never saw if this was a fix or not. Our installer was told by others in his industry that this situation between the camera and garage door openers interference was not possible and they have never heard of it. I would appreciate any information.

     

     

    Your Liftmaster Garage Door man is feeding you rubbish and if what he says was true then I'm sure the FCC would be interested. As I understand it the problem is with the range of the door controllers when the cctv is also running. IF it is an interference problem the most likely culprit will be a noisy (defective) switch mode power supply running your cameras/DVR. When these go bad they can spew huge amounts of RF garbage over the entire spectrum. Another VERY likely cause of the problem is that the receiver on the door is off frequency. These receivers are generally mounted within the motor enclosure and are subject to quite a bit of vibration from the door movement. If it has drifted off its centre frequency then it wouldn't take much in the way of interference to drown out the signal from the door opener. It may be a combination of both the above scenarios. It WONT be the hardwired control switch. This simply operates a relay within the controller and so interference on this cable will have NO effect on anything. If you dont belive me then forget the ferrite beads and wire a 1 mH choke in series at the controller end of the cable.

    If your garage opener is running at 310Mhz then your RF wavelength will be 0.9677m. So you antenna length would normally be a half wavelength harmonic ( ie 1/2 , 1/4 , 1/8 etc) with 1/4 wavelength being the best trade-off between length and gain. So I would expect your antenna length to be 24cm. As has been mentioned if it has been shortened then that will also affect the range of reception.

    This demonstrates why I never recommend wireless gear for anything unless it is ABSOLUTELY the only option. What you gain in convenience is lost in fault finding/maintenance.

     

    My credentials - Electronic security engineer for 18 yrs

    Microwave radio engeneer for 24 years

    Electronic Engineering Degree

    Diploma in Electronics & Communications

  23. Posted

    The IR on these entry level cameras is really no good for more than about 5 or 6 metres regardless of what the sales pitch says. Now remembering that the camera is working off REFLECTED IR light lets analyse your pics starting at top right.

    This pic is of driveway , lawn & road. What you are seeing at night is the reflected light from half the driveway and a bit of lawn. These two things reflect different amounts of IR and so are just discernable in your pic. Most of the IR just fades out in the distance. Letterbox & road are too far away to reflect any useable IR & so do not show. Next pic is of the front pathway. In this pic there is a rendered wall , a brick wall , pebble garden , path and column. Again all these things reflect differing amounts of IR and so show up to some extent. The column shows up best because it is front on to the IR & so reflects the most. Next comes the BBQ area. Lots of different things of different materials here to reflect the IR plus it is a more confined space. Last pic is the Gym. Again, an enclosed area with lots of different things to reflect that IR. This is helped enormously by the light coloured carpet in most of the pic.

     

    What you really need is to have people walking around these areas to determine where the pic is acceptable & where it fails. White lighting (not IR) will help to a huge extent in those outside areas.

     

    As I tell my customers - almost any camera will perform ok in daylight , the real test comes at night and these budget kits dont do the job

  24. Posted

    Whatever you do DONT USE TWIST ONs.

    Both the crimp & compression are accepted types of fittings. Compression are a bit quicker to do but I preffer the crimp as you have better control over the three stages of fitting ( stripping , pin crimp & shield crimp). If your connectors are coming off then I would say your not doing them right in the first place.

    I once did some sub-contract work for a (very) large global security company and found that one of their techs was not doing the crimp ons properly with the result that the connector would pull off leaving just the pin connected to the centre conductor. He had been doing this for 17 years so there are a lot of badly connected BNCs out there

     

    Whatever you do DONT USE THE TWIST ONs

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