|Fig 1: 11db Yagi Anttenae|
Using a Yagi Antenna.
RF Propagation at GSM Frequencies.
MMS Problems with the Acorn 5210MG and 6210MG.
Using a Yagi Antenna
At my indoor location a connection to the local cell tower is mostly non-existent and to enable bench testing I have recently set up two 11db gain Yagi Antenna.
The reason for two antenna is to enable simultaneous up and down links without insertion loss from the use of a splitter/combiner.
These antennae are the same as the one on my sales page and are working well, providing a steady 2 to 3 out of 5 bars on the Acorn wireless cameras. Since I installed them I've been able to carry out tests with a consistent almost 100% sending performance sending
images via SMTP.
RF Propagation at GSM Frequencies
The reason for the low signal problem is illustrated in the map below (figure 2) and is typical of mountainous environments and winding valleys. My tests are on Vodafone UK at 900Mhz and good signal propagation depends on line of sight.
|Fig 2: Map showing the topography|
of the cell tower to camera location.
Line of sight is not the only issue of course because the low signal situation is exacerbated by vegetation, rain and temperature combining to either boost or attenuate the signal; and this is variable through day and night and season of the year. A tunnelling affect between atmospheric layers also occurs typically at around dawn and dusk which can on occasions significantly boost the signal.
With so many variables it's not surprising that many cellular trail camera users are disappointed by the intermittent sending performance of these cameras. When considering this it is worth remembering that when the camera attempts to transmit an image it only tries once; and if the signal is sufficiently attenuated at that moment, the image will not be sent. This is not a problem with the camera but a consequence of RF propagation conditions and can be likened to when your cell phone suddenly drops a call in the middle of a conversation.
MMS Problems with the Acorn 5210MG and 6210MG
Please note that the following issue was corrected April 2013.
I've now been able to carry out properly controlled tests with the current Acorn wireless cameras, and in particular some MMS versus SMTP evaluation. Most of my focus over the last few days has been on the apparent inability of recent cameras (post SIM900 GPRS Module change) to send MMS in many circumstances.
Users have told me they can connect to some carriers and not others. In fact it doesn't seem to be a connection problem but rather more likely the module not supporting all ports. I was going to be doing tests with several carriers but cost and time constraints have caused me to think again, so all my testing is carried out using Vodafone UK.
|Fig 3: Ltl Acorn 6210MMX|
Last week I received an upgrade file acorn.cla which I'm told has been tested by a UK expert and will enable the new GPRS Module to send MMS over the main UK carriers. Well I've upgraded 6210MG serial number 202002281 and the camera tells me the upgrade has been successful; and it still refuses to send MMS over Vodafone UK.
The auto and manual MMS configuration files have both been tested in my MMX camera (M10 GPRS Module) and work 100% OK; but the new MG (SIM900 GPRS Module) steadfastly refuses to send MMS although it sends via SMTP without a problem.
I have spent days going round in circles to no good effect and have now stopped testing. As far as I'm concerned the new SIM900 will still not send MMS over Vodafone after the upgrade. What it will do over other carriers, I don't know, so if anyone wants to try it in either the 5210MG or 6210MG I have made it available to download here (removed) for you to try.
As always, you do so at your own risk; but I haven't noticed any ill affects, it just doesn't work in the camera I've been testing.
Please let me know if you have any success.