|Nov 29, 2013, 06:03 AM|
Joined May 2012
Lawmate 1.2GHz 500mW transmitter
I received a new Lawmate 1.2ghz 500mw transmitter which I purchased off HobbyKing today. I've had some clients questioning the quality of the lawmate products mostly based on what ReadyMadeRC have said about them. I've been using lawmate for my non 5.8ghz video since 2007 or so and have never had any issues with them other than snapping the SMA off on a crash.
I must admit I'm not overly fond of their input cable, but that's what you get...
I put the brand new 500mW unit on my spectrum analyser, feeding it through a lab grade 8GHz 20dBm attenuator. My spectrum analyser is calibrated and tested. The unit is powered off it's included powersupply - interesting, the advertised voltage range is 9-12v. I was able to go down to 5.1v before the signal strength dropped. (its a 5v SMPS)
Quick info on interpreting these graphs - the yellow line is "clear write" - basically what the SA saw on it's last sweep, the purple line is Power Average - the average power it saw over the past 20 sweeps (100 on some.. i changed it down to 20 half way through.)
There is no video fed into this, as the signal gets chopped up with the video being modulated, to see the actual output you need to feed it nothing.
Things to look for:
Video Power on the centre peak (determines video range)
Audio power on the side peaks (determines audio range)
Offset from "advertised" on each of the frequencies peaks (see peak table at bottom.) (any offset will severely reduce your video range)
Firstly, with no input, how much does space a 0v signal take up?
At 1180mhz the frequency 99% power occupied bandwidth is basically 25KHz - this is good.
Secondly, Carrier-noise ratio, on a 2mhz span.. basically, how good is this signal? This can determine your video quality.
48dB is very good.
So, the channels:
CH1 1080 (worst for telemetry on the audio channel by FAR):
CH5: 1140 - this was wacky, so I have provided the same centre frequency (the advertised CF) with a 15mhz span, then "zoomed" in to get a more accurate read on the peak. This is not a frequency that could be used to transmit video very far at all!
Now, it's advertised as a 6ch transmitter, but the 3 bit switch allows me to select 8... soo what happens when we select ch7 and 8? Not much sadly.
So it appears that CH7 and 8 are past the limits of the PLL.
With an ambient temperature of pretty much exactly 25C, no airflow, the unit's PCB reached a maximum temperature of around 52C, giving a 27C over ambient temperature heating.
|Nov 30, 2013, 11:21 AM|
Joined May 2012
On this unit, I'm using 1120MHz - 1160 would be nice too.
I'm using this unit with an APM/Minum OSD for a personal project, I commented to a friend that this is the clearest video I've seen in a long time - Channel selection via SA is a good way to go, and the APM/MinimOSD appears to be a really nice low noise option.
|Dec 03, 2013, 01:44 AM|
Joined May 2012
I did test the 1.2ghz 1W one awhile back, but didnt capture the output. It should be very similar, if I was designing a series of products they'd all have the same circuit with a different PA stage on them.
|Dec 03, 2013, 12:45 PM|
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