1.3 GHz options

[a_marmot]

All the >500mW types are crap, they use a simple and ancient '80s design. The 500mW and 100mW LM types use a much more modern design with a proper PLL oscillator and a proper RF section and have heaps of bandwidth for video and audio, with little to no drift on the main carrier as well as the audio channels due to the excellent crystal based PLL oscillator. The >500mW designs drift all over the place and their audio/video frequency curve is temperature dependent, which means it changes when the Vtx heats up, hence my suggestion to stay away from these. And I'm not even going to go into construction on these, I would be terribly ashamed of how they are built, a trained monkey with soldering iron can do a better job I'm sure.

Hi Sander, I'm bumping this question over from the other forum because I am hoping you can clarify something about this post. According to Lawmate, their 1000 mW Vtx IS digital PLL, like the 500 mW model. Were your comments specifically about the 1W Lawmate, or other transmitters in the 1-2.5 W range?

[ssassen]

In a nutshell it comes down to the origins of the 1W and 500mW type of transmitters.

The 1W originates from a popular ATV design of the late '80s with a design update in the mid '90s, the 500mW type is a '08 design.

This is clearly reflected in the design. On the 1W type the OSC and VCO are semi discrete and the audio channel is just tagged on with a very simple side band modulator. This results in the audio carrier specifically being very intolerant of changes in temperature which makes the frequency response, bandwidth and amplitude shift with temperature. Also the bandwidth on the video is not nearly as large as on the 500mW types and its frequency response also shifts with temperature.

The 500mW design use a proper OSC and VCO IC (RTC6502 from Richwave Semi) with tight tolerances on VCO phase noise and drift. Audio/video bandwidth is much larger and there's no temperature dependent effects anywhere. On top of that the output stage is a proper PA (on the 2.4GHz version) with internal matching to 50 ohm on the in and output, the 1.2GHz design uses a discrete output stage that is better behaved than the PA on the 1W versions though.

All in all the 500mW types run a lot cooler, are a much more mature design with less drift and phase noise and higher bandwidth. The 3dB penalty I don't mind, the receiver antenna will pick up the slack for that. One thing that's unfortunate on the 1.2GHz 500mW types is that they don't run at frequencies above 1180Mhz stock for whatever reason, but a simple reprogramming of the RTC6502 PLL lets you run at whatever frequency you desire.

[kenkos68]

All in all the 500mW types run a lot cooler, are a much more mature design with less drift and phase noise and higher bandwidth. The 3dB penalty I don't mind, the receiver antenna will pick up the slack for that. One thing that's unfortunate on the 1.2GHz 500mW types is that they don't run at frequencies above 1180Mhz stock for whatever reason, but a simple reprogramming of the RTC6502 PLL lets you run at whatever frequency you desire.

Now, how can one in the US get a hold of one of these and play with the RTC6502? I emailed Lawmate Taiwan asking about modifying the 500mW transmitters to run on 1280 Mhz and they referred me to Lawmateusa. However they were just as clueless and only sent me a wholesale price list and said "Thank you for your business".

[ssassen]

They are available from ReadyMadeRC and NGHobbies, but I'm told they don't sell these to US customers?

[kenkos68]

They are available from ReadyMadeRC and NGHobbies, but I'm told they don't sell these to US customers?

That's the problem. They can't legally send me one. If I were a distributor selling them I could get one. I can probably do the mod myself. Else I'd pay for one that has been modded.

[a_marmot]

OK, Sander. I think maybe we now have an outline for a new product from IRC! We need a VTx/Rx combo that operates on 1280 and 1255 (providing 2-channel selection in the USA), plus other frequencies allowable in europe and asia. Power 500 mW or higher. They will sell like hotcakes at $400 a pop. You on it?

[ssassen]

OK, Sander. I think maybe we now have an outline for a new product from IRC! We need a VTx/Rx combo that operates on 1280 and 1255 (providing 2-channel selection in the USA), plus other frequencies allowable in europe and asia. Power 500 mW or higher. They will sell like hotcakes at $400 a pop. You on it?

Already on it, but pesky Chinese New Year throws a spanner in the works ...

[a_marmot]

Already on it, but pesky Chinese New Year throws a spanner in the works ...

lol. Does this mean you've already done prototype testing and have volume production in the works?!

[a_marmot]

(sorry to put you on the spot!)

[volto]

I hope they aren't really gonna be $400 each, more like $40?