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Old Apr 12, 2008, 09:50 PM
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Info request regarding LP5DSM range improvement

Hello.

I am hoping to get lucky enough to find someone willing to help me with a project to increase the radio range of EFlite's LP5DSM (for Blade CX2). I would like to add a power amplifier to the transmitter, as I have found in the following posting:
http://www.rcgroups.com/forums/showthread.php?t=728078
Two forum members mentioned success adding a small linear amplifier to greatly enhance the range of the radio. This posting includes some useful data, and some photos of such modifications.

I would like to copy their implementation, but am far from knowledgable enough, I believe. So I am basically begging for some information from anyone out there who would be willing to help. So, let me explain what I know so far (very little, I'm afraid).

I believe that the range of the transmitter can be extended as described in the posting I mentioned above. One fellow forum member (fmkit) mentioned implementing a RMPA2455 power amp (Fairchild chip) to do the job. Photos of the setup are also included in the posting I referenced, but they do not provide enough for me to complete this project. It appears that this chip is no longer available (Digikey and Mouser both list as obsolete). I spent some time searching for a replacement, and came up with SST12LP14 2.4 GHz amplifier (made by SST, of course). Seems to be similar emough to be a viable replacement. Could anyone verify whether this is true or not, as my knowledge in this area is limited?
Here, also, is a link to the datasheet for this chip:
http://www.sst.com/downloads/datasheet/S71279.pdf
This datasheet includes a detailed circuit diagram for "typical" application of the chip (page 9 of the datasheet). Would anyone happen to be able to verify whether this schematic would work directly for what I intend to do? If the circuit diagram is usable for this application, then I would be able to design/build a circuit to modify the transmitter. I definitely do not have the skill to engineer the circuit myself, but I can build from someone elses schematic.
Has anyone else successfully implemented such a mod? Willing to share a little information? I would love to get some input from someone who has already done something similar to this.

Thanks.
Sean
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Old Apr 13, 2008, 04:08 AM
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Canada, BC, Langley
Joined Nov 2004
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I'm all for modifying stuff but when it comes to adding power amps I wouldn't recommend it. I made a TX module for my Futaba 9CAP using the 2.4ghz DSM2 transmitter from an LP5DSM but I wouldn't add a power amp unless I had the proper test equipment to verify the signal was clean and within spec. Adding a power amp might get you more range but it may also also end up transmitting spurious signals you never intended to transmit. If you have your own property to fly on thats far away from everything else then its not a big deal. If you want to fly at a field with other people I would expect them to not be too welcoming if they know of the mod, not only that you'd have no insurance.

Why not just invest in a DX6i? They are pretty cheap for the tx only on ebay and on forsale forums.
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Old Apr 13, 2008, 09:56 AM
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I'll probably put a 5.5db antenna on mine if I want more range, but that's about as much as I would be comfortable doing until I can get a REAL spectrum analyzer (not one of the WIFI based devices!). Adding an amp without all the other filters for the spurs is just asking for trouble.
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Old Apr 16, 2008, 02:35 PM
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I too am hoping some one will chime in with more info on the mods. I have three lp5dsm tx's as well as a dx6i. but i would like to improve the range of the lp5dsm slightly for my 24" foam warbirds that i fly at a remote field with my friends. (I supply the planes and Tx's for my lazy friends)

I do understand the concerns above and agree that it would not be a suitable tx for club flying but as a park flyer, flying little foamies i don't see why not?
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Old Apr 16, 2008, 04:14 PM
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Well, running a 5.5db antenna will double the effective output power as long as the model is within the now different RF field.
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Old Apr 19, 2008, 07:30 AM
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Thanks for the advice....

I want to thank you for the responses above. Kind of takes this project off my list of future fun, but I am sure that you guys are correct, and a mod like this would not be entirely "safe". I did not really consider the repercussions after reading the post I referenced above. Glad someone out there did.

I believe that I will change antennas as suggested, which should be pretty simple. I was hoping to use the LP5DSM with a couple park flyers that my brother-in-law and I bash around, and just wanted to be able to try out the 2.4 ghz in a little larger area than my living room.

Would anyone be able to recommend any specific antenna? I looked around and see that there are a variety that could be used pretty easily, just wonder if anyone has info to choose any specific one over another.

Thanks!
Sean
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