1 watt 433mhz - 2.4ghz rf amp... from SCRATCH! - RC Groups
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Jul 12, 2013, 04:36 PM
RC beginner
Mini-HowTo

1 watt 433mhz - 2.4ghz rf amp... from SCRATCH!


this thread is a result of losing a bet with jakestew on max power allowed in ism bands. also attempt to keep up with midelic for most threads started in a week. lol!.

this easy to build circuit cost me less than $5 and allows boosting power of uhf transceivers like openlrs or small 2.4ghz radios like hubsan (which need all the help they can get due to low output and crummy pcb antennas). for starters ive tested on the hk openlrs rfm22b module and xl7105 diy flysky rx. total cost was less than half what higher power versions of those run.

key is the low cost rf2126 rf amp ic. no pcb boards required. just glue the chip on a piece of 1oz fr4 and tack the various caps, resistors, and inductors directly onto chip pins. for both the 433mhz and 2.4ghz versions ive also mounted rx/tx modules on the board. rp-sma too for easy antenna swap.

photo of the xl7105 version from diy flysky rx below. also included mfg reference design. some component values were changed to improve performance and depending on junk box parts but no major deviation. as usual if theres interest i can provide more pics and construction info.
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Jul 12, 2013, 04:43 PM
Registered User
Well if your going for most threads started in a week, best i make sure I get second posted

Oh best I comment on what you've done too Looks very simple so kinda got to be done. Details/Ciruit Bom
Last edited by SadSack; Jul 12, 2013 at 04:45 PM. Reason: should also make a comment about topic.
Jul 12, 2013, 04:47 PM
RC beginner
rats! that dam ss always beats me out in followup post. now i got no way to:

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well... midelic had me beat there anyway.
Jul 14, 2013, 11:32 AM
We can rebuild it!
djdavies83's Avatar
Looking at the mfg diagram, what's the difference between the Vcc connection an the Vpd connection, also as its within frequency range, could I use this on a wifi router for better range?
Jul 14, 2013, 01:12 PM
Stuart
srnet's Avatar
Quote:
Originally Posted by djdavies83
Looking at the mfg diagram, what's the difference between the Vcc connection an the Vpd connection, also as its within frequency range, could I use this on a wifi router for better range?
Data sheet here, makes it clear;

http://media.digikey.com/pdf/Data%20...DFs/RF2126.pdf
Jul 14, 2013, 09:43 PM
We can rebuild it!
djdavies83's Avatar
Quote:
Originally Posted by srnet
Ah cool thanks for that, I think I got it.

While searching for supplies I found there is a ready assembled "evaluation board" RF2126PCK.
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And I also found a black and white for printing your own board.
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It would need scaling and a wire link between the middle strip and GND planes.
Jul 15, 2013, 03:23 AM
Registered User
The range on xl7105 is...???
Jul 15, 2013, 03:50 AM
Stuart
srnet's Avatar
Quote:
Originally Posted by Ivan2280
The range on xl7105 is...???
There cant be an answer to that, as the 'range' would depend on the receiver in use, the modulation method in use, the antennas in use, the frequency and the environment or terrain, the input power from the TX, and of course the power supply of the XL7105. .

As a guide, if the driving TX had an output power of 100mW and a 'range' of 1km, adding the power amplifier, and running it from 6V would increase 'range' to about 3km.

Note however that as its a wideband amplifier harmonics present in the original signal may be amplified beyond legal limits, but then anyone doing DIY for this type of stuff needs access to the equipment to check that.
Jul 16, 2013, 11:06 AM
RC beginner
in urban setting i get couple hundred feet with the 7105 1mw output. in the suburbs that doubles to pretty much cover an entire soccer field from one end to the other. then with the amp, as srnet suggests, i get almost triple again which is way overkill for small planes and copters. also tripled when added to a full range radio but its illegal here in usa and imo generally quite rude no matter where you are.

using a low noise amp in front of your rx is not only more legal and cheaper but less power hungry too. lna would be my preferred method for larger setups.
Jul 16, 2013, 02:05 PM
Stuart
srnet's Avatar
Quote:
using a low noise amp in front of your rx is not only more legal and cheaper but less power hungry too. lna would be my preferred method for larger setups
I have as you might have guessed I have tried that for the 'other' project.

An LNA in front of a RFM22B gave me a 12dB performance gain, so about 4 times the range. The RFM22B may well be popular for RC these days but they really are quite deaf.

Quote:
also tripled when added to a full range radio but its illegal here in usa and imo generally quite rude no matter where you are
Most RC most modelers would want to present a public image of being considerate and law abiding. However If they want more range, and a lot do, what is legal or not is of little concern.
Last edited by srnet; Jul 16, 2013 at 02:11 PM.
Jul 18, 2013, 10:53 AM
RC beginner
12db is incredible. i see a lpf in your design but no lna. do you have any more info? what part? specially pics because layout was where i ran into most of my problems. hard to get anything close to your gain w/o turning into an oscillator.
Jul 18, 2013, 11:42 AM
Stuart
srnet's Avatar
One of these;

http://www.ssb.de/product_info.php?l...rker-70cm.html

However, that was used to prove the concept, its not cheap or practical for in-flight use.

I did try a cheap much smaller\lighter design based on the ATF54143 PHEMT but whilst it had some gain, it also had a tendency to produce out of band spurious stuff, which seemed to swamp the wide band input of the RFM22 and actually reduced sensitivity. I tried to stabilise it by screening between the in\out sides, without any success.
Jul 18, 2013, 12:00 PM
RC beginner
not cheap is right... half grand if im reading correctly.

so we are pretty much in the same boat. ive purchased several part numbers from digikey, anything around a buck or two, and harvested quite a few from broadcast dish lna but so far no luck. after hearing your results with the rfm22b im thinking to give diy amp another try. good news is the coils are easy to wind. lol!
Jul 18, 2013, 12:24 PM
Stuart
srnet's Avatar
I think the key is to have a narrow band filtered LNA, the issue with a lot of general purpose (cheap) LNAs is that they are wide band and amplify all the out of band stuff as well.

This is not a significant problem to the average comms receiver which by design has very good out of band signal rejection, but the RFM22B has a wideband input by design, so I suspect its just getting swamped.

Its possible that the SP 7000 actually has too much gain, and a few dBs extra performance might be obtained by turning the gain down a bit, will try it one day.
Jul 18, 2013, 12:27 PM
Stuart
srnet's Avatar
Quote:
Originally Posted by dave1993
i see a lpf in your design
The LPF was there, just in case, the RFM22B is quite close to the legal limit for 3rd Harmonic, depending where you are in the world.

Not that I guess the average hobbyist would check or be bothered by that.


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