[USRP-users] Amplifiers for USRP Transmission

Marcus D. Leech mleech at ripnet.com
Mon Jul 6 15:41:54 EDT 2015

On 07/06/2015 03:32 PM, Evan Chavis via USRP-users wrote:
> Hello USRP users,
> I've been working with a USRP1 to transmit an amplitude modulated 
> signal to a very basic improvised receiver, basically just a wire of 
> length corresponding to the frequency I'm transmitting at attached to 
> a microphone such that the microphone is picking up the signals on the 
> wire as it would audible noises.  I'm using an SBX daughterboard 
> (which can produce 100 mW) and a log periodic antenna (with 5-6 dbi 
> gain).  I can get a decent transmission at a range of up to about 25 
> cm, although it is best at a distance of just a few cm.  I've got the 
> gain set with GnuRadio as high as possible without causing distortion, 
> and I'm looking to improve the range of possible transmission.
> My questions are, what do I need to consider when looking for an 
> amplifier to use with a USRP, are there any special problems a 
> beginner would be likely to miss when trying to use those 2 things 
> together?  Also, if an amplifier's gain is listed at 20 dB, would that 
> be 20 dB on top of the 31.5 the daughterboard is capable of 
> outputting, or would the amplifier be useless in that it is capable of 
> providing less power than the daughterboard itself?  And third, how is 
> a device such as this one: 
> http://www.minicircuits.com/pdfs/ZX60-V63+.pdf powered?  The 
> data-sheet gives the numbers 5 V and 69 mA but I don't see an obvious 
> way to power it aside from just soldering wires onto the marked bumps 
> that say +5 and ground, is that the actual intended way to do it?
> Many thanks for any input and have a great day
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
You don't need an amplifier.  You need a better understand of how RF 
works, and how RF receivers work.   The SBX covers 400Mhz to 4.4GHz.

Given that you don't appear to know how RF works, I'd be very reluctant 
to recommend that you augment your experiments with an RF
   power amplifier on the RX side.

How about studying how RF receivers work, how EM propagation works, etc, 
etc?    The ARRL handbook is a good place to start on basic
   RF topics. Adding an RF power amplifier to your setup will be both 
illegal, and frustrating, and totally not the right way to go about these

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