[USRP-users] Amplifiers for USRP Transmission

Matt Ettus matt at ettus.com
Mon Jul 6 17:13:38 EDT 2015


I am terribly sorry for the response you received to your question.
It was harsh and rude and not at all what is appropriate.  Everybody
starts their learning about radio somewhere, and we are open to people
at all levels here.  I will attempt to answer your questions below,
but I hope you do not tune out due to this experience.


You are transmitting at a certain frequency, although I am not sure
what frequency that is.  You are correctly using an appropriate length
receiving antenna.  The first problem is that you are feeding it
directly to a microphone.  Microphones are intended to convert audio
signals into electrical ones, and only some of them will operate in
reverse, i.e. as a speaker.  The second issue is that even if your
microphone works as a speaker, it is designed for audio frequencies
(<20kHz), not the signal coming from an SBX which must be at least 400
MHz, and neither are your ears.  To get a very basic reception of AM,
you need a diode at the very least.  You most likely would also want
some filtering and amplification as well.  I would suggest checking
out the following web page:


Also, anything about crystal radios you can find on the net would be helpful.


Again, please accept my sincerest apologies.  This is not
representative of how we want to treat newcomers, and I assure you it
won't happen again.

Matt Ettus

On Mon, Jul 6, 2015 at 12:41 PM, Marcus D. Leech via USRP-users
<usrp-users at lists.ettus.com> wrote:
> 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
>   experiments.
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

More information about the USRP-users mailing list