[USRP-users] Amplifiers for USRP Transmission

Derek Kozel derek.kozel at ettus.com
Mon Jul 6 17:12:47 EDT 2015


Hi Evan,

Could you describe the microphone and antenna setup more? If it is just a
wire antenna attached to a passive microphone acting as a speaker then I'd
suggest that the next step is to make your receiver an active one. Adding
more power onto the output of the USRP is an option, but will only get you
slightly further before becoming overly complicated and, as the
minicircuits amplifier shows, expensive.

What is your objective for system? If you are learning about electronics
and analog design then here's an example design of an active AM receiver.
It looks like a pretty reasonable one, though it's resonant frequency is
too low for the SBX daughterboard (400 MHz minimum). If you're interested
in pursuing that I'd be happy to look around a little more and see if
there's a reference to retuning a circuit like that.
http://www2.eng.cam.ac.uk/~dmh/ptialcd/trf/trf.htm

On the other hand if you are more interested in the digital signal
processing side of things then I recommend just using a commercial FM
radio. With 100 mW you can easily transmit hundreds of yards if not more
on, for instance, the Family Radio Service band. The radios are less
expensive than the Minicircuits amplifier you mentioned and you'd have the
bonus of being able to experiment with receiving on the USRP. The frequency
is also a good one if you're interested in antenna design, lots of
available resources.

Regards,
Derek

On Mon, Jul 6, 2015 at 8:41 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 listUSRP-users at lists.ettus.comhttp://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
>
>
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