Forum: GNU Radio Gain ahead of Basic RX?

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00f9c71826ac9a2c79e751116186571f?d=identicon&s=25 John Ackermann N8UR (Guest)
on 2007-01-01 19:43
(Received via mailing list)
As mentioned earlier, I'm working on a front-end board for the Basic-RX
to provide some gain and selectivity for HF use.

Question -- has anyone figured out what sort of gain is optimum ahead of
the the Basic-RX for use as an HF receiver?  I can easily tweak the
front-end design to provide anything from about 8 to 18 dB gain; more
than that might require adding a second amp stage, which is doable if
necessary.

Thanks,

John
Dc48f9c00e3e6de9640898a531c26d89?d=identicon&s=25 Charles Swiger (Guest)
on 2007-01-01 21:00
(Received via mailing list)
On Mon, 2007-01-01 at 13:41 -0500, John Ackermann N8UR wrote:
> As mentioned earlier, I'm working on a front-end board for the Basic-RX
> to provide some gain and selectivity for HF use.
>
> Question -- has anyone figured out what sort of gain is optimum ahead of
> the the Basic-RX for use as an HF receiver?  I can easily tweak the
> front-end design to provide anything from about 8 to 18 dB gain; more
> than that might require adding a second amp stage, which is doable if
> necessary.
>

John - I use 18db gain .5-30Mhz amps from Advanced Receiver Research, as
well as their 29db GAsFet amps for 7-7.4Mhz.  Another workhorse is a
29db .05-150Mhz Minicicuits ZHL-32A.

I've been playing with a mobile hamstick antenna with great success due
to two things: good band conditions recently (k index near zero) and
being able to park in a quite place away from power lines and consumer
electronics. My apartment is so noisy from all the neighbors electronics
that 40 meters is completely unusable, nothing but noise all the time.

Here's a snapshot of the 40 meter band using the ZHL-32A
and a trunk mounted 40m hamstick in the park:

http://webpages.charter.net/cswiger/40m_spectrum.jpg


Last night, using the 29db and hamstick, logged EA8EQ, FM5AN, JR1CFP,
JE6DOI, etc. - AND have the band recorded for proof ;)

--Chuck
3596cfe1d579c65b9babd35e8787977c?d=identicon&s=25 Matt Ettus (Guest)
on 2007-01-01 21:54
(Received via mailing list)
John Ackermann N8UR wrote:
> As mentioned earlier, I'm working on a front-end board for the Basic-RX
> to provide some gain and selectivity for HF use.
>
> Question -- has anyone figured out what sort of gain is optimum ahead of
> the the Basic-RX for use as an HF receiver?  I can easily tweak the
> front-end design to provide anything from about 8 to 18 dB gain; more
> than that might require adding a second amp stage, which is doable if
> necessary.
>

Using an BasicRX on a USRP with the PGA turned all the way (+20dB) up is
roughly like having a 35dB noise figure.  Based on that and your desired
system noise figure, you can tell how much gain you need ahead of it.

On the high side, with the PGA turned down (0dB), the ADCs will clip at
2Vpp.

Matt
00f9c71826ac9a2c79e751116186571f?d=identicon&s=25 John Ackermann N8UR (Guest)
on 2007-01-01 22:20
(Received via mailing list)
Matt Ettus said the following on 01/01/2007 03:52 PM:
=
> Using an BasicRX on a USRP with the PGA turned all the way (+20dB) up is
> roughly like having a 35dB noise figure.  Based on that and your desired
> system noise figure, you can tell how much gain you need ahead of it.

Thanks, Matt.  So it looks like 20+dB gain would be desired, at least
for the higher bands.  One version of the amp chip I'm using (a
Mini-Circuits 3rd generation monolithic amp called a "GALI") has about
25dB gain, 2.6dB noise figure, and an IP3 output of +37dBm (so about
+12dBm input).  Looks like that may do the trick.

John
Dc48f9c00e3e6de9640898a531c26d89?d=identicon&s=25 Charles Swiger (Guest)
on 2007-01-02 05:12
(Received via mailing list)
On Mon, 2007-01-01 at 16:17 -0500, John Ackermann N8UR wrote:
> for the higher bands.  One version of the amp chip I'm using (a
> Mini-Circuits 3rd generation monolithic amp called a "GALI") has about

I just cracked open a Ramsey PR-2. The secret sauce is a upc1678,
available at mouser for $2.50.
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