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Re: [Discuss-gnuradio] ham/amateur getting started

From: Ralph A. Schmid, dk5ras
Subject: Re: [Discuss-gnuradio] ham/amateur getting started
Date: Fri, 25 Dec 2015 15:20:18 +0100

Be careful, an antenna filters less than one would expect :)




From: address@hidden [mailto:address@hidden On Behalf Of Marcus Müller
Sent: Thursday, December 24, 2015 16:21
To: address@hidden
Subject: Re: [Discuss-gnuradio] ham/amateur getting started


Hi Daniel,

about to take a walk, so please excuse my brevity:

On 12/24/2015 01:26 PM, Daniel Pocock wrote:

On 24/12/15 08:31, Marcus Müller wrote:
[1] http://marcus.hostalia.de/sdra/pres.pdf
Thanks for the fast reply, I had a look and I notice you emphasize the
USRP products, you mention the B200 and B210 (the OZ9AEC link I found
also mentioned USRP but didn't specify model numbers)
I had a look at the FAQ[1] and spec sheet[2] to try and find comments
about amateur radio use cases, for example,
- how much TX output power?

Up to +20dBm, depending on frequency.

- suggestions about use with an external TX power amplifier

Anything goes if it has 50Ohm impedance, and can deal with the B210's output power range (so, close to zero to 20dBm).

- is RX or TX restricted on any frequencies by hardware?

No; the device really doesn't care what you do with the spectrum -- it's all yours.
Technically, as mentioned, TX power is higher on some frequencies than on others. That's a pretty intuitivie effect of covering sub-100MHz to 6GHz with one and the same device.

- antenna impedance (50 Ohm?)


and I didn't find any comments on these things.
Looking at the accessory list I found that 782781-01 is a 50 Ohm cable
so I guess everything is 50 Ohm?

Yes. The RF ports are, so is, if you want to use such a device, the input port for an external 10MHz reference (all USRPs to date have integrated oscillators and don't need one).

Even before getting into the software setup, is there any useful guide
on hardware considerations for SDR in an amateur station?  For example:
- power supply requirements

Well, the B200/B210 can work with a sufficiently "beefy" USB3 controller on a laptop computer, but I'd generally recommend using the 6V "wall wart" power adapter.

- risk of interference between difference devices in the shack, precautions

That is an interesting aspect of operation, always.

The point is that, though our filtering is quite OK, SDR devices, especially direct conversion (or low-IF) transceivers, suffer from modulation products at the harmonics of the clocks used.

However, if you put your B2x0 into a metal enclosure [1], it'll be only significant what reaches your RF port; so, if you can have an analog filter that let's say has a passband of e.g. $\frac{f_\text{desired}}2<
      f_\text{passband}<2f_\text{desired}$, you shouldn't even be having any problems with those. You definitely don't necessarily need such a filter -- you can just connect an antenna (which typically has pretty strong filter characteristics, too!), and tune to whatever carrier you want.

- use with other typical amateur equipment (antennas, RX pre-amplifiers,
TX power amplifiers)

Preamps will seldom be necessary, unless your antenna is far away. With a B2x0 as it is, you can get (if you set the RX gain high enough) Noise Figures that compete well with many LNAs.

- suitability for mobile use-cases, using DC/battery or vehicle power
and with a laptop or even a tablet as user interface

I'll refer to the Balint's show talent to answer that question :) [2]

Any feedback or links would be really helpful, maybe they could go in
the GNU Radio wiki Ham page too.

Good idea! By the way, please feel more than welcome to register on the wiki, and add & modify that with anything you find!


1. http://www.ettus.com/kb/detail/usrp-b200-and-b210-faq
2. http://www.ettus.com/content/files/kb/b200-b210_spec_sheet.pdf
[1] http://files.ettus.com/b2x0_enclosure/
[2] https://www.youtube.com/watch?v=cygDXeZaiOM

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