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

[Daniel Pocock]

On 24/12/15 16:21, Marcus Müller wrote:
> 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:
>>> Forgot:
>>>
>>> [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.

Thanks, that is about 100mW then.  Amateur operators are allowed far
more than this obviously, typically putting out 1 to 5W on handheld
devices, 50 to 100W on mobile and base stations and up to 1kW or more on
SSB in some countries.


>> - 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).

Great, there are a lot of options available, it would be helpful to make
a shortlist of devices people had used with some satisfaction already,
this could be something for the wiki too.

Not all amplifiers will be ideal with 20dBm, for example, some are
designed to work off the 5W output of a handheld.


>> - 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.

Yes, that is understandable.  Some amateur rigs and scanners have been
designed to be difficult around certain bands.

>> - antenna impedance (50 Ohm?)
> Exactly.
>> 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.

Great, using the metal box seems like the sensible thing to do.

>> - 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]

Interesting, the Thinkpad looks similar to my own.  Is that just
receiving, or is it OK to do a lot of transmitting when running off the
laptop USB power?


>> 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!
> 

OK, I'll probably get into making some contributions like that as I
start playing around with it.  I'm still at a very early stage just
working out which hardware I need and how to get it.

Will you or anybody else with an interest in this for amateur purposes
be over at FOSDEM?  There is an SDR dev-room[1] again and there was also
talk on the main FOSDEM list about an amateur radio presence[2] of some
sort.

Regards,

Daniel



1. https://fosdem.org/2016/schedule/track/software_defined_radio/
2. https://lists.fosdem.org/pipermail/fosdem/2015-August/002167.html