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

[Daniel Pocock]

On 25/12/15 19:44, Marcus D. Leech wrote:
> On 12/25/2015 09:18 AM, Ralph A. Schmid, dk5ras wrote:
>> Hi,
>>
>> First of all, the USRP radios are kind of experimental radios, using
>> them for real ham radio operation on antennas will require filters and
>> PAs. "Out of the box" it will only be some proof of concept when you
>> create a ham radio application with it.
>>
>> All 50 ohms, no limitations other than upper and lower border,
>> regarding frequency. But connecting a roof-top antenna will most
>> likely not work, due to the lack of preselection, you will receive
>> lots of images and other garble.
>>
>> Ralph, dk5ras.
> I think it boils down to "good RF hygiene is still important". Even if
> you had massive-amounts of excess dynamic range in the digital
>   domain, you don't necessarily have that headroom in all the analog goo
> that is in front of all the digital "stuff".
> 
> When I'm doing RF projects with SDRs where I care about the reliability
> and consistency of the results, I pre-select with either commercial
>   or DIY filters.
> 
> In the TX direction (which I don't do much of), you'll almost always
> need at least harmonic filtering--there isn't a synthesized superhet
>   TX chain on the planet that doesn't have *some* amount of unwanted
> harmonic and spur energy, and if you're going to be amplifying it,
>   cleanliness of what you're amplifying will not only reduce the amount
> of wasted power, it will eliminate complaints from other
>   users of the spectrum, and possibly eliminate unwanted visits from the
> authorities.
> 
> Purpose-built radios have already taken care of this, at least in the TX
> direction, by using output filters that nicely knock-down unwanted
>   mixing products and other spurs.    That's nearly impossible to do in
> a "general, not-designed-for-specific-application" radio like your
>   typical SDR.
> 


On its own the SDR device may not be ideal, but when used in conjunction
with some external input filter or power amp, can these issues be
managed by the average (or slightly above average) hobbyist?

I fully understand no one filter or amplifier will support the full
spectrum from 70MHz to 6GHz, that is OK.

It is not just harmonics that came to my mind when asking about this
before, there is also the risk of software bugs.  There is no such thing
as perfect software, sooner or later somebody may configure a flow graph
that transmits in a band they didn't intend and it would be nice if the
power amp or other components were attenuating such things or even
better, alerting the user.

Regards,

Daniel