Re: LF: RFspace SDR-IQ

["Clemens Paul" <cpaul@gmx.net>]

Hello Andy,

 

your test results show quite strong differencies between the

upper and lower IM3 product,up to 18dB.

Unsymmetrical IM3 products *always* imply  that there is more than one

IM3 producing source.

Maybe it's a good idea to check the inherent IM3 behaviour of your test

setup itself.

3dB-combiners have only 30-35dB port isolation,true hybrid combiners (6dB)

are better by at least 20dB,if they are made tunable up to 80dB isolation

is achievable.

Also the 70dB resistive isolation between the two crystal oscillators seems to

be a bit on the short side. 

 

73
Clemens
DL4RAJ

 

 

 

---- Original Message -----

From: Andy Talbot

To: rsgb_lf_group@blacksheep.org

Sent: Saturday, October 30, 2010 7:47 PM

Subject: Re: LF: RFspace SDR-IQ

http://www.g4jnt.com/SDRIQ_Linearity.pdf

 

Showing some of the minor peculiarities of DS SDRs

Andy
www.g4jnt.com

On 30 October 2010 18:04, Alan Melia <alan.melia@btinternet.com> wrote:

Hi Clemens, you seem to impute that there are no shortcommings in direct
sampling!
 :-))    I suspect there are, but they are just "different".  You may be
right about the units mentioned, but it is just as easy to make a poorly
preforming DSP radio as to make a poor analogue one. We are in danger of
being conditioned to accept that "digital" is the magic dust that solves all
problems......it is definitely not so!

Having said that, the performance of some units is quite remarkable and I do
own a couple very good conventional receivers.

Alan G3NYK

----- Original Message -----
From: "Clemens Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>

Sent: Saturday, October 30, 2010 4:11 PM
Subject: Re: LF: RFspace SDR-IQ


> Tony,
>
> the most important difference between SDR-IQ/-IP(from RF Space)
> or Perseus and the $200 SDR on
> http://www.lazydogengineering.com/LD-1A_SDR.html
> is that  the latter is no direct sampling receiver.
> It uses a downconverting technique with a number of shortcomings,e.g.
> phase noise of the LO and others.
> I would go for a direct sampling SDR like those e.g. from RF space or
> Perseus.
>
> 73
> Clemens
> DL4RAJ
>
> ----- Original Message -----
> From: "Tony" <ei8jk@o2.ie>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Saturday, October 30, 2010 3:49 PM
> Subject: Re: LF: RFspace SDR-IQ
>
>
> > Thanks guys.
> >
> > You have just tipped the balance for me and I shall be placing an
> > order
> > for one on Monday morning.
> > It's about time I joined the 21st century, but it will be
> > interesting to
> > compare it to my beloved FT 102 rx.
> >
> > Tony, EI8JK.
> >
> >
> > On 29/10/2010 16:50, Tony wrote:
> >> Hello group.
> >>
> >> Has anyone any experience with this SDR ?
> >> It looks interesting and I'm a bit tempted, especially as it works
> >> full spec down to 500 Hz and "usable" to 100 Hz.
> >> But as I have never used an SDR, I haven't got a clue if it's any
> >> good
> >> or not.
> >>
> >>
> >>
> >
> >
>
>
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