Re: LF: ROS Latest with I/Q output

[Andy Talbot <andy.g4jnt@googlemail.com>]

Not sure which G3PLX product you're referring to...

 

It is simple to do a DDS exciter, but you can only 'modulate' a DDS by reprogramming it in freq/phase /amplitude tio teh extent the chip allows.  So FSK modes like WSPR and JTxx are a doddle. 

 

Narrow band modes that need amplitude variation are possible if the sampling rate (DDS reprogramming) is a lot higher than the signal bandwidth - this is necessary to keep the alias products to a minimum as subsequent anti-alias filtering is impossible if you are generating the waveform this way.   PSK31 formed by reprogramming an AD9852 DDS at 7812.5Hz (250 samples per symbol) gives < -60dB spurious.   The next 5MHz GB3RAL when it comes on line will use this technique.

 

A DDS followed by an I/Q upconverter is also straightforward.   I've built an AD9851, IQ upconverter and allpass network into a small diecast box, frequency controlled via RS232 interface.

 

And for narrow modes, you don't even need I/Q outputs from the software.  A pair of opamp all-pass filters will generate quadrature drive for a single tone input, and can be adjusted to give a couple of 100Hz bandwidth with 40 - 50dB sideband rejection.     All the design data / circuits can be found on my website

Andy
www.g4jnt.com

On 21 November 2010 15:47, Graham <g8fzk@g8fzk.fsnet.co.uk> wrote:

 

>>> There are plenty of receiver packages for Softrock. clones  and similar - now how about more SDR transmitter software.<<<<

 

What  happened to the  G3PLX  project  , I had a  ssb  qso  with  him using  it  , but  never seen  anything  since ?

 

Surely  it  must be  'simple'   to  drive a DDS  to  make a  low  power  exciter ....  hopefully  it will  replace the  3 ft  ( 1 mtr)  cube  of racal  equipment  I need  to  use on  mf  in the  near  future

 

Its  just  occurred  to  me , if I/Q  is  now  coded, then the   ROS - VLF  , based on  25 Hz  max shift @  8 KHz    may be opened up to  other bands ?

 

G..

From: Andy Talbot

Sent: Sunday, November 21, 2010 1:41 PM

To: rsgb_lf_group@blacksheep.org

Subject: LF: ROS Latest with I/Q output

At last !!!!!!!!

 

The first software author to provide datamode stereo I/Q outputs to drive a direct image cancelling upconverter

.  

The latest version of the ROS software, Ver 5.9.8 beta, drives all my direct upconverters (LF - HF and SHF)

  http://www.g4jnt.com/IQConverters.htm    http://www.g4jnt.com/LFUpconv.pdf

perfectly,  without any need for narrowband analogue phase shift networks

 

Congratulations to Jose for listening and responding to this request.

 

The only other software I know of to provide the I/Q output option is G3PLX's SDR transmitter for SSB/FM/AM voice  http://www.g4jnt.com/SDRTxSW.htm  and one or two other 'specials'

 

There are plenty of receiver packages for Softrock. clones  and similar - now how about more SDR transmitter software.

Andy
www.g4jnt.com