From: Leif Asbrink Subject: Re: [Moon-Net] EME Conference 2014 Pleumeur-Bodou To: moon-net@mailman.pe1itr.com, moon@moonbounce.info, Hi Matej, > http://www.ok2kkw.com/00003016/eme2014/eme2014bodou_eng.htm Further down the page I find your comments with a reference to me: "Personally I have to say that although I'm not so familiar with SDR problematic and I really appreciate the work of HB9DRI with SDRs, I'm a bit afraid that Alex didn't understand to all aspects of the QRO resp. QRM issue (which is by the way very different between HF and VHF because of different dynamic range) such as phase noise, etc. and if his new SDR IQ+XT will be used for real VHF contesting in mid EU region it would create significant increase of QRM" Actually it is the other way around. The IQ+XT is significantly better than commonly used transceivers. Particularly when modulated. (See my previous mail and check this article: http://www.sm5bsz.com/dynrange/dubus205/dubus205.htm) The IQ+TX is just a frequency mixer. It can not add any splatter keying clicks or other problems by a badly designed ALC. The operator is of course responsible for keeping the signal level below saturation of his power amplifier - and to make sure his power amplifier is reasonably linear. You continue: "(everybody had similar problem with OL4A and their SDR used for TX on 2m couple year ago). The new SDR was also later on discussed between SM5BSZ and OK1VPZ, so perhaps OK1VPZ will mention about it something in his report." This is where things have gone wrong. I do not know what SDR OL4A might have used. Perhaps a Flex 1500? Please do not associate the IQ-TX with faulty designs from Flex Radio!! It is much easier to make a good Tx than to make a good Rx. Nevet?theless we have today many receivers that provide a dynamic range around 150 dBc/Hz: Perseus, QS1R, SDR-IP, ANAN 100D, Excalibur (I have tested all of those) but there are most probably several more. I have not yet seen a single transmitter with matching performance. My ANAN-100D had about 20 dB excess noise in its original shape, something that could easily be cured. The original Hermes design is much better according to published data. Actually ALL transmitters I know of have serious design errors with a single exception, the IQ+TX. Alex has made a properly optimized design for the architecture he has chosen. Surely other architectures with much better performance are possible, but there is also a cost aspect... Fairly simple modifications typically improve the performance of commercial transceivers by 20 dB. (Like going from 1kW to 10 W in interference generation.) Ever since a single Multi 2000 destroyed the 2 m band in Stockholm about 40 years ago I have devoted VERY much time on the poor design of commercial amateur transmitters. Today my modified ANAN 100D provides -150 dBc/Hz on all frequency separations but my mod is not safe. There are however other, perfectly safe ways to reach that performance (or better) I hope that real VHF contesting in mid EU region will be much more fun within less than 5 years with the usage of properly designed SDRs. I have good hope that ARRL Lab will measure both phase noise and AM noise sidebands in the future. I think we will see that AM and PM noise have similar levels which is a strong indication of design errors at levels above -150 dBc/Hz or so on 144 MHz. 73 Leif