73 de Alex, HB9DRI

From: ok1teh Petrzilka [mailto:ok1teh{zavináč}seznam.cz]
Sent: Mittwoch, 1. Oktober 2014 10:27
To: hb9dri{zavináč}emeham.com
Cc: moon-net{zavináč}googlegroups.com; linrad{zavináč}googlegroups.com; moon-net{zavináč}mailman.pe1itr.com

73 Matej, OK1TEH

73 de Alex, HB9DRI

Dear all

Although my English is rather poor, I will try express here my short opinion to Alex's quite arrogant message. Please take it as it is: I am not novice on VHF and for sure not ignorant as he wrote. And even not some "no name" stupid boy from the East as Alex thinking. I was always focused to the EMC and particularly QRM issue in central EU contesting - already within last 30 years. Alex should to know, that we have produced in OK 30 years ago transceivers with optimized sideband noise performance, which were better from such view, than any on his list. And even I could put here for him a question, why somebody, who doesn't understand the QRM problematic in VHF contesting now become so critical to the personal opinion, what has written on one private web page? And how many IARU VHF/UHF Contests he won? How many QRO+ contest competitors he has again and again in 20km distance? Or... No, I don't want to be as somebody is. It is below my dignity.

Let's look on the issue with cold head:

I wrote on our web page: "Due to my opinion Alex has little bit too much business look on this matter and some of his specific technical conclusions we found, let's say as a little bit too optimistic. Particularly VHF contest operation in Central EU has it's own specific technical categories and optimism are not in place."

Yes English is not good, but it is a clear expression. And still it is my belief. Why?

Commercial transceivers performance is not good enough to fulfil needs of QRO VHF contesting in central EU. Yes, K3 is a bit better, but still far away not enough. We are running contests in very dense populated areas and average distance between one to more QRO stations is about 25km. If you will calculate, what will be the noise level from near competitor, even if the best transceivers on both sites will be used, the noise level will be above S9. So, some additional smart solution is needed to be able make some valuable contest QSOs. Who has interest to know more about it, here is my poor translation of presentation, written for Polish VHF meeting this year: http://www.ok2kkw.com/zzz/qrm_w_zawodach_ok1vpz_en.pdf

However phase noise as well as the sideband noise (what difference in between!) are not the only critical phenomena, which have significant influence in the QRM issue. It could be very complex issue. Each theory is grey, green tree of life! For example ingress from your own antenna may be spreaded around and go back into bad screened exciter, running on low level. And particularly into the oscillator, where the loop must suddenly correct influence of high level of EM field into each active component. Commercial transceiver, even the worst noisy legendary TS770 had very well screened LO as well as all low signal level parts of transmitting chain. How looks the mechanical solution of the "reverse SDR"? How good screening is used? And what about the noise from supplying? And how looks the LC circuit of LO? As high as possible Q of LC resonator circuitry is significant part of long way to get low noise level from the LO. How high Q has LO in presented gadget? And it is not the only one group of questions - what about DAC? What dynamic range has the used DAC? How sensitive will be LO for vibrations? Any vibrations - for example from the fan from near PC may have significant influence to the LO phase noise performance. And next - what about intermodulations? The LTC5598 IQ modulator has in datasheet max output level for acceptable IMD less, than 3dBm. How bad will be the IMD in the presented "reverse SDR", if the author declares output level + 20dBm. SSB is not a FSK... I will not continue in more suspicions, why not to use it in contesting and repeat only the expression, written in the report: "VHF contest operation in Central EU has it's own specific technical categories and optimism are not in place." Next time, when you will look forward to participate in such hard core operation and you want to run QRO station, I would say: please do not use this toy. It will be in your interest as well as in the interest of all others up to 100km distance!

I have asked Alex to borrow me his product for testing, but he refused... OK, maybe it really is so good as he declares. But based on his declaration only I will not to buy it.

But anyway - it is nothing against Alex. He made an excellent job, not only in IQ SDR for both polarizations antenna for EME, but as well as with his experiments, which may help to designers find a way to a "new generation" equipment, already usable in VHF contesting, hi. And present "reverse SDR" may be for sure successfuly used in EME operation, where almost everything (except PA) is very different compare to VHF contesting.

For final: experience and knowledge of all complex aspects in EMC creates humbleness. And oposite - lack of it helps to intumescence of Ego only. And such ego is not good advisor, believe me. We should be rather modest and take all of such novelties with suspicion. And if it is really so good - well any of us want to have real happy day time to time. Isn's it?.. :-)

Best 73 to all! Vlada OK1VPZ

BTW: I have participated on first EME tests in OK on 2m already on early 80-ties, if someone remember OK1KRA call. Later on I am rather in the back of complete contesting team below OK2KKW and OK2A calls.