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Author Topic: A filtering question  (Read 2732 times)
ZL3OF
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Posts: 20




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« Reply #15 on: April 05, 2014, 12:56:03 AM »

Anything is possible.   12 volt amplifiers regardless of who makes them make poor home station amplifiers. ......................It would have been smarter to buy the FT857 then you would not have to worry about the mess of an external amplifier, their signals would have been a lot cleaner as well.

Does the FT857 not have a 12 volt PA built into it, is it 50 volt?
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G3RZP
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Posts: 4393




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« Reply #16 on: April 05, 2014, 02:20:54 AM »

Zenki,

Under the international Radio Regulations (to which the US has signed up but the FCC managed to implement incorrectly), even amateur transmitters must meet the requirements of ITU-R Rec. SM329. Interestingly, it is a very convoluted route through the RRs that brings that out. The SM 329 requirement for amateur equipment requires 'unwanted emissions in the spurious domain'  to be at 43dB + 10 log P down, but not needing to be more than 50dB down for transmitters operating below 30MHz and not more than 70 dB down for transmitters operating above 30MHz. (Harmonics above 30MHz from transmitters operating  below 30MHz were not considered, and the Chairman of the ITU Task Group decided it was easier not wake that sleeping dog up!) The spurious domain starts at 250% of the necessary bandwidth: the pragmatic approach is to use the occupied bandwidth (effectively the -20dB bandwidth) as the necessary bandwidth, so for an SSB transmission, that's 7kHz away from the centre of the transmission or say 8.4kHz away from the carrier. Now, who checks that this is really the case? There's no real type approval regime and in Europe, a manufacturer can self certify. Incidentally, the RR requirements apply to all transmitters after Jan 1 2012, regardless of when they were manufactured.

Those Yaesu transceivers which allowed the use of Class A in the PA were much cleaner than most, being of the same order as the last generation of tube transceivers....I covered this in my talk at last year's RSGB Convention, entitled 'Spreading the Sewage' (a title somewhat more genteel than 'Slinging the S***!). An analysis of over 130 transmitters/transceivers going back to 1973 or so showed how bad the solid state rigs are, especially on high order IMD - except for those few Yaesu rigs which optional room heaters when in Class A!
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ZENKI
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Posts: 906




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« Reply #17 on: April 05, 2014, 04:01:57 AM »

OK Peter

The best standard which should have been the amateur standard was the old FCC Part 80 rules for marine SSB. This standard had a well defined IMD mask which  required the 3rd order IMD to be down -30db below 1 of 2 tones. From the 5th order to the 9th order it was a few Db more, I seem recall 6db. From the 11th order and higher all products had to be 43db+10log the power exactly the same as the ITU standards. This was for IMD performance not spurious or harmonic  limits.
The net result was that marine transmitters certified under this regime were excellent transmitters.

Well the FCC does Type Certify ham transmitters and  thats why if the laws were introduced in the US market the result will be a win for hams right across the world. I dont detect a momentum from the leadership and societies like  the ARRL. Our best hope is that companies Yaesu, Icom, Kenwood etal all introduce pre-distortion technology into their product line. Lets be clear that there should be one IMD standard for all ham transmitters regardless of the price.

As for the Yaesu MK5 in ClassA. It certainly had excellent  IMD performance in class A. However the MK5 in class A also suffered from ALC induced compression which degraded the ultimate IMD performance. ALC induced splatter is more of a issue than final 2 tone IMD performance.  God help you if you have a close ham neighbor who runs one of the Icom 756 PRO series of radios. The ALC and crud that comes out of this brand of radio is horrendous. The sad part about this debate is that there is not one ham transceiver on the market that one could  say is a perfect transmitter design free from the design faults  that causes splatter. Thats a damning indictment of the ham transceiver industry.



Zenki,

Under the international Radio Regulations (to which the US has signed up but the FCC managed to implement incorrectly), even amateur transmitters must meet the requirements of ITU-R Rec. SM329. Interestingly, it is a very convoluted route through the RRs that brings that out. The SM 329 requirement for amateur equipment requires 'unwanted emissions in the spurious domain'  to be at 43dB + 10 log P down, but not needing to be more than 50dB down for transmitters operating below 30MHz and not more than 70 dB down for transmitters operating above 30MHz. (Harmonics above 30MHz from transmitters operating  below 30MHz were not considered, and the Chairman of the ITU Task Group decided it was easier not wake that sleeping dog up!) The spurious domain starts at 250% of the necessary bandwidth: the pragmatic approach is to use the occupied bandwidth (effectively the -20dB bandwidth) as the necessary bandwidth, so for an SSB transmission, that's 7kHz away from the centre of the transmission or say 8.4kHz away from the carrier. Now, who checks that this is really the case? There's no real type approval regime and in Europe, a manufacturer can self certify. Incidentally, the RR requirements apply to all transmitters after Jan 1 2012, regardless of when they were manufactured.  If you want Benchmark reference try the Collins HF8014, Racal MA7013 drive unit or  some of the early Telefunken driver units. Granted that these units were 100mw type exciters however they had perfectly designed transmitter would  a knob called the drive control rather than a horrendous ALC knob and meter. Its astonishing that one would even use a  feedback loop that does not even have a peak detection circuit  for power or compression adjustment. Its closing the door well after the horses have bolted and are grazing in the north pole!

Well maybe with experts like yourself publicizing the issue someone will take notice and try and make some recommendations. A future article from you like "How much transmitter IMD performance do you need" would be a great article for QEX that might open the eyes of more hams.  At the end of  day it will be some progressive company like Apache Labs  or Elecraft that might introduce and make pre-distortion radios available off the shelf. Certainly all the other manufacturers are intent on selling junk transmitters.

Those Yaesu transceivers which allowed the use of Class A in the PA were much cleaner than most, being of the same order as the last generation of tube transceivers....I covered this in my talk at last year's RSGB Convention, entitled 'Spreading the Sewage' (a title somewhat more genteel than 'Slinging the S***!). An analysis of over 130 transmitters/transceivers going back to 1973 or so showed how bad the solid state rigs are, especially on high order IMD - except for those few Yaesu rigs which optional room heaters when in Class A!
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W9WQA
Member

Posts: 125




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« Reply #18 on: April 05, 2014, 01:28:49 PM »

Quote
My third plan, which is the primary focus of this post, is to use one of the broad band PA stages that seem to be everywhere at the moment that have no real band pass filtering as an intermediate

where are these available. id like to look at some to see where they might fit.

i have some ss 9000 that have amps that are hard to keep alive and id like to try something new.

??
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G3RZP
Member

Posts: 4393




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« Reply #19 on: April 06, 2014, 01:36:01 AM »

Zenki,

I am firmly of the opinion that ALC is misused more than correctly used....My FT102 is a perfect example, which is why I run it a mode where the ALC doesn't get used. In fact, I'm considering that the next time I open it up, I'll look at removing the ALC.

Plus doing something about the too fine pitch metric screws fitting into an aluminium casting so the casting threads soon give up!

It's many years since I designed a marine radio transmitter: then the requirement was for 3rd order to be -31dB on PEP, which isn't that great.  The current ETSI standard requires testing with a 2 tone signal such that all IMD products are more than 1.5kHz from the assigned frequency (1.4kHz above the suppressed carrier). The limits are

1.5 to 4.5 kHz away from assigned frequency >-31dB rel PEP
4.5 to 7.5 kHz away from assigned frequency >-38dB rel PEP
>7.5kHz away from assigned frequency >-43dB rel PEP not exceeding 50mW

Which is not as stringent on high order products as the SM329 requirement for amateur equipment. 

That ETSI standard complies with  the International Maritime Organization (IMO) and ITU requirements included in the relevant provisions of the Radio Regulations, the International Convention for the Safety Of Life At Sea, the IMO Resolutions A.694 and A806. The performance required meets the SOLAS and EU Maritime Directive requirements.

There is no requirement for 'Type Approval' as such in Europe for any radio equipment: provided a manufacturer has a suitable Technical File and suitable (i.e. ISO 9000 or equivalent) QA system, it is permissible to self certify against ETSI  and any applicable CENELEC standards. Interestingly, the major cause (70% of cases) of non-compliance was found to be in the paperwork when the EU did a survey! Even more interesting is that not all Administrations and Test houses agree on exactly what information the paperwork should contain.....

So internationally, the maritime world is probably not that much better than the amateur world.
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W3RSW
Member

Posts: 78




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« Reply #20 on: April 06, 2014, 06:57:23 AM »

Various governments may regulate emission spectral purity sufficiently to protect frequencies outside the ham-bands. Inside the bands the market should be allowed to dictate standards provided emissions are clean enough to stay in camp.

Similar to the evolution of the everyday automobile, heat, hydraulic brakes, automatic transmissions, streamlining, electric everything accessories including radio and other electronic marvels , air-conditioning and now even collision avoidance , were progressively added over the decades.

 Regulation only sped up what would have been a market progression, say for example fuel consumption.  Mechanical fuel pump injection in race cars was jus one of the later trends that would have become standard for Everyman anyway.  This even in pre IC days.

Once people saw their neighbors driving the latest. Longest, widest, meanest, more horsepower chariot then better cars became "must haves."  Same is true these days for the gradual advancement of  better fuel efficiency and superior suspensions.

So Johnny Ham, once he and an increasing majority of hams realize that his $5000 to $10,000 radio is dirty, will demand that for that kind of money he'll have something to brag about to his buddies...   Or more to the point, not get teased about or worse.  The improved technology will filter down to the lesser rigs if not statically arrested by regulation.

It's up to the Zenki's of the world to keep up the drum beat, to shed the light on TeeRash so that a decent manufacturing standard becomes the norm.  Asking for governmental regulation should not have to be the way.  That just increases the number of people with cushy jobs and your tax rates.
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