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Author Topic: Which tube please to replace 4CX1600B?  (Read 2597 times)
KM1H
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« Reply #15 on: October 13, 2018, 09:58:33 AM »

That IMD is in the 4X150A/4CX250B class which goes back to the late 40's.  IMD was/is not important to the Russian military or commercial users since such operations are channelized.

Carl
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K6AER
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« Reply #16 on: October 14, 2018, 09:49:46 AM »

In the US the only operation of radios not channelized is ham radio. Marine, Land Mobile, Public Service, Maritime, Aviation, Military and even CB is channelized.

When the IC-7800 came out the radio was targeted for the US embassy communications which is channelized. When offered to the ham radio market they had to improve the IF filters in the 7800 for we (hams) like to operate 3 KHz away from other stations.
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KM1H
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« Reply #17 on: October 14, 2018, 11:27:41 AM »

Quote
When offered to the ham radio market they had to improve the IF filters in the 7800 for we (hams) like to operate 3 KHz away from other stations.

That is on a good day. With optional SSB filters as sharp as 1.8 kHz it is a lot closer and the crud still goes out to IMD 9 and beyond. Toss in CB sounding audio from wide open clippers/processors and it is a good reason I seldom use SSB.

Carl
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K6AER
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« Reply #18 on: October 14, 2018, 06:21:18 PM »

So as if you were God of the spectrum what should hams strive to keep as minimal separation. Non use of SSB is irrelevant.
« Last Edit: October 14, 2018, 06:23:23 PM by K6AER » Logged
K6AER
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« Reply #19 on: October 14, 2018, 06:32:08 PM »

Gil,
I looked at it again (and am looking at it right now)...and if I could copy 'n paste it here, I would..but will just snap a pic of it and post it here...

Please know that I mean no offense to you, or anyone with this amp...really, I don't!!
And, I am sorry I was off one db in my writing of its 7th order product...

Looking at the spectrum analyzer image in the ARRL Test report pdf (from the Sept 2001 issue of QST):



I see (worst case products):
-29db(PEP) for its 3rd order product
-31db(PEP) for its 5th order product
-36db(PEP) for its 7th order product (I guess I looked too casually at first, and saw -35)
-50db(PEP) for its 9th order product
-49db(PEP) for its 11th order product
-60db(PEP) for its 13th order product
-59db(PEP) for its 15th order product

John I think you should compare your quoted figures with the spectrum analyzer graph on the same page of the ARRL QST report and you may see that one of the extracted figures is incorrect?
Gil

Thank you for pointing out that I looked to casually (probably too late at night, hi hi) at the 7th order IMD product, and saw -35db...when it was actually -36db...(or maybe it was just a typo)

73,
John,  KA4WJA



Third order product looks to be 222 dB at best.
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K6AER
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« Reply #20 on: October 15, 2018, 07:14:57 AM »

That is 22 dB.
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KM1H
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« Reply #21 on: October 15, 2018, 07:33:52 AM »

So as if you were God of the spectrum what should hams strive to keep as minimal separation. Non use of SSB is irrelevant.


That is an individual choice based upon band useage at the time and we are discussing only SSB so try to stay on track.
SSB contests have their own "rules" of survive or die.
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KW4JX
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« Reply #22 on: October 16, 2018, 04:37:45 PM »

John I was only teasing you.
Perfectionism is a killer.
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