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Author Topic: RM Italy FCC Approved  (Read 24453 times)
K6AER
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Posts: 5689




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« Reply #30 on: March 23, 2016, 09:07:36 AM »

Given some heavenly power made some ham the IMD god of the universe, what would be the ideal IMD for a amplifier?

The Alpha 8410 is specified at -30 dB for the second to third harmonic on a two tone transmitter mix.

The THP-2.5 K was specified at 27 dB second to third. at 1500 watts out, Note the amplifier is in hard compression at 1800 watts out. I suspect the IMD numbers are a bit fudged.

ACOM 2000 measured third and fifth order IMD are typically 40dB and 45dB down. No mention of even order IMD numbers.

None of the published numbers are verified by any federal agency I am aware of. So with out specific measurement skills this becomes a game of liars poker.

Now the big marketing question.

So for a $2 per watt QRP amplifier what would be your design goal and would you have a market for such a product?

Does the price have to go to $3 or $4 per watt. Would a QRP fan pay $1200 ($3 per watt) for a 400 watt amplifier to be clean at 200 watts with 6 watts drive knowing his IMD is better than the latest Shack in the Box from ICOM, Yaesu and Kenwood. Mind you the low cost QRP radios have very poor IMD. Garbage in Garbage out.

Dishtronix went down that road with a $14,000, 1500 watt amplifier, the DX2400L1 ....dead end.






« Last Edit: March 23, 2016, 09:21:49 AM by K6AER » Logged
G3RZP
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« Reply #31 on: March 23, 2016, 09:43:43 AM »

Quote
No mention of even order IMD numbers.

Probably because they are covered by harmonics. F1 +/- F2, (2nd order) 2F1 + 2F2 (4th order) 3F1+/-F2 (4th order).

Of the last of the tube transceivers, the FT102 3rd order is good enough for point to point commercial HF ISB use at -38dB rel single tone of a 2 tone signal (-44dB rel PEP). Add an SB220 at 1100 watts and there's about a 6dB degradation.
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KD8MJR
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« Reply #32 on: March 23, 2016, 03:00:08 PM »


The THP-2.5 K was specified at 27 dB second to third. at 1500 watts out, Note the amplifier is in hard compression at 1800 watts out. I suspect the IMD numbers are a bit fudged.


Not sure were you got that info from but the worst case IMD for the THP-2.5Kfx was about -36dB down.
As for output, it will do 2200W PEP on certain bands, so I doubt 1800W is hard compression.  And the numbers are not fudged.
Here is a real world test of a 2.5kfx



73s
Rob
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“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
K6AER
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« Reply #33 on: March 23, 2016, 05:42:35 PM »

The -27 dB second to third is listed on a product brochure from THP.

On your analyzer photo, one third shows 31 dB the other shows 36 dB. No reference to what the power is other than -6dBm on the analyzer. That would average about 34 dB. I notice the phase noise of the exciter looks to be only down 65 dB at 10 KHz. Is the two tone source audio derived or two transmitters combined?

The 1800 watts was demonstrated by THP at Dayton in 2011 during a product review demonstration. The amplifier uses two ARF-1500 RF transistors which list their power at 750 watts from 2-40 MHz.  I would think 1800 watts was really pushing it. The HL-2.5KFX manual lists the operational Vdd at 100 VDC at 25 amps, that is 2500 watts input. At 60% efficiency (a bit hard with class AB) the output should be a maximum of 1500 watts. There is no flywheel effect with transistor amplifiers. 1500 watts CW, SSB or pulse is all the same.
« Last Edit: March 23, 2016, 06:17:39 PM by K6AER » Logged
KD8MJR
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« Reply #34 on: March 24, 2016, 10:40:10 AM »

Well My LP-100A meter will fly up to 2200W PEP on this amp if I drive it at 100 watts.
If you look at eHam reviews you will see the same comments.   I run mine at 1000 typically because the high speed fan noise is just unbearable.  As for the brochure that you saw, I have seen several brochures and none of them mentioned the IMD.
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“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
N7BMW
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« Reply #35 on: March 24, 2016, 02:37:04 PM »

Where is ZENKI???  Haven't seen him post in a long time.  I was sure he would chime in on this with his traditional rant.
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K6AER
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« Reply #36 on: March 24, 2016, 03:23:48 PM »

I know this is like red meat to a starving dog. I suspect possible health issues or ISIS is holding him ransom. If we had his ham call we could send help
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W1BR
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« Reply #37 on: March 24, 2016, 03:27:18 PM »

ZENKI???  Reply 27. One page back.
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N4ATS
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« Reply #38 on: March 24, 2016, 06:04:42 PM »

When you start to square wave, power meters become happy meters....Google it....just stick a 9 volt battery on the input of most power meters and you will read a killowatt!
« Last Edit: March 24, 2016, 06:09:32 PM by N4ATS » Logged
KK5DR
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WWW

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« Reply #39 on: March 25, 2016, 03:13:13 AM »

Just run your gear like 90% of hams do, WFO!
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HB9PJT
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« Reply #40 on: March 25, 2016, 07:16:43 AM »

Bill, I haven't found meaningful information with Google. Thank you for providing more details.

73. Peter - HB9PJT

When you start to square wave, power meters become happy meters....Google it....just stick a 9 volt battery on the input of most power meters and you will read a killowatt!
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K6AER
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« Reply #41 on: March 25, 2016, 07:34:20 AM »

When you start to square wave, power meters become happy meters....Google it....just stick a 9 volt battery on the input of most power meters and you will read a killowatt!

The RF throughput connection on a watt meter is not DC connected to the metering electronics. Putting a 9 volt batter on the RF connector will do nothing.
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W1BR
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« Reply #42 on: March 25, 2016, 08:16:54 AM »

Just run your gear like 90% of hams do, WFO!

Sure, overdrive the ALC,  put the amplifier well into compression--very effective RF clipping. Really increases "talk power and Bird Watts." 
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W3RSW
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« Reply #43 on: March 25, 2016, 08:35:29 AM »

Concerning an RF wattmeter unable to show DC, it's the transients, the rise and fall of the make and break of the 9 volt connection that will simulate the square wave.

Analogous to the way you test head phones but loaded differently of course.   You sure don't hear the DC, just the clicking of make and break.

Don't think I'll try it though.  Grin

Another fun Gordonian thread.   ...wandering into the Aether.
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Rick, W3RSW
K6AER
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« Reply #44 on: March 25, 2016, 10:21:47 AM »

Well a 9 volt battery applied to the center pin of a watt meter that is terminated into 50 ohms will produce 1/4 of a square wave. 9 volts squared divided by 50 ohms equals 1.62 watts for the rise time of 9 volts. That is 1/4 cycle at about .0000001 second. The meter will never move. Even with a peak reading watt meter you will not get a reading with only 1/4 cycle.

Now for the fun part. I took my peak reading Bird model 4314B and placed a 5 watt 2-30 MHz slug in it and set it on peak. Modulated 25 volts into the input connector at 1000 HZ square wave and the meter did not move at all. Now mind you this is a true watt meter and not a voltage sampling circuit of a cheap CB watt meter.
« Last Edit: March 25, 2016, 11:00:49 AM by K6AER » Logged
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