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Author Topic: Amplifier IMD  (Read 1637 times)
KB6DYA
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Posts: 40




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« on: May 27, 2017, 10:51:07 AM »

Which amplifier has the best IMD.
 Alpha 8410 running 4cx1500b
 Acom 1500 running 4cx1000a
 OM   2000A running FU 728f
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W1QJ
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Posts: 2599




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« Reply #1 on: May 27, 2017, 11:36:25 AM »

I would say the OM amp.  But it all depends on what output you test them at. 
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KC4ZGP
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Posts: 1637




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« Reply #2 on: May 27, 2017, 12:25:39 PM »


The EB104 from Communications Concepts. It is the top-of-the-line amplifier.
All new technology.

73

Kraus
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K6AER
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Posts: 4669




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« Reply #3 on: May 27, 2017, 12:58:58 PM »

I have tested all three. They are about 41 dB on the 8410  (both tubes) and 42 dB on theo OM2000+. The exciters on the 8410 test may have been not as clean. The OM-2000+ used a pair of 7300's.  Your transceiver will be the limitation in either case. This is for the third IMD average. I posted  number numbers for the OM-2000+ a while back. Real numbers need two separate excites with good  port to port isolation on the combiner.

Both Alpha and OM Power use 3 kw transformers. Alpha-Iron and OM POWER-toroidal. The OM Power uses 4 each 900 volt power supply units in series. Little better voltage regulation. The FU728F is about a 1800 watt dissipation tube. The Alpha will almost never exceed the tube ratings even at 10,000 feet where the FCC testing was done.

BTW my measurement on the EB-104 board was no better than 23 dB, 3Rd and 25 dB, 5th at 600 watts out.  At that point with a high gain antenna up 100 feet the amplifier was a non starter.
« Last Edit: May 27, 2017, 01:19:29 PM by K6AER » Logged
KC4ZGP
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Posts: 1637




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« Reply #4 on: May 27, 2017, 06:01:48 PM »


See, I told you it's the creme de amplifiers.

73

Kraus

« Last Edit: May 27, 2017, 06:03:57 PM by KC4ZGP » Logged
G4ZOW
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Posts: 69




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« Reply #5 on: May 27, 2017, 09:03:52 PM »

Kraus,

You have a warped but dry sense of humour  Grin

G4ZOW/M
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PA0NVD
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Posts: 15




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« Reply #6 on: May 28, 2017, 03:28:10 AM »

I have two EB104 boards a little modified (one turn more at the output transformers to get approx 100 Ohms) combined in a simple combiner. The boards use BLF177 FET´s at approx 550 mA bias and I get close to 36 dB IMD3 seen at a SDR receiver at an output of 1 kW PEP  (can´t measure better than that) When driven max 1100 Watts at the Bird. They seem close to indestructable, I can transmit full power into a short, an open antenna, the wrong low pass filter, but never had a failure. The only thing is that the feedback resistors get hot at constant carrier.
So I am happy with that. Not top of the line but low cost and rugged Grin
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K6AER
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Posts: 4669




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« Reply #7 on: May 28, 2017, 12:25:42 PM »

Just so Kraus knows, the higher the IMD number the better. It is the difference between the two tone and the third level reading.

Big difference between a MRF-150 and the BLF-177 in performance. The BLF-188is is the next current level.

At Xenia I saw a company called RF-Kits from Germany. 2500 watt amplifier for $2800. Nice looking unit with touch screen operation. Lightweight and mid size.
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K1ZJH
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Posts: 3303




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« Reply #8 on: May 28, 2017, 12:37:43 PM »

Just so Kraus knows, the higher the IMD number the better. It is the difference between the two tone and the third level reading.

Big difference between a MRF-150 and the BLF-177 in performance. The BLF-188is is the next current level.

At Xenia I saw a company called RF-Kits from Germany. 2500 watt amplifier for $2800. Nice looking unit with touch screen operation. Lightweight and mid size.

Your IMD data is based on the difference, with no -6dB correction?

Pete
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K6AER
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Posts: 4669




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« Reply #9 on: May 28, 2017, 01:53:59 PM »

My reference  was from the combined two tone. Not from the single tone which adds 6dB like the ARRL does.
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G3RZP
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Posts: 8123




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« Reply #10 on: May 29, 2017, 07:21:26 AM »

The important part is IMD5, 7, 9, 11 and possibly even higher, as these are the really antisocial intermodulation products, and were generally negligible - at least above 5th order - in tube amplifiers. The mathematics of device transfer functions tells one that they aren't so negligible in SS amplifiers unless special measures are taken.
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