Multi octave does not mean 7 octaves, TWTs as far as I know are limited to about 2.5 octaves I’m sure there are ones that go beyond this but not much. The second link/paper listed below refers to reaching 2 octaves.
The IFI amp is not a TWT but a Tube amp. TWTs can only be extended a little below 1GHz. These are different technologies and different characteristics. Broad frequency coverage for powers we are talking about can not be distributed across frequency the only way to extend frequency is to either start out that with an amp module that can cover the range or have band switching. Band switching is just 2 amps in the same box only one working at a time. I’m not any TWT expert as well but do know what is available. Tim, I do believe your story and that the harmonics were the contributing factor and reason for the fire. This does make sense on what I have seen. Just having difficulty understanding how the 7th harmonic can contribute with a horn antenna that increases in gain forever. We need to get one of these on our product list :-) Not an expert on antennas by any accounts just know what’s available and their characteristics. . Thank you, Jason H. Smith Manager Applications Engineer ar rf/microwave instrumentation ________________________________ From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Haynes, Tim (SELEX GALILEO, UK) Sent: Tuesday, November 03, 2009 5:35 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: RE: [PSES] 61000-4-3 and 61000-4-20 Field Uniformity Requirements All, I did say it was an experimental multi-octave TWT amplifier. Not being a TWT expert, I could not say how this was achieved. Can TWT’s be used in a distributed line amplified configuration (as some of the wide band EMC amplifiers? E.g. IFI 400W 10kHz-200MHz amplifier circa 1982?) A quick search on the net gets a few multi-octave TWT claims – I can not verify then however (do the first two references seem a little dubious to you?? :-)) . Take a look at http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1476399 http://adsabs.harvard.edu/abs/1975MiJo...18...35G http://www.ramayes.com/TWT_Amplifier_High_Power_Microwave.htm The story is true and the cautionary note is valid. With new immunity requirements in the commercial (non-military!) field, some people will find out about TWT’s and harmonics the hard way – I though this story might help. Regards Tim ************************ Tim Haynes A1N10 Electromagnetic Engineering Specialist SELEX Sensors and Airborne Systems 300 Capability Green Luton LU1 3PG * Tel : +44 (0)1582 886239 * Fax : +44 (0)1582 795863 * Mob : +44 (0)7703 559 310 * E-mail : tim.hay...@selexgalileo.com P Please consider the environment before printing this email. There are 10 types of people in the world-those who understand binary and those who don't. J. Paxman ________________________________ From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Haynes, Tim (SELEX GALILEO, UK) Sent: 03 November 2009 10:08 To: Price, Edward; EMC-PSTC@LISTSERV.IEEE.ORG Subject: RE: [PSES] 61000-4-3 and 61000-4-20 Field Uniformity Requirements Hi Ed, The TWT only ever produced power within its operation frequency range and within the total rated power. However, as the harmonics were (more or less) the same level as the fundamental, the total power was (again, more or less) split equally between the harmonics (this gives the 1/7 factor). E.g. if the TWT was 7W total power, then the fundamental and harmonics would be each 1W of power. However, the gain of the antenna is created by directivity – and this is related to the dimensions of the antenna and the wavelength. As the frequency increases the gain or directivity increases – and the radiated power (for a fixed input power) increases with the square of the harmonic number. Hence the on axis radiated power (or power density) was 20 times higher than originally predicted due to the antenna gain at the high harmonics. I hope that this explains. Regards Tim ************************ Tim Haynes A1N10 Electromagnetic Engineering Specialist SELEX Sensors and Airborne Systems 300 Capability Green Luton LU1 3PG * Tel : +44 (0)1582 886239 * Fax : +44 (0)1582 795863 * Mob : +44 (0)7703 559 310 * E-mail : tim.hay...@selexgalileo.com P Please consider the environment before printing this email. There are 10 types of people in the world-those who understand binary and those who don't. J. Paxman ________________________________ From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Price, Edward Sent: 02 November 2009 16:48 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: RE: [PSES] 61000-4-3 and 61000-4-20 Field Uniformity Requirements Tim: I’m not doubting your story, but, I’m having some difficulty understanding where this power came from. If the sum of the incident power applied to the RAM was 20 times the level of the fundamental, then are you saying that the TWT tube was delivering 20 times its rated power, and that the amplifier was supplying 20 times its design level? And that the instrument was drawing 20 times its normal AC input power? Ed Price ed.pr...@cubic.com <blocked::mailto:ed.pr...@cubic.com> WB6WSN NARTE Certified EMC Engineer Lab Rat (day shift) Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 Military & Avionics EMC Is Our Specialty From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Haynes, Tim (SELEX GALILEO, UK) Sent: Monday, November 02, 2009 8:19 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: RE: [PSES] 61000-4-3 and 61000-4-20 Field Uniformity Requirements Dear All, A cautionary tale. Some twenty years ago, a young engineer was doing some “immunity testing” of a circuit to high power uWave. The engineer “cranked” up the power into the TWT until the output was as high as he could get. The TWT was an experimental wide-band amplifier (many octave wide). The test set-up had a horn antenna radiating towards the circuit with a block of RAM behind – all in a screened room. He had done the safety calculations for the maximum power output of the TWT, the gain of the horn at the operating frequency and the distance between horn, and the RAM was within its ratings. Then the fire started – the RAM was smouldering, choking fumes everywhere. After the “fire” was out – I was called in to investigate. I am not going to describe how this was all investigated – but the findings were that the TWT was so overdriven that the harmonics were within fractions of a dB of the fundamental. The measuring equipment could only measure to the seventh harmonic and all the harmonics and the fundamental were present. The antenna was fed with waveguide which, although overmoded, presented little in the way of attenuation at the harmonics. The antenna itself also worked quite efficiently at the harmonics and the effective gain increased with the square of the harmonic number (approximately). The power at each harmonic was approximately 1/7th of the rated TWT output Instead of there being one unit of power at the RAM he had created 1/7+4/7+9/7+16/7+25/7+36/7+49/7 = 140/7=20 times the original incident power! It is the best example of harmonic induced problems that I have ever seen. Regards Tim ************************ Tim Haynes A1N10 Electromagnetic Engineering Specialist SELEX Sensors and Airborne Systems 300 Capability Green Luton LU1 3PG * Tel : +44 (0)1582 886239 * Fax : +44 (0)1582 795863 * Mob : +44 (0)7703 559 310 * E-mail : tim.hay...@selexgalileo.com P Please consider the environment before printing this email. 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