|
THanks, very interesting. I wonder if anyone's tried paralleling up
half a dozen of 'em for more power? ================================== Mind in-&output capacitances ,which add-on when parallelling. Frank GM0CSZ / KN6WH |
Highland Ham wrote:
THanks, very interesting. I wonder if anyone's tried paralleling up half a dozen of 'em for more power? ================================== Mind in-&output capacitances ,which add-on when parallelling. Frank GM0CSZ / KN6WH Not to mention that "critical layout". -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
Highland Ham wrote:
THanks, very interesting. I wonder if anyone's tried paralleling up half a dozen of 'em for more power? ================================== Mind in-&output capacitances ,which add-on when parallelling. Frank GM0CSZ / KN6WH Not to mention that "critical layout". -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
On Thu, 6 May 2004 17:56:06 +0100, "Highland Ham"
wrote: THanks, very interesting. I wonder if anyone's tried paralleling up half a dozen of 'em for more power? ================================== Mind in-&output capacitances ,which add-on when parallelling. Indeed, but there must be some current-pumping circuit that might assist here? -- The BBC: licenced at public expense to spread lies. |
On Thu, 6 May 2004 17:56:06 +0100, "Highland Ham"
wrote: THanks, very interesting. I wonder if anyone's tried paralleling up half a dozen of 'em for more power? ================================== Mind in-&output capacitances ,which add-on when parallelling. Indeed, but there must be some current-pumping circuit that might assist here? -- The BBC: licenced at public expense to spread lies. |
"Walter Harley" wrote in message ... Modern commercial radio transmitters (including FM band, 88-108MHz) by, e.g., Harris use MOSFETs. So clearly it is possible to get up to 25kW. I believe they also use them in 100kW AM band transmitters. A bit of meandering on Harris' web page will tell you more. I rather doubt that there are any tube-type 50 kW AM broadcast band transmitters sold these days. The 50 kW solid state Harris unit seems to be extremely widely used. Such transmitters use lots of hot-swappable modules - and can operate quite well with a few modules removed. At least some of these high-power AM rigs are essentially huge D-to-A converters. Look in the IEEE Transactions on Broadcasting for some ideas. The 88-108 MHz units are conventional amplifiers, made of a number of modules and combiners. The trick in the near future is adding IBOC digital to these rigs without non-linearities and unacceptable mixing products. Although "digital", the RF is of course analog in nature. I gather that solid state rigs accommodating IBOC were at the NAB show a couple of weeks ago. When WTOP was running IBOC tests on 1500 kHz I don't know whether they were using their main solid state 50 kW Harris rig or the tube Continental 50 kW backup. |
"Walter Harley" wrote in message ... Modern commercial radio transmitters (including FM band, 88-108MHz) by, e.g., Harris use MOSFETs. So clearly it is possible to get up to 25kW. I believe they also use them in 100kW AM band transmitters. A bit of meandering on Harris' web page will tell you more. I rather doubt that there are any tube-type 50 kW AM broadcast band transmitters sold these days. The 50 kW solid state Harris unit seems to be extremely widely used. Such transmitters use lots of hot-swappable modules - and can operate quite well with a few modules removed. At least some of these high-power AM rigs are essentially huge D-to-A converters. Look in the IEEE Transactions on Broadcasting for some ideas. The 88-108 MHz units are conventional amplifiers, made of a number of modules and combiners. The trick in the near future is adding IBOC digital to these rigs without non-linearities and unacceptable mixing products. Although "digital", the RF is of course analog in nature. I gather that solid state rigs accommodating IBOC were at the NAB show a couple of weeks ago. When WTOP was running IBOC tests on 1500 kHz I don't know whether they were using their main solid state 50 kW Harris rig or the tube Continental 50 kW backup. |
"Walter Harley" wrote in message ... "Paul Burridge" wrote in message ... On Wed, 05 May 2004 20:13:01 -0400, Ken Scharf wrote: Mosfets in the MRF5xx series (511, 521 for example) have been used up to the 10 meter band with good results. A pair of them can give at least 50w pep output. Depending on the input/output circuitry used and the transistor they require 12-28v power supply. Layout is somewhat critical. THanks, very interesting. I wonder if anyone's tried paralleling up half a dozen of 'em for more power? Modern commercial radio transmitters (including FM band, 88-108MHz) by, e.g., Harris use MOSFETs. So clearly it is possible to get up to 25kW. I believe they also use them in 100kW AM band transmitters. A bit of meandering on Harris' web page will tell you more. Their AM transmitter combines the outputs of 60 some modules to get the instantanous PEP they need. All modules are fed the same square wave signal, and modules run class E (I think). They don't say what the sampling rate is, but I would guess ~20 KHz. There is a WLW related web site that has more info than the Harris site. If I run across it again, I will post it. Tam |
"Walter Harley" wrote in message ... "Paul Burridge" wrote in message ... On Wed, 05 May 2004 20:13:01 -0400, Ken Scharf wrote: Mosfets in the MRF5xx series (511, 521 for example) have been used up to the 10 meter band with good results. A pair of them can give at least 50w pep output. Depending on the input/output circuitry used and the transistor they require 12-28v power supply. Layout is somewhat critical. THanks, very interesting. I wonder if anyone's tried paralleling up half a dozen of 'em for more power? Modern commercial radio transmitters (including FM band, 88-108MHz) by, e.g., Harris use MOSFETs. So clearly it is possible to get up to 25kW. I believe they also use them in 100kW AM band transmitters. A bit of meandering on Harris' web page will tell you more. Their AM transmitter combines the outputs of 60 some modules to get the instantanous PEP they need. All modules are fed the same square wave signal, and modules run class E (I think). They don't say what the sampling rate is, but I would guess ~20 KHz. There is a WLW related web site that has more info than the Harris site. If I run across it again, I will post it. Tam |
On 6 May 2004 21:13:57 GMT, "Walter Harley"
wrote: THanks, very interesting. I wonder if anyone's tried paralleling up half a dozen of 'em for more power? Directly parallelling the semiconductors have several drawbacks. First of all, the capacitances are in parallel thus limiting the frequency response. Also load sharing between the semiconductors can be hard to achieve. Modern commercial radio transmitters (including FM band, 88-108MHz) by, e.g., Harris use MOSFETs. So clearly it is possible to get up to 25kW. I believe they also use them in 100kW AM band transmitters. A bit of meandering on Harris' web page will tell you more. They are complete amplifier modules with well specified output impedances that are combined. If e.g. Wilkinson dividers/combiners are used, these have a limited bandwidth, but this is usually not a big issue in broadcasting, in which the frequency remains the same and if changes are needed, the relative frequency range is limited. However, Wilkinson dividers and combiners would not be suitable for 1.8-50 MHz amateur linear amplifier due to the huge relative frequency range. Paul OH3LWR |
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