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
news
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
news
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