Fwd: [rfamplifiers] 300W mosfet rf amp PCB's
- Hi All,
Just wanted to pass this on to the group. For anyone interested in higher power levels for their softrcoks, these PCB's might provide that answer. I'm not selling them and have no first hand knowledge of them.
This message was sent to the rfamplifiers mailing list after someone pointed out that these modules are now appearing on ebay as surplus.
1 milliwatt in, 300 watts out. But the IMD is less than spectacular, your neighbors won't be very impressed.
Below is the complete message.
From: "Dave" <emailw8nf@...>
Subject: [rfamplifiers] Re: Erbtec MRF-150 Board(s) now on ebay
Most guys tear these boards apart for the parts. However, with some
work, they could be put on the air.
I was brought on board Erbtec as the senior design engineer just as
these boards hit production...so I got to do all the massaging and
final design to make them actually manufacturable. We shipped 1400 of
them during the five years I was with the company, each one of them
used to drive a YC-156. Either the solid state amp would drive the
YC-156 directly to 5kW, or we'd put a 3CPX800A7 in as an IPA and get
20kW from the YC-156. Those were fun amps to design.
Anyway, I eventually ended up writing a service chapter for this board
for our major customer - no, it's not available in any form I know of.
Basic stuff: 300 watts at onset of saturation. The IMD at this power
level would be consistent with today's admittedly poor ham
transceivers, high 20dB range, not quite 30dBc. To get that power
output, the input level could be as low as one milliwatt. The board
has a lot of gain on board.
Starting from the output: A pair of MRF150s in push pull, driven by
what originally was a pair of MRF148s in push pull, evidently replaced
in later production by MS4550s. The MRF148s are delivering about 20
watts, and the interface from MRF148 to 150 is push-pull. To break
the amp at that point you'd have to design the correct balun. The
MRF148s are driven by a pair of MRF134s. All three stages are running
class AB, emphasis on Class A for linearity. You can break the amp at
the input to the MRF134s, and then drive it with about one watt at
The input stage is a CATV ultralinear hybrid module - the blue block
you see on the far right. This takes in about 1mW and delivers nearly
a watt output. The "string of resistors" you see is actually a string
of inductors. Between the BNC input jack and that CATV hybrid is a
switchable attenuator...zero to 40dB I think, in one dB steps. Each
stage has a 1N5767 PIN diode, and associated carbon comp 1/4 watt
resistors and choke inductors.
The biasing scheme has to be replaced. The whole thing was
accomlished by a serial string of data fed into registers. Without
the right external microprocessor to do the job, you're hosed. By
simple inspection, you can figure out the bias insertion points for
the six FETs and just add trimpots and be done with it. There's a
dandy current monitor on the board that will read the bias current
level of any one transistor when you turn it on, but will saturate at
about one amp, so it won't tell you the peak current when you're
The FET stages are all fed back, so the gain is stable versus temperature.
Freq response as supplied is about 10-90 MHz. The upper end is
dominated by the feedback around the MRF150s. The low end is
dominated by interstage coupling capacitors. By making those coupling
caps larger, you can move the low end down to about 3-4 MHz. Below
that, and you'll have to start adding windings to the ferrite
transformers. Most of those ferrites are type 61.
I've got two of the boards that I'm putting together with a power
supply (requires 48 and 24 for the FETs...since you'll discard the
digital circuitry, you don't need anything else) and a power combiner
so that I can have a ready two-tone test source for amp IMD testing.
Well, that is, I have two of these boards in a box with other parts,
but haven't actually gotten 'round to making them play.
Hope that helps in your enquiry.
--- In email@example.com, kd4e <kd4e@...> wrote:
> Can you explain the features of the boards as they
> apply to Ham radio, please?
> Power output
> Band coverage
> Amp mode "C", "AB", etc.
> SWR protection
> Also, for what is that long row of resistors?
> > A while back someone asked about the group home page picture, which
> > was a view of an Erbtec Board purchased off Ebay from CTR Surplus.
> > CTR has more of these great parts boards up for ebay auction. I have
> > nothing to do with the auction, seller other than passing the word
> > to you about this really good deal on a source of mrf-150 devices.
> > Not to mention all the other "goodies" that are part of the supplied
> > board.
> > cheers,
> > skipp
> > ERBTEC RF AMPLIFIER BOARD (2)MRF150 (2)MS4550 (2)MRF134
> > Item number: 290086495405
> Thanks! & 73, doc, KD4E
> Projects: http://ham-macguyver.bibleseven.com
> Personal: http://bibleseven.com
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