Hello,

having seen that's really difficult to make a working MOSFET linear
amplifier
for 6m, I started looking for a bipolar design and components. The
MRF448
transistors seem very expensive. Can anyone suggest an alternate part
or
a different approach (not tubes, I wanted to put this amplifier at the
antenna)?
thanks

Francesco IS0FKQ

On 16 Sep 2005 07:16:33 -0700, wrote:

Hello,

having seen that's really difficult to make a working MOSFET linear
amplifier
for 6m, I started looking for a bipolar design and components. The
MRF448
transistors seem very expensive. Can anyone suggest an alternate part
or
a different approach (not tubes, I wanted to put this amplifier at the
antenna)?
thanks

Francesco IS0FKQ

MRF492A usually under 22$US new and good for 70W or more. There are
published designs using it that work well for all modes.

Most of the VHF power mosfets are priced around $1US/Watt it seems
and are dreadfully expensive compared to bipolars.

Allison
KB1GMX

Where can I find such a design?

Dan/W4NTI

wrote in message
...
On 16 Sep 2005 07:16:33 -0700, wrote:

Hello,

having seen that's really difficult to make a working MOSFET linear
amplifier
for 6m, I started looking for a bipolar design and components. The
MRF448
transistors seem very expensive. Can anyone suggest an alternate part
or
a different approach (not tubes, I wanted to put this amplifier at the
antenna)?
thanks

Francesco IS0FKQ

MRF492A usually under 22$US new and good for 70W or more. There are
published designs using it that work well for all modes.

Most of the VHF power mosfets are priced around $1US/Watt it seems
and are dreadfully expensive compared to bipolars.

Allison
KB1GMX

Try the ARRL website under TIS. It's called the "Compact 6M brick".
It was published in the OCT 1990 QST.

The circuit is very close to the Motorola test circuit for the device
with bias for linear operation.

FAR Circuits has the board for it. I think they can supply a reprint
as well.

If thats not enough power two of them with 2 port splitter/ combiners
will get you better than anywhere from 150-180W. A Wilkinsen
splitter and combiner is fairly easy to do at 6m either as lumped
elements or maybe even coax.

Allison
KB1GMX


On Fri, 16 Sep 2005 23:11:48 GMT, "Dan/W4NTI"
wrote:

Where can I find such a design?

Dan/W4NTI

wrote in message
.. .
On 16 Sep 2005 07:16:33 -0700, wrote:

Hello,

having seen that's really difficult to make a working MOSFET linear
amplifier
for 6m, I started looking for a bipolar design and components. The
MRF448
transistors seem very expensive. Can anyone suggest an alternate part
or
a different approach (not tubes, I wanted to put this amplifier at the
antenna)?
thanks

Francesco IS0FKQ

MRF492A usually under 22$US new and good for 70W or more. There are
published designs using it that work well for all modes.

Most of the VHF power mosfets are priced around $1US/Watt it seems
and are dreadfully expensive compared to bipolars.

Allison
KB1GMX

Thanks, I'll check things out.

Dan/W4NTI

wrote in message
...
Try the ARRL website under TIS. It's called the "Compact 6M brick".
It was published in the OCT 1990 QST.

The circuit is very close to the Motorola test circuit for the device
with bias for linear operation.

FAR Circuits has the board for it. I think they can supply a reprint
as well.

If thats not enough power two of them with 2 port splitter/ combiners
will get you better than anywhere from 150-180W. A Wilkinsen
splitter and combiner is fairly easy to do at 6m either as lumped
elements or maybe even coax.

Allison
KB1GMX


On Fri, 16 Sep 2005 23:11:48 GMT, "Dan/W4NTI"
wrote:

Where can I find such a design?

Dan/W4NTI

wrote in message
. ..
On 16 Sep 2005 07:16:33 -0700, wrote:

Hello,

having seen that's really difficult to make a working MOSFET linear
amplifier
for 6m, I started looking for a bipolar design and components. The
MRF448
transistors seem very expensive. Can anyone suggest an alternate part
or
a different approach (not tubes, I wanted to put this amplifier at the
antenna)?
thanks

Francesco IS0FKQ

MRF492A usually under 22$US new and good for 70W or more. There are
published designs using it that work well for all modes.

Most of the VHF power mosfets are priced around $1US/Watt it seems
and are dreadfully expensive compared to bipolars.

Allison
KB1GMX

We pirates have made the common, ordinary IRF 510 MOSFET work much
higher than the 6M ham band-like at 88MHZ! For several months WSQT
Guerilla Radio(The Squat in DC) was on 87.9 at 10W with a single IRF
510 as the final. Details are in an old post to alt.radio.pirate. We
later went up to a dual 6146 tube final for more range, and are now
relocating because FEMA didn't like our Katrina coverage and whined to
the FCC ,who only seem to trouble us around things like Katrina or the
Inauguration. Four months of 10W and 3 at 40-50W with no trouble, but
1 1/2 weeks of Katrina coverage and they came running! Well,we'll soon
be back, but meanwhile I figured you guys would appreciate some design
info. Never have I found any article on the IRF 510 at VHF, so I did
all my own research.

Although I understand many hams don't like pirates, we read your
newsgroups and manuals to learn how to build decent transmitters that
don't pur out spurs and hash, and I figured maybe you guys would enjoy
a return of the favor.

Anyway, I've gotten 13 watts from one IRF 510, with a little over 1
watt of drive. This is with tuned input and output circuits, not
broadband. I've heard others have broadbanded these things that high,
but I can't possibly see how with all that input C! I've never sen an
article on how they did it, only a comment to my original research data
and article an alt-reaido.pirate.

That 13 watts could in turn be used to apply greater drive to
another 4 of these things either in parallel push-pull(possible
oscillation problems but I've done this with the 2N2222 for a driver),
or with resonant 3 winding combiner transformers. Estimated output: 60
watts if you get it right!

Given that I can make the IRF 510 operate at 88MHZ, it should
operate at considerable greater efficiency and gain(better input Q and
higher capacitive reactance)at 50-54 MHZ. What I want to know is this:
can any of you guys one-up me and get at least 8W from one IRF 510 on 2
meters?

If we pirates can make this device operate at 87.9MHZ, surely one of
you can get it to work at 144! Best thing about the IRF 510-it costs
less than $2 and is available at any Radio Shack!