Homebrew 2m (and maybe 70cm) linear (solid state, 20~30W)
Stuart Longland
here]
Hi all,
I was wondering if anyone knew of a solid state 2m linear amp project
that I could build. I'm looking for no more than about 30W. It'll be
primarily used for FM, driven from my handheld radio. Bonus points if
it can do 70cm too (or at least allow pass-through unattenuated...).
Most of the designs I've seen are for tubes with an output power in
the KW-range... my radio license only allows me to transmit 30W FM or
100W SSB... so these are massive overkill (and not desirable for other
reasons).
The only project I've seen that fits the bill so far is
http://www.falara.org/tektalk/GPOAmp.html which calls for a PCB made
with G10 stock. I have no idea where to obtain that here in Brisbane,
I have some blank PCB, but have no idea what grade it is, or how much
impact on performance using it would have. The MRF1946A is also
difficult to source.
Does anyone know of a good project to start on this sort of thing?
Regards,
Stuart Longland (VK4MSL)
Scott
You can homebrew a very simple amp that should meet your specifications...
A generic PC board can be found at http://www.rfparts.com/pcb.html
and I would recommend part number DEM2330. There is a link to "View a
pdf of the DEM2330 Instruction Sheet." You could build everything as
they show in the instruction sheet (which is for a 1300 MHz amp) and
just substitute the RF module with the Mitsubishi RA30H1317M module for
2M or the RA30H4045MR for 70cm. The data sheets for the modules are at
http://www.rfparts.com/module_sau-sav.html#ra and there are also more
module choices there. Both modules specify an input power of 50 mW
maximum, so you would need an attenuator (pi type is easily done by
cutting a break in the input lead on the circuit board and installing
the correct resistors around the cut). If you have 1.5W from the HT,
you would need about 16 dB of attenuation. You would need a pair of RF
relays, one at the input and one at the output to route TX signals
through the amp on TX and bypass around the amp during RX.
Good luck with the project!
73,
Scott
N0EDV
Stuart Longland
> You can homebrew a very simple amp that should meet your specifications...
>
> and I would recommend part number DEM2330. There is a link to "View a
> pdf of the DEM2330 Instruction Sheet." You could build everything as
> they show in the instruction sheet (which is for a 1300 MHz amp) and
> just substitute the RF module with the Mitsubishi RA30H1317M module for
> module choices there.
Ahh right... I had a look around, looks like Minikits[1] sell the
power modules (and even a PCB). This looks promising.
> Both modules specify an input power of 50 mW
> maximum, so you would need an attenuator (pi type is easily done by
> cutting a break in the input lead on the circuit board and installing
> the correct resistors around the cut). If you have 1.5W from the HT,
> you would need about 16 dB of attenuation.
The handheld can be wound right back to 50mW when running off
batteries... otherwise 0.5W. A pi network isn't hard though. That
said... I won't make the mistake I made last time -- last time I tried
making it with 5W wire wound resistors... and wondered why it didn't
work.
I shall do some further investigation.
Thanks.
Stuart Longland VK4MSL
1. http://www.minikits.com.au/kits2.html
Rob
> Ahh right... I had a look around, looks like Minikits[1] sell the
> power modules (and even a PCB). This looks promising.
Maybe with some more searching you can find PCBs that include the tx/rx
switching, preferably with PIN diodes. That will save you a lot of
money and construction effort.
(with a bare amplifier PCB as shown on that site, you will need relays
and a circuit to drive them when transmitting, in addition to the
amplifier PCB)
> The handheld can be wound right back to 50mW when running off
> batteries... otherwise 0.5W. A pi network isn't hard though. That
> said... I won't make the mistake I made last time -- last time I tried
> making it with 5W wire wound resistors... and wondered why it didn't
> work.
It is better not to rely solely on lowpower settings of the handheld,
as sooner or later you'll forget to set it to lowpower, it will drive
5W into the module, and destroy it.
So it is best to have some attenuation in front of the module, such that
it will survive accidental input of the full power of the handheld.
You can then still use lower power in normal use, so the handheld will
not run too hot. Find the maximum allowable input power for the module
and design the pi network so it will attenuate the highest output power
of the handheld sufficiently. Then calculate the nominal power to
the module (for driving it to e.g. 90% of its max output) and use the
handheld at that power level. That could be 0.5 W or so.
Robert Cherry
Stuart,
Unless you absolutely want the experience of building, you may (I don't
know the situation in Australia) be able to find a used mobile 2m or
2m/70cm tranceiver for a reasonable price. My used Yaesu FT-2800M cost
me 100 Canadian dollars. I had been thinking of buying an amp for my HT
but discovered it is easier to simply buy a transceiver that gives me 25
watts along with 3 other power choices.
I hope the suggestion helps.
Robert VE2AGE
Gatineau, Quebec
Canada
--
Robert Cherry
Bob Spooner
news:Robert.Che...@radiobanter.com...
Yes, and the transceiver will give you an additional advantage over your
handheld - better dynamic range on receive because the filtering is better
because there's more space for good filters.
73,
Bob AD3K
Tim Wescott
Tim Wescott
If one were very clever one may be able to make the last leg of the
attenuator a pair of back-to-back diodes that would clip at a moderately
low level, protecting the module while still allowing it to work when you
_do_ set the radio to low power.
I'd have to work through the details to see if it's feasible, but it sure
sounds cool.
Rob
> If one were very clever one may be able to make the last leg of the
> attenuator a pair of back-to-back diodes that would clip at a moderately
> low level, protecting the module while still allowing it to work when you
> _do_ set the radio to low power.
I don't think it is a good idea to have a signal clipped by diodes,
then amplified by a wideband amplifier and fed into a transmitting antenna.
But hey, to each his likings!
Scott
>
> If one were very clever one may be able to make the last leg of the
> attenuator a pair of back-to-back diodes that would clip at a moderately
> low level, protecting the module while still allowing it to work when you
> _do_ set the radio to low power.
>
> I'd have to work through the details to see if it's feasible, but it sure
> sounds cool.
>
You mean like a pin diode attenuator controlled by a sort of ALC? ;)
Scott
N0EDV
Scott
...And wallet size if FCC attention is grabbed ;)
Stuart Longland
Robert Cherry wrote:
> Stuart Longland;685473 Wrote:
> > I was wondering if anyone knew of a solid state 2m linear amp project
> > that I could build. I'm looking for no more than about 30W. It'll be
> > primarily used for FM, driven from my handheld radio. Bonus points if
> > it can do 70cm too (or at least allow pass-through unattenuated...).
>
> Stuart,
>
> Unless you absolutely want the experience of building, you may (I don't
> know the situation in Australia) be able to find a used mobile 2m or
> 2m/70cm tranceiver for a reasonable price. My used Yaesu FT-2800M cost
> me 100 Canadian dollars. I had been thinking of buying an amp for my HT
> but discovered it is easier to simply buy a transceiver that gives me 25
> watts along with 3 other power choices.
This is the ultimate aim... will be to purchase a newer radio. I have
my eyes set on a FT-897D, but it'll require quite some saving to
acquire the necessary cash.
I would still like to homebrew a linear amp though, as the final stage
for homebrew transceivers. This would be something that I'd be
looking to do in order to improve my understanding of
radiocommunications.
I'm also aware that I need not use a linear amp for FM (or CW/PSK,
class-C amps work for these modes), but since the homebrewing
mentioned above may also include AM and SSB, I figure a linear is
going to give me much better flexibility.
highlandham
> snip
> class-C amps work for these modes), but since the homebrewing
> mentioned above may also include AM and SSB, I figure a linear is
> going to give me much better flexibility.
Before considering a RF power amplifier for SSB operation ,get the best
possible antenna(s) for the relevant bands .
These will give you even better fexibility .
Frank GM0CSZ / KN6WH