Few watt RF amplifiers

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Hi, all,

Happy New Year.  I'm working on a parts list for a medium-fancy demo  
system, and I need a couple of RF amps that are good for 2-3 W at 1 dB  
compression, over a frequency range of about 30-100 MHz.  I need them to  
drive acousto-optic deflectors.

Naturally I started with Mini Circuits, but then the sticker shock set  
in--their 1-watt amps are a couple of hundred bucks, which is okay for a  
demo, but if you really want 2W or more, they instantly jump to over a  
grand each, and pull about 12W of quiescent power!

Anybody got a good source of few-watt power amps in that range?

Thanks

Phil Hobbs
--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Few watt RF amplifiers

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You might search around for CATV amplifier modules. Especially the backhaul  
types. There may be some good deals on surplus modules.



Re: Few watt RF amplifiers
On Mon, 05 Jan 2015 20:48:37 -0500, Phil Hobbs

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What's the voltage and load impedance? There are opamps that might
work.

Can you resonate the load?


--  

John Larkin         Highland Technology, Inc
picosecond timing   laser drivers and controllers

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Re: Few watt RF amplifiers
On 1/5/2015 10:50 PM, John Larkin wrote:
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It's an octave-band acousto-optic deflector (45-90 MHz).  Pretty much 50  
ohms, apart from a 2:1 VSWR--most of the power actually goes into the  
acoustic wave.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Few watt RF amplifiers

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I searched ebay using 'rf power amplifier hf vhf uhf' without the
quotes.  

eBay has two models that give 1.5W, but the power drops off either side
of the optimum frequency. These have fairly high gain - 0dBm max input
for around 32dBm output. Here's the two results. Funny thing, the first
one gives a different price every time I click on the link.  

RF 20--500MHZ 1.5W HF VHF UHF Power Amplifier For Ham Radio
US $38.81 to US $40.94
http://cgi.ebay.com/111440519984
  
1MHz--500MHZ 1.5W HF FM VHF UHF RF Power Amplifier for ham radio +
Heatsink US $53.29
http://cgi.ebay.com/121496088135

If you really need more power, maybe two or more could be combined using
a Mini-Circuits power splitter:  

http://www.minicircuits.com/products/Splitters.shtml

Most of these are 0.5W to 1W max, which would be fine for the input
side. I could not find any that would handle 3W or more for the output.
It might take finding an Amidon core and winding your own output
combiner. Joerg would probably have a lot more info.

http://www.amidoncorp.com/ferrite-toroids/

Mini-circuits has some app notes on combiners and spltters:

http://www.minicircuits.com/app/PWR2-4.pdf
http://www.minicircuits.com/app/AN10-006.pdf
http://www.minicircuits.com/pages/appnote/do-it-yourselfsplitters.pdf

I don't know how well the amplifiers output phase would match.
Presumably a phase error of 10 degrees or less would have a small
effect. The amplifiers might be able to hold that over the part of the
frequency range that you need.  

You certainly have all the equipment needed to do it yourself!

Re: Few watt RF amplifiers
On 1/5/2015 11:06 PM, Tom Swift wrote:
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Thanks.  What I don't have is the time, and the customer is very nervous  
about schedule risk.  Since it's a demo, and this amp is a small part of  
a big system that I'm building by myself, something from an onshore  
vendor with a good track record would be very comforting.

I've gotten in touch with an outfit previously unknown to me, RF Bay  
Inc., who claim to sell a nice-looking 4W unit for $470 in onesies (p/n  
MPA-40-40), which is more in the price range I was expecting.

Cheers

Phil Hobbs


--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Few watt RF amplifiers

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In case that doesn't pan out, here's another offshore eBay item that might  
be interesting as a backup. You could ask them to ship via DHL or air  
freight and get it next week.

New 2MHz - 80MHz 5W RF Wideband Amplifiers / Frequency amplifier
power amplifier
US $63.55
http://cgi.ebay.com/121506227782


Re: Few watt RF amplifiers
On a sunny day (Tue, 06 Jan 2015 00:15:03 -0500) it happened Phil Hobbs

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Well, that is real wallpaper.

Long time ago I did some spice slimulations with NPN/PNP complementary output stages.
With the right transistors you can get to 100 MHz.
What sort of voltage and current do you need?
Else small wideband transformers can be used.
Push pull on transformer with center tap should work too.
4 W is nothing...

Re: Few watt RF amplifiers
Phil, I left you a voicemail.  I have a couple of digital Neos Technology Drivers that are  FM Capable with a internal DDS for fast sweep as well as analog AM.

Amps used for this task are transformer coupled, push pull stages. Small units use CATV bricks, ie stuff from RFPARTS.com and other vendors.  Large units use broadband RF stages right out of Helge Granberg's Motorola App Notes.

Steve  

Re: Few watt RF amplifiers
There is also  

http://www.communication-concepts.com/amplifiers/

They have a FM band amp for 375$ that may be of use.

Steve  


Re: Few watt RF amplifiers
On 01/06/2015 08:55 AM, snipped-for-privacy@gmail.com wrote:
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Thanks, Steve, you're a brick yourself. ;)  I'm going to roll my own DDS  
board, because it has to have the amplitude and phase digitizers on it  
anyway, so everything needs to be phase coherent.  I can smooth out the  
amplifier and LPF variations by dorking the DDS amplitude.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Few watt RF amplifiers
On Tuesday, January 6, 2015 10:36:33 AM UTC-5, Phil Hobbs wrote:
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Hi Phil,  lurking...  
I was hoping you would decide to roll your own.  
And I could hear /tell of a good RF power transistor.  
I've got a(n) Rb discharge lamp with a 60-80 MHz few watt oscillator.
It uses a 2N3375 (an old part that we get from advanced seimconductor.)  
I expect it to go away some day, and I'll have to find a replacement.  

George H.    

Re: Few watt RF amplifiers
George, call up the guys at RFParts, and ask them what will be stable for a few years.  Phone is (800) 737-2787

Steve  

Re: Few watt RF amplifiers
On Tuesday, January 6, 2015 3:33:01 PM UTC-5, snipped-for-privacy@gmail.com wrote:
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Ahh a second source!  Thanks Steve.  
(octoparts doesn't know everything.)

George H.  

Re: Few watt RF amplifiers
On 1/6/2015 3:56 AM, Jan Panteltje wrote:
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That's true, particularly when the application is narrowband, as in a  
ham transmitter, and there isn't too much else going on in the system.

For this job I need reasonable gain and power output flatness (say +-1  
dB) over an octave band, to drive acousto-optic cells.  The gain needs  
to be stable, because you get best deflection efficiency right near the  
point where the AOD roasts.

I'm already doing the theory, the optics, the mechanics, the RF section,  
the nulling amplitude and phase digitizer hardware and firmware, and  
software for navigation, scanning, control, deconvolution, and display.  
  For this I have some PC board layout help, but am otherwise a one-man  
band.

We got the contract in place just before Christmas, and it all has to  
ship by April and be fully acceptance-tested by May.  Plus I have a  
2-week hiatus in February to testify in a trade-secret trial, as well as  
a couple of other smaller projects.

So I'm a busy guy at the moment, and the client would rather write  
cheques than suffer delay.  Five bills isn't outrageous for a 4W  
instrumentation amp, especially with 200:1 bandwidth, but I was pretty  
surprised by Mini Circuits' jump from $220 for 1W (ZX60-100VHX+) to $535  
for 2W (ZHL-1-2W-S+) to $1k for 5W (ZHL-5W-1X).

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
We've slightly trimmed the long signature. Click to see the full one.
Re: Few watt RF amplifiers
On a sunny day (Tue, 06 Jan 2015 09:09:43 -0500) it happened Phil Hobbs

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I was talking about wideband DC - 100 MHz amps.


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Well the complementary pair itself has a gain of about 1 :-)
How you drive it is what limits things, but quite standard stuff.

High voltage versions of this, and totem pole versions using only NPN,
were common in CRT rgb drivers to >>100 MHz (pixel frequency VEGA).
 http://tinyvga.com/vga-timing

Look up the LM2406 and LM2427 datasheets for example,
although those do not go so high, the 27 can dissipate up to 10 W or so.
I tried making my own with discrete transistors, that is why the slimulation.
If you needed only a high voltage / low current that could be a solution,
there are chips for this that go much higher than those 80 MHz.

That is why I asked about voltage / current.

High power RF transistors usually are low voltage types (unless you use MOSFETs)
and driving a transformer in push pull mode with 2 is common place.
Above a few MHz you probably can use air coupled coils, but there are plenty
ferrites for that frequency.
I have a 30 MHz wide band 100W push pull transistor linear upstairs.



Re: Few watt RF amplifiers
Have you checked with ENI in Rochester, NY?  Never used their stuff  
personally but I've seen many of their amplifiers built into various mass  
spectrometers and other analytical instruments and never heard any  
complaints.  Web site is http://www.eandiltd.com/index.html , no online  
pricing but worth a look and a call or email.

Regards,
Carl Ijames carl.ijames aat deletethis verizon dott net


On 1/6/2015 3:56 AM, Jan Panteltje wrote:
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That's true, particularly when the application is narrowband, as in a
ham transmitter, and there isn't too much else going on in the system.

For this job I need reasonable gain and power output flatness (say +-1
dB) over an octave band, to drive acousto-optic cells.  The gain needs
to be stable, because you get best deflection efficiency right near the
point where the AOD roasts.

I'm already doing the theory, the optics, the mechanics, the RF section,
the nulling amplitude and phase digitizer hardware and firmware, and
software for navigation, scanning, control, deconvolution, and display.
  For this I have some PC board layout help, but am otherwise a one-man
band.

We got the contract in place just before Christmas, and it all has to
ship by April and be fully acceptance-tested by May.  Plus I have a
2-week hiatus in February to testify in a trade-secret trial, as well as
a couple of other smaller projects.

So I'm a busy guy at the moment, and the client would rather write
cheques than suffer delay.  Five bills isn't outrageous for a 4W
instrumentation amp, especially with 200:1 bandwidth, but I was pretty
surprised by Mini Circuits' jump from $220 for 1W (ZX60-100VHX+) to $535
for 2W (ZHL-1-2W-S+) to $1k for 5W (ZHL-5W-1X).

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
We've slightly trimmed the long signature. Click to see the full one.
Re: Few watt RF amplifiers

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The RF Bay Inc MPA-40-40 has impressive documentation, but it doesn't  
talk about one spec that is very important for lab work. There is no data  
on load VWSR, which could range from a short to open and everything in  
between. The reflected power could blow the output MOSFETS. It might be a  
good idea to talk to them about this.

In case it doesn't handle the load, there is another option. Thanks to  
Steve for the information on Motorola's H.O. Granberg. He wrote numerous  
articles on HF and VHF wideband amplifiers which are very informative.  

One article is AR313, a 10MHz to 150MHz 300 watt amplifier.  

You certainly don't need 300 watts, but the amplifier will operate over a  
wide range of supply voltages. This means you can drop the supply voltage  
and it will survive any VWSR you can give it.

One option might be to run it at 30 watts into a 10 dB attenuator to  
drive the acousto-optic cell. This should reduce the harmonic distortion  
and provide immunity to any reflected power. Ebay has a 100 Watt 10 dB  
2GHz attenuator for US $29.95:

http://cgi.ebay.com/330840774610

Communication Concepts, Inc, in Beavercreek, Ohio, has a nice business  
selling amplifiers based on Granberg's designs. The AR313 is $291.50  
fully assembled. It is shown on their page at

http://www.communication-concepts.com/ar313-1/

They also state:

"As the MRF141G is basically made for operation from a 28 volt supply,  
lowering the voltage down 20 volts or lower would make the unit almost  
indestructable against load mismatches such as open coax or a broken  
antenna."

With lower supply voltage and a 10 dB attenuator, your lab amplifier  
would be bulletproof.

Re: Few watt RF amplifiers

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Oops - it is a kit. But it should only take an hour or so to solder the few  
parts and mount it in a suitable enclosure. Maybe you know someone who  
could do it for you.

Re: Few watt RF amplifiers
On 01/06/2015 04:12 PM, Tom Swift wrote:
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Thanks, good point.  I'll ask RFBay about it.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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