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Author Topic: Amp solutions for QRP rigs  (Read 11183 times)
NI0Z
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« on: July 26, 2012, 10:14:57 AM »

I know, a little off topic, but I am guessing someone has the answer here.

So I know there are Amp solutions to get to 100, even 200 watts for a 10 Watt QRP rig.  Anyone found or using a solution to get to 500 to 1K watt?

Thanks in advance for entertaining my solution.  There are those of us that want both QRP and solid SSB performance out of a single rig.  I do know about the Elecraft 500 watt amp, so looking for other options.
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AE4RV
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« Reply #1 on: July 26, 2012, 10:33:38 AM »

Just stumbled upon this amp for sale, 10 in, 200 out: http://forums.qrz.com/showthread.php?355468-TX-5300-Solid-State-Amplifier

I know not exactly what you asked for but it's a new listing, take a look.
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NI0Z
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« Reply #2 on: July 26, 2012, 10:44:46 AM »

I can get up to 260 watts right now off my Ameritron 811 HD off just 10 watts in, what I really want is a solid 500 watts off 10 watts in!  Smiley.   I know, it's such a small ask!

One is always allowed to dream so long as there is no expectation that dreams become reallity.
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AE4RV
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« Reply #3 on: July 26, 2012, 10:54:54 AM »

I see, good luck.
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WB6BYU
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« Reply #4 on: July 26, 2012, 12:12:11 PM »

The notes that came with my old Ten-Tec Argonaut 505 and the matching 405 amp
(50 watts output) had a comment about using the combination to drive an additional amp.
Something like the HF Packer might give you enough of a boost to reach 500W on your
present amp.

You probably won't find anything commercially available for ham use due to the gain
restrictions on external power amplifiers (or every CBer would be using one.)  But there
have been some used in other services - I think one of the Marconi marine systems
used a 1W exciter with a matching 1KW amp.  (That would really give a Pixie or
Rock-Mite some umph!)  I had an industrial amp on 13.56 MHz based on one of the
early Motorola 1kW solid state designs that would run on 1 watt input, but it had been
biased into Class C because linearity wasn't inportant.  It ran on 50VDC @ 40A, and
would have required a fair bit of work to make it usable on the air.

Otherwise a grid-driven pair of 4CX250s might get you there.  Grid drive gives higher
gain than grounded-grid.
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NI0Z
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« Reply #5 on: July 26, 2012, 12:27:07 PM »

I wondered if double amping would be an option, so like if one could use the forth coming Elecraft amp for the KX3 to get to 70 watts and then feed that to the Ameritron.  Two thoughts came to mind though, possible distortion and whether it would be safe to even try.

Thanks for chiming in!
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WB6BYU
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« Reply #6 on: July 26, 2012, 02:51:32 PM »

No reason you couldn't do it - most transmitters are a sequence of amplifier stages,
and the only difference is that in this case they are built into 3 boxes rather than 2.
An amp that gives 1kW output with 5 watts of drive typically just has two amp stages
in series.

You might have to get a bit creative with the switching / sequencing. 

The amps shouldn't cause any more distortion than they already do.

And I can't see where there would be any more risk in that situation than
in otherwise using the amps (and rig) as they are normally used.  Each is
still within it's rated input and output power levels.
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ZENKI
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« Reply #7 on: July 27, 2012, 01:56:20 AM »

Just avoid all the Class C CB rubbish that causes a lot of splatter. Its also some of the badly designed ham amps that are just as bad as the CB amps.

Most of the ham solid state accessory amps are  nothing more than glorified CB amp designs with filtering. Filtering unfortunately cant get rid of IMD and splatter, its surprising the number of hams that think  you can filter out splatter!

These QRP radios create more problems than they solve. Companies like Elecraft would be better off designing 100 watt versions of their QRP radios with properly designed 100 watt amplifiers built in. Its easy enough to turn down the power for QRP operation. These days its easy to control the bias current versus the power output for better matching, efficiency and IMD. Adding on an accessory amp is just a mess of cables and reliability problems. Its also very bulky.
A radio like the FT857 is a good example of a well designed radio that can operate QRP or portable with a 100 watts. Compare this to a bulky KX3 and its companion amplifier. I dont personally think its worth having extra receiver performance which is not needed for portable operation when you have the inconvenience of a  bulky accessory PA.  Its just easier buying a radio like the IC7000 or FT857 if you need a 100 watt portable radio.

I dont know why the manufacturers rather just dont build a 50 watt PA into qrp radios, you can operate either at 10 watts variable, or turn the 50 watt PA on when you want extra power. Nobody would notice the extra 3db at 50 watts of output power. You could then have the best of both worlds, QRP battery operation or 50 watt high power when a power source or bigger batteries are available. Such a radio would also be a neat travel radio. To me a radio like a KX3 with an external PA is a unruly mess that I dont need in my life, there are much better solutions available even if they dont offer contest grade receiver performance. I should also stress that you will hardly challenger any receiver these days operating with a wire or portable  antenna!



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NO2A
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« Reply #8 on: July 28, 2012, 11:09:25 AM »

An AL-1500 amp might give you 500 watts out with 10 in,maybe.Not sure what 5 watts drive would do though. That`s a 15db gain amp,which you would need to accomplish that. Alinco makes a rig that will do true qrp to 100 watts.
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LA9XSA
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« Reply #9 on: July 29, 2012, 08:02:38 AM »

As WB6BYU points out, the common 100 watt radios you can buy already contain several stages of amplifiers. There is of course no difference in the signal (quality, purity or level) between a radio which has the 100 watt stage built in, and one that has an external 100 watt stage of the same quality.

Due to economies of scale, it might be cheaper to just buy one QRP radio and one 100 watt radio than buying a QRP radio with a 100 watt external amplifier, but if you've invested in a high quality QRP radio then a 100 watt amplifier could be an economical choice.

It follows that you can connect the output from the 100 watt amplifier into a 1000 watt amplifier, but the control cable setup might be a bit complicated by this daisy-chaining.

If you've come across "ZENKI" before you'll know that he has some rather "original" ideas about math, physics and radios - ideas which aren't shared by scientists, engineers and other amateurs. Since he seems to be against the idea of radios which are light enough to carry on hiking trips, I find it strange that he reads the QRP forum instead of sticking to the automobile, fixed or electric wheelchair stations where excess weight is less of an issue. Even a 10 kW AM broadcast station can be run at QRP levels, but it's not a very practical QRP setup. Neither is an IC-7000. An FT857 is what I'd call a marginal backpack radio - you can take it hiking but it is a bit of excess weight and power draw in it.
« Last Edit: July 29, 2012, 08:06:10 AM by LA9XSA » Logged
NI0Z
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« Reply #10 on: July 30, 2012, 07:58:30 AM »

I have an IC 7000 and I would not want to try and run it backpack in the field, providing enough juice for it would be problematic for sure.

The idea here is that a KX3 is really a very nice transceiver as it is a QRP rig and so if one can solve the problem outlined here then you can use it as a nice second base station Rick as well if we get the Xmit power up to 400-500 watts which is enough for my personal needs.

Anyways, thanks to all for your feedback and for answering a few of my questions!
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GILGSN
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« Reply #11 on: July 30, 2012, 03:11:04 PM »

"These QRP radios create more problems than they solve."

Well, not everyone wants or needs 100W. There is the problem of cost, size, weight, RF exposure and current draw. If I could find a radio that fits in my pocket, outputs 100W and runs on a few AA cells, I'd buy one... Until then, I don't think so. What kind of problems do these radios create? To Whom? I think using 1.5Kw creates more problems than using 5W.
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W4OP
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« Reply #12 on: July 30, 2012, 05:20:22 PM »

The SPE Expert 1K-FA will produce 500W output with 10W of drive. My 12W K3 makes as much as 800W. The gas plasma display typically reports 17dB+ of stage gain.
Not cheap, but a spectacular amplifier.

Dale W4OP
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WX7G
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« Reply #13 on: July 31, 2012, 10:54:34 AM »

Amateur HF amps are limited by FCC rules to 15 dB of gain. With 10 watts in that's 316 watts out.

http://law.justia.com/cfr/title47/47-5.0.1.1.6.4.155.9.html

« Last Edit: July 31, 2012, 10:57:30 AM by WX7G » Logged
W4OP
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« Reply #14 on: July 31, 2012, 11:15:21 AM »

That may be, but I  have owned two of the SPE amps and both  report gain as high as 17.8 dB gain and verified with my Bird meters in/out. A wonderful amp with terrific fault protection.

Dale W4OP
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