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Author Topic: Amp solutions for QRP rigs  (Read 20387 times)

Posts: 1556

« Reply #15 on: July 31, 2012, 04:58:32 PM »

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

Dale is correct.  I've always wondered how SPE got around the 15dB FCC limit.
Phil - AD5X

Posts: 376

« Reply #16 on: July 31, 2012, 05:46:44 PM »

While section 97.317 contains the standards for certification of amateur amplifiers, including the 15 dB gain limit, sub-paragraph 97.315 (b) (3) seems to say that if the manufacturer, importer or dealer makes sure that they only sell to licensed hams, the amplifier doesn't need certification - just like if the ham built it themselves.

As I understand it, this makes it easy to market amplifiers that are gain-limited and CB-blocked, since they can sell them to anybody, but it also makes it possible to sell higher performance amplifiers to verified hams; the tradeoff is that it takes a bit more of due diligence and record keeping to sell non-certified amplifiers legally.
« Last Edit: July 31, 2012, 05:52:31 PM by LA9XSA » Logged

Posts: 128


« Reply #17 on: August 01, 2012, 12:22:54 PM »

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.

Because many QRP operators don't want to pay for something they will never use, or carry extra weight they will never use, because a radio that has 50w output doesn't fit the generally accepted standard of "QRP radio", etc.

Nobody would notice the extra 3db at 50 watts of output power.

That totally depends on condx, antennas, etc.  If 3db makes a difference at the 5 watt level, it would at the 50 watt level also.

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!
Here we go again...sheesh!

My FT817ND's RX is definitely challenged using a portable wire antenna at times.


Posts: 683


« Reply #18 on: August 02, 2012, 06:33:51 AM »

Wow!  That is a nice looking amp spec wise!  Thanks for sharing this, I have never come across it before when I was looking for Amps.  This looks like a really nice item to put on my wish list!


Posts: 683


« Reply #19 on: August 02, 2012, 06:49:37 AM »

Thanks to all for your input here!  There are certainly lots of viable options and short term I am going to see what my little AL811HD can do with the KX3 when it shows up.  It might just be enough power.

QRP is intriguing and very challenging.  Certainly more power makes things easier and even the 500 watts I typically run for tough DX's sometimes isn't enough to break pileups.  The Hex beam I put up did as much if not more for me than the amp itself ever did.

Learning about propogation forecasts and good DXing skills I think is what makes QRP even more rewarding.  It takes either luck or solid skills to make those low watt long DXs.  When we make them using our skills the thrill and high we get is exhilarating. 

Having a light light rig one can carry along like a nice small portable shortwave radio is going to be really nice.  In my case it's use will be somewhat limited as far as portable work goes.  So, being able to hook it up in the shack and run a little extra power for SSB is all I am really looking for.  It will be fun to try some QRP on the hex as well and see if I can home those skills.

Thanks again!



Posts: 1

« Reply #20 on: October 06, 2013, 04:51:38 AM »

Has anybody had success finding an amp that will get the KX3 close to 500W??  Daisy chaining a KXPA100 to something else seems like too expensive an option...   15dB....roger...   73

Posts: 7718

« Reply #21 on: October 06, 2013, 09:43:14 AM »

A few years ago - I think it was on eham, W8JI (the designer of the ALS-600), said the gain could be increased for QRP input levels.

I think the mod consists of changing the feedback resistors R225-230 (22 ohm, 2 watt). To increase gain by 6 dB (enough to allow the KX3 to drive it to full power) you could try changing R225-230 to from 22 to 47 or 100 ohms. The input VSWR will rise to about 1.5:1 unless the 35 ohm power resistor R301 is reduced in value. Note that IMD will increase with reduced feedback.

The TE Connectivity 47 ohm, 2 watt MOX resistor part number 5-1625890-3 is available at Digikey for $0.36.
« Last Edit: October 06, 2013, 10:08:55 AM by WX7G » Logged
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