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 on: Today at 12:13:57 AM 
Started by W4DNR - Last post by W4DNR
Ah Ha !! Grin      ALC..... I hadn't factored that into the equation ! 
A perfectly created 25 watt carrier and 100 watts at peak modulation
is squished in the next stage by the ALC.

I'll have to do another scope measurement on my TS-2000.
Last time I measured, 25 watts carrier was pretty close to 100 peak
with no ALC.   Close enough that it isn't worth an effort to improve.

With a 200 watt radio like the TS480 ,  25 watts carrier should be well below
any ALC action.     

I have an old FT-757GT ( no DSP )  that always sounded good on AM, but I don't
remember looking at it on a scope.

Then there is the Valiant, the DX-60, and the DX-40 that need  some "tweaks".
At least when I retire, I won't run out of projects.

Thanks Everyone ! !   Great Information.


 on: Yesterday at 10:29:24 PM 
Started by k1kp - Last post by K1JJ
Hi Tony,

Good show!

Yes, -40 DB 3rd would be a huge improvement over the typical -28 DB or worse we often hear on the bands.  However, a ricebox driver if often the worse part of the RF chain. Even a super clean amplifier is ruined by a poor driver. IE, amplifier cleanliness can never be any better than the driver itself.

It is good that you are doing these figures with a built-in driver to eliminate that problem.

I spent a lot of time building an old school legal limit class A and AB1 tube RF chain that eventually did about -55 DB 3rd IMD, but it took a huge effort and lots of heat.

Over the years I have often asked RF people smarter than I, why haven't they come up with a ham amplifier that runs class D that used an SDR digital modulation (power supply) system to achieve 90% efficiency?  I was told it was coming, but that was 20 years ago.

So here we are and I'm glad you are making such great progress. I'll keep an eye on how it works out.
In addition to the very successful Pure Signal technology, this is a great addition to on-air cleanliness.

Why did it take so long? I would think one of the big guns like Yaesu, Anan, etc would have done something. Was it software or hardware or was it a cleanliness design issue?  Hopefully you can stay ahead of the competition curve.

BTW, I visited your website with the question, "How do they generate 80-90% eff ? Using what basic technique?  The text below is taken from your site at Polex-Tech.com and will answer this question for others:

Good luck -

Tom, K1JJ


"How does it achieve High Efficiency?

The Power Amplifier stage of traditional RF amplifiers must be biased in the linear region to avoid creating distortion and harmonics. This constrains the efficiency to be around 55-60%, which means that for every watt of RF output, an additional .8 watts of power is wasted. This wasted power contributes to power supply costs, cooling requirements, and ultimately, cost, weight, and size.

By using a class D power amplifier, much higher efficiency can be achieved, between 80 to 90%. A class D amplifier is not linear, so instead of attempting to linearly amplify to SSB signal, it is actually created in the RF Power Amplifier stage. The class D power amplifier is driven by a phase-modulated signal, which is amplitude modulated by the drain supply in the amplifier."

 on: Yesterday at 09:49:56 PM 
Started by W4DNR - Last post by DMOD
A friend of mine has a IC-7300 and also complained about the "AM Carrier Shift".  When asked what he was referring to, he replied that when you transmit in CW mode the max power out is 100 watts, but when in AM mode, the unmodulated carrier dropped to less than 25 watts keeping the modulated peaks from achieving 100 watts on peaks.  To me that is not "AM Carrier Shift", but I believe some folks use that terminology to describe the above.  He called Icom about it and was told that in AM mode, the IC-7300 will not allow for 25 watts AM carrier in the software to help protect the finals.  I guess the designers believed that AM mode with 100% modulation was too much if peaks reached 100 watts.  Thus it will not modulate to 100 watts peak, but will go up to about 90 watts max.


Ok, that is not carrier shift but is a result of transceiver design and math.

25 Watts AM carrier is 100 Watts Peak-Envelope-Power at 100% Modulation. The maximum PEP for SSB is 100 Watts as well, the limit of the internal Linear Amp stage.

See the listing in the PDF file for a transmitter capable of 25 Watts AM carrier and compare the real AM output power with the so-called PEP values.

The ICOM-7300 Specifications show this:

Output Power:
100W (25W AM)
RX Frequencies:
Receiver Type:
    Direct sampling

Output power (HF/50MHz)   SSB/CW/FM/RTTY: 2100W, AM: 125W
Modulation system SSB AM FM   
Digital P.S.N. modulation
Digital Low power modulation
Digital Reactance modulation
Spurious emission   Less than 50dB (HF bands), Less than 63dB (50MHz band)
Carrier suppression   More than 50dB
Unwanted sideband   More than 50dB
Microphone impedance   600Ω



 on: Yesterday at 08:49:49 PM 
Started by k1kp - Last post by W1ITT
We could live with 40 db third order.  The old sweep tube stuff did well to make it into the low 20s and most of the modern twelve volt finals do well to make 30 or 33 db third order.  And that's when the DXpedition excitement doesn't push the knobs a little further to the right.  Original S-Lines could be made to get 36 db or so, but it was mostly downhill after those days.  So if we could get more people at 40 db IMD numbers the world would be a better place.  But I'll have to take my vitamins to live long enough to see people phase out the current crop of radios.

 on: Yesterday at 08:45:05 PM 
Started by WA2SQQ - Last post by AJ1G
Maybe Doc Brown dropped it off when he paid a visit in the Delorean.

 on: Yesterday at 08:00:33 PM 
Started by w9jsw - Last post by w9jsw
6 days from order to boards in my hands, from china. Unreal.

 on: Yesterday at 05:15:32 PM 
Started by k1kp - Last post by k1kp
Materials cost for a Beta unit would be around $1000 in single quantities. If there are 10 or more beta testers, then obviously the parts cost can be reduced.

As for TX IMD, it is still a works in progress. The Polar Explorer achieves better than 40db on IMD3/5, as per standard ARRL testing methodology, on 160 and 80 meters, without using any precorrection at all. It naturally degrades with frequency, but by applying a static (one-time per specific load) measurement of output amplitude and phase, the numbers improve and approach 40 db on all bands. In the future, more development may lead to improvement of these figures using the static correction, or a dynamic correction approach may also lead to further improvement. 40db may not beat what Anan can achieve, but it certainly beats what any non-corrected 500W (amateur) amplifier currently can achieve.

-Tony, K1KP

 on: Yesterday at 04:57:22 PM 
Started by k1kp - Last post by W1ITT
Do we have 3rd and 5th order transmitter IMD numbers yet?  Years ago I worked for a boss who told me that "really good" wasn't a valid measurement.  He said that if I couldn't show measured data it wasn't engineering, but just an opinion.  If this implementation can show high efficiency as well as IMD that meets that of HPSDR  (Anan, etc ) running Pure Signal, it'll be a real game changer.

 on: Yesterday at 04:24:58 PM 
Started by W4DNR - Last post by Bob W8LXJ
  On the Kenwood , when using it as an AM exciter, AM mode, power output wide open, carrier level on zero and then insert carrier for desired output of RF amplifier. Often run a passive grid driven 4-1000a in ab2, 4000vdc plate , 500vdc on the screen, 300 watts out carrier, 1,200 watts out on audio peaks.. If I want more power out, turn up the mic gain or increase the screen voltage to 600vdc and will go the 1500 out with no problems. THE KENWOOD shows about 10 watts output for carrier and 15 watts for audio peaks

 on: Yesterday at 03:47:44 PM 
Started by k1kp - Last post by KA0HCP
Can you give us a ballpark cost for materials?  Thanks, Bill.

p.s. Nice interview with Burt.

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