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Power Genius XL Design Details – Installment #2

HCampbell  WB4IVFHCampbell WB4IVF Member ✭✭

For those who do not receive the PG XL Insider updates, below is the second installment of PG XL design details from Flex.  This time focus is on the diplexed filters and harmonic dummy load. 

From the schedule side, looks like testing/production of Tuner Genius is on hold for the time being while PG XL production is ramping up.   



 Power Genius XL Update

This week I would like to share another of the unique design features of the Power Genius XL, the incorporation of diplexed (high pass/low pass) output filters. While this feature adds cost and complexity, it significantly enhances amplifier linearity and materially reduces harmonic output. Other amplifiers in the amateur market exclusively utilize low pass filters. 

On Power Genius XL, the high pass filter passes only the harmonic frequencies to the 500 Watt dummy load where the harmonic energy is transformed into heat. The low pass filter passes only the fundamental frequency to the antenna. This means that harmonic emissions are reduced by as much as -20 dBc compared to other products. This is very important in SO2R and multi-op contesting and further reduces QRM to others on the bands.

In other amplifiers, the harmonic energy inherently generated in the amplifier stage, is reflected off the low pass filter and ends up back in the output stage transistors, which reduces linearity and increases heating in the transistors and filter components.

Significant heat can be generated in the filter components themselves, especially as frequency increases and the skin effect becomes more dominant.

Power Genius XL incorporates significantly larger T-157 (1.57 inch) toroidial filter inductors on the lower bands, and silver plated 3 mm copper coils, which are pivotal to optimal performance during legal limit high duty cycle applications such as FT8 and RTTY contesting. We also use highest quality capacitors sized in current and voltage ratings for the application. All filters and the associated harmonic dummy load are assembled in the commercial grade module shown in the photo below. A visual comparison of Power Genius XL construction to other products speaks for itself.


 Delivery Update

As communicated in previous updates, we are in the process of completing the remaining filter module upgrades to all previously shipped amplifiers. The upgrade resolves an issue reported earlier that was discovered on 6m when running FT8 continuously. We have incorporated heavy gauge silver plated coils on 6m and 10m (see photo above) to significantly enhance skin effect conductivity. This has enabled us to meet our design goal of providing legal limit power on all modes and bands even under the most strenuous operating conditions. 

Based on our current upgrade throughput we remain confident that we will resume production shipments to our pre-order backlog beginning in November. I don’t have an exact date yet but you will be contacted when you come up in the list. Since we have been primarily focused on delivering the amplifier, work on Tuner Genius has been temporarily delayed. Once we resume production shipment flow, we will return to completion of testing and production roll out of the tuner.

We continue to receive a high level of interest regarding sales of Power Genius XL in Europe and other parts of the world. Our initial orders were from US customers as FCC certification was received in advance of CE certification. While CE certification has been completed, we are not yet ready to begin shipments outside the US. This amplifier will still need to undergo rigorous testing, but we are keeping an interest list for those who wish to be contacted when we begin sales in other areas of the world. Regardless of your locale, please contact [email protected] if you wish to be added to the growing list of customers interested in this transformative product.


Gerald, K5SDR

CEO FlexRadio


  • Pierre MartelPierre Martel Member
    edited June 2019
    Is it me or ft8 in high power station is not what I call a good match? For the discution, here is section 4.7 fron ft8 operating tips at https://www.physics.princeton.edu/pulsar/K1JT/FT8_Operating_Tips.pdf 4.7 Although FT8 is a weak signal mode, not a QRP mode per se, please keep your transmit power down. Be nice! Generally on HF, if a path is open, just a few watts will do. Put your amplifier on standby. Turn down the wick to QRP levels. Try it! If you don’t get any responses at all, try 10 watts, maybe 20 or 30. If you find that you routinely ‘need’ 100 watts or more, that is a strong hint that your feeder and antenna system are inefficient. Check for corrosion and loose connectors. Try making a simple halfwave dipole as a comparison antenna. You will find that you can receive better if your antenna is in good shape, and reception is kinda useful for DXin. Aside from QRO being antisocial and usually unnecessary, if your signal is too strong, it may be dirty and may overload receivers and audio cards at the DX end, preventing your signal from decoding reliably. Take your cue from the signal reports you receive: if you are getting positive reports, you can probably do just as well (maybe even better) with a fraction of the power. Remember: decibels are logarithmic. Cutting your power in half will reduce average reports by just 3 dB; cut it by half again to lose another 3 dB. If you are receiving mostly negative or zero reports, you are in the right region. I normally adjust my transmit power to get reports between 0 and -10 dB. If you receive a 58 report and you’re not using SSB, something may be seriously amiss!
  • HCampbell  WB4IVFHCampbell WB4IVF Member ✭✭
    edited October 2018

    Pierre -

    Thanks for posting.  The article states that QRO is usually not necessary for FT8 - it doesn’t state it’s always unnecessary.  I’m not an FT8 user yet, but from what I’ve read you only use enough power necessary to make the QSO, like for other modes.  If that requires high power that is ok, as long as you follow other good operating practices and don’t drive the amp into distortion. 

    BTW, one of the reasons I decided on the PG XL was the clean signal engineering that went into it, which should make it a cleaner amp in any mode. 


  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited October 2018
    I think the design of the XL is that you can run at full power on FT8 for endless hours without problems, most amps just can not do that. The intention of the letter was not to promote operating in that manner.
  • Pierre MartelPierre Martel Member
    edited October 2018
    I do agree with you that it is a good way tto promote the design of the amplifier, in fact I am looking at buying one cause I want to run my station remotely and with such amplifier I would run it confident that I wont A) send spurious all over the place B) wont be in fear of busting the finals if there is an intermitent problem on the antenna system while xmitting remotely. But it would be a nice addition to the install,ent news letter to specify that althought the amp can do it, it is not good practice to do it. Ham radio is like the rest of the population, my car can run 200 miles an hour for many hours, but it is not because I can do it that it is a good idea to do it. Some will take that possibility and use it, like the guys that like to speed run on the highways.
  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited October 2018
    From all the reading I have done, FT8 is widely misunderstood. It is a weak signal high power mode, There has been a lot of discussion about this in other threads explaining this.

    here is a post from Howard.

     KY6LA - Howard, Elmer

    • I normally run about 75W into a gain antenna with an ERP near 600W

    However when I try to work any station below -18dB I always kick up the power to 1.5KW with an ERP around 12KW.

    I might note that my 6700 usually hears about 6dB better than the legacy radio at the other end hears me when we are running the same power levels so if I hear them about -18dB they are most likely hearing me around -24dB or more likely not hearing me at all...

    So power is the only way that they can copy me.

    The MYTH of low power is a legacy of PSK31 which is overly sensitive to XMT IMD hence the need to keep power levels low for PSK31.

    This is NOT TRUE for FT8 which is a WEAK signal Mode NOT A LOW POWER MODE.

    • Like

    • Pierre MartelPierre Martel Member
      edited October 2018
      Just remember how the kilowatt club work, I have legal limit and I will use it! When on 40 meter you dan hear 2 station that both run. Full legel limit and they are in range to shout at each other by the windows.... But they dont care that they are disturbing a qso in barcelona that try to catch that elusive vietnamese signal. This will bring the exact same situation in ft8. At least let hopes that the people using those amp will have the good sense of using the required power only.... And just for that particuliar qso.
    • Gerald-K5SDRGerald-K5SDR FlexRadio Employee ✭✭
      edited October 2018
      Let me speak first hand that FT8 is not a low power mode when you can hear better than the station on the other end. I only run 100W at my home QTH. I find that stations below roughly -13 dB cannot hear me on my tri band beam pointed right at them. An extra 12 dB of power would really help. I can copy stations down to -24 dB on my FLEX-6700 but they sure can’t hear me. A better receiver on the other hand would probably help too. FT8 on 6m can surely benefit from QRO as well. FT8 is taking over that band for DX that would never be worked otherwise especially at the bottom of the sunspot cycle. Gerald
    • Pierre MartelPierre Martel Member
      edited October 2018
      Like I said before, the problem is not people that use there power amp properly but the one that will run a power amp no matter what it need it or not. We have some guys that runs 3 kilowatt on local nvis net just cause they can. Every one hear them. Every one is heard at 10 watts

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