RS-HFIQ 5 Watt HF SDR Transceiver by HobbyPCB

Discussion in 'Amateur Radio News' started by M0DQW, Sep 5, 2021.

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  1. KE0EYJ

    KE0EYJ Ham Member QRZ Page

    After lots of QRP work, and playing around with wattage in between, I am a fan of running at 20 to 25w. I find the difference between it and 100w is very livable.
    W3PX likes this.
  2. PA0MHS

    PA0MHS XML Subscriber QRZ Page

    Of course it will happen. Wether somebody notices it, is the question. But if the RF envelope raises from oW to a certain value linearly and the bias is enabled after a certain threshold, the the RF envelope on the output of that amp will certainly not be equal to the envelope of the input. So there is at least some extra distortion at the start of a tranmission and it depends on the RC time of the bias circuit how often during one transmission of speech this distortion occurs.
    WY7BG likes this.
  3. MW1CFN

    MW1CFN Ham Member QRZ Page

    What's its frequency stability like if sending WSPR, for example?
  4. AE0Q

    AE0Q XML Subscriber QRZ Page

    It does happen each time, of course, but the RF output of the amp is so low that it isn't significant. The amp is putting out 5w or less at the switch.

    Alpha and Acom amps that run GU74b tubes at their max need the heat-saving in heavy contest use. Use in CW and SSB contests showed the tubes run too hot without the EBS.
    Being in Europe, you probably already know the reason the GU74B was used, there were thousands available surplus in the 90's and they were really, really, really cheap.
    Last edited: Sep 9, 2021
  5. WY7BG

    WY7BG XML Subscriber QRZ Page

    Unfortunately, you seem to fail to understand the design of amplifiers and the markets for them. Amplifiers, by their nature, must be designed to have both minimum and maximum input power to maintain linearity. Too weak a signal will cause crossover distortion or be swamped by the bias current or voltage. Too strong a signal will, of course, cause clipping or worse. The FCC limits on gain prevent an amplifier maker from setting a weak input signal as the default, and so virtually all amplifiers with capacities of more than 100W (and you want to run an amp at half its capacity for modes with high duty cycles, such as RTTY, so you want an amp rated at 200W or more to run 100W) require high drive power... at the expense of enough wasted power to keep your shack quite toasty. Were the FCC limit not in place, it would be possible to set the required input power for even a legal limit amp at QRP levels - saving energy and making it easier to obtain high power output from simple SDRs. But due to the gain limit, manufacturers can't do that.

    Most of us also know why the FCC did this: to monkey wrench CBers who wanted to use ham radio amplifiers. Commercial CB radios are limited to 5W output power, and so won't excite an amp that requires 50-90W input power. But now that the CB fad is past, and manufacturers have imposed other impediments to using amateur radio amps for CB, the limit is unnecessary and should be struck from the rules.
    AA5BK likes this.
  6. WY7BG

    WY7BG XML Subscriber QRZ Page

    Alas, those are expensive (because they are "max legal" amps) - a lot to pay for only 150W output. Also, I have to wonder how linear they are with only 5W input, since the manual says they expect much more. Have you measured harmonic distortion? Also, a factor of 40 would be above the FCC gain limit (roughly a factor of 30). Are you sure you're getting 400W out with only 10W in?
  7. HC6PE

    HC6PE Ham Member QRZ Page

    nope. I have it running via Quisk installed on a Raspbian, Raspberry Pi3 /Pi4, not a big issue.
    72 de HC6PE
    AB2YC likes this.
  8. DO1FER

    DO1FER Ham Member QRZ Page

    Please take a look at page three, where the link to the SDR Software is listed. When the SDR runs with the typical Linux software, its ok. But in the begin of this thread and in the video, everybody just talked about the Windows solution.
  9. F5NPV

    F5NPV Ham Member QRZ Page

    AA5BK likes this.
  10. W1YW

    W1YW Ham Member QRZ Page

    The point is that going to 100 watts from 5 watts is not limited by FCC rules, for an amplifier.

    13dB< 15 dB.

    What W3PX said is perfectly correct.

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