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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. WY7BG

    WY7BG XML Subscriber QRZ Page

    Nope; it is. Manufacturers of amplifiers assume that you always want to drive them to full power (even though in real life you have to scale the power back for a high duty cycle to keep from frying most of them) and so set the minimum input power so that one can do that without exceeding the FCC gain limit (or, in many cases, even getting too close to it).

    Let's put it another way. Suppose I want 300W of output power and buy a 600W amp so that I can work digital modes at half the maximum (as is recommended by virtually all manufacturers). Many such amps will require 20W or more of input power from the exciting transmitter to avoid exceeding 15dB of gain (roughly a factor of 30). So, a QRP transmitter won't excite the amp, even if it has automatic level control (ALC).
    Last edited: Sep 8, 2021
  2. WY7BG

    WY7BG XML Subscriber QRZ Page

    That's another one worth considering. Only downside is that I use a remote tuner (an SGC-237), which wants 10-12W when you first transmit on a new band to tune up. The TenTec doesn't seem to have a switch that lets you start at a low output power (possibly bypassing the amp altogether) and then go to full power after the remote tuner signals that it's found a match at your chosen frequency.
  3. AB2YC

    AB2YC Premium Subscriber QRZ Page

    When I had the Tentex 418 I also had a SGC-230

    All you need to do is to disable the amp during antenna tuning

    I forget how I did it but something a simple as putting a switch
    in the PTT line between the rig and the amp would work
  4. W3ATT

    W3ATT Ham Member QRZ Page

    Try a TenTec Titan. 5w in gives me 150 out. I get 400 out with my 10w k2.
    Try a Ten Tec Titan... you'll get well over 100w out with 5 in.
  5. W3PX

    W3PX Ham Member QRZ Page

    W3ATT, I think your comments were mis-directed to me and should have gone to the station who my original comments were directed towards. He was lamenting the lack of amplifiers that will take 5W and produce 100W output (13 dB gain), and blaming that lack on the FCC's 15 dB amplifier gain limit, which obviously is not a factor. I was trying to demonstrate the fallacy of that argument.
  6. KB6QXM

    KB6QXM Ham Member QRZ Page

    I have been involved in SDR since the early days. Flex Radio fan. Life is too short for QRP!
    AA5BK likes this.
  7. W3ATT

    W3ATT Ham Member QRZ Page

    Roger that.. and while a 100w amp is good, one can get by with a readily available QRP 50w amp... going from 50 to 100w is merely 3db which is only a half an S-unit on the receiving end!
  8. W3PX

    W3PX Ham Member QRZ Page

    Thanks, and agree 100 percent on that. 50 watts (10 dB gain) is a nice step up from a 5W QRP rig. The amplifier would have a modest power supply requirement too.

    On the other end, if a manufacturer chose to, they could produce an amplifier that would supply 150W output for 5W input, with a linear gain of 14.8 dB, and still meet the FCC's requirement of 15 dB maximum gain. Such an amplifier would have a good bit of overhead for operators who would want to use it for high duty cycle digital modes at power levels around 50W.

    73 Frank W3PX
  9. KISEL39671

    KISEL39671 QRZ Member

  10. KE0EYJ

    KE0EYJ Ham Member QRZ Page

    Good stuff.

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