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Re: Power Amps

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  • wb6yte
    John, My Softrock is driving the amp with the MoBo 4.3 which puts out 2 - 3 watts average on PSK31. It can drive the amp to over 20 watts but I think the IMD
    Message 1 of 11 , Apr 1 12:56 AM
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      John,

      My Softrock is driving the amp with the MoBo 4.3 which puts out 2 - 3 watts average on PSK31. It can drive the amp to over 20 watts but I think the IMD suffers a bit at that level. According to other reports, with 5 watts of CW drive the maximum output varies from 38 watts up to 50 watts depending on the band. I have found 10 watts to be sufficient to make contact with almost everyone I can hear. Since the QRP-PA2008 amp has two gain stages, it can easily be driven to 10 watts output with the Softrock.

      One of the keys for making contacts for me has been to watch for CQs with S/N > +5dB to +10dB. Most digital software reports S/N which will enable you to estimate whether it will be likely for them to hear you. Since PSK31 decodes well down to a little less than -10dB S/N and most people are running at 25 to 50 watts, then when receiving a station that shows S/N >= +10dB, it is likely you will be heard by that station with 1 watt output (14dB below 25 watts) - assuming the noise level is the same at both locations.

      I do have a bit of an advantage with the QTH on top of a small hill and beam antenna for 20/15/10M at 40 feet. However many of the contacts have been made with a dipole (30/17/12M at 45 feet) or a G5RV (80/40) that slopes down to near the ground at both ends.

      Operating with 1 watt can be challenging - it does require a bit more patience - but it can also be very satisfying to make QSOs with a homebuilt radio at very low power.

      Ed
      WB6YTE

      --- In softrock40@yahoogroups.com, John Williams <KE5SSH@...> wrote:
      >
      > Ed,
      >
      > Have you considered using this PS2008 amp or another design as a RF
      > preamp to the WA2EUJ amp to drive it to a full 50W for SSB? Should only
      > need around 10db of gain to take 500mW to 5W.
      >
      > Your results on PSK31 at 1W are better than mine. I have yet to get a
      > QSO with either PSK31 or JT65-HF at 1W. I get excellent results on WSPR
      > regularly getting spots from Europe and Australia on 20M.
      >
      > John
      >
      > On 3/30/2011 8:15 AM, wb6yte wrote:
      > >
      > >
      > >
      > > I have been using one of these since last Dec with an SR RXTX
      > > V6.3/MoBo 4.3 with excellent results. It comfortably runs 10 watts
      > > output with PSK. With 10 watts I can work almost all stations I can
      > > copy. With 5 watts on 15 meters last weekend I made many QSOs into
      > > Europe. For pictures and log reports:
      > >
      > > http://members.cox.net/ehekman/HamRadio/Softrock.htm
      > >
      > > With digital modes you will be very surprised at the number of
      > > contacts that can be made with 1 watt or less. The reaction you get
      > > when you tell the other station that you are running 1 watt is quite a
      > > thrill.
      > >
      > > I just bought one of the QRP-PA2008 kits. It is a small fraction of
      > > the size of the WA2EUJ PA - but doesn't include the output LPFs - and
      > > it does have much more gain so you should be able to get the 10 watts
      > > out with much less than 1 watt drive.
      > >
      > > http://www.qrp-shop.de/200/cgi-bin/shop.dll?SESSIONID=0437892540358007&AnbieterID=1
      > > <http://www.qrp-shop.de/200/cgi-bin/shop.dll?SESSIONID=0437892540358007&AnbieterID=1>
      > >
      > > Ed
      > > WB6YTE
      > >
      > > --- In softrock40@yahoogroups.com
      > > <mailto:softrock40%40yahoogroups.com>, John Williams <KE5SSH@> wrote:
      > > >
      > > > And there are some nice features - 5 lpfs for broad band coverage,
      > > led's
      > > > for power/swr readings, cor/ptt mode, RF FETs. According to
      > > designer, 1W
      > > > in will yield around 20W out, depending on band. Depending on mode,
      > > > drive and heat sink cooling can go higher than 50W.
      > > >
      > > > Take a look, revised schematic, gerbers and BOM posted today. Kit is
      > > > being priced now.
      > > >
      > > > John
      > > >
      > > > On 3/28/2011 4:57 PM, Joel Black wrote:
      > > > >
      > > > > There is a new run starting of the WA2EUJ amps featured in the ARRL
      > > > > Homebrew Challenge. You can find out more info at:
      > > > >
      > > > > http://groups.yahoo.com/group/ARRLHBC/
      > > > >
      > > > > Amp will come as a kit - no enclosure. Cost is ~$100. Output is ~50W.
      > > > >
      > > > > 73,
      > > > > Joel - W4JBB
      > > > >
      > > > > On 3/27/2011 1:42 PM, Bernie Hunt wrote:
      > > > >>
      > > > >> I'm approaching completion of the Ensemble TX/RX and I'm wondering
      > > > >> what are the options for increasing the TX drive. What are guys
      > > using
      > > > >> for PSs? Is there a general consensus on a good solution?
      > > > >> I'm not looking for legal limit but I would like more than the 1
      > > watt.
      > > > >>
      > > > >> Bernie
      > > > >> K2YO
      > >
      > >
      >
      > --
      >
      > John Williams
      > WQKA523
      > KE5SSH
      >
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