Input impedance on the W7IUV preamp is determined almost entirely by the DC bias currents.
Clifton Labs used to have a really nifty set of pages on modeling and measurement of the various high performance preamps. I really miss that site. Tim N3QE On Mon, Nov 27, 2017 at 9:46 AM, Roger Kennedy < ro...@wessexproductions.co.uk> wrote: > Hi Don > > Gosh, really? Looking at the circuit, and given the resistors used, I > would > have thought the input impedance would be about 800 ohms . . . > > And hard to estimate the output impedance, but wouldn't have thought it was > about 50 ohms. > > Guess I'm wrong then ! Sorry about that. > > (I already built a FET pre-amp for my Loop . . . but was just commenting.) > > 73 Roger G3YRO > > > _____ > > From: Don Kirk [mailto:wd8...@gmail.com] > Sent: 27 November 2017 13:09 > To: Roger Kennedy > Cc: topband > Subject: Re: Topband: BOG pre amp info ? > > > > HI Roger, > > > You said "However, the circuit seems odd . . . I used transformers in and > out on my Loop Preamp, to give a match to 50 ohms." > > > I believe your above statement was in reference to the W7IUV preamp. I've > measured the W7IUV preamp input and output impedances and also modeled the > W7IUV preamp using LTspice, and both methods yield input and output > impedances of close to 50 ohms. Therefore no additional components (such > as > matching transformers) are required for impedance matching purposes on the > W7IUV preamp. > > Just FYI, > Don (wd8dsb) > > > On Mon, Nov 27, 2017 at 5:36 AM, Roger Kennedy > <ro...@wessexproductions.co.uk> wrote: > > > > That's a nice cheap board, and worth using considering it has relay > switching too . . . > > However, the circuit seems odd . . . I used transformers in and out on my > Loop Preamp, to give a match to 50 ohms. > > Roger G3YRO > > ------------------------------------------------------------ > --------------- > > Try this guy he does good quality boards and it's easier than importing > from > the states, > > https://m.ebay.co.uk/itm/ > <https://m.ebay.co.uk/itm/W7IUV-Beverage-preamplifier- > PCB-for-experimenters- > 2N5109-or-DCP68-transistor-/261634019988> > W7IUV-Beverage-preamplifier-PCB-for-experimenters-2 > N5109-or-DCP68-transistor-/261634019988 > > Trevor > EI2GLB > > _________________ > Topband Reflector Archives - http://www.contesting.com/_ > <http://www.contesting.com/_topband> topband > > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband