Topband: BOG pre amp info ?

[Tim Shoppa]

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 <
roger at 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:wd8dsb at 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
> <roger at 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
>
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