Topband: BOG pre amp info ?

[Roger Kennedy]

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

_________________
Topband Reflector Archives - http://www.contesting.com/_
<http://www.contesting.com/_topband> topband