[Amps] 8877 input Z

[Vic Rosenthal K2VCO]

You can design the input circuit as a pi-section lowpass filter with a 
cutoff above the highest band (I used 32 MHz). You can use standard 
tables for a 50-ohm input/output impedance because 54 ohms is close 
enough. Then subtract 42 pf from the computed value of the output 
capacitor.

This will result in an input circuit that will work on all bands without 
switching.

On 3/28/2014 10:54 AM, TexasRF at aol.com wrote:
> Hardy, the 54 ohms is a nominal figure that will vary with rf drive level.
> Certainly close enough for designing input networks. Higher drive levels
> will  result in a lower input impedance; lower drive levels will result in a
> higher  input impedance.
>
> The 42 pF is the capacitance between the cathode and grid primarily. So,
> you will need to provide an inductance to cancel that out. The inductance
> will  be different for each band of course.
>
> 73,
> Gerald K5GW
>
>
>
>
>
> In a message dated 3/27/2014 7:55:49 A.M. Pacific Daylight Time,
> n7rt at cox.net writes:
>
> I am  looking for the input impedance of an 8877. I found one source and
> that was  K6DC's (SK) article years ago that said it was 54 ohms with no
> frequency  dependency or reactive component. The input C is 42 pF according to
> the data  sheet. So I will assume I can use 54 ohms in parallel with 42 pF.
> Anyone have  anything different?
> 73 Hardy  N7RT


-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/