[Amps] 8877 input Z

[Carl]

That sounds like you can use an old Drake, Johnson, B&W, etc LPF right at 
the socket and replace the fixed output cap with a trimmer for a perfect 
match.

Carl
KM1H


----- Original Message ----- 
From: "Vic Rosenthal K2VCO" <k2vco.vic at gmail.com>
To: <amps at contesting.com>
Sent: Friday, March 28, 2014 2:00 PM
Subject: Re: [Amps] 8877 input Z


> 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/
>
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