[Heathkit] SB200 SWR Meter

[manualman at juno.com]

If you read the SB-200 manual or look at the schematic, you'll read or
see that the SWR bridge is set up for a nominal 50 ohm impedance.

Input impedance is set up for ~52 ohms unbalanced.

((As a side note, the input side of the SB-200 is where many solid state
exciters run into problems. If you put an "accurate SWR meter between the
exciter and the input of the SB-200, as you modulate the exciter on SSB,
and sometimes even on AM, the SWR will vary with the modulation. Also if
you have the Harbach soft key installed, sometimes RF floating around
under the chassis, will cause strange RF envelopes on the SB-200 output.
This is especially noticeable on 15 and 10 meter operation))

Output impedance is typically 50 to 75 ohms unbalanced. Remember, the
SB-200 has a pi-network on the output so output impedance could be almost
anything (even metal bed springs).

I would suggest reading, starting on page 39 of the SB-200 manual, the
procedure for wiring up the SWR bridge section. Review the dimensions for
various connections and even the positioning of several components
related to the bridge. In the end, you'll probably still find that the
SWR position still sucks for accuracy. But, you can feel good that it was
wired and/or confirmed it was wired correctly.

Pete, wa2cwa



On Wed, 26 Oct 2022 10:57:27 -0400 Ron W4BIN <ka4inm at gmail.com> writes:
>   Bruce Hudler WK3A wrote:
> 
> > Thanks for the reply Ron.
> > Never considered that but why would they do 75 ohms.
> > I'll try connecting something 75 ohms with the amp off and see 
> what 
> > happens.
> 
>    I have a Heath fone patch+SWR bridge+(possibly) a speaker of the 
> SB 
> line that was
> setup for 75. O *  because we use RG59 and RG11 (73. O)  coax 
> with 
> dipoles, don't we?  I do. (or RG6)
> 
>     * The IB tells how to convert it to 50. O  (by changing 
> several 
> resistors)
> 
> -- 
>     Ron  W4BIN - Understanding is much better than
>                                        knowing how.MX
> 
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