[Heathkit] SB-200 Input Inpedance.. Frustration Continues...

[Kenneth G. Gordon]

On 14 Aug 2007 at 12:32, KBØNLY wrote:

> Unless i find someone to buy the POS for what i have into it i need to
> fix it.  I installed new caps as suggested by many reflector members
> and as shown on the website by NE7X, and it didn't make one damn
> difference.

Strange....

> 
> Sure, i can get 50 ohms at the input according to the MFJ-259, but the
> SWR meter still shows infinite.

REALLY weird!

>  So how is that possible?

Open cable between SWR meter and one of your radios? Shorted 
cable between one of your rigs and the SWR meter? Bad 
connector on one end or the other of one or both cables? Bad 
connections at one or all four ends?

>  I have
> 50ohms but infinite SWR on the 259 that is?

>  I have never seen it do
> that.

Look on page 13 of the on-line PDF manual. Here is what it says.

"An IMPEDANCE of 50 ohms can be composed of both resistance 
and reactance. If the impedance is 50 ohms (or whatever the meter 
measures), but the SWR is not 1.0 to 1, reactance is probably 
making up part or all of the impedance. 

Contrary to popular misconception, it is impossible to obtain a 1:1 
SWR when the load is reactive. This is true even if the complex 
impedance is exactly 50 ohms. 

A good example is a 50 ohm load with almost pure reactance and 
almost zero resistance. The MFJ-269 LCD will indicate R=0 X=50 
while the impedance meter reads 50 ohms or the Z display indicates 
a 50 ohms impedance. 

The SWR would overflow (SWR>25) because the nearly-pure 50 
ohm reactance and impedance load absorbs almost no power from 
the source.

It has a nearly infinite SWR, despite having an impedance of 50 
ohms.

On the other hand if resistance is near 50 ohms and reactance near 
zero, the impedance would remain 50 ohms. SWR would be 1:1 in 
this case, since a dissipative resistance readily accepts power from 
the source."

What this is telling you is that SOMETHING is shorted, or possibly 
the length of coax you are using is long enough that an OPEN looks 
like a SHORT to the meter.

Why your system "sort of works" on 40 meters may have something 
to do with the length of the interconnecting cables.

The intermittant activity of your transceiver's SWR indicator may 
ALSO mean some thing is not right with the switching network in 
one end or the other.

I really suspect your interconnecting cables or connectors at this 
point.

As I said, when I first got my SB-200, I had a cable problem that 
took me several hours to discover.

Ken Gordon W7EKB