[Kenwood] TS-930 YG-455C-1 Filter removal jumper?

[Dr. David Kirkby]

On 06/23/11 02:08 AM, Roger Shultz wrote:
> I want to remove the above filter from my TS-930 and though I have the
> instruction sheet for installation where it reads in step 4 to remove the
> short connector attached to the filter position, it does not elaborate on
> what that is or if I can fabricate it.
>
> The filter was in the radio when I purchased it which is why I don't know
> how to successfully remove it.
>
> Any help is greatly appreciated including a picture of the original
> configuration.
>
> TNX es 73, Roger, NJ2R

Roger,

I'll look in the service manual and see if I can work this out. My *guess* is 
that the small board may have 3 resistors on it.

According to the service manual, the YG-455C-1 filter has an attenuation of less 
than 6 dB. The impedance is 2000 Ohms. So if the rig had no filter and one 
inserted one, there would be reduced gain in the IF stages due to the filter's 
insertion loss.

This is going to happen whenever a filter is put in, but I guess in most cases 
this is just ignored - it is in the TS-940S.

One way Kenwood could have kept the gain constant is to put an attenuator in 
line when the radio was sold. If that had a loss of about 5 dB, then removing 
that board and inserting the filter would have negligible effect on the gain in 
the IF stages. (One might reasonably assume the loss of the filter is somewhere 
between 4 and 6 dB if the data sheet says less than 6 dB, a 5 dB attenuator 
would be a reasonable choice, but it would be very uncritical).

Whether one used a T or Pi attenuator would really just be a matter of 
convenience. Either would do equally well.

http://www.random-science-tools.com/electronics/PI_attenuator.html
http://www.random-science-tools.com/electronics/T_attenuator.html

This however is just a guess. Perhaps it consists of nothing more than a single 
series resistor, which would not present the correct impedance, but could be 
made to have the same loss, which is probably good enough.

In most cases one just cuts a wire link.

That's my best guess of what that board might consist of, but the service manual 
should have it. I'm just trying to find my way through it.

Dave