Topband: The Magic-T

[Joe Subich, W4TV]

On 2021-02-10 5:25 PM, P H via Topband wrote:

> A loss of 3 dB may be like "to be or not to be" of a QSO on 160
> meters.

That is extremely unlikely.  The limiting factor on 160 meters is
signal to noise ratio, not absolute signal levels.  Most amateur
receivers have absolute sensitivities of -130 dBm or greater while
the background noise is as much as 20 dB higher than that.

Since 3 dB loss in a splitter applies to both the signal and the
noise component, there is no net loss in signal to noise ratio.
In fact one may want to apply attenuation at the receiver input to
reduce strong adjacent (broadcast) signals and prevent receiver
overload.

73,

    ... Joe, W4TV


On 2021-02-10 5:25 PM, P H via Topband wrote:
> My impression is that a hybrid combiner, which introduces 90 degree shift (hence two identical signals of amplitude A fed to its inputs will give in total a signal with the amplitude of 1.41*A) is 3dB less efficient in comparison to a simple combiner where A+A gives 2*A at the output.
> Do you have any thoughts on this?
> A loss of 3 dB may be like "to be or not to be" of a QSO on 160 meters.
> Regards
> Piotr, SP2BPD