The problem with a T connector is that VERY few recievers actually have a 50
ohm input. The ones we have checked on a bridge were all over the lot, with a
few between 40/60 ohms and most in the 15 to 110 ohms range and a few beyond
that.
Everything considered, I suspect reciever input impedance is low on many rig
designers list of priorities. From my viewpoint, understandably so.
When you connect two recievers to an antenna with a T connector the already
poor SWR gets worse, you can have an appreciable and unpredictable impedance
transformation in the jumper from the T to the reciever, etc., etc.. So the
result is not likely to be representitive of a typical user's results.
A double resistive pad will work - provided the difference in input
impedances is taken into account. If it isn't taken into account the signal
input to the reciever can vary widely. With proper precautions, any of
several styles of signal dividers will also do. And I have seen a Johnson
"active TR switch," the one with the 6CB6 tube, feeding a pair of 1K
resistors used to slightly amplify the source signals and isolate the rigs
from each other.
But when it's all said and done, a GOOD A/B switch has proven the most
effective source of live comparison signals.
73 Pete Allen AC5E
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