23 July 2010

The perils of cheap adaptors II

The "T" adaptor in the photo was the reason a WACOM WP-639 duplexer cavity couldn't achieve a notch of more than about 12dB. As you may notice, there is a small helicoidal spring "joining" the two center conductor members in the adaptor. Being a small inductor, you may imagine what effect the presence of this spring has on VHF signals!
This is quite evident in the SA-TG screen photo. The response dip (notch depth) should have been about 35dB, but only 12 dB could be achieved, because of the impedance and loss of the spring, on the signal's way to the resonant cavity.
An "Amphenol" adaptor cleared the problem immediately and restored the notch depth to 35dB.

This unacceptable adaptor was the reason the duplexer had to be hauled down from the mountain and retuned. Even on HF, this kind of connection might create problems with its reactance - to say nothing of its deplorable reliability.

Do you have any such garbage in your VHF-UHF setup? 

If the captions in the photos all seem Greek to you, that's because they indeed ARE Greek! (Well, mostly!)