TopBand: Re: Interference problems

[P&V Nesbit]

Hi Tom,
Further to the advice of Ward and Tom (W8JI) on what might be causing the
IMD in your system, I suggest checking its coaxial adaptors, specifically
any BNC and UHF 90 degree bends and T pieces.

As a cost-cutting measure, most retailers over here have ceased stocking
branded connectors, and now import "no-brand" connectors from Taiwan.
Sometimes they come via Japan, and might even be in branded plastic bags,
but the connector inside the bag originates from Taiwan and is still
unbranded. I assume the same thing happens in the US.

If you saw apart one of these connectors, you are likely to find the
internal connections made using an unplated STEEL SPRING, because it makes
the connector easier and cheaper to assemble. The trouble is, the spring is
inductive, lossy, and often loose.

These evil pieces of trash have cost me heaps of time and trouble, ranging
from SWR oddities and IMD in my own antenna, to hours (days?) wasted at
work thanks to adaptors with high VHF loss and intermittent connections. In
the end I threw out a whole boxfull of these monstrosities, as over the
course of a year the failure rate approached 100%.

No doubt the manufacturers are cashing in on the limited RF knowledge of
most CBers and LAN technicians, and of course few importers/retailers can
pass up the opportunity to make a fast buck.

I my view the extra dollar or two for known brand-name connectors is repaid
many times over in terms of performance and reliability. Connectors are the
last thing anyone should skimp on.

73,
Peter VK3APN

pnesbit@melbpc.org.au


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