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GregS[_2_] · July 9th 08, 02:30 PM posted to rec.radio.amateur.equipment

In article , (GregS) wrote:
In article ,
(GregS) wrote:
In article , "Ralph Mowery"
wrote:

wrote in message
...
I'm not a ham operator! But I figure you guys can explain what an
Isolation Transformer does.

I came up with one at an estate sale this weekend of a former TV
repairman. Among the 1970s vintage test equipment and color bar
generators was this xfmr. This unit says "Isolation Transformer 5
Amps, 600 Watts" on one side and "Isolation: Primary 120 VAC,
Secondary 120 VAC" on the other. It's about 8" square and as you can
imagine, quite heavy.

I was guessing it keeps voltage spikes out of the equipment that's
plugged into it, but then I saw some old posts in this group which
mentions grounded chassis.

Do people who have fairly modern ham equipment still use these things?

The transformer is not to keep out the spikes. Some of the older equipment
(vacuum tubes) did not have transfromers in them and one side of the chassie
was connected to the neutral side of the power plug. If the house
receptical was not wired correctly or if the plug was put in backwards then
the chassie of the equipment would be connected to the hot wire and if you
touched it and were grounded you would get shocked or worse and could die.

Sometimes when testing equipment without a transformer in it the isolation
transformer was used to make sure the grounded chassie would not be
connected to the hot side of the incomming AC power.
Many times the test equipment would have its chassie connected to the ground
and the chassie of the two pieces of equipment would be connected together.

Modern equipment with transistors seldom have this problem.

Isolation transformers such as the ones Tripplite sells, do filter well.
They also eliminate the ground to line spike issue. One leg of the secondaries
is tied to ground, eliminating any differential noise.

greg

As Trip Lite says...

* Superior line noise reduction and spike suppression
* Faraday Shield offers 100% isolation from the input AC line
* Secondary neutral to ground bonding eliminates common mode noise
* Removes EMI/RFI noise, utility switching transients and background spikes
* Select models feature hospital-grade plug and receptacles

But, there are transformers without the bonding, as most service shops would use.
It would be easy to add a switch to bond either leg to ground. Might be handy.

greg