[TenTec] Built in SWR meter bannans

[shristov]

Jim Brown <k9yc at audiosystemsgroup.com> wrote:

> On 4/24/2013 2:22 AM, shristov wrote:
> > Heat is produced in both the wire and the core.
 
> That is a common, but incorrect assumption.

All cores are lossy, and their loss manifests itself by heat generation
within the core whenever there is an RF field inside the core.
This has nothing to do with wires.


> My statement is on the basis of a controlled experiment,
running 1.5kW through a choke for a while

Running 1.5 kW through a choke will test only
the transmission line mode of the choke (i.e. the coax).
That's how Jerry Sevick "tested" his baluns.
The core does not participate in the test and does not heat.

The real choke test applies a common mode voltage
between input and output shield terminals.
The realistic common mode voltage for the test
would be at least the half of the line voltage:

  Vcm  >=  sqrt (50 * 1500) / 2 = 137 V

Here's an example.

A 3-turn choke on FT240-43 provides a common mode
impedance around 1 kOhm on 28 MHz.
Sounds like a perfect choke, isn't it?
Yes, but only for RX and low power TX.

With 137 V of common mode voltage, the core
dissipates almost 20 W and overheats quickly.


73,

Sinisa  YT1NT, VE3EA