[Towertalk] HyGain Balun

[Tom Rauch]

>     The BN-86 voltage balun is a good example of the style of balun
>     once
> popular in amateur antenna installations.  This style of balun is
> characterized by limited common mode or choking impedance
> (a.k.a."balun action"), a vulnerability to "saturation" of the ferrite
> core, and relatively narrow bandwidth compared to the alternatives. 
> When originally popularized, this style of balun was a useful advance
> in antenna technology.

HyGain no longer manufactures a "voltage-balun". The baluns have all 
been changed to current baluns, although I'm not sure the paperwork 
has caught up yet.

Long before a balun "saturates", it will overheat. People often 
confuse over-heating with saturation. Even a very small amount of 
power loss can make a balun overheat, especially if the balun is 
placed in an enclosure that limits heat flow. As little as 50 watts 
of loss would severely overheat most bead baluns. The exception is 
pulse operation or very low duty cycle operation, where the 
instantaneous power is very high compared to power averaged over 
perhaps 15 or 20 minutes of time.

As a general rule the worse problem with soft-iron core baluns is the 
heating causes the balun to fail, or the material in the balun to 
reach curie temperature where the balun core loses all magnet 
properties. With a choke (current) balun, you would almost never 
notice a remote balun reaching curie temperature. The balun would 
just quit acting like an effective balun. With a voltage balun or "un-
un", the SWR would radically change if curie temperature was reached.

For high duty-cycle operation, high common mode voltage operation, or 
baluns subjected to high SWR I'd always use an air-core or lower 
permeability high-Q core. Applications would include baluns installed 
on large antennas mounted on or near shunt-fed towers or verticals, 
open wire line fed mismatched antennas (like all band doublets), or 
even typical yagis for CW or RTTY operation.

I have yet to test a bead balun from **any manufacturer** that holds 
up well in the conditions above, because the balun simply can 
NOT obtain high enough choking impedance with high-Q core materials. 
The string of beads would be far too long. I've tested dozens 
of bead baluns, from everyone from HyGain to Force 12 to other 
sources, and they all overheat with high-duty cycle 1500 watt or high 
common mode voltage applications.

While bead baluns work well for casual SSB or CW operation **if** the 
balun does not have too much common mode voltage across it, they can 
be problems in many applications.

Multiple turns through the **proper** mix toroids  (something with a 
low loss-tangent at the operating frequency, like a 65 material at 
HF) or air-core baluns work best for applications that "stress" the 
balun.73, Tom W8JI
W8JI@contesting.com