"Ralph Mowery" wrote in
news
Does anyone make a 4:1 balun that I can use for an off center fed
antenna that will take the legal limit of power ?

Is it too hard to quantify the power limit? It is jurisdiction dependent.

Talking in numbers is the beginning of understanding the problem. (A
loose paraphrasing of Lord Kelvin).

I did find one that is around $ 80 to $ 100 that is suspose to handle
it. I hate to pay that much for a ring of 'iron' and a few feet of
wire wound on it and it will not work.

I have up a home made version of the Carolina Windom. Bought a balun
rated for 1.5 kw. I only run around 1200 watts out of a Drake L4B

The Carolina Windom seems to use a 4:1 voltage balun and a 1:1 current
balun closer to the tx. (I say seems because IIRC it is a proprietary
design.)

The loss in the voltage balun can be expected to be severe when the load
impedance is very high due to the resultant high flux level in the core.

Whilst commercial producers commonly state power limits, and often
extravagantly, few manufacturers give you loss characteristics,
especially for impedances a long way from nominal.

For an experiment, I measured the "heavy duty" 4:1 Ruthroff balun in a
popular 300W rated ATU with a VNA, and calculated efficiency of the balun
feeding a G5RV on five bands. Efficiency of the balun varied from 66% to
almost 100%. (Notes at http://vk1od.net/blog/?p=568 .)

It is my guess that the balun could safely dissipate say 10W continuous.
Then at 66% efficiency, it would only safely accept 30W continuous input.
Fortunately, the peak to average ratio of SSB is something like 30:1, so
it would probably handle 1000W PEP SSB telephony ok.

Rule no 1: Balun manufacturers often supply little information.

Rule no 2: Information that is supplied is of little use in establishing
behaviour on extreme loads.


amp. That balun will heat up and quit working ( swr goes way up from
about 1.7:1 at the frequency I use most) if I run more than about 500
to 600 watts SSB to the antenna for any length of time. The antenna

Using my peak to average ratio, you are talking about an average power of
perhaps 20W.

You have probably reached the Curie point of the core, and it can be
quite low depending on the mix.

It is not unusual that 4:1 voltage baluns that have adequate performance
on a 200 ohm load have efficiency less than 50% on extreme loads such as
might be experienced with the CW.


is fed with a good grade of rg8 and about 20 feet from the antenna is
a current balun (the one with the beads over the coax). It will heat
up some but when I take it out of the line, the 4:1 balun still heats
up . The 1:1 bead choke does not heat up to any big ammount when I
put it on a dummy load and put 1200 watts to it.

The heating of a choke is due to flux cause by common mode current, and
some copper loss. Did your test configuration have zero common mode
current?

Though some show mathematical derivation for the magnitude of common mode
current based on Zo alone (which leads to Rule 500), it is my contention
that approach is not valid in an antenna application, and common mode
current may be much higher or lower than indicated by that method.


I had a low power balun up with the same antenna and running 100 watts
the antenna seemed to work fine.

If it was not for the wide bandwidth and good results I have been
getting , I would just run an 80 meter dipole and no balun. Also want
an antenna for 40 meters.

Don't overlook that a lossy balun leads to lower VSWR, and that is often
erroneously interpreted as an indicator of "good results".

Owen