RadioBanter - View Single Post

July 24th 05, 06:14 AM

In article . com,
wrote:

Telamon wrote: ------------------------------- In article
.com,
wrote:
Telamon wrote:

That depends on the core. Some are no good for 3 to 30 MHz. TV
operates at 50MHz.

-- Telamon Ventura, California ----------------------- So people
keeep telling me. I have built many, around 30,of these little gems
and they all worked down to below MW with minimal losses. Read Mr
Doty's comments. They have all worked great from .5MHz to above
20MHz with every scalvaged TV core I have used. Perhaps I have
just been lucky, or maybe, just maybe for cores so small loss are
not as high as many people think. I will include an observation
from Mr Doty himself:"

Snip

Well then how many times am I going to have to tell you then is the
only question left.

All cores have a frequency response range. You have to pick an
appropriate one depending on where you intend it to operate. I have
come across ferrite cores that are worthless 10 MHz so it may work
well on the upper bands and poorly on the lower. You may not notice
this right off because evening and nigh time signals on the lower
bands generally have more signal power.

I believe you have some basic equipment so you can check it out.

I think you may have better luck in the power supply section of
equipment you are tearing apart for components. Specifically the EMI
section will likely have some common mode chokes that are designed to
operate over the short wave spectrum to suppress conductive noise.

TV RF ferrites are designed for 50MHz to 500MHz or something along
those lines and their response of some falls off on the low end so I
don't recommend using them unless you can test them.

You either need to know that the material is of a certain type or be
able to test it.

-- Telamon Ventura, California
----------------------------------------- OK I am trying to be
polite. There is already enough anger in the world. But, this is
getting silly, back in Nov 2001 this same thread came up and John
Doty explained why, for this application, with small TV cores, the
ferrite type didn't mater that much. He gave actual loss values. Your
response was: ---------------------------

Snip

I have made and tested choke type Baluns from impedance transformers
used for TV and FM devices. Some cores worked well right on down to the
bottom of the AMBCB band and others stopped working in the 10 to 15 MHz
range. All worked just fine above 15 MHz. Let me define working well
as I got the impedance transformation I designed it to have above 15
MHz and not below that frequency. Because I scavenged them I don't know
what the cores were made of other than they were ferrite.

When you made one from scavenged parts I suggest that you test them.

--
Telamon
Ventura, California