On Aug 22, 2:49 pm, Denno wrote:
On Aug 22, 12:34 am, wrote:

On Aug 21, 5:11 am, Denno wrote:

Hi All. I recently received a GrundigS350as a gift from my son.
They were on sale at the time, and after reading all the reviews he
could find on MW DX, decided it was the best "bang for the buck" at
that time.

I love this radio! Like I said, it's primarily for AM DX.
Unfortunately, I use it in my basement office were the reception is
spotty at best. Picking up local stations is no problem, but DX'ing
from inside an 8" thick concrete foundation is out of the question.
Above the basement, such as using the radio on the second floor, I can
actually pick up Montreal stations 300 miles away with no external
antenna!

So I need a remotely mounted, external antenna to get full use of my
radio from the basement. My options are limited: I don't have a good
yard for a long wire or beverage. Whatever I use will be confined to
therooftopor inside the house. I have a small DC motor ideal for
rotating the antenna remotely from the basement, but any tuning
capacitors would have to be near the radio.

What I would REALLY like to do is put together the longestferritebar
possible, with an optimum number wire turns around it, connected to a
coax which would run down to my office and clip into the external
antenna connections on the radio. A separate control line will also
run down there for rotating the antenna.

I have not been able to find much info on externalferritebar
antennas. Could this be because there is no advantage toferriteover
an air core antenna outside of the radio?

So my question(s): Are there any plans or illustrations for an MW DX
ferritebar antenna available anywhere? (Web, ARRL pubs, etc) Is it
just a matter of connecting 2 or 3 feet worth offerritebars with

Thanks for the responses! There was a lot of good information and
references in the replies. I especially liked the stormwise site.
Funny how I can google for hours and still miss some of the best web
sites.

I had read in some other articles on the net that a longer ferrite bar
can be made from two shorter bars by using epoxy to glue them
together. I have my doubts about this. I realize that the inductance
may not know the difference and just "jump" across the glue joint, but
does it really? Perhaps winding the bar so the coil spans the glue
junction would compensate for the separation between the bars? Do
you think gluing two bars together would truly behave as one long
ferrite bar?

Thanks,
Denno

epoxy and then winding as many turns of light gauge wire as possible
around it? Do I need any sort of balun or isolation transformer?
(Lightning protection is not an issue. I always disconnect my
antennas when not in use)

Thanks,
Denno

http://www.stormwise.com/page26.htm

I've fiddled with loops and a North Hills transformer for the balun.
Still not as good as a wellbrook, but interesting from a hacking
perspective. Ebay has North Hills transformers from time to time, so I
wouldn't pay real money for one.

I think the bigger issue is the permeability of the core. I've fiddle
with air core loops and the North Hills. The signal strength isn't as
high as the wellbrook, but the signal quality isn't bad. I haven't put
a cap across the loop to tune it.

There is some fancy way to make the loop if you are going to put a cap
across it. It involves two loops and maybe two caps (but on the same
knob). I don't recall the details, but it is on the net someplace.

I don't particularly like tuned loops since you need to tune them as
you change frequency. If your radio has decent filtering, the tune
loop isn't really needed.

If you wanted to match impedance, you could determine the L of the
loop, and then use wL as the impedance. It really wouldn't be matched
since the inductor is reactive. The parallel LC is resistive at
resonance. I think it is real and infinite. [Too many years since I
had to know that stuff, but it should be on the net.]