Baluns for RX doublet
 

I am trying to get the best performance from my Ten Tec RX-320 when it
is connected to my shack's QRP 40M extended double zepp (176 ft
overall, fed with 300 ohm twinlead).

Performance on HF improved when I inserted an LDG 4:1 balun. I
substituted a $3 TV balun (300/75) and the improvment remained.

However, I noticed that VLF/LF -- for which my radio has the AMRAD mod
-- has gone more or less deaf. I can't even hear Loran on 100 kHz;
without the balun it was 59. BCB -- already attenuated with an I.C.E.
BCB filter but also 59 -- has also gotten worse.

Why would a balun made for high frequency impede low frequency (i.e.
below 1.5 kHz)?

Ken KC2JDY

Ken
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On Mon, 03 Jan 2005 00:34:04 -0500, Ken wrote:

I am trying to get the best performance from my Ten Tec RX-320 when it
is connected to my shack's QRP 40M extended double zepp (176 ft
overall, fed with 300 ohm twinlead).

Performance on HF improved when I inserted an LDG 4:1 balun. I
substituted a $3 TV balun (300/75) and the improvment remained.

However, I noticed that VLF/LF -- for which my radio has the AMRAD mod
-- has gone more or less deaf. I can't even hear Loran on 100 kHz;
without the balun it was 59. BCB -- already attenuated with an I.C.E.
BCB filter but also 59 -- has also gotten worse.

Why would a balun made for high frequency impede low frequency (i.e.
below 1.5 kHz)?

Ken KC2JDY

Ken
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remove "zz" from address)
Ken,
When I was reading articles on home-rolled baluns the "TV balun" was
referenced a few times in regard to use on HF. From what I recall,
they started to poop out around 10 MHz and got worse as the frequency
lowered which would explain why you're okay on HF but worse on
MW/LF/VLF. From what I recall it has to do with the fact that those
"TV baluns" just don't have a sufficient number of windings to "prime
the electron pump" at lower frequencies. I've taken a couple apart to
use the torroid for a 9:1 transformer and the winding ratio on each
was 2:1. Are you okay on the lower frequencies with the LDG balun?
If so then at least it's narrowed down to one component.
Perhaps it's time to bust open the balun, remove the torroid and roll
your own. Use #26 or smaller enamel wire (magnet wire) and a 20:10
winding ratio for your 4:1 balun and you may find your problem on the
lower frequencies goes away ....... or at least isn't as bad.

Hope that helps,
Howard

"Ken" wrote in message
...
I am trying to get the best performance from my Ten Tec RX-320 when it
is connected to my shack's QRP 40M extended double zepp (176 ft
overall, fed with 300 ohm twinlead).

Performance on HF improved when I inserted an LDG 4:1 balun. I
substituted a $3 TV balun (300/75) and the improvment remained.

However, I noticed that VLF/LF -- for which my radio has the AMRAD mod
-- has gone more or less deaf. I can't even hear Loran on 100 kHz;
without the balun it was 59. BCB -- already attenuated with an I.C.E.
BCB filter but also 59 -- has also gotten worse.

Why would a balun made for high frequency impede low frequency (i.e.
below 1.5 kHz)?

Ken KC2JDY

Ken
(to reply via email
remove "zz" from address)

Ken,
I swept a pair of 300:75 Ohm TV baluns back/back on an HP network analyzer
once. As I recall, they were useless below about 7 MHz.

Tam/WB2TT

It's not surprising a balun intended for TV frequencies doesn't work at all
on MF and LF.

The inductance of the balun windings is far too small. Like-wise, the
ferrite core dimensions and the number of turns. The windings are
practically short-circuits.
----
Reg, G4FGQ