Hi, folks - thanks to the recommendations of the good folks here, and
having reasonably assured myself that the MFJ-1026 does not have
plastic pots inside (or any other similarly sensitive innards), I gave
a couple quick squirts of DeOxit D5 Power Booster 5% to each of the
three key pots (main antenna gain, aux antenna gain and phasing
adjust), rocked the knobs several times as prescribed on the DeOxit
can, and allowed the stuff to evaporate for about 24 hours. I was
careful to gently cover the rest of the innards with a clean cotton
terry cloth while spraying the stuff into the pot holes. Two amazing
things happened:

(1) The static of the dirty pots is GONE GONE GONE! Huzzah!
(2) The degree of AM BCB intermod, especially below 4 MHz, is
dramatically increased, almost to the point where nothing legitimately
below 4 MHz can get through. All preamps off, still get the gunk
where it wasn't before. Booo.

So, a mixed bag (it least for now)!

It could be that the DeOxit worked so well that it brought the unit
back to its normal operating status - that is, a collector of intermod
junk from lower freqs (I do live in an area where BCB powerhouses
abound, on the edge of SF Bay). Or, it could be that I did not let
the stuff evaporate enough (so it gets another 24 hours as we speak).

Or, the DeOxit had some unintended effect on the unit, either inside
or outside the pots. I think this is unlikely.

As I investigate more, I will try to fill in the gaps. I also have a
PAR BCB intermod reduction filter I will try ahead of and behind the
unit. Meanwhile, I will appreciate any other ideas folks might have.

73, and don't let the political junk get you down,
Bruce Jensen

Hi, all - Last night, I tried the use of a PAR BCB High-Pass filter to
substantially weaken the signal of AM BCB stations coming into the
system via the antenna. This device works great - it is obvious from
listening to the MW spectrum that MW stations are attenuated
enormously; signals as high as S-7 or 8 are made unreadable without
the preamp, and even powerhouses are cut way down to size.

With this thing in line, both before and after the MFJ-1026, the
intermod products are *still there* on many frequencies from 5 MHz and
down, and even show up as high as the 31 meter band, plus one spot on
25 meters. Some of the products heard reflect stations that, with the
PAR filter, only register about S-3 or 4 on their home frequency!

I cannot believe that the 1026 is causing this weird siuation, despite
the fact that it appeared simultaneously with the use of the DeOxit on
the pots. The same problem happens on both radios that are attached
to this antenna system, so I do not think it is with radios
themselves. Moreover, it seems at worst before sunset, with gradually
diminishing severity as the evening progresses.

The only other path I can think of is that *the signals being mixed in
are coming over the 115VAC electrical lines.* I had never considered
this before, but with miles of power lines fairly close to several
high-power AM BCB transmitters, it does not seem far-fetched to think
that some resonance may be occuring in the lines. We don't get this
problem on any other equipment in the house (portable radios, TV,
etc.) so I am not yet married to this idea; but, if this is the case,
then it may be that the only way stop it is to run the whole works
from a 12v battery, which I am not quite prepared to try yet. I have
placed RF chokes (ferrites) on the power cords coming into the R75
wall wart, both the 115VAC and 13.8VDC sides, and will soon place one
or more on the MFJ-1026 power supply and more on the antenna cables as
well, especially either side of the PAR filter.

Aside from this particular annoying problem, I have already managed to
get the radio's RF background quieter than at any time in the past,
using the chokes and some coax coil "baluns." As I keep track of what
works and what does not, I will try to report my results.

73, and remember that the U.S. and the world will survive regardless
of which candidate is elected...

Bruce Jensen
************

(bpnjensen) wrote in message . com...
Hi, folks - thanks to the recommendations of the good folks here, and
having reasonably assured myself that the MFJ-1026 does not have
plastic pots inside (or any other similarly sensitive innards), I gave
a couple quick squirts of DeOxit D5 Power Booster 5% to each of the
three key pots (main antenna gain, aux antenna gain and phasing
adjust), rocked the knobs several times as prescribed on the DeOxit
can, and allowed the stuff to evaporate for about 24 hours. I was
careful to gently cover the rest of the innards with a clean cotton
terry cloth while spraying the stuff into the pot holes. Two amazing
things happened:

(1) The static of the dirty pots is GONE GONE GONE! Huzzah!
(2) The degree of AM BCB intermod, especially below 4 MHz, is
dramatically increased, almost to the point where nothing legitimately
below 4 MHz can get through. All preamps off, still get the gunk
where it wasn't before. Booo.

So, a mixed bag (it least for now)!

It could be that the DeOxit worked so well that it brought the unit
back to its normal operating status - that is, a collector of intermod
junk from lower freqs (I do live in an area where BCB powerhouses
abound, on the edge of SF Bay). Or, it could be that I did not let
the stuff evaporate enough (so it gets another 24 hours as we speak).

Or, the DeOxit had some unintended effect on the unit, either inside
or outside the pots. I think this is unlikely.

As I investigate more, I will try to fill in the gaps. I also have a
PAR BCB intermod reduction filter I will try ahead of and behind the
unit. Meanwhile, I will appreciate any other ideas folks might have.

73, and don't let the political junk get you down,
Bruce Jensen

"bpnjensen" wrote in message
om...
[snip]

(2) The degree of AM BCB intermod, especially below 4 MHz, is
dramatically increased, almost to the point where nothing legitimately
below 4 MHz can get through. All preamps off, still get the gunk
where it wasn't before. Booo.

You might want to look it over for a wire pulled loose, a cracked circuit
board trace or a poor solder connection. It's possible you did some
inadvertent damage as you disassembled it. Happens to me from time to time.
Even if I didn't spot anything, I would probably shotgun a bunch of solder
joints with an iron.



Or, it could be that I did not let
the stuff evaporate enough (so it gets another 24 hours as we speak).

Evaporation shouldn't be a factor. The solvent is flammable and it's wise
to give it time to evaporate if the stuff got into a power switch. But just
having the stuff sloshing around inside a pot isn't going to change it's
performance. The solvent isn't conductive. The solvent does have some
dielectric constant, and can effect the way a tuning capacitor tunes until
it evaporates.



Or, the DeOxit had some unintended effect on the unit, either inside
or outside the pots. I think this is unlikely.

As I investigate more, I will try to fill in the gaps. I also have a
PAR BCB intermod reduction filter I will try ahead of and behind the
unit. Meanwhile, I will appreciate any other ideas folks might have.

Look for damage.


73, and don't let the political junk get you down,
Bruce Jensen

Frank Dresser

Subject: DeOxit on MFJ-1026 pots - more
From: (bpnjensen)
Date: 10/14/2004 2:59 PM Central Daylight Time
Message-id:

Hi, folks - thanks to the recommendations of the good folks here, and
having reasonably assured myself that the MFJ-1026 does not have
plastic pots inside (or any other similarly sensitive innards), I gave
a couple quick squirts of DeOxit D5 Power Booster 5% to each of the
three key pots (main antenna gain, aux antenna gain and phasing
adjust), rocked the knobs several times as prescribed on the DeOxit
can, and allowed the stuff to evaporate for about 24 hours. I was
careful to gently cover the rest of the innards with a clean cotton
terry cloth while spraying the stuff into the pot holes. Two amazing
things happened:

(1) The static of the dirty pots is GONE GONE GONE! Huzzah!
(2) The degree of AM BCB intermod, especially below 4 MHz, is
dramatically increased, almost to the point where nothing legitimately
below 4 MHz can get through. All preamps off, still get the gunk
where it wasn't before. Booo.

So, a mixed bag (it least for now)!

It could be that the DeOxit worked so well that it brought the unit
back to its normal operating status - that is, a collector of intermod
junk from lower freqs (I do live in an area where BCB powerhouses
abound, on the edge of SF Bay). Or, it could be that I did not let
the stuff evaporate enough (so it gets another 24 hours as we speak).

Or, the DeOxit had some unintended effect on the unit, either inside
or outside the pots. I think this is unlikely.

As I investigate more, I will try to fill in the gaps. I also have a
PAR BCB intermod reduction filter I will try ahead of and behind the
unit. Meanwhile, I will appreciate any other ideas folks might have.

73, and don't let the political junk get you down,
Bruce Jensen







De-Oxit D-5 isn't the best chemical from Caig Laborities for carbon block
potentiometers. The have a product called Cailibe which replenishes the
lubricant after the pot is cleaned.

D-5 is a great cleaner, but Cailube is specifically for potentiometers.

And, there is no need to wait 24 hrs. for anything cleaned with D-5 to
evapotate. It leaves a slight film.

Les

"Frank Dresser" wrote in message ...
"bpnjensen" wrote in message
om...
[snip]

(2) The degree of AM BCB intermod, especially below 4 MHz, is
dramatically increased, almost to the point where nothing legitimately
below 4 MHz can get through. All preamps off, still get the gunk
where it wasn't before. Booo.

You might want to look it over for a wire pulled loose, a cracked circuit
board trace or a poor solder connection. It's possible you did some
inadvertent damage as you disassembled it. Happens to me from time to time.
Even if I didn't spot anything, I would probably shotgun a bunch of solder
joints with an iron.

Thanks for this Frank - I will look and maybe solder too, although all
I really did was take the top off - I doubt if I will find anything
(not having any significant experience with looking at a circuit
board, much less with a soldering iron) - but I am still puzzled as to
how the signals are getting into the equipment in the first place -
with the preamps all off, the MFJ's built-in MW attenuation and the
PAR filter there, the signal strength just isn't there - on the
antenna at least.

After another experiment, FWIW, I get this on the radio without the
MFJ-1026 installed, too. The RFI is just *everywhere* around here.

Thanks,
Bruce

Maybe the case top isn't making a good ground, or a ground connection
is lost elsewhere.

The thing can feed back into itself, which will overload things in
general and any frequency can pop up anywhere.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

Ron Hardin wrote in message ...
Maybe the case top isn't making a good ground, or a ground connection
is lost elsewhere.

The thing can feed back into itself, which will overload things in
general and any frequency can pop up anywhere.

Thanks, Ron - Could be - but I am not the person to try to figure this out!

As I mentioned, the effect seems to be there whether the MFJ-1026 is inline or not.

Bruce Jensen

(bpnjensen) wrote in message . com...
Ron Hardin wrote in message ...
Maybe the case top isn't making a good ground, or a ground connection
is lost elsewhere.

The thing can feed back into itself, which will overload things in
general and any frequency can pop up anywhere.

Thanks, Ron - Could be - but I am not the person to try to figure this out!
As I mentioned, the effect seems to be there whether the MFJ-1026 is inline or not.
Bruce Jensen

Followup to this, and maybe problem essentially resolved ~ ?

When I reported earlier, I had two makeshift antennas plugged into the
rear of the MFJ unit. I have since upgraded the main antenna to a
DX-Ultra fed by RG-213 cable, and featuring a sizable coiled-coax
choke under the antenna (14 turns x 7 inches diameter, approximately
25 foot coil). Now, on this antenna, the band backgrounds from 9 MHz
and up are essentially *silent*, just a gentle hush between myriad
booming stations, and while not as quiet, the bands down lower are
significantly reduced in noise *and* these intermod effects, even when
the auxilliary antenna is still the makeshift one (which I will be
upgrading shortly). From 7 MHz and up, S-0, 1, 2 and 3 signals were
popping out on frequencies formerly swamped by messy noise.

The effect of the coax choke is so substantial, in fact, that it is
fair to say that the MFJ-1026 has become *almost* an afterthought for
those bands above 8-9 Mhz - the noise that I formerly battled is
practically gone on those frequencies, with only an occasional
malfunctioning streetlight rendering static. It still helps for
constant static that affects the longer wavelengths, but since the two
input antennas do not quite "hear" the same way, some noises cannot be
effectively reduced.

Another benefit of this configuration is that the DSP on the Icom R75
seems to work better - it requires lower DSP values to reduce most
noise, and when the higher values must still be employed, they can be
employed more effectively (I can now use the full range of the DSP
from 1 to 15, and the voices and information remain fully intelligible
while the noise is subdued).

I also did add some ferrite chokes to various lines on the radio, the
MFJ-1026 and the computer to see if those would help - there was a
very modest improvement on some specific noises, but nothing compared
to the effect of the coax coil choke. Still, it was worth the $10 I
paid for the batch of 'em. I will add some to the TV, VCRs and DVD
players shortly,

Not wanting to make the choke coil much bigger, I think I am going to
add one or more ferrite chokes to the RG-213 below it outside (and
maybe at the receiver) to see if the noise reducton can be extended to
lower frequencies. I may even stick a 1:1 un-un inline somewhere to
see what that will do, but since that will require chopping into the
coax or adding an additional 10' or so of same, I think I will save
that as a last resort.

The best part of all of this is that none of this was difficult to
accomplish for a technical numbskull like me. Getting the DX-Ultra up
on the pole with that somewhat heavy coil under it was tricky (RG-213
is substantial stuff to say the least!) but brute force can accomplish
wonders when cleverness finally fails :-)

A drawback to the DX-Ultra, at least at my location (San Francisco Bay
Area) and with this somewhat minimal height (27 feet to center hub,
oriented so that broadside faces WSW - ENE), is that it is somewhat
deaf on 60 through 160 meters. The makeshift antenna I have in the
aux plug on the MFJ-1026 (essentially a 45-foot wire slung up on the
roof, hi-Z) is significantly better for these wavelengths. I checked
for electrical continuity from the coax at the radio out to the ends
of the DX-Ultra, and that's fine - the full half-wavelength is being
represented if one considers the coils. The upgrade to the makeshift
antenna is going to have to be at least as good, and hopefully better
than, either existing antenna on the lower freqs. If I can get it as
quiet as the DX-Ultra on upper frequencies, I may dispense with the
MFJ-1026 altogether, as good as it is on some noises.

Sorry for the rambling - I was excited about the results, and just
hoping this can be informative for someone.

Bruce Jensen