RadioBanter - View Single Post - DeOxit on MFJ-1026 pots

October 21st 04, 04:27 PM

(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