Hi Tobanders,
I am sorry to come on the reflector with an old discussed item, the
MFJ-1025, but I have been unable to get any assistance or direct reply from
the top wisdom on the subject, Tom Rauch W8JI.
My unit was bought in march 1998 from HRO but I have never been able to get
any good result with it, even with the use of different kinds of receiving
or sense antennas, despite all the favorable comments I read in the past
years on this reflector.
I am not suffering any BC QRM at my QTH, nor any defined local interference,
but I just want to take full advantage from my several (and growing)
receiving antennas by trying to phase them (in addition to the classic
broadside set-up with some pennants).
So I recovered again that MFJ from the junk in order to try the
modifications suggested by W8JI (www.w8ji.com/mfj-1025_1026.htm) and WA1ION
(www.hard-core-dx.com/mordicdx/antenna/special/mfj1026.html) and opened the
box to localize the parts to be changed, but I realized that the components
on the board don't exactly correspond to the scheme (both marked Model 1025
/ rev. 1 / P/N 862-1026 / date 12/17/1996).
The following are some of the mod. instructions, but I found the noted
discrepancies, or I need a further explanation:
1) Remove D1, D5 at the output, and D10, D11 and D6,D9 at the inputs.
On the schematic there is none of them, .....but in the box I see two back
to back diodes instead of "Lamp 2" (are those D1,D5 ?); in the AUX input I
see two back to back diodes on JMP3 to Q8, but I don't find any of them on
the MAIN input ....
BTW in the schematic D1 is paralleling the relay coil, but its place is
clear on
the board.
2) R25 - 220 ohm - in the schematic is NOT in its place on the board
3) Remove C5 : thus D3 and D4 are to be connected directly to RLY1/TRANS ?
4) Mark Connelley also removes R26 and R27 - 100 ohms, or changes to higher
values: W8JI does not mention that, right ?
5) Filter modifications: increase the value of C12 and C13 by the same
factor as the decrease in frequency; they will reduce upper frequency limit
proportionally to the change. Actually C12, which covers low bands, is 470pF
(XC=188 at 1.8 MHz, 97 at 3,5 MHz and 48 ohms at 7 MHz) and C13, which
covers high bands, is 120 pF (XC= 95 ohm at 14 MHz,etc.). As I am not
interested on the bands above 1.8 MHz, which values are suggested ?
Scuse me if I put trivial questions, but I have never been in electronics
or communications studies or business, so my technical basics are rather low
and sometimes I need some kind help.
Many thanks and season's greetings to everybody on the Topband!
Best 73
Luis IV3PRK
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