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GM7HUD > SIX 22.12.05 01:22l 78 Lines 4517 Bytes #999 (0) @ WW
BID : 3A3168GM7HUD
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Subj: CB to 6m conversion 4
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<DK0WUE<I0TVL<ED1ZAC<GB7YKS<GB7SYP<
GB7ESX
Sent: 051221/2224z 71793@GB7ESX.#31.GBR.EU $:3A3168GM7HUD [Witham, Esx]NNA V3.1
*CB TO SIX METRES* Part4 - The Reciever Section
By Shawn Baris ZR1EV
PO BOX 212
Brackenfell
7561
Republic of South Africa
*Anyone is free to use the following information for private use on the
provision that it is not used for commercial purposes . Permission is
granted by the author , ZR1EV , to publish and or distribute all or part of
the following on the condition that recognition is given to the author . In
the case of it being used in a newsletter or magazine , a copy of the
aforementioned should be sent to the above address.*
Now that the rig has been converted to 10 meters and it has been
thoroughly tested there , we can proceed with the conversion to 50Mc . You
may by now have noticed that the chassis of the rig is isolated from the
earth-plane on the printed circuit board itself . This was done to enable
the rig to be installed in either a positive- or negative earth vehicle .
The chassis must be at RF earth though , as the antenna socket must "see"
the earth on the PCB . This is where a lot of "conversions" fall short in
performance . So what needs to be done first is to replace all the disk
ceramic capacitors that connect earth and ground together . All round the
PCB where it is screwed to the metal chassis , you will see them . Don't
forget the two caps on the DC connector ! Change all the capacitors with a
value of 0.047æF (47nF) to 0.022æF (22nF) .
Now for the reciever section . Change C100 (33pF) to 18pF and remove T7 .
Carefully disassemble T7 so you can get to the windings . Hold the coil
former upright (pins facing down and the side with the 3 pins facing you) .
CAREFULLY liberate the wire from the righthand pin and unwind the existing
windings , taking care not to break the delicate strand . You'll see that
the former has 4 "ribs" to hold the winding . Leave the wire attached to
the leftmost pin and proceed to first wind 4 turns onto the second "rib"
from the top in a clockwise direction . The "ribs" have a gap in the middle
so cross over to the topmost "rib" and wind 4 more turns on there in the
same direction , feed the wire down to the righthand pin and solder it onto
the pin . The secondary winding stays as is . Carefully reassemble , not
forgetting the green plastic spacer on top of the coil former , and solder
back into the printed circuit board . T7 is a Mitsumi type ETR0333 .
Next , change C102 (47nF) to 22nF disk ceramic . Remove T8 and dismantle
as with T7 and remove the small tubular ceramic cap . I found that a small
surgical knife to be ideal here ,as you can then just cut the leads off the
capacitor , instead of battling to get them off the pins in an orderly
fashion . You will now notice that this time the winding has a tap that
goes to the centre pin . In this rig the tap is not used , so we can just
rewind as for T7, except this time it will be 1turn second rib from the top
and 4turns on the topmost rib back to the righthand pin and solder .
Assemble and solder back into the printed circuit board . This time you
have to add a capacitor to the print side of the board . T8 has 5 pins ,
grouped 2 on the one side and 3 on the other : the side with the 3 pins is
the primary in this case . Solder a 39pF ceramic capacitor accross the
outermost 2 pins of the primary winding on the foil side of the board . T8
is a Mitsumi type 10CA006 .
Now remove T9 and strip down as before . This coil has a pink pot core and
is a Mitsumi type 10CB001 . Wind 3turns onto the second rib from the top
and 1turn on the topmost rib . Solder back into the printed circuit board
and add a 39pF capacitor onto the primary as for T8 .
If your rig was operating for eg. on 28.790 on a specific channel , switch
it back to that channel and calculate the new six metre frequency as
follows : [10metre frequency] + 21.39 = [six metre frequency] . So in our
example it would be : 28.79 + 21.39 = 50.180 . Set your RF generator to
that frequency and (using the correct trimming tool) adjust the cores of T7
T8 and T9 for maximum "S"-meter reading . Do not be concerned at this point
if the recieve sensitivety is not too good . We still need to change the
Low Pass Filter on the transmitter section when we get to that stage .
You will also notice that USB and LSB have swapped around and dont seem to
be on frequency ... more on that in part 5
CU in part5
vy 73 de Shawn ZR1EV JF96ic
73 de Andy GM7HUD
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