[INRAD] YAESU FT-847 ROOFING FILTER MOD

[Charlie Mazoch Jr.]

Hi All:
 This is a modification to incorporate an INRAD roofing filter and 
performance board into the Yaesu FT-847 1st IF.
The INRAD roofing filter performance board used is the Icom 765 type 
with INRAD's FT-847 Yaesu 45.705 Mhz crystal roofing filter. On the 
INRAD board R8 is unsoldered at the junction of C7, J2 and soldered to 
the ground plane. This allows a current path to ground for switching. 
The +8 volts for the INRAD board was derived by soldering an LM7808 to 
the input and ground leads of Q1111. It is positioned over Q1111 and 
held in place by the soldered leads.. The output lead is bent over and a 
wire soldered to it for positive 8 volts. The transceivers +8 volt buss 
had too much noise and hash to be utilized. A simple means of switching 
the filter in or out can be had by installing a miniature toggle switch 
into the external die cast enclosures cover and supplying it with the +8 
volts mentioned. A more complex method using the transceivers mode 
button switches can also be employed. Epoxy glue two 2N5447 PNP TO92 
transistors top down near CF1002 The emitters are soldered together and 
tied to the +8 volts described. The collectors have individual wires 
soldered to them and routed through the top rear air slot behind the 
transceivers RF section and to +8T and +8R on the INRAD board. One base 
goes through a 4.7 K ohm 1/8 or 1/4 watt resistor soldered vertically to 
TP1013. Test pads TP1014 and TP1015 each have shortened cathode leads of 
1N4148 diodes soldered to them. These are mounted upright. The anodes 
tie together and go through a 4.7 K ohm 1/8 or 1/4 watt resistor to the 
other transistor base. When CW or SSB is selected these test points go 
low. When AM or FM is selected TP1013 goes low. The transceiver uses 
its  +8 volt buss for switching filters so utilizing this switching 
scheme using PNP transistors the added supply can't be higher than the 
buss voltage. Be very careful in construction if using this method of 
switching as the test pads and circuit traces are extremely fragile! The 
RF cable at J3009 on the RF board is unplugged from the AF/CNTL board 
and routed through the upper rear air slot behind the RF board. I 
purchased an RF cable from Yaesu and pulled its connectors off. Then I 
reamed the pins with a miniature drill bit and soldered the connectors 
to a 19 inch long  RG-188A/U 50 ohm Teflon coax. This cable is routed 
from J1001 on the AF/CNTL board to the transceivers upper side and out 
the upper rear air slot also. The RF cable connectors are replaceable 
with RFM-2100-1 which are available from  online sources. Powell 
Electronics or jkelect.com were a couple of sites. If INRAD kit's this 
mod they may supply the RF cable with connectors.  The die cast 
enclosure used is a Hammond 1590M,  Mouser part # 546-1590M. Looking at 
the back measure 1.820 inward from the right edge. Measure .780 from the 
lower edge. Where these points intersect drill a #20 hole. Countersink 
it on the enclosures inside for a 4 mm x 16 mm flathead screw. This 
screw is available at most hardware stores. On the vertical edge of the 
enclosure facing the transceivers center measure .300 inch from the 
upper lip where the cover goes. From the lower edge measure .830 inch. 
 From the upper edge measure .830 inch. At these intersecting points 
drill two 3/16 inch holes and slot them inline with the enclosures side. 
This is so the RF cable connectors will clear. Between the upper slotted 
hole and the upper edge drill a clearance hole for the +8 volt wire or 2 
filter switching wires to go through. Drill four #34 through holes in 
the enclosures back for mounting the performance board and use 4-40 
screws, an internal tooth LW plus 6-32 and 4-40 nuts inside for board 
stand offs. The die cast enclosure is fastened to the transceivers 
ground lug with the 4 mm flathead screw using a 10-32 nut between the 
enclosure and ground lug as a spacer. If additional support is desired 
one can also drill a #34 hole in the transceivers side cast ear and 
through the die cast enclosure side for a 4-40 screw, LW and nut. Do all 
the drilling on the die cast enclosure before mounting it to keep the 
transceiver free of metal chips.
The miniature drill bit mentioned in the mod is a pin vise type with 
several very small diameter drill bits in its body and is normally used 
as a tip cleaner for acetylene torches. These can be purchased at any 
welding supply. Specify the drill bit type if purchasing a set. They are 
also great for cleaning solder from thru holes on PC boards. A drill bit 
of desired size is chucked in the pin vise and turned by hand.
 I will be adding this modification to dk.mods with photo's. My Nikon 
digital camera is in for repair at the present time. The FT-847 does 
have an exceptionally quiet receiver. Gleaning over the RF section Yaesu 
did use some very low noise figure transistors (2SC3356) in the first 
two stages.         73's  Charlie  W5VIN
-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/list_inrad.net/attachments/20060602/26c5354c/attachment.html