[INRAD] [Fwd: YAESU FT-847 ROOFING FILTER MOD]

Fri Jun 9 06:40:13 CDT 2006

Hi All:
  This is a revision to the Yaesu FT-847 INRAD roofing filter 
modification posted earlier. I decided to use a smaller enclosure to 
house the INRAD performance board and roofing filter.
Charlie W5VIN

-------- Original Message --------
Subject: 	YAESU FT-847 ROOFING FILTER MOD
Date: 	Fri, 09 Jun 2006 06:24:15 -0500
From: 	Charlie Mazoch Jr. <w5vin at earthlink.net>

Hi All:
 This is a modification to incorporate an INRAD roofing filter and 
performance board into the Yaesu FT-847 1st IF. These are listed as VHF 
filters for experimenters on International Radio's site
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 groundplane side of C9. 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, (near the large power leads on the AF/CNTL board) 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 FT-847 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 1590L,  Mouser part # 546-1590L. It measures 
4 x 2 x 1 inches.  Looking at the back measure 1.820 inward from the 
right edge. Measure .750 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 scribe a line  .300 inch from the upper lip where the cover goes. 
Clip off all four corners of the PC board at a 45 degree angle about 
half way across the existing mounting holes so it will fit and then 
place the PC board into the enclosure. Mark where the RF connector 
centers are on the enclosure. 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 slotted holes drill a 
clearance hole for the +8 volt wire or 2 filter switching wires to go 
through.  Drill a #34 hole through the PC board in an open area between 
D1 and the filter. Center the board in the enclosure and drill one #34 
hole through the back in line with the drilled PC board hole. Insert a 
4-40 screw through the enclosures back and an internal tooth LW plus 
4-44 nut inside for a board stand off. Remember to clip off all soldered 
connections on the PC boards trace side to prevent shorts. The die cast 
enclosure is fastened to the transceivers ground lug with the 4 mm 
flathead screw.  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. If one uses the toggle switch method of switching the INRAD 
filter in or out this is actually an easy mod. Other than adding the 
LM7808 regulator no surgery on the transceiver's pc boards is required 
and the performance board to transceiver uses existing RF connections. 
Either downloading or purchasing a service manual is a big plus. I 
assume no responsibility for someone damaging their rig. If you feel 
unqualified get someone knowledgeable to help.
 I also experimented with the INRAD feedback amplifier by changing out 
the transistors to 2SC3355, (lower noise figure) R5 to 18 ohm and R6 to 
270 ohm, (several combinations were tried) for a circuit gain of 6 db 
over bypass mode. Audio spectrum sweeps taked at the data port output 
indicated that no signal internal receive noise dropped by 4-5 db even 
with the added rf gain of the feedback amplifier. A lot of this is 
probably due to the INRAD roofing filter 5 Khz passband and shape factor 
which tends to limit internal noise generated in the receivers first 
stages of RF amplification. MDS with DG2IAQ's, (see dk.mods) Shottsky 
diode mod approaches -135 to -138 in CW position. MDS in SSB is -133 to 
-135 db. The bandpass diode mod is a big plus on lowering receiver 
quiescent noise levels and improves MDS. I agree with W8JI on his 
comments about the PIN diode issue versus switching diodes when used as 
low level signal path switches.
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.         
73's  Charlie  W5VIN
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