[INRAD] [Fwd: [Fwd: Re: FT-980 Yaesu Roofing Filter Mod]]

[Charlie Mazoch Jr.]

-------- Original Message --------
Subject: 	[Fwd: Re: [INRAD] FT-980 Yaesu Roofing Filter Mod]
Date: 	Wed, 08 Feb 2006 17:27:13 -0600
From: 	Charlie Mazoch Jr. <w5vin at earthlink.net>
To: 	Phil Smeaton <philhss at tpg.com.au>, George Cutsogeorge 
<w2vjn at rosenet.net>, List at inrad.net





-------- Original Message --------
Subject: 	Re: [INRAD] FT-980 Yaesu Roofing Filter Mod
Date: 	Wed, 08 Feb 2006 16:09:24 -0600
From: 	Charlie Mazoch Jr. <w5vin at earthlink.net>
To: 	List at inrad.net, George Cutsogeorge <w2vjn at rosenet.net>
References: 	<43E81349.9010202 at earthlink.net> 
<1139378202.43e9881aafbc0 at postoffice.tpg.com.au>



Hi Phil:
I don't know what went wrong but here is the mod.
Remove the coax from the IF board to the RF board at the If board end. 
This will now go to J1 on the INRAD board. This coax plugs in near the 
OEM filter on the Rf board. The Inrad amplifier board is modified by 
adding a 10 micro henry choke from the output, J2 to ground. This 
supplies a DC path for the diode switches. The input is modified by 
cutting the circuit traces near J1 center conductor. A 0 .1 micro farad 
capacitor  is soldered across the cut traces and it's other lead is 
soldered to J1's center conductor. This adds capacitive input to the 
feedback amplifier. The photo may show these changes. Remove R6, a 220 
ohm resistor on the INRAD board and replace it with a 120 ohm. The gain 
through the amplifier with this change is about 1 S unit more than in 
bypass mode. Too much gain here only drives up the quiescent noise level 
of the Receiver. This resistor provides negative feedback. The transmit 
lead, yellow is hooked to Q03's outer lead on the RF board through a 
7808 voltage regulator. The regulator has it's center lead cut off and 
is grounded by the RF board corner screw. It's visible in the photo 
under the attenuator switch shaft. The center lead, red is tied through 
a 7808 voltage regulator to the terminal strip at the rear of the rig. 
With the knobs facing you it is the 3rd solder lug from the right. I cut 
the center lead off this regulator also and mounted it under a lug 
screw.  Both of the points that switch Rx and Tx voltages are 12+ volts 
thus the need for 7808 voltage regulators. Check with a voltmeter that 
these voltage points are present in Tx or Rx! The supplied coax jumper 
is connected to J2 and to the IF board RF connector. I simply wrapped 
the INRAD board with 33+ 3 M electrical tape in two layers and it 
resides on top of the RF board. There is ample room for the bottom 
cover. The INRAD cascade filter mod sure tightened up the 2nd IF's pass 
band. With a 2.1 Khz INRAD for a second filter the difference is very 
evident when switching it in. This works great in crowded conditions.
In my opinion the Yaesu FT-980 is one of their better rigs. It has one 
of the quietest receivers I've listened to. The diode switches in it's 
Rx input filter networks are Shottky diodes and this translates to less 
electron or resistor noise.  For old technology it's still a great 
radio. The photo's will probably be deleted at  the INRAD site but I'm 
forwarding a copy to George.
73's  Charlie  W5VIN




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