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Kenwood TS-850S RX I.F. Board Modifications:
850 I.F. board mods


As with the DSP-100 TX mod, if you are a purist and want the fullest and flattest receiver response possible with the 850/DSP-100 combination for SSB, you will want to perform this modification which enables the receiver to respond flat from 20hz to 6kHz, including speaker, headphone, and ACC2 outputs.

850 Before - After Comparisons


Kenwood TS-850S i.f. Board Flat Frequency Response Modifications Instructions:


  • Place the 850 upside-down and remove all the screws on the bottom and sides of the case.
  • Remove the bottom cover.
  • Locate the I.F. board (X48-3080-00) and remove all Molex connectors and Ribbon Cables from the board.
  • Remove all screws and carefully remove the board.


Note: If you will be completely replacing the .1uF capacitors,
use the following replacements available at Mouser:

All capacitors listed below are rated at 16 Volts.

Click here for a global view of capacitor locations...
Capacitor Value Changes: Click Corresponding Links Below For Photo Details
NOTE: Please notice the installation notes below for convenience
C151 .047uF to 1uF
Mouser Part # Vishay (case 0805 1uF)
77-VJ0805V105MXJCBC

(Click to See Photo C151) Located on foil side.
C155 1uF to 10uF
Mouser Part # 667-ECA-1CM100
(Panasonic Electrolytic)
(Click to See Photo C155) This cap is an Electrolytic.
C156 .1uF to 1uF
Mouser Part # Vishay (case 1206 1uF)
77-VJ1206V105MXJTBC
(Click to See Photo C156)
C164 1uF to 10uF
Mouser Part # 667-ECA-1CM100
(Panasonic Electrolytic)
(Click to See Photo C164) Remove this cap BEFORE installing C 161. This cap is an Electrolytic.
C161 .1uF to 1uF
Mouser Part # Vishay (case 1206 1uF)
77-VJ1206V105MXJTBC
(Click to See Photo C161) Install this cap before re-installing C 164
C163 1uF to 10uF
Mouser Part # 667-ECA-1CM100
(Panasonic Electrolytic)
(Click to See Photo C163) This cap is an Electrolytic.
C167 10uF to 100uF
Mouser Part # 667-EEU-FR1C101B
(
Panasonic Electrolytic)
(Click to See Photo C167) This cap is an Electrolytic.
C168 470pF to 270pF
Mouser Part # Vishay (case 0805 270pF)
VJ0805A271KXJPBC
(Click to See Photo C168) Monitor Low-Pass
C169 .1uF to 1uF
Mouser Part # Vishay (case 0805 1uF)
77-VJ0805V105MXJCBC
(Click to See Photo C169) Monitor Low-Pass
C170 .1uF to 1uF
Mouser Part # Vishay (case 0805 1uF)
77-VJ0805V105MXJCBC
(Click to See Photo C170) Monitor Low-Pass
C172 .1 uF to 1uF
Mouser Part # Vishay (case 0805 1uF)
77-VJ0805V105MXJCBC
(Click to See Photo C172) Located on foil side.

C178 changes to 250 or 270pF
Mouser Part # Vishay
77-VJ0805A271KXJPBC (case 805)

(Click to See Photo C178) Monitor Low-Pass
C187 470uF to 1000uF or greater
Mouser Part # 667-EEU-FR1C102LB
(
Electrolytic) In series with the speaker/headphones
(Click to See Photo C187) This cap is an Electrolytic.
 

CAPACITOR ORIENTATION NOTE:
The orientation is relevant ONLY if using any polarized electrolytic capacitors.

When using the Electrolytic type capacitors as in C155, C163, C164, C167 and C187.
(The polarity of those electrolytics is clearly marked on the I.F. board.)

If you will be performing the direct Balanced Modulator feed for AM, leave the I.F. board out and see the "AM MODS" page.
Otherwise, you can now reinsert the I.F. board, replace the screws, connectors and bottom cover.


455 kHz I.F. RECEIVER FILTER MODS:
If you would like the widest receiver bandwidth possible, (RX and TX on AM) there are two methods of doing this:

- Place a jumper wire from pin 2 to pin 2 of the optional 455 kHz 500 Hz filter pins. (Photo 21)
Or:
- Install a Murada 20kHz filter on an Inrad/850 filter adapter board and install in the 455 kHz 500 Hz filter position. (Photo 22)

Make sure that you enable the 455 kHz I.F. 500 Hz position by setting the top panel dip switches appropriately.

These 455 kHz filter mods dramatically improve the receiver frequency response on SSB and AM but is most useful on AM.
Additionally, you can transmit through this filter position on AM when using the direct balanced modulator feed.
When using the DSP-100 with SSB, the 455kHz I.F. filter is not active, since the DSP-100 does all 455 kHz I.F. processing.


Kenwood TS-850 I.F. TX Bandwidth Power-On Menu Settings:
1 With the 850 turned off, press and hold the "SCAN" and the right "M.Ch" buttons simultaneously while turning on the radio.
2 Select menu 1 by rotating the "M.CH/VFO.CH" knob.
3 Turn the option to "ON" by pressing the "UP" button.
4 Press the "CLR" button to exit the power-on menu.
5 On transmit, you can now select the following filters in the 8.83 MHz I.F. resulting in the following on-air bandwidths (with the DSP-100):

None
= 6 kHz TX bandwidth (with DSP-100)
6k
= 4.5 kHz TX bandwidth
2.7k
= 2.4 kHz TX bandwidth

WARNING!!!
If the transmitter 8.83 I.F. filter is bypassed, it is highly recommended to use a Low-Pass filter at the output of the transmitter to prevent out-of-band products.

 

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