Icom R9000 Discriminator Tap?

Status
Not open for further replies.

kruser

Active Member
Premium Subscriber
Joined
Nov 25, 2007
Messages
3,262
Location
St. Louis County, MO
I know this question has been asked here and other online sources but I've yet to find an accurate answer.

Is there a discriminator tap point in the IC-R9000 receiver?

This receiver appears to have multiple possible tap points but I can't tell if there is more than one for the various modes the R9000 can receive.

I don't feel like experimenting on it with its age plus physically pulling it out of the rack!


I also have an Icom R7000 that has a listed discriminator tap that does pass unfiltered audio using just a 10K ohm resistor but when done that way, the meters center tune reading causes the meter to deflect almost all the way to the right side so there is obviously something the tap loads down.

I played with ceramic caps of 1.0 uF and lower with bad results. They all acted as filters and caused the tap to no longer pass the audio needed for programs like DSD+ to work.

I found a 4.7uF non polarized cap to work for systems up to 9600 baud that did not cause any problems with the radio's center tune meter reading but not sure if that value may cause me other issues. The actual signal strength the meter indicates was not bothered by the tap with no cap inline.
Does anyone know of a proper cap value I can use in series with the 10K resistor that will not filter the taps frequency and render it useless as a tap point? I'm not really worried about finding an FM or NFM tap point in the R9000 but it would be nice having it if anyone knows the real tap point.

I'm mainly just interested in finding the proper capacitance value for the R7000 so an external tap will not render its center tune meter reading useless.
I also used a 2.2uF non-polarized lytic in series with the 10k resistor and that value cap also seemed to allow the radios center tune indication to stay accurate when hooked to an external audio input like DSD uses.
Bing as 4.7uF also worked and did not seem to filter any frequencies from higher baud rate systems, I ended up using the 4.7uF cap as it seemed less likely to cutoff frequencies from the baseband audio signal.
I know caps and resistors are often used in a parallel/series setup to filter unwanted RF signals that may be riding on the baseband audio tap point but in my case, when the published tap point is hooked up to an audio input for DSD, it really loads up the baseband output to where the center tune function is trashed.
The tap itself seems to work fine and the radios meter still shows accurate signal strength readings but when put into center tune mode, the tap loads the circuit so center tune readings are useless.
Using the non-polarized cap at 4.7uF does work but I feel I may still be filtering some needed signal if a higher baud rate system comes on the air and the 4.7uF cap is acting as a frequency filter. That cap does do a good job at filtering out any loading of the center tune function though.

Anyone have any advice for a DC blocking cap in series with the 10k resistor that will not block any baseband audio frequencies?

I could probably also increase the resistor value as there appears to be plenty of audio after the resistor but that is not the proper way to fix this problem.
I also tried some 1:1 audio isolation transformers but they also killed the center tune function of the R7000. So DC blocking is needed without also acting as an audio frequency filter when higher baud rate systems come on the air!

Thanks everyone.
 

bagmouse7

Member
Premium Subscriber
Joined
Jan 19, 2003
Messages
205
Location
NC, USA
Have you tried using pin 5 on the ACC socket on the back panel?
It's the AF detector output pin.
Good luck
 

slicerwizard

Member
Joined
Sep 19, 2002
Messages
5,595
Location
Toronto, Ontario
I also have an Icom R7000 that has a listed discriminator tap that does pass unfiltered audio using just a 10K ohm resistor but when done that way, the meters center tune reading causes the meter to deflect almost all the way to the right side so there is obviously something the tap loads down.
No DC blocker (no cap) will do that.


I played with ceramic caps of 1.0 uF and lower with bad results. They all acted as filters and caused the tap to no longer pass the audio needed for programs like DSD+ to work.
Of course. The smaller the series cap, the more it kills lower frequencies.


I'm mainly just interested in finding the proper capacitance value for the R7000 so an external tap will not render its center tune meter reading useless.
Just use a large one. I'd use 10 uF or more. You can parallel whatever you've got, like a couple of 4.7's, etc.
 

kruser

Active Member
Premium Subscriber
Joined
Nov 25, 2007
Messages
3,262
Location
St. Louis County, MO
Have you tried using pin 5 on the ACC socket on the back panel?
It's the AF detector output pin.
Good luck
I did try that pin on the rear but it is not unfiltered audio like the manual says.
It may pass 300 to 2400 baud HF packet signals but that is about it. Anything running at a higher baud rate is filtered.
 
Last edited:

kruser

Active Member
Premium Subscriber
Joined
Nov 25, 2007
Messages
3,262
Location
St. Louis County, MO
Just use a large one. I'd use 10 uF or more. You can parallel whatever you've got, like a couple of 4.7's, etc.
That's pretty much what I ended up with by using two 4.7's in parallel giving me 9.4uF.
So far, I've not found a signal it will not pass and the center tune function of the R7000's meter still works fine.
Even just a 4.7 cap seemed to pass everything but I decided to raise it.
 
Status
Not open for further replies.
Top