Icom R-75 DRM modification

LeonKoning · 29-12-2007, 15:56

http://www.stoepplernet.de/drm/IcomR75DRMmixer.zip

The zip containes 7 jpg's which discribes the ready built mini-mixer from Sat Service Schneider and the build-in in the Icom R-75 receiver

If you need more support then please send a e-mail to
LeonKoning@Hotmail.com

Icom R-75:
Use AM Wide, AGC OFF, ANF OFF, NR OFF
(keep AGC key pressed until it says AGC Off).
Use manual RF gain knob for best signal quality on Input Spectrum scope of DREAM (turn knob slowly).

DREAM:
select "Flip Input Spectrum"

Thanks to Simone

Grtz Leon

jabi · 13-01-2008, 11:22

Dear Leon:
N't is possible adquiry the 450 KHz signal from the unused connector Optional Xtal filter BPF?
Salu2, de Jabi, EA2ARU.

LeonKoning · 17-01-2008, 09:25

Dear Jabi,

It'doesn't harm to try but i think that the 455kc signal is to low at that point. I didn't try'd this point because i'm planning to buy the filter options in the near future. After the amplifiers Q891, Q912 and Q1031 the signal is stronger and the AGC and Manual RF gain works better at this point.

If you want the Service Manual (pdf) then plz ask me via e-mail.

Grtz, Leon

KD7YUF · 06-11-2009, 11:13

I am going to modify an R75 myself but using the ON6MU 455 KHz to 12 KHz down mixer based on the Philips SA602 IC given that I can actually build the thing myself and that the SA602 seems to offer good performance as shown in the audio samples and also the spectrum samples from the Dream software. The optional IF filter connectors are attractive to me as well given that standard solid core hookup wire seems to fit into the socket quite nicely and stays in place. I will of course switch to something else if there turns out to be interference problems caused by the wires acting as antennas. Even if this point for IF extraction does not work its still worth a try and if it does then the R75 might be one of the few receivers that can be modified without any solder points to the radio's main board.

KD7YUF · 16-11-2009, 06:11

Sorry to double post but I finally got a down mixer built! It was made around the Philips SA602 mixer/up/down converter IC and I unfortunately have not had a chance to test it because I might have an IF transformer/inductor in the parallel L/C circuit which tunes the SA602 local oscillator for 462 KHz hooked up wrong. I have one capacitor which is .001 pF connected to one leg on one side along with two ceramic capacitors hooked up in parallel to (hopefully) result in a capacitance of .002 pF from pin 2 on the IC to a leg on another side of the inductor and a second leg on the opposite side going to ground. This is my first RF circuit ever and I am just trying to make sure I have this part hooked up correctly. If needed I think I can take a picture of my board layout.

29-12-2007, 15:56	#1
LeonKoning Registered User Join Date: Nov 2007 Posts: 2	Icom R-75 DRM modification http://www.stoepplernet.de/drm/IcomR75DRMmixer.zip The zip containes 7 jpg's which discribes the ready built mini-mixer from Sat Service Schneider and the build-in in the Icom R-75 receiver If you need more support then please send a e-mail to LeonKoning@Hotmail.com Icom R-75: Use AM Wide, AGC OFF, ANF OFF, NR OFF (keep AGC key pressed until it says AGC Off). Use manual RF gain knob for best signal quality on Input Spectrum scope of DREAM (turn knob slowly). DREAM: select "Flip Input Spectrum" Thanks to Simone Grtz Leon Last edited by LeonKoning : 09-01-2008 at 22:52.

13-01-2008, 11:22	#2
jabi Registered User Join Date: Sep 2003 Posts: 2	DRM with the R-75 Dear Leon: N't is possible adquiry the 450 KHz signal from the unused connector Optional Xtal filter BPF? Salu2, de Jabi, EA2ARU.

17-01-2008, 09:25	#3
LeonKoning Registered User Join Date: Nov 2007 Posts: 2	DRM with R-75 Dear Jabi, It'doesn't harm to try but i think that the 455kc signal is to low at that point. I didn't try'd this point because i'm planning to buy the filter options in the near future. After the amplifiers Q891, Q912 and Q1031 the signal is stronger and the AGC and Manual RF gain works better at this point. If you want the Service Manual (pdf) then plz ask me via e-mail. Grtz, Leon Last edited by LeonKoning : 17-01-2008 at 09:29.

06-11-2009, 11:13	#4
KD7YUF Registered User Join Date: Nov 2009 Location: Toledo, Washington Posts: 5	I am going to modify an R75 myself but using the ON6MU 455 KHz to 12 KHz down mixer based on the Philips SA602 IC given that I can actually build the thing myself and that the SA602 seems to offer good performance as shown in the audio samples and also the spectrum samples from the Dream software. The optional IF filter connectors are attractive to me as well given that standard solid core hookup wire seems to fit into the socket quite nicely and stays in place. I will of course switch to something else if there turns out to be interference problems caused by the wires acting as antennas. Even if this point for IF extraction does not work its still worth a try and if it does then the R75 might be one of the few receivers that can be modified without any solder points to the radio's main board. Last edited by KD7YUF : 09-11-2009 at 12:48.

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16-11-2009, 06:11	#5
KD7YUF Registered User Join Date: Nov 2009 Location: Toledo, Washington Posts: 5	Sorry to double post but I finally got a down mixer built! It was made around the Philips SA602 mixer/up/down converter IC and I unfortunately have not had a chance to test it because I might have an IF transformer/inductor in the parallel L/C circuit which tunes the SA602 local oscillator for 462 KHz hooked up wrong. I have one capacitor which is .001 pF connected to one leg on one side along with two ceramic capacitors hooked up in parallel to (hopefully) result in a capacitance of .002 pF from pin 2 on the IC to a leg on another side of the inductor and a second leg on the opposite side going to ground. This is my first RF circuit ever and I am just trying to make sure I have this part hooked up correctly. If needed I think I can take a picture of my board layout.