DRM Converter for ICOM (9 MHz IF)

[ik1zyw]

I am pleased to announce the availability of DRM downconverters for ICOM RX/RTX that do not have a 455 kHz IF, but allow optional filters at 9.01 MHz.

Some of those are: IC706 (all series), IC725/726/728/729, IC735, IC-R70/71/75.

Further details at http://spazioinwind.libero.it/ik1zyw...DRM/index.html

[dk8cb]

Sorry to say, but instead of advertising here that you WANT TO SELL the converter, you should publish the schematic for those unable to design such a circuit themselves.
Those who cannot or do not want to build it would still be able to buy it from you.
It's only a mixer IC with a few parts anyway. No real secret about it.

Roland

[ik1zyw]

An article featuring the diagram and a complete description of the project is in the publish queue of the Italian magazine RadioKit Elettronica. That's the reason why the page does not show a diagram, whilst the rest of the website makes no secret about other projects and software. This information didn't make it to the first version of the page, that has now been corrected.

Those unable to design such a circuit may reproduce the diagram published on QST October 2003, fitting a 9MHz XTAL in place of the LC resonator. NE602 datasheet is self-explainatory. I might publish that basic diagram if time and other activites allow.

[dbird]

Has anyone actually done this or any similar mod to the IC-R71?

The BW is 6KHz in the wide position for AM. Seems like this should be too small for DRM for decent performance.

Has anyone done any filter mods to to the R71 to help DRM reception?

Thanks,

Dave

[ik1zyw]

It is indeed possible on IC-R71 to use the converter shown at the page linked in the original post (it was also mentioned). R71 is no different from IC706s, IC725s, ... Moreover that is not a mod, but a no-solder plug-in.

The 6 kHz AM BW is too narrow.

Paolo IK1ZYW

[DG9BFC]

Originally Posted by ik1zyw

It is indeed possible on IC-R71 to use the converter shown at the page linked in the original post (it was also mentioned). R71 is no different from IC706s, IC725s, ... Moreover that is not a mod, but a no-solder plug-in.

The 6 kHz AM BW is too narrow.

Paolo IK1ZYW

dear drm friends
when in a receiver the am bandwith is set to 6 khz it is +/- 6khz
am is carrier plus upper and lower sideband so 6khz am = 12 khz BW
so the 6khz bandwith will be just fine !

best wishes and good luck for all drm listeners
sigi

[dk8cb]

Originally Posted by DG9BFC

... when in a receiver the am bandwith is set to 6 khz it is +/- 6khz

Not really!
If a 6 kHz wide filter is used, it will not become a 12 kHz filter when the receiver is switched to AM mode. The receiver can be tuned to receive a single sideband plus the carrier of an AM transmission such that the full audio bandwidth is obtained, but the receiver bandwidth will still be only 6 kHz.

If however, the receiver is tuned in such a way, that the AM carrier is in the centre of the 6 kHz filter, the audio bandwidth will be limited to 3 kHz.

All my receivers keep their bandwidth when the demodulator is switched to AM. A receiver which switches from 6 kHz to 12 kHz when AM is selected would require an additional 12 kHz wide filter (which the R-71 does not have)!

Roland

[zfyoung]

Hi,everyone.I have done some experiment with R71E.Actually, R71 does provide 455Khz IF with over 10Khz bandwidth.That depends on which point you extract the IF.Please take a closer look at the block diagram in the user manual.If you obtain the IF right before the 3rd IF filter,you should get IF well over 10Khz bandwith.
BTW that is where FM domulation board is connected into the mainboard.One can also use the wide band IF by tuning in FM Mode.

Z.F.Yang

[DG9BFC]

Originally Posted by dk8cb

Not really!
If a 6 kHz wide filter is used, it will not become a 12 kHz filter when the receiver is switched to AM mode. The receiver can be tuned to receive a single sideband plus the carrier of an AM transmission such that the full audio bandwidth is obtained, but the receiver bandwidth will still be only 6 kHz.

If however, the receiver is tuned in such a way, that the AM carrier is in the centre of the 6 kHz filter, the audio bandwidth will be limited to 3 kHz.

......
......
excuse ... it is correct that when a 6khz wide filter is uses, the bw is 6 khz
but in many radios the manual says 6 khz am and the filter is a 12 khz filter
if you have the opinion to switch bw independent of the mode than roland is right ..... :-)
the icom manual of my 765 says for the (optional) fl102 bw 6 khz.....
but when you look on the pic you see a bw of 12 khz.....
funny isn´t it :-)
fl102.gif

[dbird]

Thanks guys.

ICOM's service manual for the IC-R71 distinguishes between +-BW specs and BW specs and makes clear which is being referenced.

So, from the discussion, in order to modify the IC-R71 for DRM, it must be done by taking the signal from the 455KHz IF. If the tap is taken from the 9MHz mixer output, the bandwidth will suffer.

Thanks again,

Dave

[KB7GF]

Hello Paolo,

Last month I purchased a 9.01 MHz mixer board on Ebay and installed it on my R71A. The narrow CW filter on my R71A was factory installed, so it couldn't be easily removed. Instead, I removed C26 and installed a coaxial cable connected to the cathode of D15 and the shield to ground. I routed and connected the the cable to the SCOPE RCA connector. From there, I connected the mixer. The 9 MHz RF is now switched to the SCOPE connector when I select the narrow CW filter. Selecting other filters restores normal radio operation.

Overall, the results have been quite satisfactory for such a basic circuit / modification. I have observed several stations with > 30 dB SNR on the west coast of the U.S.

Best Regards,

Mark, KB7GF

Originally Posted by ik1zyw

It is indeed possible on IC-R71 to use the converter shown at the page linked in the original post (it was also mentioned). R71 is no different from IC706s, IC725s, ... Moreover that is not a mod, but a no-solder plug-in.

The 6 kHz AM BW is too narrow.

Paolo IK1ZYW

[ik1zyw]

Glad it works Mark. Thank you for the extra R71 info; hopefully will be useful to someone!

Originally Posted by KB7GF

Last month I purchased one your 9.01 MHz mixer boards on Ebay and installed it on my R71A. The narrow CW filter on my R71A was factory installed, so it

Just want to add that I am not selling my converters on eBay and I have never seen their diagram. Moreover mine are sold tested on a real Icom and include all connecting cables.

73

[KB7GF]

Thanks for the clarification!

73

Mark, KB7GF

[KB7GF]

Hi Paolo,

My mistake - the paperwork from the transaction is for an I5XWW converter...and all reference is to this call sign. Since this callsign does not match yours - then there is no problem. I apologize for the confusion!

Mark

[joe]

Hi,everyone.I am new on the forum and just starting with DRM,i purchased an icom ic-r2500 and an elad dc12,i can't see @ the back of my radio the 12 khz if connector,any idea or suggestions on how to put this together?
Tanks for your help
Joe