Thursday, November 24, 2011

DRM can be DIY

Our friend Alan Shea mentioned the need for some DIY posts on how to get started in the DRM monitoring hobby. I sent an email to another friend Crispino I5XWW. Crispino's IF converters were the first way I got active in DRM. Although Crispino doesn't promote himself much, his IF converters are top notch. I have used them with my Yaesu FT-817 and Icom PCR-100 with great success.

Here is an excerpt from him about what he is currently offering. I can tell you from experience that his boards are made of high quality components and excellent electronic craftsmanship. He will make sure you are happy and his prices are excellent.

"Yes, I still build and sell the old DRM converters in the 455 / 12 kHz version and the 450 / 12 kHz versions for Sony, Sangean and some other brands. There is also a version for Icom radios that have an IF at 9010.6 kHz (most of the time it just connects to the same pins of an unused optional CW-narrow filter slot) and another version 10700 / 12 kHz for radios with an IF at 10.7 MHz.

This last is retuneable to 10.695 MHz to be used with Kenwood radios that have this IF.
Application may be in the same similar way as above: just connect to the same unused pins of an unused CW filter slot. So, in the case of connection to the spare filter slot, it is better to bridge input and output pins of the slot by use of a capacitor, say 1000 pF.

That way AGC of the radio will continue working.
The radio is put in CW-N mode. You will listen "shhhhhhhhhhh" from the radio speaker when tuning a DRM signal. You can also read signal strength from the radio s-meter. That way you will use a stable signal from the radio IF into the converter. In case of no bridging in and out pins you are to move up and down the RF gain manually according to on-air signal strength.

I understand that some radios have an IF output socket at 10.7 MHz. Most of the times my 10700 / 12 kHz converter does not work, due to a broadband and very low level signal available at this socket. I read that a 30 dB amplification is needed
My 10700 (10695) / 12 kHz works best when connected to a tap in the IF circuit inside the radio, specially after a 12 or 15 kHz wide filter. "

My suggestion is to check for reports of radio conversions for any model of rig you might have. DRMRX forum houses just such reports here.

Then if it looks like you want to dig in, stop by Crispino's site and send him an email. Be sure to report back to the DRMNA Yahoo Group with your discoveries, conversions, experiences, etc. Tell Crispino that you heard about him on!