Monday, 2 May 2011

LF reception on a Kenwood R2000

Tonight I tapped the 9.8MHz IF of my Kenwood R2000 (also known as the Trio R2000).  A little poking around with an oscilloscope probe and my SDR told me I needed to tap it at the emitter of Q8, just before the 2nd IF filter.

Well, it works - I can now view nearly 100kHz of spectrum around a centre frequency.  There is a slight disadvantage in doing this.  At the 2nd IF, the receiver only tunes in 50kHz steps.  So, if you're not on a 50kHz multiple, your centre frequency may or may not be in the passband of your SDR.

The reason for this is that the 2nd IF is very wide at this point (500kHz?), its possible to tune your SDR around 'inside' the IF of the receiver by altering the local oscillator frequency of your SDR (in my case, an Si570).

So, its a little tricky, but hey, it cost me a lot less than an RFSpace SDR-IQ (which by the way I would love to own).

Anyway, back to my original point - the lower limit of the R2000 is 100kHz.  You can't tune any lower, the synthesiser just stops at 100.  Ah-hah thinks I, but I can tune my SDR inside the passband of the IF, so lets see what is below 100kHz... lo and behold, the radio receives down there.

I've annotated the picture for those non-LF geeks.  I've tuned the SDR to exactly 9.9427MHz, which puts MSF 60kHz right on a marker (zoom in).  You can count up to 70kHz and this is how I ID'd HBG and thence DCF 77.5. (Wags will note I goofed on the frequency of HBG... This is what I get for doing this at nearly 1am...).

There's not much under 60kHz that my R2000 can see, but you can also see the synth noise at 100kHz.

Just as an aside, I listened to some NDBs with my Kenwood R2000 and SDR combination, at around 400kHz.

That's all for now - the Kenwood / Trio R2000 service manual is easily found via Google.  There's a handy panel on the back of the radio to drill for a BNC socket - that's assuming you don't have the VHF converter.

I haven't tried decoding DRM yet, but that's next.  You can do it without a downconverter, as the SDR / WRPlus will do that for you.

Any questions, just leave me a comment.

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