ICOM IC-R7000

[w8cbc]

Looking for a project, I got a crate of semibroken parts on eBay. I wound up with two chassis and plenty more than enough boards to populate them..


One was mostly complete. I finished putting it together and wound up replacing several individual components before I could bring it up to scratch. I then lined it up to factory spec with high-end V/U test gear from work.


Here's the result -


Power supply: 100/117/234V ac, easily modifiable to run from 13.8V dc.

Frequency coverage: 25-999.9999 and 1025-1999.9999 MC, the high range with a 1000 MC front-end mixer.

Modes: SSB, AM, FM

Bandwidths: 2k8 SSB, 6k/15k AM, 6k/15k and 150k FM.

Sensitivity: Excellent. The results exceed the published specs (look them up). It's essentially even from 25-1000 MC (I lack equipment to test over 1000). The thing is a VHF/UHF DXer's dream.

Selectivity: very good, even in FM wide. This one will cleanly separate adjacent channels in a jammed-full 3-metre FM broadcast band. I didn't do a detailed spectrum analysis but all the filters fall off quite sharply at their edges.

Dynamic range: Good for a solid-state device. Strong (pinned S meter) FMBC signals will mix in the front end and produce spurs. They're not bad, but noticeable nonetheless. However, I intentionally defeated the 80-110 MC attenuation that normally switches in between 90 and 250 MC so a factory-original would doubtless do better in this range. I haven't noticed any other signs of overload.

Sound: a bit thin.

Noise blanker: not hooked up yet, will edit this when I get around to it.

General operation: Smooth for the most part. The memories are a little awkward and scanning could be more sophisticated (multi-range would be nice, for example). It's a very nice box for idly tuning around and exploring the spectrum.

Intriguing bits: buffered wide-band 10.7 MC IF output, perfect for various addons such as a TV demodulator or various digital gear. Room inside for official options that can also be used for custom boards. A "spare" jack on the rear is obviously meant for tinkering. That's one of the things I especially like about ICOM - they expect you to take their stuff apart.

Notes: I hooked the 10.7 MC IF output to the IC-751A out of curiosity. Either it's a little noisy or the 751A isn't as good with weak FM signals as the R7000. I intend to investigate this further as I have plans for that output. Alignment is quite exacting as the front end has several varactor-tuned stages. There are a dozen or so birdies, some quite strong. It could be due in part to inadequate shielding on the PLL unit - its cover is one part I didn't get with the rest.


I've started in on the second R7000. This one's a little tougher to bring up to spec as the best parts went into the first. I spent several hours jumpering cracked traces to get the display working. The IF unit has heat-related problems. And so on. But from what I learned in making the first one work, I expect I'll get second up to scratch sooner or later.

[n8yx]

Power your 7000 from an external 12V supply; it'll run MUCH cooler.

I've had one of these radios for years and greatly enjoy it.

[w8cbc]

I can see where that DC plug is supposed to mount. I've already used that area for something else. http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

One of the nice things about putting together gear from busted bits is there's a lot less reluctance to modify and possibly screw up a good thing.

So. I've had a LM1800 (stereo decoder for FM composite) sitting in my parts box for decades. I looked up its specs and found an application sheet with a circuit diagramme. Last night I built the circuit, tapping off the FM-wide detector output using a 2N3904 set up as an emitter follower (the 1800's input impedance is a bit low) and mounting the results on that bottom divider panel where the voice and remote options normally go. Output goes to a 1/8" stereo jack on the rear panel on that little plate that covers the DC plug knockout. Since it turns out that TV stereo audio uses the same composite scheme as FMBC (verified by tuning the pilot frequency control around - I didn't know where to look up the specs), I added a small switch below the output jack to change the pilot frequency as appropriate.

Though it's supposed to be line-level (and I use it thus), there's enough output from the 1800 to drive a pair of cans if need be. The resulting sound is much better than I get out of that record jack. And it is in full, clean stereo where applicable.

This of course applies only to FM-wide reception. I may do a shut-off circuit on it for other modes. There's more than enough room left on the board.

Why'd I do this? Because I felt like it. This little project helped further refine my work. I followed ICOM's example, making use of plugs and jacks and proper-length wiring so I can pull the module out without having to unsolder wires.

There's room down there for another board. I'm thinking video demod unless I can find a TV-R7000 somewheres.

---edit---

Oh, I got 'round to hooking up the noise blanker. Naturally, there's been no buzz or hash since to try it on.

The heat-related problem in number two is evidently in the first audio stage. I'll track it down when I get the ambition. Other than that, number two is now pretty much working, if a bit weaker than number one (it just meets spec instead of comfortably exceeding it).

So - one crate of parts for $343 (including shipping) resulted in two operational receivers that generally go for $400+ per. If I get pedantic and include the time spent fixing them at my current rate of pay, I come out even. The stuff I've learned about V/U construction and troubleshooting - a big plus. The joy in firing up the results, and: Hey! It works!!! - priceless. http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

---edit---

I found a TV-R7000 somewheres. If it don't get bid up too high, I'll go for it. Then I'll figure out something else to build into that empty space next to the stereo board.

---edit---

The audio problem in number two was a leaky coupling cap in the first stage. C135 is 1 uF to an extremely high impedence op amp input, no external DC reference. As the radio warmed up, C135 leaked more and more current until it drove the 4558 close to the positive rail. I decided to try a 1 meg resistor to ground at the + input before replacing C135. That snapped the DC level to zero, problem solved.

Number one was doing the same thing, if less severely. It was C135 again.

One more IF board, a spare, also has this problem.

So, a note for those with distorting audio in their R7000s. Check the DC voltage on the top lead of R169 on the IF board - it's connected to IC6a's output circuit and easily accessible. If it's off zero by more than a volt (mine was reading +7), C135 is more than likely leaking and you should replace it and/or establish a DC reference the way I did.

Other notes:

Replacing R18 (270k) on the logic board, next to J5, with 100k gives a much better top scan speed. Any less than 100k lets it scan faster than it can reliably catch a broken squelch.

Of four DC-DC converter modules I have, three were giving me about -22V at the -12V terminal. One would gradually drift toward spec over a few minutes. I fixed that one - it turned out to be a leaky pass transistor, Q4, a 2SB562. Much of the preselector circuitry is varactor-tuned and depends upon that -12 (it's closer to -11V actually) voltage being right. If it's wrong, you can't align the front end. In my case, it made about 20-30 dB difference.

ICOM do excellent service manuals. Download it if you don't have it. Not only does it tell you how to fix and align, it has excellent working descriptions of how each stage operates.

---another edit---

I've remarked elsewhere that Icom seem to rely overly much on component quality. I had to replace another leaky transistor on number one's IF board that was driving the AGC nuts in FM wide.

I also fixed up some spare boards - IF (had the leaky C135 problem), RF (bad connectors), DC-DC (leaky pass transistor), display (cracked traces, quite a job).

I know these things did tough military service. They're evidently not meant for it.

---edit---

That TV-R7000 (video demod accessory) I was after went for $350 US. Incredible. No, I wasn't the one. I decided to pass on it when it got bid up over $200. The yuppies-with-money syndrome strikes again.

A R7000 with the TV-R7000 included went for something on the order of $400 the same week I got my crate-full. That package would have been my second choice.

Oh - I was wrong about the spurs (see dynamic range category in my first comment). One of the local Infinity FM stations - WKRQ - is very damned wide. It appears the main signal is beating against the lower IBOC carrier somewhere in their transmitter room and the results are getting to air. Why am I mentioning this in detail? Because I have four IBOC-and-RDS-equipped FM stations (three class B and a class A) at the same site and they're all spectrally clean.