Expanded FMTV Reception for the Icom IC-R3

Last weekend I learnt something new about a piece of equipment I have had for a number of years now, the Icom IC-R3. One of my favourite achievements over the years has long been “teaching old equipment new tricks”. For example, in the old days I discovered that my Kenwood TH-75E could be expanded to allow some ‘out of band’ reception from the 2 metre and 70 centimetre amateur bands. Although the need has diminished over time since amateur transceivers nowadays come with expanded receiving coverage as standard.

A number of the Realistic/RadioShack scanning receivers came in two variants, the only difference being in the VHF low band coverage, 29 to 54 MHz for the USA version and 68-88 MHz for the UK/EU version. Although in my view, banded scanners have by now had their day since general coverage scanners (with say continuous coverage between 25 to 1300 MHz, or more) cost little more. Well examining the service manuals revealed that in some cases the low band coverage could be changed, to allow either or both of the UK/USA low band to be enabled. Usually by adding or removing either a diode or jumper wire.

Well, the IC-R2 could be programmed to allow receive coverage to be extended from 1309.995 to 1599.995 MHz using  software called R2 commander (albeit not in VFO, but only directly programmed into a memory channel). The CS-R2 software and other third party applications wouldn’t allow frequencies above 1309.995 MHZ to be entered. But IC-R2 commander did!

Well, I have long suspected that the IC-R3 could be expanded to allow FMTV (frequency modulated) television signal reception to take place outside the normal 900-1300 MHz and 2250 to 2450 MHz range. The reason being that the VFO tuning is rather like a truncated sequence counter. To explain, a 4 bit counter can have values 0 to 15, or 0000 to 1111 in binary. However, to display a single digit in decimal the sequence is truncated at 9, or 1001 in binary.

Now to take the example of the IC-R2, although capable of tuning above 1309.995 MHz, the VFO is truncated so as not to permit tuning above this frequency. But it does not prevent the entry of frequencies above this using IC-R2 commander. And the low band coverage sequence truncation of the Realistic scanners was obviously controlled via the presence or absence of a diode or jumper wire. As was the case with early US version scanners which could have a similar modification to permit cellular reception.

Well, in the IC-R3’s case, although AM TV reception is possible out of the box from 30 to 2450 MHz, the FMTV coverage is restricted to just the 900 to 1300 MHz and 2250 to 2450 ranges in VFO mode. And the CS-R3 software as well as the ARC3 software from Butel refuses to allow the entry of frequencies outside these ranges.

Well, experimentation with the TK3 program from http://parnass.com/tk3/ does! Now my first attempt to enter experimental values resulted in having to clear the memory of the IC-R3 (I think any value above 2700 MHz is out of range). But I later found I could enter frequencies in the 1300 to 1325 MHz range (for amateur television repeater outputs on 23cm), 1394 MHz for long range CCTV and wireless cameras, (1/2 watt permitted) and at long last it covers the whole of the 2.4 GHz ISM band, which ends at 2483 MHZ. Icom obviously overlooked this and ended coverage at 2450, the top of the 13cm amateur band! In fact values up to 2699 MHz appear to be usable, allowing access to the outside broadcast cameras and JFMG links in this range!

Well I haven’t had time as yet to test performance (the IC-R2’s sensitivity seemed to hold up to 1599 MHz reasonably well), but suffice to say that I managed to receive a perfect picture from a wireless CCTV camera on 1394 MHz, so reception does appear to function – so the phase locked loop was obviously not out of lock as used to happen with the Kenwood TH-75E if one tried to tune too far out of band. I need to also carry out some tests on sensitivity also.

The image below proves that FMTV reception outside the 900 to 1300 and 2250 to 2450 MHz range is successful.

David, G7VDI

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