Hamble RadioZone

Amateur Radio

Both Shirley and myself hold amateur radio callsigns


Boat Anchors

A term describing heavy pieces of junk which really do not deserve anything more than being used as scrap metal.

I was given two items which had once been used for analogue cellular radio R&D and which had proven to be unrepairable. An HP141T Spectrum analyser and a Schlumberger Solartron Stabilock 4040 communications test set. I decided to go for the spectrum analyser first as it was likely to be useful in repairing the communication test set.

HP141T spectrum analyser restoration

This is technologically a 1970's piece of kit but I think it remained in production for quite a time as it it did its job well. It was eventually superseded by the kind of computer controlled analysers I was using at Philips Research in the mid to late 1980's.  I describe  fixing this here.

Schlumberger Solartron Stabilock 4040 communications test set restoration

This is more mid-1980's and is for testing out pre-digital radio communications kit. It came to me with a failed self-test and lots of treble-beep error messages when I tried to control it from the keypad. I describe fixing the problem here

Seavoice RT225 Marine VHF transciever

When I bought a yacht, it came fitted with a 1980-ish Seavoice RT225, which is about one model newer than the type which has crystals for each channel. It contains an interestingly designed synthesiser board which relies on minimalist techniques to implement a PLL.

Inside are a set of CMOS divider chips , a prescaler and a phase comparator chip. Channel programming is via a pair of  2716 EPROM chips.

It relies on the limited tuning range of a bandswitched VCO to minimise the number of  bits required to program in the frequency of the synthesiser for each channel.

It also uses one of the bandswitch diodes as a transmitter modulation  varicap (discovered when I replaced it with a PIN diode and lost all of the modulation on transmit)

This type of design is capable of losing single channels over time due to EPROM bit aging, or DIP switch creeping.

On the front panel is a 24 way 1 pole rotary switch, the position of which  is converted to a binary address and connected to some of the address pins of the EPROMS. In addition, the switch position is directly used to enable a diode and dip switch 'ROM' which allows the user to choose one of 16 marine channels for each position of the switch.

The channel 16 override is provided for by having an additional address pin and half of  the contents of the ROM are programmed with identical values for channel 16
 
The channel change switch appears to use Letraset to allow the user to change the indicated channel number . These days one uses DTP or Corel Draw or similar to place lettering on laser film.

The channels chosen were such that certain combinations of channels were impossible.

As this I started this conversion in the days of  Ship-to-Shore telephone calls and gunnery ranges in Plymouth Sound using channel 11, I realised that for a cruise along the south coast of  England that I would need more than 24 channels , in fact more like 48  to cover all of  the channels that were used by Coastal Radio stations.

So I sketched out the schematic of the radio synthesiser and then proceeded to decode the ROM contents. After a bit of work the meaning of all of the bits became clear. I even found a mistake in the original programming of the EPROMS (or maybe they had faded away, after all the radio is over 10 years old)

I then decided to fit an extra inner/outer toggle switch and use this in place of  the diode + switch ROM to define 2 different channel groups, giving me the 48 I wanted.

I wrote a program in Acorn Basic to define new ROM contents and re-programmed the EPROM

I then replaced the single LED illuminating the back of the channel switch dial with a pair of  rectangular LEDs connected also to the inner/outer switch with a  piece of plastic between them, and laid out a new dial in an Acorn DTP package. The result is that I have an inner and outer set of channels and no more missing channel problems.

The only real issue is that the 'special UK' channel M2 is too high in frequency for the set to transmit but it can be adjusted to recieve on that frequency. The transmitter is disabled if the PLL fails to lock.

Of course now I only ever need to use less than 12 channels in total. For all other traffic I use GSM900.

If anybody is interested in changing the channel assignments or refreshing the EPROMS for this radio, please email.

Problems in 2006

I took a DSC course and then ...
The radio started jumping channels, and would tend only to receive a channel for about 10 seconds.
I took the radio off the boat and looked for evidence of problems.
Of course the jumping problem only happened on some channels and these were generally quiet in the evening (channel 72).
So I reprogrammed the EPROMS, converting the channel programming code from BBC BASIC to C  (and repaired the EPROM programmer which was eaten by a leaking NiCd memory backup battery) and the problem persisted.
I eventually traced the problem to a ribbon cable from the channel change switch to the main PCB that has plugs at both ends. The end nearest the channel change switch had been vibrated off the connector.
So I pushed the cable back on and put a cable tie round a loop in the cable to keep tension on the cable to hold the cable plugged in. Back to the boat for the fourth try ....

Hacking the Yaesu FT411

In 1998, I had the misfortune to drop my FT-411 in the sea, and myself with it.
I got over the near hypothermia in about 3 hours and then I noticed the radio was wet and not working. Although it was in a waterproof bag, this had split.

The radio was bought in Andorra as a European version. It came with extended coverage recieve.
After I had washed it thoroughly, totally dismantled evey module from the motherboard, and replaced the odd component eaten away by leaving the battery connected for three hours, I again had a working handheld.
The emitter lead on the low-battery detector transistor was the most elusive to find and repair, as it was thin, vanished , and connected to the B+ rail. All I did was connect a Zetex E-line device in parallel with the missing device.

Solder Jumper Settings

Within the FT411 there are 11 numbered solder jumper positions:
The positions 3,5,7,9, and 11 are connected in my version.
These are accessed via removal of the screw holding down the screening can over the microcontroller and desoldering the two joints holding it down. Then carefully lifting the 24 way flex cable, while keeping a finger on the soldered end.

Alternative jumpers

1
If connected in place of 3, the dial tunes the American 220MHz band (wont work, wrong RF module).
2
If connected in place of 3, the dial tunes the 430-440MHz band (wont work, wrong RF module).
3
If disconnected, unit powers up on 144-146MHz only.
4
If connected in place of 3, the dial tunes the 1296MHz band (wont work, wrong RF module).
9/10
One of these jumpers is connected for continous tone or tone burst.
11
If connected, the lithium cell is in circuit. It is connected via a series resistor that stops you blowing things when the unit is reset ....

Full Reset Procedure

If you mess up, power down, reset and start again.

I have just replaced the batteries in 2006 as I have started using it again. I went from 10x 700mAH 2/3 AF NiCd to 8x1800mAH AA NiMH in the same volume battery pack (well actually the Dremel tool was used to thin down the casing of the pack to make it easier to fit the cells.)

Page © Mike James 25th November 2006
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