Marconi Challenger

Commissioning Challenger

Hello Peter,
Thanks for your thoughtful reply. I do intend to write an article on the restoration of our Challenger, and will cover the Challenger history in general by way of background.
With your three for Southern Shipping Corporation, we can account for 6 out of the 12 (or so) Challengers actually sold. However, the provenance of the one in Australia is unkown.
Our antennas are a 40 metre Inverted L for Transmit and a slightly shorter Long wire for receive. We have a stainless HF vertical to add to the antenna farm at some time in the future.
You are right about the Oceanic, although the one in the picture is a fully working example, I am very nervous about using for extended periods. I know this is contrary to shipborne use where it would have been on 24 hours every day. However, at the risk of digressing - we had (still have) another Oceanic, a dead one. Breifly, I believe the pathology before we obtained it was, 1) Stopped working one day, owner probably checked a few obvious things, turned it off and on a few times, 2) Finally disovered that the 5Volt rail had gone sky high, 3) Replaced the 5Volt pass transistor, 3) Still didn't work, sold it to us. I strongly suspect that the 5Volt Pass transistor failed short, rather than open, thus dumping 20(ish)Volts across the 90 odd TTL ics, all of which are soldered in - a nightmare to repair. According to my research, this is not an uncommon failure point with Oceanics. The pass transistor on our working one does get very, very hot, so rather then invite failure I avoid using it at present. A single TO220 style pass transistor for over 90 TTL devices is bound to be struggling. The long term intention is to fit an external, more substantial 5Volt supply with over voltage clamp and current limiting (both omitted from the Oceanic design). Aside from this shortcoming, it is a very capable and pleasant receiver to use.
Michael.

Paul, While not wishing to stray too far off topic, you mention the front panel crystal socket on the Oceanspan. What I've done with ours is feed an Arduino based VFO output into the external Crystal socket, that puts us on the Amateur Bands, but not 14MHz as this falls in the cracks in the 'span's tuned driver circuit. Ours was a VIIE (Emergency) which I reverted to Main Transmitter status. It had the 24VDC Dynamotor which was noisy, so built a 650VDC mains supply which is a bit quieter and doesn't drop 100Volts when transmitting. Both units are heavy, unfortunately we don't have the very rare Marconi extension rails which means we can't work on the transmitter when it is live which is fine for Health and Safety but it make it very difficult to adjust the tuned circuits which, if you remember, are on the bottom of the transmitter. If I could do that it could be put onto 14MHz quite easily!
Back on topic, I think I mentioned that do***entation is rare for the Challenger, fortunately we have a full set of manuals for the Conqueror which, apart from the final stages is remarkably similar to the Challenger - sufficiently so to enable me to sort out its last mysteries. (The main console is now giving me headaches!) We are now waiting for parts and hope to have it gracing the airwaves in a few weeks time.
Thanks for comments - Michael.

Progress Report

After a short holiday I found that an MRF393 had arrived at the museum to replace the unobtainable CTC BAL0000L10 (Dual NPN power transistors). This was fitted to the driver section and when fed with HF from my signal generator now produced a much greater voltage swing which increased a little with frequency. I was a little uneasy about this transistor as it is only specced from 30 to 500MHz and I am going to use it below 30MHz, they still cost nearly £100.00 and it's the museum's hard earned money. On the other hand the MRF393 and 392 are the only bipolar NPN transistors I could find in a 744A-01 package. The other option of using two separate power transistors, while technically feasible would require an unacceptable (at this stage) amount of hardware modification. However, it seems to have worked out OK.
Also 4 x 4cx350s arrived. after carefully setting up screen voltages (400V) and bias (-27V) with the old valves still in place, I replaced one of the old valve with a new one and nothing bad happened, in fact a considerable amount of antenna current was generated. Emboldened, I replaced a second old valve wiht a new one and was rewarded with and even more considerable amount of RF into the dummy load. The anode current on the two old valves is just a little below that of the new valves so I think they are probably contributing something to the output. After quickly trying to load into the antenna (45 Metres of inverted L), I found it wouldn't load. I suspect there is a minor fault in the antenna circuit that I will address on Friday and fit the remaining two new valves.
A further update will follow on Friday/Saturday.

Michael

I am pleased to announce that the Museum's Marconi Challenger is now working! Reports received on Saturday morning following the VMARS' 80 metre net indicate that signal strength is very good and excellent audio, so all in all a very pleasing result.
There is a fly in the ointment: the drive protection circuit trips out randomly and for no apparent reason, which is annoying. There are five lines going to the protection circuit and they are the same status in both fault and no-fault conditions. It's not overheating, which would worry me, as I can see the bi-metallic strip that detects valve box air temperature >125DegC is still open. So far I've only checked the input lines with a voltmeter. On Monday I'll a) check them with a scope incase there is noise on one of the lines and b) failing that I will check the circuit backwards from the trip relay to see where the fault is registering.
Picture attached.

Challenger now fixed - fingers crossed!

The Challenger has two protection circuits: 1)the HT protection trips if the bias supply fails or the airflow through the valve box fails, a drawer is opened, or excessive current is drawn; 2)the drive protection circuit, the one giving me problems, trips if final valve air temp exceed 125DegC, critical controls are moved after tune up, frequency data input is incomplete, or the PLL drifts out of lock. If any of these last four faults occurs the drive trip LED illuminates, but it doesn't tell you which of the faults have occurred. Another annoyance is that not all of the fault lines coming into the protection circuit are, for instance, low for no fault, Hi for fault. Some are high, some are low. Anyway I made a simple table of the status of all four lines under no-fault conditions, measuring them again under fault conditions gave the same readings on a meter. So was it a transient fault or noise on one of the inputs, or even a fault in the protection circuit itself?
The whole thing was frustrating on Saturday as I was able to make some good contacts on 80Metres, but the drive would trip out part way through.
I decided to spend today (Monday) sorting it out. I made a small board to fit onto the header for the drive protection circuit with four LEDs to monitor each of the fault lines. Powered up the transmitter and it behaved perfectly for about 2.5 hours. It did trip while I was probing after everything was well warmed up. I decided that it was time to apply the Mk1 test strategy and give it a good thumping! A healthy tap in the PLL area caused it to go reliably out of lock and trip the drive. Some gentler tapping with the plastic end of a screwdriver indicated something sensitive in the area of the divider chip, gave it a push into its socket and the problem went away. To make sure I removed and reseated both the divider and the synthesizer chips. It was obvious from the condition of the pins that they had been removed before a few times! That seems to have fixed it. It behaved itself for about 2 hours this afternoon and would not suc***b to any amount of abuse.
Picture of synthesizer draw attached. PLL in screened box on right, drive protection circuit on large board right of centre under long shaft with two UJs.
If anyone is able to listen in, I intend to join in the VMARS 80 Metre USB net on 3.615MHz on Wednesday evening between 20:00 and 21:00.
Michael (GW7BBY/GB2MOP)

Challenger Transmitter Working - Replies.

A few of you have raised points about Challenger and associated equipment.
Andrew, I am pleased that you were able to listen in on VMARS on Wednesday evening, Conditions were atrocious, not just atmospheric noise, but adjacent stations overlapping our transmissions and tuning up nearby. However, it was a great pleasure to run the Challenger for an hour and to get some very encouraging reports. Oddly, and this applies to my home station in Llangeler as well, there are a number of stations in the Swansea and Merthyr area that are barely audible at the best of times, yet at the same time we have no trouble with the rest of the country or even northern Europe - geography I guess. Will we see you at the Crank-Up this weekend, Sat and Sun? ( I doubt I will be able to demonstrate the Challenger as with everything else running in the Museum, there won't be enough amps left for me!)
Earthing: At present it is earthed to the lattice mast, which is in turn well earthed. A good method I found with the Oceanspan was to connect the ground side to the tin roof covering the Radio and Telehone areas and about 10 metres or so below the horizontal part of the inverted L. I tried it briefly with the Challenger, but didn't seem to be any improvement. It is something to be addressed during the winter shutdown as there is scope to improve the antennas, in particular the receive side. We can get out far better than we can receive.
Paul: Oceanic and IC sockets. Most of the more common (cheaper?) ics in Challenger are in fact soldered directly to the boards. Only the bigger ones such as the 40 pin Divider and Synthsizer chips are in sockets and, guess what, these are the ones that cause problems! It is actually the same in the Oceanic: most ICs are soldered, but the processor, EEPROMs and a few larger chips are socketed. I might take you up on your offer and send you the Oceanic boards and a bucket-ful of TTL.
As you like my pictures so much, attached are left, right and top views of the RF unit.
Finally, I must mention that this project has only been successful through the generosity of EIMAC (now part of CPI) who actually donated the four 4CX350s to the project. The museum would have found it difficult to justify the cost of £1000.00 + worth of valves.
73 all - Michael.

Marconi Challenger - Rvator

Hello Rvator, nice to have you join the forum. Since the Challenger has been operational, there's not been a lot more to report, partly because the museum is closed for the winter and doesn't re-open until next Easter with a weekend crank-up. Also this is the time when maintenance, new displays and infrastructure changes can be done. As to the Challenger another reason for not using it much is that our 3 phase inverter is not quite up to the job and will trip out if I am not careful! The museum's electricity supply is right on the limit when the museum is open so this is another issue to be addressed over the winter. More interesting things: as it stands the challenger can only be used on 3.5Mhz and 1.8Mhz Amateur bands on USB, the higher amateur bands fall in the cracks between marine bands. I'm going to make a small modification to the band oscillator which generates the MHz component of the wanted frequency. It runs at between 41.7 and 66.7 MHz and is then mixed down to the required frequency. I shall pull the crystals out for the upper marine bands from 6MHz to 24MHz and use a DDS module controlled from an Arduino to inject the correct frequency for the higher amateur bands according to the band switch position.
The MHz component of the digital display is hard wired by diode or gates to the bandswitch so to get the correct digital display the diodes will have to be reconfigured. Nothing major and nothing irreversible.
For LSB operation I shall use a spectral inversion technique. A very interesting device was described in Practical Wireless in January this year. It is fitted in the microphone input and audio output and converts USB to LSB and vice-versa. When you think about it, the reason you can't resolve LSB with a receiver set to USB is that the carrier insertion is on the wrong side of the sideband resulting in unintelligible audio. With a clever bit of signal processing that a PIC processor can do, the audio spectrum is transposed to make it intelligible to a USB receiver. Conversely, if the transmit USB audio is transposed it can be resolved on a LSB receiver. Its not an unknown technique, but Ron Taylor (G4GXO) developed this PIC based device for users of commercial and military equipment which is usually limited to USB. If it is successful then I will make another unit for the Kelvin Hughes Zealand M-1250 transmitter which is my big winter project.
Finally, for Paul who like pictures, here is one of the challenger in action.

Best wishes to all - Michael (GW7BBY/GB2MOP)

Hi Paul, thanks for the festive greetings and apologies for not responding sooner. We have been away over Christmas and have just returned home. Over the winter shutdown I shall be modifying the Challenger for the higher amateur bands that fall in the cracks between the available marine bands, and will also add LSB capability.
The next big job will be the Kelvin Hughes Zealand M1250 transmitter (see picture). The receive side is working well, I've not yet tried the transmitter. I've provided a 3 phase supply, and the loom appears to be present to connect it to the console. We have all the manuals, the 4CX1500B is present but of unknown provenance, we also have a spare exciter also with its 4CX1500B present. I know a small PSU repair is needed. Hopefully it will soon be on the air, it is a 1.5KW transmitter, synthesized ( I don't think any mods will be needed for amateur bands, but will have to add LSB at some point) It provides for more modes than the Challenger: AM, ISB, DSB, USB, CW. However, before someone jumps on me, I'll be starting a new thread for this one shortly.
All best wishes to everyone for the New Year, we might even get to chat on the air!

Michael. (GW7BBY/GB2MOP)

Re Kelvin Hughes

Just a quick reply, before staring a new thread. Paul, the "jewellery" on the kelvin Hughes equipment is KH's take on control handles - its different and feels good to handle! (Pic Attached)
No, there are no Nixie tubes, just good old numbers printed on a disk to give a "digital" readout - see pic of M1250 Synthesizer and Receiver.
GURK was "RFA Orangeleaf" - another pic.
Troppo - nice to hear someone who sailed with KH Kit.
And Duncs, I've heard of NERA, in fact I think we have a cannibalised Nera ATU from I don't know what in our store. I'm not familiar with it.
OK Really going to start that new thread for KH.
Best wishes to all - Michael.