Valve & Vintage

Dear Don,

Thank you for December’s issue. I am impressed by the quantity of letters you’ve published; an active Letters page indicates to me that the magazine has a very active readership.

I think I have noticed some typos or transcription errors in the article about G6YL.

1. “Dunn’s interest in wireless communication was enhanced in 1923 .. enjoyed listening to the newly established British Broadcasting Corporation’s (BBC) transmissions ..” (p.46, top of centre column).

In 1923 the BBC was the British Broadcasting Company. It became the Corporation in 1927.

[I think the Company was formed in 1922 in which case the BBC may be commemorating its centenary in 2022.]

2. “In the 1930s .. Provincial District Meetings of ‘The Society’ that would later become ‘The Radio Society of Great Britain’ ..” (p.47, foot of left column).

The Radio Society of Great Britain came into existence in 1922.

3. The Old Old Timers Club (p.47, right column).

This one intrigues me. If membership of the OOTC was limited to those who had made two-way wireless communication in 1907 or earlier, then I doubt anyone would have had membership number 910 and the OOTC would die out when the last such member passed away. I doubt the 910 because the RSGB’s Amateur Radio − the first 100 years says there were about

The Equal potential zone is generally the four walls of the property and the PEN conductor should be connected to every conductive part within the installation. Technically, an outside tap or a steel heating oil tank connected with copper pipes should have an insulated section where it enters the house. The only services connected from outside the property should be the water and gas mains, for other reasons.

So, I would say no, the RF earth should 250 licences in force in 1912, nearly 1,000 in 1913 and about 1,600 in 1914 and I assume there’d be fewer than 250 licences in 1907.

There seems be an inconsistency here because the RSGB’s The Bright Sparks of Wireless includes the Gamage’s Directory of Experimental Wireless Stations, March 1914, which has around 400 entries (it consists of 17 pages each with around 25 entries).

I am wondering if these licensing numbers are irrelevant if membership of the OOTC was limited to those who had “made two-way wireless communication” rather than to those who held a licence.

If membership was open to those active in or before 1907, then I wonder how G6YL became a member when she was licensed in 1927? Might it be that membership of the OOTC was actually open to those who had been experimenting in wireless for at least 40 years. This would permit G6YL to become a member in 1967 and I think that would tie in better with her membership number.

Ian Brothwell G4EAN Nottingham

( The author responds: Thanks for this insightful response. On your first point, yes, agreed, British Broadcasting Company became the British Broadcasting Corporation on January 1st 1927. On point (2) my source was the tribute to Barbara Dunn G6YL on the K8CX Ham Gallery: http://hamgallery.com/Tribute/G6YL

not be connected to the main earth terminal on a PME installation. I know an amateur who did this and was instructed by the distributor to remove it.

If it was permitted to connect the RF earth to the mains earth, I would say the cable would need to withstand the full fault current on the system, which would depend on the type and size of the protective device on the distributor’s transformer, not the fuses in your house. So, undoubtedly, something much larger

“In the 1930s, ladies rarely attended PDMs. Provincial District Meetings were localised meetings of ‘The Society’, later to become RSGB. There were two important exceptions. Barbara Dunn G6YL was the first exception. Being of a quiet and retiring nature, few of the hundreds who contacted her efficient and intensely active low power station at Stock in Essex knew the operator was a lady. Gerry Marcuse G2NM, President of The Society 1929 to 1930, did know, however, and it was he who was probably responsible for persuading Miss Dunn to come to the 1930 Convention.

A few weeks earlier, G6YL had been awarded the newly donated 1930 Committee Cup for outstanding work in the first series of 1.7Mc/s tests. Her presence at the Convention Dinner caused quite a stir as did the fact that when G2NM made the presentation she became the first lady to become the holder of a Society trophy. Barbara Dunn, who was licensed in 1927, remained Britain’s only YL transmitting amateur until 1932 when Nell Corry (the second exception) of Tadworth, Surrey, doubled the number by becoming G2YL.”

On point (3), my source was again the K8CX website. The site does not say she became a member in 1947. Only that the OOTC was established in 1947 by a group of amateurs who had played a part in laying the foundations of electronic communications. The requirement for membership was twoway communication by wireless 40 or more years prior to 1947. At that time the members were ‘spark’ operators in 1907 or earlier when there was no licensing authority. The requirements have continued to this day. The current requirements are two-way wireless communication by amateur, military or commercial means 40 or more years ago. Barbara was member #910.)

than a 10mm2 CSA earth conductor would be necessary. This would also require the RF earth electrode to have a low enough impedance to operate the distributor’s protective device within the required time and the cables to your house from the network to withstand the fault current, both unlikely.

The notion that RCDs or isolation transformers would give any protection against this type of fault, as I have read on social media, is nonsense. The hazard is

caused by the distributor’s earth potential rising to a potentially lethal voltage above that of real earth.

The distributor’s earth is permanently connected to the installation so even if the main isolator and all of the trips are turned off in your house, the potentially lethal voltage would still be present.

The neutral return path is shared by all the houses on your circuit and the magnitude of the fault voltage would depend on the impedance of the fault, the load and the phase balance on the system.

Fortunately, this type of fault is rare because, without causing alarm, the chances are most properties have this type of earthing arrangement. G4GLM correctly highlights the possibility of potential difference between the mains earth in the house and the RF earth imported from outside the house. He has overlooked, though, the reverse. If the RF earth in the garden is connected to the main earth terminal and the impedance is not low enough to operate the distributor’s trips, the chances are the antenna system will have lethal voltages and you could well be standing on wet ground in the rain when you find this out.

Another but quite important point is that of the unintentional and unknown ‘RF Earth’. Many PSU manufacturers connect the negative terminal to earth, which in turn is connected to the chassis of your rig. A typical installation of, say, a collinear fed with coax on a scaffold pole strapped to a fence post.

So the board’s earth goes high as does earth in the ring main, the PSU, the negative to the rig, the rig, the coax outer and the scaffold pole, and anyone who happens to touch the scaffold pole will complete the circuit to ground. This means the PEN conductor is exported unintentionally. Obviously, this also goes for mains powered radios.

You may think your RF earth is excellent and assuming your property had big enough cables to support the fault current, if your earth is not of low enough impedance to operate the distributor’s trip, the hazard of voltage gradients can then occur, as voltage decays with distance from the earth stake. This can be particularly hazardous to four-legged animals because voltage difference between front and hind legs results in current through the animal’s heart. Hence never install safety earth electrodes in a paddock.

Incidentally, if your RF earth to the scaffold pole is excellent on the typical installation, the fault current would probably melt the earth wire in the mains lead to the PSU.

From a radio amateur’s point of view, TT systems are great because we have sole ownership of the earth arrangement, but TN-C-S and TN-S should be handled with great care because even with TN-S the earth is shared with other households. Once again, these faults are very rare but with just a high impedance crimp on an overhead, if you had been on PME and that crimp was nearer the transformer, you would have been in this situation.

My advice if I were to give any is, make sure you know what type of earthing arrangement you have, be aware of the risks in the way you set up your station and take steps to minimise these risks as much as possible.

Mike Lane G1SCT

Spalding

The MRF300

Dear Don,

In Electronic Design & Test Magazine October 29th (you can see it online) there is a detailed article on the MRF300 power LDMOS power device. It is for frequencies of 1.8-250MHz in the hundreds of watts. It is produced by NXP Semiconductors power range and there are sample modules that can be used for whole frequency ranges 1.8-250MHz.

It may be of interest to readers of PW for their perusal.

Dick Joyce G3WLM

Luton