Calling all Marconi experts! Can you help to identify this component
If you attended last week’s CARS Skills Night, you will have heard a plea from Terry G3VFC from the Medway Club for help and information regarding a mystery piece of Marconi equipment.
What is this?
This is apparently part of a 50 ohm dummy load power meter, and is stamped with Marconi.
We’ve had a couple of guesses, with the most recent suggestion being a Marconi TF2503 (suggested by Rob M0KCP on this week’s Monday Night Net).
Any suggestions? Please add your comment in the box below, and we’ll pass this along to Terry…
Thanks to Geoff Blke for submitting the following via our Facebook page:
“It is the load element of a co-axial load. Probably 50 ohms it is tapered to match the reducing impedance down the length of the resistive part, thus increasing the SWR bandwidth.”
I agree–it’s the resistive element of a coaxial dummy load. Older ARRL Handbooks had a plan for building a crude approximation of something like this and I believe the old Heathkit Cantenna dummy load used a tapered element as well.
Hmmmmmm…When I look at this, the “Wouff-Hong” of ARRL lore comes to mind! 73 de K4YZ
it think it was marconi insturments or sanders marconi
It looks like the 50-ohm resistor core for a Marconi TF2503 RF power meter.
I have several 52 Ohm RF loads with a transition of this design, it’s very typical.
Thanks for all info so far.
Now – is it the resistive element itself (it measures very high resistance so could be broken) or is it simply a capacitive jacket which tapers to be closer to one end of a carbon-like rod which would have been the real load, and if it did exist it doesn’t now? 73 – Terry G3VFC
It looks like the 52-ohm resistor for a Marconi TF2503 RF power meter
I can also confirm it is the load resistor from a Marconi Instruments TF2503 100W thermal power meter. It would have been manufactured in the mid-1970s. I worked in the design lab in St Albans where this power meter was designed and worked for MI from 1968 to 1998 when the company was sold by GEC to IFR in USA. This type of load is known as a tractorial load where the load is tapered unlike earlier MI power meters. The finned body should have contained a RF inert oil. The resistor should measure about 49.5 Ohm as it is intended to work with an in-line thermocouple that makes up the missing 0.5 Ohm. 73 Bryan, G8DKK ex-product manager Marconi microwave products & spectrum analysers
Hi Terry, It is the resistive element. It was made by sputtering the resistive material on to the glass blank in a vacuum chamber. The photo seems to show it has been burned out, the evidence being the black ring close to the connection to the N connector.
73 Bryan, G8DKK
Thanks to everyone who has offered information on this item – I feel that Bryan has confirmed our suspicion that it’s a was-load, and the remainder of the TF2503 has now been fitted with a lesser 50R resistor. Still useful and not bad value at £5 at Sevenoaks Rally. Will know what to look for next time…