Londex Antenna relay - UK Vintage Radio Repair and Restoration Discussion Forum

RF Burn · 3rd Jun 2020, 2:22 pm

While searching through my stuff I found a long forgotten pair of antenna changeover relays marked "LONDEX CCX 70X 24V.D.C."

Does anyone have the specs for these relays? The internet is almost silent about them.

Adrian

m0cemdave · 4th Jun 2020, 12:24 am

I have had a few of these over the years and still have a BCX 50X, fitted with BNC connectors.
From memory, the number indicated the impedance, so 70CX was 72/75 ohms and 50CX was 50/52 ohms.

Humber888 · 4th Jun 2020, 8:41 am

Some of those old Londex relays were fitted with Burndept sockets rather than N type. The Burndept plugs were a pain to assemble. I remember buying one relay which came with spare plugs with cut-off cable stubs and they were filled with wax to seal the inners. A picture of the relay would help but, if I am thinking of the same style, they should handle at least a hundred Watts of RF - probably more.

RF Burn · 4th Jun 2020, 10:20 am

Photos attached. It was the impedance (confirmed 70-80 Ohms) and the power rating and frequency range that I am interested in. I guess the range must cover at least 0 - 30MHz with good VSWR . . .

Adrian

Humber888 · 4th Jun 2020, 3:58 pm

Interesting that your relay is fitted with SO239 'UHF' sockets. These are non constant impedance types and worse at high frequencies than BNC or N-type. They could be the limiting factor in your relay's high frequency performance. However they were (are?) popular on 2-metre rigs so the relay may well be OK at 144MHz. I was going to suggest that if you or a local amateur radio enthusiast had a 2-metre TX and an SWR meter, you could put the relay in-line and see how it affects the SWR. However, most rigs are intended to feed 50 Ohm coax and aerials, so a 75 Ohm relay will be less than optimum. Might still be worth a try. My guess is still about 100W switching capacity.

3rd Jun 2020, 2:22 pm	#1
RF Burn Hexode Join Date: Apr 2008 Location: Ramsgate, Kent, UK. Posts: 252	Londex Antenna relay While searching through my stuff I found a long forgotten pair of antenna changeover relays marked "LONDEX CCX 70X 24V.D.C." Does anyone have the specs for these relays? The internet is almost silent about them. Adrian

4th Jun 2020, 12:24 am	#2
m0cemdave Octode Join Date: Feb 2009 Location: Bletchley, Buckinghamshire, UK. Posts: 1,214	Re: Londex Antenna relay I have had a few of these over the years and still have a BCX 50X, fitted with BNC connectors. From memory, the number indicated the impedance, so 70CX was 72/75 ohms and 50CX was 50/52 ohms.

4th Jun 2020, 8:41 am	#3
Humber888 Heptode Join Date: Jul 2012 Location: Bromley, London, UK. Posts: 702	Re: Londex Antenna relay Some of those old Londex relays were fitted with Burndept sockets rather than N type. The Burndept plugs were a pain to assemble. I remember buying one relay which came with spare plugs with cut-off cable stubs and they were filled with wax to seal the inners. A picture of the relay would help but, if I am thinking of the same style, they should handle at least a hundred Watts of RF - probably more.

4th Jun 2020, 10:20 am	#4
RF Burn Hexode Join Date: Apr 2008 Location: Ramsgate, Kent, UK. Posts: 252	Re: Londex Antenna relay Photos attached. It was the impedance (confirmed 70-80 Ohms) and the power rating and frequency range that I am interested in. I guess the range must cover at least 0 - 30MHz with good VSWR . . . Adrian Attached Thumbnails

4th Jun 2020, 3:58 pm	#5
Humber888 Heptode Join Date: Jul 2012 Location: Bromley, London, UK. Posts: 702	Re: Londex Antenna relay Interesting that your relay is fitted with SO239 'UHF' sockets. These are non constant impedance types and worse at high frequencies than BNC or N-type. They could be the limiting factor in your relay's high frequency performance. However they were (are?) popular on 2-metre rigs so the relay may well be OK at 144MHz. I was going to suggest that if you or a local amateur radio enthusiast had a 2-metre TX and an SWR meter, you could put the relay in-line and see how it affects the SWR. However, most rigs are intended to feed 50 Ohm coax and aerials, so a 75 Ohm relay will be less than optimum. Might still be worth a try. My guess is still about 100W switching capacity.