Wireless Set No. 19 to variometer coax cable advice. - UK Vintage Radio Repair and Restoration Discussion Forum

normanmk1 · 2nd Mar 2018, 11:09 am

Hi Guys,
ref Wireless set 19 mk2 - I am needing to make up a coax cable to run from the 'A' set aerial socket to the variometer.From 'Wireless for the Warrior' I under stand that this should be of 80 ohm impedance - I can find 50 ohm but not 80 ohm.What coax cable should I use? I also understand that the cable should be 42" long - is that correct?
Sorry if this seems a silly question but I am new to military radios so any help/advice that you can give me would be much appreciated.Thank you.
Kevin.

G8HQP Dave · 2nd Mar 2018, 11:15 am

If it is designed for 80 ohm then 75 ohm is the nearest widely available coax.

n_r_muir · 2nd Mar 2018, 11:24 am

Hi,

I don't think that the length of the cable is at all critical, it is more a function of the particular vehicle installation than anything else. I have used two different versions, one 18" long and the other 24" long, there was no noticeable difference. The variometer setting for tuning up the antenna was just the same in either case.

Ross

M0SOE_Bruce · 3rd Mar 2018, 7:35 am

I believe Ross is correct. The length of the A set cable is not critical. It is dependent on the installation kit that was supplied. The B set had only two lengths that were tuned to match the aerial.

You can even run a piece of RG8 from the A set to a commercial tuner. If I recall the output impedance of the set was around 40 Ohms.

normanmk1 · 3rd Mar 2018, 11:10 am

Hi Guys,
Thank you for your very helpful replies.

Ref the length of coax cable - you have confirmed what I had thought ie that the length depends on where the variometer is situated in the set up,which would I guess vary from 1 vehicle type to another.

As for the ohm rating am I right in thinking that this is not critical?
What ohm rating have other ws19 owners used?
Thank you.
Kevin.

HamishBoxer · 3rd Mar 2018, 11:33 am

50 Ohms.

Radio Wrangler · 3rd Mar 2018, 11:48 am

So long as the cable length is small compared to a wavelength, you can get away with murder in terms of cable impedance.

8MHz is your top freq if I remember. 300/8=37.5m, so a couple of metres will be fine.

David

normanmk1 · 4th Mar 2018, 1:38 pm

Hi Guys,
Thank you for your informative replies.
I will get myself some RG213 50 ohm coax cable, which I think should do the trick nicely.

All the best, Kevin.

Radio1950 · 5th Mar 2018, 8:16 am

Hi there

if you find that 1/2 inch RG213 is a bit thick and not so flexible, I would try any rugged and flexible (both inner and outer) 50 or 75 ohm coax that fits the existing connectors, and is practical in use. Don't use the very thin 1/8 cables in this application.

As others have eloquently said, it wont matter much what impedance cable is used for such a small coax run, especially if your TX load impedance will be varied by the variometer tuning, when an antenna is connected.

It is only a low power TX with a single 807, so even RG58 should be fine.

For the picky ones like me, or you have to stay close to the original, flexible inner 75 ohm RG59 is available.

If you really must have the closest possible cable to the original (80 ohms?) try 1/2 inch 75 ohm URM70 available ex Maplin by the metre.

Good luck

M0FYA Andy · 5th Mar 2018, 9:31 am

Why not be authentic and use an original cable? They turn up quite regularly on ebay and doubtless elsewhere.

normanmk1 · 6th Mar 2018, 1:31 pm

Thank you for your replies.

Radio1950 - for a beginner like me your comments ref impedance and coax cable are very interesting and informative thank you.

Andy - origenal cable eg ZA3141 do indeed turn up sometimes but it tends to be pricey eg there is such a cable on an auction site just now for £48 incl p&p. R213 coax cable can be obtained for just over £1/mtr - I already have the 2 end sockets so I could make up a suitable cable,very similar to the origenal, for just over a quid. With limited funding that makes a lot of sense to me.
All the best,
Kevin.

Radio1950 · 7th Mar 2018, 12:25 am

Hi again,

Thanks.
I made a mistake in suggesting URM70 as close to original.
It is 75 ohm, but it is 6 mm outer diameter, and not 10 mm, and may not look very original.

Rather than suggesting other uncommon cables, and which are not readily available in small lengths, I would stay with your choice of RG213.

When you buy the cable, it may be marked along the length with brand and type.
Chose and cut your piece of cable so that this will not be visible on your set.
If the cable outer is too glossy and doesn't look authentic, (most RG213 and RG214 cables are glossy) lightly rub a scotch-brite soaked in alcohol along the cable before you finally cut to length for attaching the connectors. This helps to remove some of the gloss, and maybe any type marks.

If your connectors are solder types, have every thing squeaky clean and finally brush with alcohol before soldering.
Use a hot iron, larger rather than smaller, and be quick, as the relatively large RG213 copper inner conducts heat away from the joint to be soldered, and can also melt the cable insulation, and maybe even damage the connector.
Perhaps practice on a scrap piece of cable first, to ensure that your solder iron is OK for the job.

Just to elaborate a little bit on the theory of things.
"Electrically very short" transmission lines, ie much smaller than a quarter wavelength, tend to act more like shielded cables than actual transmission lines.
This is why we say that the cable impedance wont matter too much in this particular case.

good luck

Radio Wrangler · 7th Mar 2018, 8:22 am

If you use a good, powerful soldering iron, you can get the joint up to temperature quickly, the joint made and soon left to cool.

With a low power soldering iron, you have to leave the iron on the joint for a long time to get the joint to soldering temperature and this time allows more heat to travel further, and though it sounds counter-intuitive, you get more melting of insulation.

David

M0FYA Andy · 7th Mar 2018, 10:24 am

The WS19 uses Pye connectors, arguably rather crude by later standards, but we are talking wartime 70+ years ago. They use a grubscrew to grip the centre conductor. Critical to success is to use a ferrule on the centre conductor. This came with the connector, so a NOS example should have one. Otherwise use a little bit of tube from a model shop soldered to the inner conductor.
(The H2S radar which I'm interested in also uses lots of Pye connectors).
Andy

7th Mar 2018, 4:47 pm

Quote:

soldered to the inner conductor.

Don't solder, solder creeps over time, just use the tube a a protector and screw home.

M0FYA Andy · 7th Mar 2018, 5:17 pm

Whilst I'm aware that tinning multi-strand wire which is to be gripped by a terminal screw is not recommended due to solder-creep, I'm not sure the same applies to soldering wire inside a ferrule/tube applies. Whilst the solder might creep directly under the point of contact of the grub-screw if it crushes the ferrule, it won't creep over the whole length. Otherwise we'd have to worry about all soldered joints failing over time!

ex seismic · 7th Mar 2018, 5:56 pm

RG213 might be a touch too large for your Pye connectors, if so a little attention with a round file or suitable reamer will soon make the cable fit.

Gordon
WS19 Mk3 Canadian

G6Tanuki · 7th Mar 2018, 6:30 pm

Quote:

Originally Posted by M0FYA Andy

Whilst I'm aware that tinning multi-strand wire which is to be gripped by a terminal screw is not recommended due to solder-creep, I'm not sure the same applies to soldering wire inside a ferrule/tube applies. Whilst the solder might creep directly under the point of contact of the grub-screw if it crushes the ferrule, it won't creep over the whole length. Otherwise we'd have to worry about all soldered joints failing over time!

Having terminated stranded-centre-coax in grub-screw fittings like the WWII Pye-plugs for a decade or so I'd say twist the coax-centre-strands *tightly* [get at least ten twists-per-inch] then wind the screw down as tight as you can.

Don't 'tin' the twisted-coax centre-strands: solder makes them slippery and so more-likely to pull put of the bite of the screw. Trust me - this is not good news when it's 03:00z, the failure is 140-feet-up a mast, it's -5 degrees and blowing a gale.

vosperd · 7th Mar 2018, 9:20 pm

Hi Kevin,
If you intend to use the WS19 on the air I wonder what sort of aerial you will be using.
Don m5aky

normanmk1 · 8th Mar 2018, 9:49 am

Hi Guys,
Thank you all very much for all your helpful and informative replies. It's good to know that there are enthusiasts out there willing to take the time and trouble to share their knowledge and experience with struggling beginners like myself -it really is appreciated.

This will probably make you experienced guys throw your hands up in horror but I had never even thought about the power of the soldering iron let alone heat transfer to the insulation! It all makes perfect sense to me now!

In answer to Don's question - No I dont intend going on air with the ws19 at present - for one thing I do not have a licence. I also believe that to go on air using an ex-military set I would need proper training and at least an Intermediate licence. I intend using the set (on receive) in a display along with a WW2 battery charger.

All the best, Kevin.

2nd Mar 2018, 11:09 am	#1
normanmk1 Triode Join Date: Jan 2018 Location: Newton Abbot, Devonshire, UK. Posts: 23	Wireless Set No. 19 to variometer coax cable advice. Hi Guys, ref Wireless set 19 mk2 - I am needing to make up a coax cable to run from the 'A' set aerial socket to the variometer.From 'Wireless for the Warrior' I under stand that this should be of 80 ohm impedance - I can find 50 ohm but not 80 ohm.What coax cable should I use? I also understand that the cable should be 42" long - is that correct? Sorry if this seems a silly question but I am new to military radios so any help/advice that you can give me would be much appreciated.Thank you. Kevin.

2nd Mar 2018, 11:15 am	#2
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: ws19 to variometer coax cable advice. If it is designed for 80 ohm then 75 ohm is the nearest widely available coax.

2nd Mar 2018, 11:24 am	#3
n_r_muir Hexode Join Date: Jul 2007 Location: Edinburgh, UK. Posts: 344	Re: ws19 to variometer coax cable advice. Hi, I don't think that the length of the cable is at all critical, it is more a function of the particular vehicle installation than anything else. I have used two different versions, one 18" long and the other 24" long, there was no noticeable difference. The variometer setting for tuning up the antenna was just the same in either case. Ross

3rd Mar 2018, 7:35 am	#4
M0SOE_Bruce Pentode Join Date: May 2013 Location: Deal, Kent, UK. Posts: 139	Re: Wireless Set No. 19 to variometer coax cable advice. I believe Ross is correct. The length of the A set cable is not critical. It is dependent on the installation kit that was supplied. The B set had only two lengths that were tuned to match the aerial. You can even run a piece of RG8 from the A set to a commercial tuner. If I recall the output impedance of the set was around 40 Ohms.

3rd Mar 2018, 11:10 am	#5
normanmk1 Triode Join Date: Jan 2018 Location: Newton Abbot, Devonshire, UK. Posts: 23	Re: Wireless Set No. 19 to variometer coax cable advice. Hi Guys, Thank you for your very helpful replies. Ref the length of coax cable - you have confirmed what I had thought ie that the length depends on where the variometer is situated in the set up,which would I guess vary from 1 vehicle type to another. As for the ohm rating am I right in thinking that this is not critical? What ohm rating have other ws19 owners used? Thank you. Kevin.

3rd Mar 2018, 11:33 am	#6
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: Wireless Set No. 19 to variometer coax cable advice. 50 Ohms. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

3rd Mar 2018, 11:48 am	#7
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,868	Re: Wireless Set No. 19 to variometer coax cable advice. So long as the cable length is small compared to a wavelength, you can get away with murder in terms of cable impedance. 8MHz is your top freq if I remember. 300/8=37.5m, so a couple of metres will be fine. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

4th Mar 2018, 1:38 pm	#8
normanmk1 Triode Join Date: Jan 2018 Location: Newton Abbot, Devonshire, UK. Posts: 23	Re: Wireless Set No. 19 to variometer coax cable advice. Hi Guys, Thank you for your informative replies. I will get myself some RG213 50 ohm coax cable, which I think should do the trick nicely. All the best, Kevin.

5th Mar 2018, 8:16 am	#9
Radio1950 Hexode Join Date: Apr 2017 Location: Buderim, Queensland, Australia. Posts: 428	Re: Wireless Set No. 19 to variometer coax cable advice. Hi there if you find that 1/2 inch RG213 is a bit thick and not so flexible, I would try any rugged and flexible (both inner and outer) 50 or 75 ohm coax that fits the existing connectors, and is practical in use. Don't use the very thin 1/8 cables in this application. As others have eloquently said, it wont matter much what impedance cable is used for such a small coax run, especially if your TX load impedance will be varied by the variometer tuning, when an antenna is connected. It is only a low power TX with a single 807, so even RG58 should be fine. For the picky ones like me, or you have to stay close to the original, flexible inner 75 ohm RG59 is available. If you really must have the closest possible cable to the original (80 ohms?) try 1/2 inch 75 ohm URM70 available ex Maplin by the metre. Good luck

5th Mar 2018, 9:31 am	#10
M0FYA Andy Nonode Join Date: May 2007 Location: Preston, Lancashire, UK. Posts: 2,511	Re: Wireless Set No. 19 to variometer coax cable advice. Why not be authentic and use an original cable? They turn up quite regularly on ebay and doubtless elsewhere.

6th Mar 2018, 1:31 pm	#11
normanmk1 Triode Join Date: Jan 2018 Location: Newton Abbot, Devonshire, UK. Posts: 23	Re: Wireless Set No. 19 to variometer coax cable advice. Thank you for your replies. Radio1950 - for a beginner like me your comments ref impedance and coax cable are very interesting and informative thank you. Andy - origenal cable eg ZA3141 do indeed turn up sometimes but it tends to be pricey eg there is such a cable on an auction site just now for £48 incl p&p. R213 coax cable can be obtained for just over £1/mtr - I already have the 2 end sockets so I could make up a suitable cable,very similar to the origenal, for just over a quid. With limited funding that makes a lot of sense to me. All the best, Kevin.

7th Mar 2018, 12:25 am	#12
Radio1950 Hexode Join Date: Apr 2017 Location: Buderim, Queensland, Australia. Posts: 428	Re: Wireless Set No. 19 to variometer coax cable advice. Hi again, Thanks. I made a mistake in suggesting URM70 as close to original. It is 75 ohm, but it is 6 mm outer diameter, and not 10 mm, and may not look very original. Rather than suggesting other uncommon cables, and which are not readily available in small lengths, I would stay with your choice of RG213. When you buy the cable, it may be marked along the length with brand and type. Chose and cut your piece of cable so that this will not be visible on your set. If the cable outer is too glossy and doesn't look authentic, (most RG213 and RG214 cables are glossy) lightly rub a scotch-brite soaked in alcohol along the cable before you finally cut to length for attaching the connectors. This helps to remove some of the gloss, and maybe any type marks. If your connectors are solder types, have every thing squeaky clean and finally brush with alcohol before soldering. Use a hot iron, larger rather than smaller, and be quick, as the relatively large RG213 copper inner conducts heat away from the joint to be soldered, and can also melt the cable insulation, and maybe even damage the connector. Perhaps practice on a scrap piece of cable first, to ensure that your solder iron is OK for the job. Just to elaborate a little bit on the theory of things. "Electrically very short" transmission lines, ie much smaller than a quarter wavelength, tend to act more like shielded cables than actual transmission lines. This is why we say that the cable impedance wont matter too much in this particular case. good luck

7th Mar 2018, 8:22 am	#13
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,868	Re: Wireless Set No. 19 to variometer coax cable advice. If you use a good, powerful soldering iron, you can get the joint up to temperature quickly, the joint made and soon left to cool. With a low power soldering iron, you have to leave the iron on the joint for a long time to get the joint to soldering temperature and this time allows more heat to travel further, and though it sounds counter-intuitive, you get more melting of insulation. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

7th Mar 2018, 10:24 am	#14
M0FYA Andy Nonode Join Date: May 2007 Location: Preston, Lancashire, UK. Posts: 2,511	Re: Wireless Set No. 19 to variometer coax cable advice. The WS19 uses Pye connectors, arguably rather crude by later standards, but we are talking wartime 70+ years ago. They use a grubscrew to grip the centre conductor. Critical to success is to use a ferrule on the centre conductor. This came with the connector, so a NOS example should have one. Otherwise use a little bit of tube from a model shop soldered to the inner conductor. (The H2S radar which I'm interested in also uses lots of Pye connectors). Andy

7th Mar 2018, 5:17 pm	#16
M0FYA Andy Nonode Join Date: May 2007 Location: Preston, Lancashire, UK. Posts: 2,511	Re: Wireless Set No. 19 to variometer coax cable advice. Whilst I'm aware that tinning multi-strand wire which is to be gripped by a terminal screw is not recommended due to solder-creep, I'm not sure the same applies to soldering wire inside a ferrule/tube applies. Whilst the solder might creep directly under the point of contact of the grub-screw if it crushes the ferrule, it won't creep over the whole length. Otherwise we'd have to worry about all soldered joints failing over time!

7th Mar 2018, 5:56 pm	#17
ex seismic Heptode Join Date: Sep 2009 Location: Tonbridge, Kent, UK. Posts: 686	Re: Wireless Set No. 19 to variometer coax cable advice. RG213 might be a touch too large for your Pye connectors, if so a little attention with a round file or suitable reamer will soon make the cable fit. Gordon WS19 Mk3 Canadian

7th Mar 2018, 9:20 pm	#19
vosperd Hexode Join Date: Oct 2007 Location: Bristol, UK. Posts: 444	Re: Wireless Set No. 19 to variometer coax cable advice. Hi Kevin, If you intend to use the WS19 on the air I wonder what sort of aerial you will be using. Don m5aky

8th Mar 2018, 9:49 am	#20
normanmk1 Triode Join Date: Jan 2018 Location: Newton Abbot, Devonshire, UK. Posts: 23	Re: Wireless Set No. 19 to variometer coax cable advice. Hi Guys, Thank you all very much for all your helpful and informative replies. It's good to know that there are enthusiasts out there willing to take the time and trouble to share their knowledge and experience with struggling beginners like myself -it really is appreciated. This will probably make you experienced guys throw your hands up in horror but I had never even thought about the power of the soldering iron let alone heat transfer to the insulation! It all makes perfect sense to me now! In answer to Don's question - No I dont intend going on air with the ws19 at present - for one thing I do not have a licence. I also believe that to go on air using an ex-military set I would need proper training and at least an Intermediate licence. I intend using the set (on receive) in a display along with a WW2 battery charger. All the best, Kevin.