Avoiding transmitting - UK Vintage Radio Repair and Restoration Discussion Forum

TonyDuell · 30th Mar 2018, 4:59 pm

If I power up a small transceiver (say a WS88. as I have one next to the bench) in transmit mode with no aerial plugged in, would it radiate enough signal to cause interference and/or be illegal? What about if the metal casing was removed?

The reason I ask is that I have no intention of transmitting illegally but would like to see what the WS88 does with a 'scope, etc. That would mean having it open on the bench, powered up, but with no aerial connected.

MrBungle · 30th Mar 2018, 5:11 pm

You should probably connect a dummy load to it. That won't radiate much RF if any and should be considered reasonable.

Also depending on the output network in the transmitter, if you connect a scope to it and there is no load it might blow the scope up. The transient voltages can be quite high even at the quoted 8-15W. I've seen 100V p-p on a 1W output with no load!

Have a look at this, which explains it in detail: http://www.ab4oj.com/test/pwrmeas.html

G6Tanuki · 30th Mar 2018, 5:37 pm

I wouldn't worry yourself about the legality issues of inadvertently squirting a few tens /hundreds of milliwatts of RF around for a short time[1]: my greater concern would be that in the absence of a RF load/antenna your WS88 or whatever could see some seriously high RF voltages/currents in its output stage which could cause damage.

Sticking a dummy-load on the output will be protective against damage - though the feed-impedance of the usual 'short whip' on the likes of a WS88 is very high so don't go connecting a modern amateur-radio 50-Ohm dummy load to its antenna/earth terminals!

[1] in times-past I spent something like six months trying to interest 'the authorities' in a defective piece of kit located in the UK that was randomly but persistently spewing significant noisy and frequency-unstable RF over a HF allocation I had a professional interest in. No action was taken; in the end we got ourselves a new frequency.

HamishBoxer · 30th Mar 2018, 5:49 pm

Certainly,goodbye output stage,so use a dummy load.

TonyDuell · 30th Mar 2018, 6:01 pm

I had wondered about needing a dummy load. I assume a non-inductive resistor would be fine, but what sort of value? A few hundred ohms?

G6Tanuki · 30th Mar 2018, 6:17 pm

Anything's better than nothing. I'd go for a couple of hundred Ohms - but remember that a lot of modern resistors use a spiral track so could well be inductive as well as resistive!

Just so long as you provide *somewhere* for the RF to go. The WS88 as well as working with a whip-antenna was also specced to work with a 'trailing wire' of around six feet - that must have presented a really random and variable load on the output-stage so you don't need to be too paranoid about precise load-values.

TonyDuell · 30th Mar 2018, 6:23 pm

As an aside... I seem to recall reading that as the WS88 was watertight, it was not to be opened in the field, not even for valve replacements. And you can bet that at some point in the height of action somebody would press the transmit button without fitting the aerial, or the aerial would have come off or something. So I would hope it would not do major damage to the set.

That said, a dummy load is clearly a good idea. And yes, I know that modern resistors are often quite inductive. I wonder if I have an old carbon composition 220 ohm thing somewhere....

ex seismic · 30th Mar 2018, 7:50 pm

Get hold of the relevant EMER, it will almost certainly tell you what the official dummy load was for testing purposes.

Gordon

Herald1360 · 30th Mar 2018, 8:01 pm

Isn't a WS88 pretty much fleapower around 45 MHz? As such its whip would have been close enough to quarterwave to be fairly low impedance, son I'd expect a 50R load to be fine. It only has B7G battery valves to play with.

If it isn't squaddie proof, it's a pretty poor design!

TonyDuell · 31st Mar 2018, 5:15 am

The transmitter output valve is a 3A4 (DL93), the data sheet on that valve claims a possible output power of 1.2W when used as a transmitter. Quite how much the WS88 manages to get out of it I don't know.

Alas I can't access the royalsignals site (I only have a 'free' e-mail address) so I don't have the EMERs for this set. I did find pictures of the working instructions card on one site, on there you check the set by listening for noise after removing the aerial (in receive mode). It then says to press the transmit button and check you can hear your own voice (from the microphone) in the headphones. And then it goes on to using the set to talk to others. At no point does it tell you to refit the aerial so whether that is done for the 'own voice' test I don't know.

llama · 31st Mar 2018, 8:36 am

Wireless for the Warrior vol 2 (WS88 - 15) shows the dummy load to be a pi of resistors fed by an 18 pF capacitor. The pi is made from 62 Ohms to deck, a 180 Ohms series resistor, followed by a 110 Ohms resistor to deck.
HTH
Graham

Terry_VK5TM · 31st Mar 2018, 11:32 am

The WS88 manual on VMARS lists the output power as 250mW, which seems somewhat low.

TonyDuell · 31st Mar 2018, 11:36 am

I assume some test gear is connected to the point beteen the 180 and 110 ohm resistors.

Without the test gear (which I would assume was high impedance anyway), that is equivalent to a 51 ohm resistor. So the dummy load could be a 51 ohm resistor in series with an 18 pf capacitor.

Assuming I've not mis-calculated something, at 41 MHz that has an impedance of around 220 ohms.

G8HQP Dave · 31st Mar 2018, 12:33 pm

But 18pF in series with 51ohms is very different from a 220 ohm resistor.

I am going to hazard a guess that the pi network described above has an output impedance of around 75 ohms which may match the input of some piece of ancient test equipment. That is why a pi was used: you can get a rough match both sides.

llama · 31st Mar 2018, 4:00 pm

"The RF output is measured by connecting a (valve) voltmeter directly to the spade terminals situated on the side of the dummy aerial. A signal generator is connected to the coaxial socket for making receiver sensitivity measurements".

Both the co-ax socket and the spade terminal are across the 110 Ohm resistor so I presume the impedance has been designed to be right for both Tx and Rx measurements.
Graham

CambridgeWorks · 31st Mar 2018, 6:33 pm

Regarding the first post by OP,
Personally I would not be concerned. I am sure a lot of "pantry transmitters" featured on this forum are knowingly expected to radiate to a level that would exceed your innocent bench testing.
Such testing would not cause me any problems or concerns.
Being qrp and valve pa, it should not cause any problems or self destruct.
If you are arrested, I am sure we would all chip in a bit to defend you!
Rob

HamishBoxer · 31st Mar 2018, 6:38 pm

I will send the hat around now!

TonyDuell · 31st Mar 2018, 6:47 pm

My current thoughts on this (as it is my WS88) :

There should be no harm done if I use a small dummy load. Or if I use none. As Herald1360 (I think) said, the thing has to be squadie-proof, and a set which is damaged if the transmit button is pressed when the removable aerial is not plugged in is certainly not that. A war is not an electronics lab, a squadie is not (always) a radio engineer.

One of the user tests on the instruction card could be to run it in transmit mode with no aerial. Given that there was no instuction to follow proper comms procedure when doing that, I would guess it would not interfere with other similar sets nearby on the same frequency (remember this thing has 4 channels -- 4 crystals, it is not continuously tuned). So I guess little signal gets out.

I won't be running it for very long, a few seconds at most to start with.

I wonder if one of my other receivers could pick it up. I do have an ICOM that covers that band with an FM demodulator. If so, I can see if I can detect a signal across the workshop, in another room, etc. If not, then I am going to assume that very little is getting out.

G0HZU_JMR · 31st Mar 2018, 7:06 pm

It's worth checking all your cables and connections are healthy even into a dummy load. I can remember at work someone swept a 50W transmitter into a decent dummy load up at UHF and it managed to prevent members of staff opening their car doors in the car park outside. It turned out that one of the RF cables had faulty screening at one end. It was a serious event and caused quite a shakeup at work.

So it isn't just about legality, you can actually cause problems to other wireless users close by. Maybe check with a wavemeter if you aren't certain? But as long as your cables and connections are healthy it should be fine. At work now we don't allow any unbranded coax cables or any cables that are starting to look old. All Tx testing into loads is done via premium cables from the top manufacturers now and we have large screened enclosures for the high power stuff and we monitor RF leakage levels.

GMB · 31st Mar 2018, 7:44 pm

The WS88 is military, low powered and uses valves. So there is no chance of blowing up anything, whatever the loading.

In real life it drives a near quarter wave dipole so any old low resistive load like 50R will be fine to see the output. In real life the loading varies wildly depending on body position relative to the aerial - something that all small radios are designed to cope with. The exacting specification for loadings that you might see in a manual is about making precise and repeatable measurements to accurately assess performance.

It will radiate and I suspect that it would do so illegally but not at a very high level that anyone is likely to notice so long as you do not make a habit of it. It will be in what is still a military band unless it has been modified for ham band use.

30th Mar 2018, 4:59 pm	#1
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Avoiding transmitting If I power up a small transceiver (say a WS88. as I have one next to the bench) in transmit mode with no aerial plugged in, would it radiate enough signal to cause interference and/or be illegal? What about if the metal casing was removed? The reason I ask is that I have no intention of transmitting illegally but would like to see what the WS88 does with a 'scope, etc. That would mean having it open on the bench, powered up, but with no aerial connected.

30th Mar 2018, 5:11 pm	#2
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Re: Avoiding transmitting You should probably connect a dummy load to it. That won't radiate much RF if any and should be considered reasonable. Also depending on the output network in the transmitter, if you connect a scope to it and there is no load it might blow the scope up. The transient voltages can be quite high even at the quoted 8-15W. I've seen 100V p-p on a 1W output with no load! Have a look at this, which explains it in detail: http://www.ab4oj.com/test/pwrmeas.html

30th Mar 2018, 5:37 pm	#3
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Avoiding transmitting I wouldn't worry yourself about the legality issues of inadvertently squirting a few tens /hundreds of milliwatts of RF around for a short time[1]: my greater concern would be that in the absence of a RF load/antenna your WS88 or whatever could see some seriously high RF voltages/currents in its output stage which could cause damage. Sticking a dummy-load on the output will be protective against damage - though the feed-impedance of the usual 'short whip' on the likes of a WS88 is very high so don't go connecting a modern amateur-radio 50-Ohm dummy load to its antenna/earth terminals! [1] in times-past I spent something like six months trying to interest 'the authorities' in a defective piece of kit located in the UK that was randomly but persistently spewing significant noisy and frequency-unstable RF over a HF allocation I had a professional interest in. No action was taken; in the end we got ourselves a new frequency.

30th Mar 2018, 5:49 pm	#4
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: Avoiding transmitting Certainly,goodbye output stage,so use a dummy load. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

30th Mar 2018, 6:01 pm	#5
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Avoiding transmitting I had wondered about needing a dummy load. I assume a non-inductive resistor would be fine, but what sort of value? A few hundred ohms?

30th Mar 2018, 6:17 pm	#6
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Avoiding transmitting Anything's better than nothing. I'd go for a couple of hundred Ohms - but remember that a lot of modern resistors use a spiral track so could well be inductive as well as resistive! Just so long as you provide somewhere for the RF to go. The WS88 as well as working with a whip-antenna was also specced to work with a 'trailing wire' of around six feet - that must have presented a really random and variable load on the output-stage so you don't need to be too paranoid about precise load-values.

30th Mar 2018, 6:23 pm	#7
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Avoiding transmitting As an aside... I seem to recall reading that as the WS88 was watertight, it was not to be opened in the field, not even for valve replacements. And you can bet that at some point in the height of action somebody would press the transmit button without fitting the aerial, or the aerial would have come off or something. So I would hope it would not do major damage to the set. That said, a dummy load is clearly a good idea. And yes, I know that modern resistors are often quite inductive. I wonder if I have an old carbon composition 220 ohm thing somewhere....

30th Mar 2018, 7:50 pm	#8
ex seismic Heptode Join Date: Sep 2009 Location: Tonbridge, Kent, UK. Posts: 686	Re: Avoiding transmitting Get hold of the relevant EMER, it will almost certainly tell you what the official dummy load was for testing purposes. Gordon

30th Mar 2018, 8:01 pm	#9
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Avoiding transmitting Isn't a WS88 pretty much fleapower around 45 MHz? As such its whip would have been close enough to quarterwave to be fairly low impedance, son I'd expect a 50R load to be fine. It only has B7G battery valves to play with. If it isn't squaddie proof, it's a pretty poor design! __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

31st Mar 2018, 5:15 am	#10
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Avoiding transmitting The transmitter output valve is a 3A4 (DL93), the data sheet on that valve claims a possible output power of 1.2W when used as a transmitter. Quite how much the WS88 manages to get out of it I don't know. Alas I can't access the royalsignals site (I only have a 'free' e-mail address) so I don't have the EMERs for this set. I did find pictures of the working instructions card on one site, on there you check the set by listening for noise after removing the aerial (in receive mode). It then says to press the transmit button and check you can hear your own voice (from the microphone) in the headphones. And then it goes on to using the set to talk to others. At no point does it tell you to refit the aerial so whether that is done for the 'own voice' test I don't know.

31st Mar 2018, 8:36 am	#11
llama Octode Join Date: Jun 2006 Location: St Osyth, Nr Clacton, Essex, UK. Posts: 1,482	Re: Avoiding transmitting Wireless for the Warrior vol 2 (WS88 - 15) shows the dummy load to be a pi of resistors fed by an 18 pF capacitor. The pi is made from 62 Ohms to deck, a 180 Ohms series resistor, followed by a 110 Ohms resistor to deck. HTH Graham __________________ Half my stuff is junk - trouble is, I don't know which half!

31st Mar 2018, 11:32 am	#12
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,339	Re: Avoiding transmitting The WS88 manual on VMARS lists the output power as 250mW, which seems somewhat low. __________________ Terry VK5TM https://www.vk5tm.com/

31st Mar 2018, 11:36 am	#13
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Avoiding transmitting I assume some test gear is connected to the point beteen the 180 and 110 ohm resistors. Without the test gear (which I would assume was high impedance anyway), that is equivalent to a 51 ohm resistor. So the dummy load could be a 51 ohm resistor in series with an 18 pf capacitor. Assuming I've not mis-calculated something, at 41 MHz that has an impedance of around 220 ohms.

31st Mar 2018, 12:33 pm	#14
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Avoiding transmitting But 18pF in series with 51ohms is very different from a 220 ohm resistor. I am going to hazard a guess that the pi network described above has an output impedance of around 75 ohms which may match the input of some piece of ancient test equipment. That is why a pi was used: you can get a rough match both sides.

31st Mar 2018, 4:00 pm	#15
llama Octode Join Date: Jun 2006 Location: St Osyth, Nr Clacton, Essex, UK. Posts: 1,482	Re: Avoiding transmitting "The RF output is measured by connecting a (valve) voltmeter directly to the spade terminals situated on the side of the dummy aerial. A signal generator is connected to the coaxial socket for making receiver sensitivity measurements". Both the co-ax socket and the spade terminal are across the 110 Ohm resistor so I presume the impedance has been designed to be right for both Tx and Rx measurements. Graham __________________ Half my stuff is junk - trouble is, I don't know which half!

31st Mar 2018, 6:33 pm	#16
CambridgeWorks Nonode Join Date: Jun 2010 Location: Spalding, Peterborough, Cambridgeshire, UK. Posts: 2,859	Re: Avoiding transmitting Regarding the first post by OP, Personally I would not be concerned. I am sure a lot of "pantry transmitters" featured on this forum are knowingly expected to radiate to a level that would exceed your innocent bench testing. Such testing would not cause me any problems or concerns. Being qrp and valve pa, it should not cause any problems or self destruct. If you are arrested, I am sure we would all chip in a bit to defend you! Rob __________________ Apprehension creeping like a tube train up your spine - Cymbaline. Film More soundtrack - Pink Floyd

31st Mar 2018, 6:38 pm	#17
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: Avoiding transmitting I will send the hat around now! __________________ G8JET BVWS Archivist and Member V.M.A.R.S

31st Mar 2018, 6:47 pm	#18
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Avoiding transmitting My current thoughts on this (as it is my WS88) : There should be no harm done if I use a small dummy load. Or if I use none. As Herald1360 (I think) said, the thing has to be squadie-proof, and a set which is damaged if the transmit button is pressed when the removable aerial is not plugged in is certainly not that. A war is not an electronics lab, a squadie is not (always) a radio engineer. One of the user tests on the instruction card could be to run it in transmit mode with no aerial. Given that there was no instuction to follow proper comms procedure when doing that, I would guess it would not interfere with other similar sets nearby on the same frequency (remember this thing has 4 channels -- 4 crystals, it is not continuously tuned). So I guess little signal gets out. I won't be running it for very long, a few seconds at most to start with. I wonder if one of my other receivers could pick it up. I do have an ICOM that covers that band with an FM demodulator. If so, I can see if I can detect a signal across the workshop, in another room, etc. If not, then I am going to assume that very little is getting out.

31st Mar 2018, 7:06 pm	#19
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: Avoiding transmitting It's worth checking all your cables and connections are healthy even into a dummy load. I can remember at work someone swept a 50W transmitter into a decent dummy load up at UHF and it managed to prevent members of staff opening their car doors in the car park outside. It turned out that one of the RF cables had faulty screening at one end. It was a serious event and caused quite a shakeup at work. So it isn't just about legality, you can actually cause problems to other wireless users close by. Maybe check with a wavemeter if you aren't certain? But as long as your cables and connections are healthy it should be fine. At work now we don't allow any unbranded coax cables or any cables that are starting to look old. All Tx testing into loads is done via premium cables from the top manufacturers now and we have large screened enclosures for the high power stuff and we monitor RF leakage levels. __________________ Regards, Jeremy G0HZU

31st Mar 2018, 7:44 pm	#20
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,095	Re: Avoiding transmitting The WS88 is military, low powered and uses valves. So there is no chance of blowing up anything, whatever the loading. In real life it drives a near quarter wave dipole so any old low resistive load like 50R will be fine to see the output. In real life the loading varies wildly depending on body position relative to the aerial - something that all small radios are designed to cope with. The exacting specification for loadings that you might see in a manual is about making precise and repeatable measurements to accurately assess performance. It will radiate and I suspect that it would do so illegally but not at a very high level that anyone is likely to notice so long as you do not make a habit of it. It will be in what is still a military band unless it has been modified for ham band use.