thank you for this video richard. I am trying to diagnose a highish swr so following your advice,.purchased two resistors off ebay and had 49.5 ohms for an swr of 1.2.I shall look elsewhere cheers
I always used light bulbs. You get one twice the wattage of the transmitter and it brightness tells you how good your output is. But this is a pretty good idea since light bulbs with a filament are getting harder to find.
my first dummy load was four 47ohm resistors (bought from anchor supplies) around 10w each in series parallel and fitted inside a cheap three way switch box/dummy load unit, i ended up selling it to a local screwdriver merchant who after 25 years still had it and used it often. (until he died)
I under stood what he was saying and proceeded to build one for my CB base station...if the camera angle could have been from the front instead of just seeing the hands it would have made for a better video. Thanks for posting.
Interesting. At a pinch I have used metal film resistors for HF dummy loads I'm not aware metal film are ridiculously inductive and not to be confused with wire wound. Obviously depends on frequency. Nice little project that's very useful. Thanks for making these videos
I looked inside a Zetagi 30W load & it certainly wasn't carbon resistors in there, but of course is screened. Anyway, this shows an SWR of 1:1. I may have time to do the next video tonight.
Hi Richard To be honest I have found at HF you can use pretty much anything. Unless you are actually going to do a power measurement referenced to 50 ohm the value of resistance is not to critical either. God knows what antenna impedances that I must have transmitted in over the year without issue. Many designs do however use more high resistance value load resistors in parallel combinations and this is to reduce the inductive reactance. I am always amazed at your repairs, I’m rubbish at it. Looking forward to part 2. Regards Chris
I made one similar to this back in the 1970s, still use it to this day. Not a complaint as such, more of a suggestion: You should use a different camera angle, your hands block the view of the item being worked on.
We do all service work on test instruments & into a dummy load as all service manuals dictate. We do air test all repairs just in case, for example, the FM detector is on a false peak. Richard. G0OJF, UK
Yes, but as this is a CB project 5W was deemed to be more than adequate. This type of construction isn't really suitable for use over 30Mhz. Richard, G0OJF, UK
Brilliant series Richard. I've just made my 2nd dummy load using a 47ohm series/parallel matrix setup. Resistors are 1/4w each but as there's 4x4 it works out at 4w on the button. Short tx only obviously and built with bits from the odds and sods box. Please continue this series as these videos are golden. 👍🏼
If you get 3 watt resistors it will handle transmit power a lot longer. Do not get wire wound ones. The resistors will get hot if transmitting for a while. Keep transmission short they will work fine. Better that one Screwdriver so called expert used to do, he used to transmit into an aerial through his cheap power meter which will quite happily read the harmonics as well as the frequency he is tuning up on. The dummy was not plugged into the CB, he was adjusting it! Richard, it is all the average person will ever need. Not got this far back in your videos yet, UA-cam just threw it at me out of the blue. Have you built a salt water dummy load or an oil filled one? I had a very old oil filled one, couldn't read who made it, but it started leaking, even though it was oil filled, it rusted through the top. I threw it out, I should have kept it. I'm sure I took a photo of it at one time, but it may be one of the photo's that was thrown out during house moves. :-((
We do little over 25W business radios so have a 300W max for 15 seconds dummy load for bigger jobs. None of the test gear here goes beyond 30W. Richard
Twazzle? is that a technical term? :p thanks for an informative video.... i look forwards to more from this series. one little thing it would be useful if you put all the servicing on a shoestring videos into a playlist. kindest regards Martin
Thank you for this, I really didn't want to spend a lot of money on a dummy load. I got my resistors in the mail yesterday so hope to build it soon. Weird question for you, have you seen the one on EBay that only uses a light? (It's like $10.00 on Ebay). I wrote that guy and he says the light burns off the rf energy, but his wouldn't work would it? The light bulb won't equal the 50 ohm requirement, would it??
The USA available lamp just happens to be a 50 ohm load & I understand will take up to 5W. I've never seen one in person & what I'm telling you here is what I remember from American textbooks from the 60's & 70's. It isn't some special kind of bulb ,but happens to work as a dummy load. Richard
@@ukfmcbradioservicingTango21 Thank you for the information. I'm going to build one like in this video, but wanted to find out about the light bulb type before I possibly bought one since it's only $10.00. Thanks again!
@@ukfmcbradioservicingTango21 Thank you for this video. I built my resistor cb dummy load this weekend and it works great, with a flat 1.0 swr on the cb's internal swr meter. I also ordered one I talked about earlier, with the light bulb and guess what?? The light bulb one measured 1.5 on the same cb/swr meter. I like your two resistor idea better and it works better, too!! Thanks!
Nice for a 5 watt dummy load. If you don't mind me asking, but to make a 20 watt dummy load, what would be the calculations for that? I'm thinking 200 ohm 5 watt resistors × 4. Would that be accurate? I want to use a minimal amount of resistors.
Yes, that sounds right. However, 200R (ohms) is not a European or UK 'preferred' value...but a quick look on ebay & I spotted this 141768770983. You will see he has 200R; and dead cheap too. Richard
vbe carefull tu use only resistive resistors... Often the power resistors a selfics, then ih HF frequencies, load is not 50 ohms... Or yoy use carbon resistors, or film non inductive resistors...
They are metal film. Resistors have to be 'non reactive' & when the text books were written there was only carbon & wirewound. As you know, wirewound resistors are reactive so no use in this application. If it worries you, make one with carbon resistors. Now think of the people using a particular American light bulb as a dummy load which is going to be reactive to some extent! Richard, G0OJF, UK
So why make a 5W dummy load for a 45W radio? This project was intended for 4W UK CB radios. If you are working on LMR equipment surely that is VHF or UHF & requires a screened dummy load of suitable power rating & terminated in either a BNC or N-type connector. I was asked to do this series of 'CB servicing on a shoestring' for a reason, and that wasn't for business radio, in which I worked full time for 16 years. When you assembled the dummy load & tested the finished item, did it test OK on your multimeter? Did the heat shrink insulation fed up the inner of the plug fail because it overheated & cause a direct short? Why otherwise was the VSWR so high as to reflect 45W back to a 45W source? You say the finals blew...but how many are there in that radio & why did more than one fail...I ask this because after years in business radio I remember many a customer with ridiculously wrong aerials...including a front door key as an aerial; in all cases the driver transistor failed & not the finals. Richard (UK)
I'm 60 and just getting back into CB this was fantastic vid thanks
thank you for this video richard. I am trying to diagnose a highish swr so following your advice,.purchased two resistors off ebay and had 49.5 ohms for an swr of 1.2.I shall look elsewhere cheers
It's best to use carbon resistors..I used metalfilm ones & it was OK. Wirewound resistors are a no no as they become reactive.
Richard
I always used light bulbs. You get one twice the wattage of the transmitter and it brightness tells you how good your output is. But this is a pretty good idea since light bulbs with a filament are getting harder to find.
There was/is a filament bulb in America that works perfectly. That bulb wasn't a thing here in the UK.
Richard, G0OJF, UK
Brilliant video, really appreciate this education, many thanks for doing this series. Your a very good teacher.
Very interesting and informative. Really appreciated and I will gather the components to make ono 👌
my first dummy load was four 47ohm resistors (bought from anchor supplies) around 10w each in series parallel and fitted inside a cheap three way switch box/dummy load unit, i ended up selling it to a local screwdriver merchant who after 25 years still had it and used it often. (until he died)
I under stood what he was saying and proceeded to build one for my CB base station...if the camera angle could have been from the front instead of just seeing the hands it would have made for a better video. Thanks for posting.
this is a brilliant idea and great chain of videos for you to make for people like me, as simple as possible please
Interesting. At a pinch I have used metal film resistors for HF dummy loads I'm not aware metal film are ridiculously inductive and not to be confused with wire wound. Obviously depends on frequency. Nice little project that's very useful. Thanks for making these videos
I looked inside a Zetagi 30W load & it certainly wasn't carbon resistors in there, but of course is screened. Anyway, this shows an SWR of 1:1. I may have time to do the next video tonight.
Hi Richard To be honest I have found at HF you can use pretty much
anything. Unless you are actually going to do a power measurement referenced to
50 ohm the value of resistance is not to critical either. God knows what antenna
impedances that I must have transmitted in over the year without issue. Many designs do however use more high resistance value load resistors in parallel combinations and this is to reduce the inductive reactance. I am always amazed at your repairs, I’m rubbish at it. Looking forward to part 2.
Regards Chris
nice simple idea ill give it a try thanks for sharing
Thank you Richard, on the video on how to make 50 ohm dummy load. Cheers!
i know Im pretty randomly asking but does anyone know a good place to watch newly released movies online ?
@Morgan Bjorn lately I have been using flixzone. Just google for it :)
@Davion Cullen Definitely, I have been watching on FlixZone for years myself :)
@Davion Cullen Thank you, signed up and it seems to work =) Appreciate it!!
@Morgan Bjorn Glad I could help xD
Just the job for QRP work, thanks!
Genius!!! Awesome for a little barefoot radio with a single final.
I made one similar to this back in the 1970s, still use it to this day.
Not a complaint as such, more of a suggestion: You should use a different camera angle, your hands block the view of the item being worked on.
Brilliant really looking forward to the servicing videos thankyou
Do you have a 2nd radio setup to test receive? I heard you can do it with a dummy load and not have to have 2 antennas setup.
We do all service work on test instruments & into a dummy load as all service manuals dictate. We do air test all repairs just in case, for example, the FM detector is on a false peak.
Richard. G0OJF, UK
Just have to make sure you use carbon film, not metal film, otherwise it causes problems, I built a 200w dummy load for my test bench.
By using the two 5 watt resistors wouldn't that make it a 10 watt dummy load instead of 5 watts?
Yes, but as this is a CB project 5W was deemed to be more than adequate. This type of construction isn't really suitable for use over 30Mhz.
Richard, G0OJF, UK
Brilliant series Richard. I've just made my 2nd dummy load using a 47ohm series/parallel matrix setup. Resistors are 1/4w each but as there's 4x4 it works out at 4w on the button. Short tx only obviously and built with bits from the odds and sods box. Please continue this series as these videos are golden. 👍🏼
Yes, I know I need to do the RX videos but am struggling for time!
If you get 3 watt resistors it will handle transmit power a lot longer. Do not get wire wound ones. The resistors will get hot if transmitting for a while. Keep transmission short they will work fine. Better that one Screwdriver so called expert used to do, he used to transmit into an aerial through his cheap power meter which will quite happily read the harmonics as well as the frequency he is tuning up on. The dummy was not plugged into the CB, he was adjusting it!
Richard, it is all the average person will ever need. Not got this far back in your videos yet, UA-cam just threw it at me out of the blue.
Have you built a salt water dummy load or an oil filled one?
I had a very old oil filled one, couldn't read who made it, but it started leaking, even though it was oil filled, it rusted through the top.
I threw it out, I should have kept it. I'm sure I took a photo of it at one time, but it may be one of the photo's that was thrown out during house moves. :-((
We do little over 25W business radios so have a 300W max for 15 seconds dummy load for bigger jobs. None of the test gear here goes beyond 30W.
Richard
Twazzle? is that a technical term? :p thanks for an informative video.... i look forwards to more from this series. one little thing it would be useful if you put all the servicing on a shoestring videos into a playlist. kindest regards Martin
I make it up as I go...I originate from Yorkshire. twazzle, must have picked it up somewhere for twist. Just checking if people are listening!
a great weekend project,, I thank you sir
Thank you for this, I really didn't want to spend a lot of money on a dummy load. I got my resistors in the mail yesterday so hope to build it soon. Weird question for you, have you seen the one on EBay that only uses a light? (It's like $10.00 on Ebay). I wrote that guy and he says the light burns off the rf energy, but his wouldn't work would it? The light bulb won't equal the 50 ohm requirement, would it??
The USA available lamp just happens to be a 50 ohm load & I understand will take up to 5W. I've never seen one in person & what I'm telling you here is what I remember from American textbooks from the 60's & 70's.
It isn't some special kind of bulb ,but happens to work as a dummy load.
Richard
@@ukfmcbradioservicingTango21 Thank you for the information. I'm going to build one like in this video, but wanted to find out about the light bulb type before I possibly bought one since it's only $10.00. Thanks again!
@@ukfmcbradioservicingTango21 Thank you for this video. I built my resistor cb dummy load this weekend and it works great, with a flat 1.0 swr on the cb's internal swr meter. I also ordered one I talked about earlier, with the light bulb and guess what?? The light bulb one measured 1.5 on the same cb/swr meter. I like your two resistor idea better and it works better, too!! Thanks!
A number 47 6v bulb is used. I don't know if you need a screw or bayonet type for the dummy load you are looking at but no more than 5 Watts
@@bradleyfishel4233 I ended up buying the light bulb type also. Thank you! One day I'm going to buy a regular one. These both work great though!
Top tip Richard. Thanks.
Nice for a 5 watt dummy load. If you don't mind me asking, but to make a 20 watt dummy load, what would be the calculations for that? I'm thinking 200 ohm 5 watt resistors × 4. Would that be accurate? I want to use a minimal amount of resistors.
Yes, that sounds right. However, 200R (ohms) is not a European or UK 'preferred' value...but a quick look on ebay & I spotted this 141768770983. You will see he has 200R; and dead cheap too.
Richard
I have followed these instructions, no shorts, measures 50 ohm across the plug, but SWR reads like a short !, where have I gone wrong ??????
How bizarre. All I can think of is the possibility you've used wirewound resistors which is a no-no.
Richard
vbe carefull tu use only resistive resistors... Often the power resistors a selfics, then ih HF frequencies, load is not 50 ohms... Or yoy use carbon resistors, or film non inductive resistors...
What will I need to build a 50 watt 50 ohm dummy load? Using 1/2 watt resistors
You need 1 watt resistors
WELCOME, WHERE HAVE YOU RECEIVED THESE RESISTORS?
I use two UK wholesalers, RS Components & CPC PLC. These particular resistors came from CPC.
Richard
Good Job.
Ah, but are the carbon resistors?
They are metal film. Resistors have to be 'non reactive' & when the text books were written there was only carbon & wirewound. As you know, wirewound resistors are reactive so no use in this application. If it worries you, make one with carbon resistors. Now think of the people using a particular American light bulb as a dummy load which is going to be reactive to some extent!
Richard, G0OJF, UK
Ottimo
Did everything you said and I blew the finals in the radio 45 watts reflected back into radio not happy
So hows does a 4W radio reflect back 45W?
45 watt commercial land mobile (Australian)
So why make a 5W dummy load for a 45W radio? This project was intended for 4W UK CB radios. If you are working on LMR equipment surely that is VHF or UHF & requires a screened dummy load of suitable power rating & terminated in either a BNC or N-type connector. I was asked to do this series of 'CB servicing on a shoestring' for a reason, and that wasn't for business radio, in which I worked full time for 16 years.
When you assembled the dummy load & tested the finished item, did it test OK on your multimeter? Did the heat shrink insulation fed up the inner of the plug fail because it overheated & cause a direct short? Why otherwise was the VSWR so high as to reflect 45W back to a 45W source? You say the finals blew...but how many are there in that radio & why did more than one fail...I ask this because after years in business radio I remember many a customer with ridiculously wrong aerials...including a front door key as an aerial; in all cases the driver transistor failed & not the finals.
Richard (UK)
It's wrong Bcz it's not pure resistive load if u break these resistors u can see nicrom coil inside