RX Alignment setup

[2FB327]

Step 2 says AF VTVM? Where does it go in your bench setup and what do you use? A photo would be helpful.

 

[RatsoW8]

They don't make VTVM's any more. I believe you can use a newer DMM for the reading.

 

[sp5it]

I use DMM connected to AM detector. Don't forget to disable AGC before.
Mike

 

[Robb]

Because we are dealing with such a small input signal (1-2uV) to get good tune-up results, it most important to use a quality sig gen that doesn't go over that amount. Accuracy here is vital. As sp5it points out, the AGC ('automatic gain control' - part of the receive circuit) is a hurdle that can only be appeased or disconnected. Otherwise, going over 2uV will skew the results and activate this signal compressor ('AGC'). Using a cheap sig gen just will not cut it if it cannot keep this small output signal - accurate.

 

[sonoma]

i think he is wanting to know where to hook up the rec meter to get the reading. I have a old vtvm meter and I hook it to the speaker leads or plug it into the external speaker jack. I have a BK1040 that has the swing meter on it so it hooks straight to the ext speaker plug. make sure you turn off the anl/nb/ controls and rf gain and squelch are all turned for full listening of the radio. trying to make this as simple as I can for you to understand. what gets me is you have to do step 1 to align then it says in step 2 the same as step 1. you ask about step 2 and not step one. not sure if it clears up what you asked.

 

[Robb]

i think he is wanting to know where to hook up the rec meter to get the reading. I have a old vtvm meter and I hook it to the speaker leads or plug it into the external speaker jack. I have a BK1040 that has the swing meter on it so it hooks straight to the ext speaker plug. make sure you turn off the anl/nb/ controls and rf gain and squelch are all turned for full listening of the radio. trying to make this as simple as I can for you to understand. what gets me is you have to do step 1 to align then it says in step 2 the same as step 1. you ask about step 2 and not step one. not sure if it clears up what you asked.

The very same the page he printed and posted above (post #1) shows the diagram on what equipment is needed and how it is put together for the radio under test. Its all in the service manual - as you and I already know.

Guys doing receive alignments - beware! Unless you use the right gear, you may do more harm to the radio's receive. A high quality sig gen is absolutely necessary. Go just slightly above 4uV output, and the the AGC circuit will cut in and further complicate and ruin your receive alignment effort. Those old/cheap sig gens cannot give neither a stable freq nor a stable output level. Beware!

Furthermore, if you use a VTVM or DVM to adjust receive levels when tuning - will NOT suffice. The VTVM is used to raise the volume knob level high enough to reach the required level for testing; not for adjusting receive. A VTVM is BLIND to signal vs distortion levels! To do it right requires a SINAD meter. Yet another piece of gear mentioned in the Service Manual that IS required to do the job accurately. Better off leaving the radio alone - IMO.

You aren't going to break or damage the receiver if not done correctly, but unintentionally raise distortion level up with the incoming signal. There is a fine line between distortion and signal you cannot hear. If you get it wrong, weak signals can be heard; but strong local signals may be wildly distorted.

 

[sonoma]

the best thing I can tell you since you do not understand the service manual is to search some you tube videos and watch some of them that the guy's are showing you how to do the alignment. have not looked for any lately but there was some a couple years ago that might help you. another guy was wanting to learn how to do all of this and wanted some one to walk him through every thing. found him some videos which helped him some.

 

[2FB327]

Thanks Mike, that's what I was looking for.

I'm thankful for the help, but it's funny when I first asked for help on this form I was told to get some old radios, I did, get the right equipment, I did. When I asked about that equipment I was told to reread the manual, I did. Now I'm told to leave it alone.

Robb, Yes I did see the page of the manual where is shows the hook up, but without someone explaining what a "audio VTVM or AF VTVM" let alone where or how to hook it up doesn't make sense unless I know why and yes I thank you for your info on the sinad software. By your above answer should I assume that you use only sinad?

Sonoma, I watch everything I can on the tube, if you or someone who point me to any videos/photos showing me any RX setups would be helpful.

 

[Robb]

Thanks Mike, that's what I was looking for.

I'm thankful for the help, but it's funny when I first asked for help on this form I was told to get some old radios, I did, get the right equipment, I did. When I asked about that equipment I was told to reread the manual, I did. Now I'm told to leave it alone.

Robb, Yes I did see the page of the manual where is shows the hook up, but without someone explaining what a "audio VTVM or AF VTVM" let alone where or how to hook it up doesn't make sense unless I know why and yes I thank you for your info on the sinad software. By your above answer should I assume that you use only sinad?

Sonoma, I watch everything I can on the tube, if you or someone who point me to any videos/photos showing me any RX setups would be helpful.

Hey; you are trying. Keep on trying. When I first started doing this just a few short years ago, I felt like a pig on roller skates. Not much of it made sense. So, keep on trying, and keep on asking questions. There are others like you that have the same questions. Many on this forum helped me considerably get there, and I appreciate it still.

Both the VTVM (or a DVM is fine too) AND the SINAD are used at different points of this alignment. Take it in steps as it is laid out in the manual.

 

[2FB327]

Thank you Robb, just trying to get it right.

Next question: On the next page in the Alignment of the transmitter it states:
Scope to lead of R61, set the cores of L17, L20 at the bottom....
What do they mean at the bottom? The lowest point on the scope before the can cuts out the signal? I have tried this a couple ways and seem to get better readings on the RF output when I start with these set at midpoint or higher.

 

[sonoma]

I just searched you tube looking for some info that might help you but it has all been deleted or hidden. can not find any info pertaining to what you are wanting to do.
sounds like you have bought some equipment to tune a cb radio but you do not know how to use what you have bought or understand what the service manual is telling you to do.
sounds like you are wanting some one to set down with you and show you how to do the alignments. that is why I was trying to see if any videos are posted right now. and it looks as if they are not there now. a guy I know in Penns and started trying to repair radios a few years ago and he was going to open a shop but he has the same problems you are having. I even tried talking him through an alignment on the phone but no luck.
just keep reading and see if a video is online to show you.
the last thing you posted is self explainitory as far as putting 2 cans to the bottom to adjust, the others. what radio are you trying to align. a few radios for peaking output you have to tunr 2 L cans to the bottom but they are a power balance and if not done right will throw the radio way off since the 2 cans are for power balance.
an example is the president Jackson radios it shows to turn 2 cans to the bottom and peak the others then go back to the 2 you turned to the bottom to peak the upper and lower bands. if you do not know what you are doing on the jackson you will kill the radio.

 

[2FB327]

Thanks Sonoma, I have been collecting over the past few years and have a pretty good grasp from what I could read or find. It's just I never saw phrases like "set the cores at the bottom" and found that if I bottomed the screw in the can it either would lose the signal or fall out the other side. Perhaps, "Set the signal to the minimum on the scope would have been appropriate"

With the few helpful videos still left and Lou Franklin's books I have been trying to teach myself radio repair and alignment and tuning being the last step I want to get it right.
I am lucky enough to have been given a bunch of old radios and have been able to get quite a few working again.

Thanks out to Mike's Radio repair and the Radio Shop and everyone on this site who has helped.

 

[sonoma]

you did not say what radio you are trying to align. normally knowing what radio it is helps on my end to help explain some.if it says bottom out the slug is what is meant to do and peak the others 1st before you peak the others but not knowing the radio makes it harder to explain. you have to be careful turning the slugs to the bottom because some will stick and you have to pull the cans out of the radio to get them to go back up or they will even crack.
if the radio you are working on has more bands than the cb band it is hard to realign them to all the bands . a lot will be trial and error on radios since you do not understand what you are doing. you can use a scope also for peaking the receive just by watching the scope as the line across the scope increases it is peaking and when you get to the peak area it will start closing the band across the scope.
even look up some videos on how to use a scope should help you to understand what you are doing.
please post what radio you are trying to align.

 

[M0GVZ]

Signal generator as described in the service manual, you can pick up good used Racal/Marconi etc on Ebay, and use an oscilloscope connected to the speaker wires instead of the audio voltmeter and measure the peak to peak voltage of the waveform. Use a proper trimmer tool to adjust the ferrite slugs, not a screwdriver.

If you're going to be repairing a lot of radios you can't beat getting a Radio Communications Test Set like a Marconi 2955B. It has everything all in one box. You're looking at a good couple of thousand dollars but it has everything you need.

 

[2FB327]

It is a Cobra 29LTD.
MOGVZ I went the component route, when I was starting out I had the fear of buying a test center with everything and having it fail, not to mention a budget. I have put together a HP 8656B signal generator, a couple of scopes, bird meters, frequency counter, DVM's and a list of things. Now I'm down to the Sinad which Robb has helped with and the VTVM which was the start of this post.