Excellent video explaining a really great feature and why you might hear a difference when using it versus not hearing any difference at all. You're the best, Mike.
As Mister Hat said with no incoming signal the AGC circuit is going to have all the stages turned up to maximum. Once a signal is received the gain of the stages is lowered. The higher the incoming signal the less gain there is. Also the volume was turned up really high at several points in this video, up the whole way in some parts.
When the points are closed, they completes a circuit that applies power (12 volts) to the primary of the ignition coil. When the cam on the distributor opens the points (the condenser helps protect the points from some of the arc) the magnetic field in the ignition coil collapses through the secondary which creates a high voltage. The high voltage goes from the coil through the high voltage wire to the middle of the cap located on the distributor. The rotor directs the high voltage to whichever plug is supposed to fire next. The rotor only has physical contact with a cap in the middle. There is a small gap between the end of the rotor and the cap, that is where ignition noise is created.
Yep, any spark-noise from the spark plug is contained (shielded) by the cylinder head and engine block. The distributor cap is where most of the impulse noise escapes. Resistor wires limit the current flowing between the gap of the rotor button and the distributor cap electrodes.
That was spot on in what a noise blanker does and I think everyone has has a car go past a TV with the noise interference and even the clicks affecting the picture. The demo at the end showed what it does perfectly.
Great video Mike, your not the only person who gets asked that question about the Noise Blanker!!!! It’s probably the number 1 thing people ask me also. Very good explanation and now I don’t have to explain it any more they can just watch your video mate!!!!
i like the honesty. would be very easy to just say yea it was broken and make money. kind of hard to find now days. if i ever need something repaired and cant do it myself i know where to send it cause i know my money is being well spent. keep up the good work mike.....
thanks mike. love your videos and love these little quick and to the point videos explaining things. i kniw myself and others would love for you to explain how and why every function/circuit in a radio works...thanks keep up the good work.....
Yep - the NB circuit basically "blanks" out the receiver for the period of a short-duration impulse spike. They taught me that the "background noise" heard in an unsquelched AM/ SSB receiver was actually "thermal noise" created when any electrical circuit is active. With no antenna connected, each stage of the receiver introduces thermal noise into the signal chain and processes this as a "signal": It (1) amplifies it - RF stage, (2) mixes it (the mixer also gets thermal noise from the IF stage), (3) detects it and (4) the audio stages amplify it into the noise heard in the speaker.
Noise blankers should be adjustable for best control. In my TS-590S I have timing control for NB1, NB2 or both. They are all useful for various kind of noise. In my case its mostly static noise during hail and winter storms.
Nice explanation and video! I don't know if you've worked on the old Alinco DX-70 at some point, but I owned several during it's run and while they had a great display and xmit audio, the NB sucked. Not only would it not tackle ignition noise, but when turned ON, it actually injected a lot of noise of it's own into the receiver, making it a terrible choice for mobile operation.
The noise blanker in my ICOM 746 isn't broken - it just doesn't work very well. Pressing the NB button doesn't eliminate the transmission line spark-gap type noise that's cropped up in my neighborhood recently. It instead chops up the signal and reduces the noise only slightly. But the noise blanker algorithms in newer radios and even in the cheap SDRs running SDR# or SDRUno software (with adjustable NB thresholds) work great to eliminate that same transmission line noise completely.
QUESTION ! ! ! Got a Rigol4102 signal generator with noise generator, this noise is not blanked, I suspect this noise is not the "right type" of noise? Have had trouble doing alignment on radios. Have restored a ts-530, ts-940s, and an ft-980. Show us how to make the box? The ts-940s works. the ft-980 works but has a "slow to recover" type action to it. P.S. Use ds-815 spectrum analyzer, MSO 4000 scope, dm3068 DMM. Seeking a better stand alone frequency counter and seeking a way to do SINAD measurements, homebrew of sorts perhaps. Ugg, more equipment to get/build. Actual RF sg gen wanted as well. Sorry for the rant. 73's.
Great explanation as usual.. I actually understood what the NB was supposed to do before watching but I have never understood one thing about the NB, maybe you can help. Given the fact the NB is switchable on most front panels suggests it’s not desirable to have it on when not required, so what is the down side to having the NB on? Does it desensitise the RXer due to it being switched off, all be it momentarily?
Hi, I have Cobra 2000 GTL I would like to get a Channel King board install. Would you have time to do it ? what would it cost and how much time would it take? Please let me know .Thanks
Hey Mike I'm putting up a 40-foot Tower at my house with a 24-foot solarcon IMAX 2000 on it what would be the best coax to use, about 75 ft will be needed, cb band thanks
The best coax for any application is the best you can afford. The higher the quality of the coax the more it cost. You can get crazy and spend thousands of dollars on large diameter premium hard line or use something more reasonable like LMR240 or LMR400.
Do you have any videos on how to block LED light cb interference? I have LED signals and brake lights. I can hear them in my Cb when the turn signals are flashing, and the brake lights are applied.
Honestly I have never heard of automotive LED lights causing noise in a radio. The noise is usually with 120V AC house lights. They use a switch mode power supply which is very noisy. I suspect your light's may have a buck converter to reduce the voltage or more correctly a constant current supply to the LED's. Only a guess however since I have never run into this myself. Two things I would suggest. Make sure the radio is grounded, not the power cord ground but make sure the radio chassis/cabinet is grounded. Second you might try a DC power cord inline filter. I suspect the noise may be getting into the radio through the power wires. Powerwerx makes a nice heavy duty power line filter. powerwerx.com/dc-line-noise-filter-oemt
Have a question I'm hoping someone here can answer. I purchased a Dynascan Cobra 29 23 channel cb I am hoping to restore. I got the sams photofact cb-56 for this radio but am A bit confused about the electrolytic capacitor list. For some of them there are two different values shown, such as c46 10mf at 16v and 10mf 10v. Another is c51 1mf at 50v ans 1mf at 16v. There are several like this listed. Should I just go with the higher v caps? Thanks for any replies.
Are their any radios on the market that are AM only with variable talkback and echo? I’m not interested in sideband or anything extra. I’m looking for a box stock AM radio with variable talkback and echo that I can order or pick up locally......
Honestly I'm not the right person to ask about that. I don't sell radios, I only do repairs. The best people to ask about something like that would be a shop that sells radios. They are going to have a better idea of what is currently available that would meet your requirements.
Any modern radio that uses surface mount components is going to be more resistant to damage from shock and vibration. One of the biggest problems in high vibration environments is bad solder joints. Older through hole design boards are more susceptible to solder joint failure because the parts are hanging off the board by their wire leads. Surface mount parts have no wire leads, they are soldered directly to the surface of the circuit board.
What's the difference from 500 ohms. to. 1000ohms. .mics? ??.. mike from minnesota. ....question. . 5watt. dead key. to much.??? 20 watt peak swing to much..???? on midland 5001z. radio. ...
Hello. I am looking at a never used Royce 604 in box from 1977. I don't know much about Royce. Good radios? Very clean. $50. I have a brand new Cobra 25 LTD Classic, mic mounted on the front, China made. I bought the Cobra rather impulsively but wanted something vintage. Was Royce a good brand?
Royce was a good manufacturer. They did things a little different than many other manufacturers. The 604 is a good example. It has what I would call a "one chip wonder". Most of the receive circuit to include RF Amps, mixers and IF stages are all done on a single IC.
@@mikesradiorepair Hi , I have a Whistler 900 that was working and quit a few months ago . Sent it to a local cb guy and it is now dead ! Just lights up ! No audio and no transmit ! I dont know what he did but he offered me another radio for free because it quit while he had it ! Fair enough , but I miss my neat Whistler 900 ! Could you have a look at it ?
No, it works on fast rise time pulses. It will still blank the sound if a pulse triggers the circuit while someone is talking but you will never hear it. The amount of time the audio is "blanked" or muted is so short our brain can not hear it. Same effect as a flashing light. Flash a light fast enough and we can not tell it's flashing, it looks like a light that is on continuously but it can be turning on and off 30 or less times a second. Our brains are VERY slow.
I’m working in Gettysburg PA until tomorrow then I’m driving back home to Indiana for surgery Tuesday. I can spend some recovery time with a bread board Wednesday. I assume that the heart of the device is a 555?
Probably not the type of ignition noise you are thinking about. You probably don't have spark plug wires. Most vehicles these days have coil on plug packs, there is no spark plug wire in most cases. There is however a bunch of other electronics in modern vehicles that cause interference on HF. Proper grounding, connection directly to the battery and judicious application of ferrite cores/beads to power and coax cables can greatly attenuate this interference.
@@mikesradiorepair Thanks for the reply. I do have the power grounded to the battery terminal. Someone suggested that I should move it off the terminal to the chassis ground.
No, it needs to have a very fast rise time and be a very short duration pulse. I'll make another video this evening with a schematic and demonstration of the circuit. Might be tomorrow until it gets uploaded.
My uniden pro 538w picks up all the car electrical noise. It doesn't have a NB or ANL switch so I use the squelch and RF gain to tune it out. Unfortunately that makes for lousy RX sensitivity.
If it's a modern car join the party. All the noise from the vehicle computers is horrible in some of my newer vehicles. I installed a Powerwerx line filter in those vehicles and it pretty much eliminated it. powerwerx.com/dc-line-noise-filter-powerpole-connectors
You're mistaken about the brain not being fast enough. What's really happening is, the brain it's so sophisticated that it can compensate. Just saying.
Are you sure it's engine noise? In modern vehicles it's not engine noise but electronic noise generated by the vehicles electronic systems that create a lot of the noise. If the noise doesn't change with engine speed then it's not engine noise. I have a fairly new car here that it took me a good bit of fiddling with to finally get rid of all of the electronic noise generated by vehicle computer systems.
@@mikesradiorepair Thanks for the reply. It's an 88 pickup with older internals. I swapped out all of the "newer" in favor of an older setup with carb and HEI distributor. It does change with engine RPM, the high pitch whine gets louder as I hit the accelerator. When I'm driving it's almost impossible to hear above it. At idle, it's still annoying, but bearable.
