Do radio equipment share a common ground?

[greusome1]

I had a 12v radio running off my atv battery......not wanting to over-do my charging system, I just brought along a marine battery thinking i could use it for my other equipment which would be hooked up through coax to my radio..... well my radio blew a fuse and smoked my finals... (guess they were my finals,,, tx lights up but no bars to show modulation) I know I should use 1 power source for my radio and all other equipment hooked to it..but the radio was already installed where it was (long story) So could this fry my radio? I'll post a crude diagram of how it was hooked up...Here is how the radio acted before the smoke...1. Hooked everything up according to diagram. 2.. turned on radio and equipment and heard talk. 3. Keyed up and let off key, at this point with the mic un-keyed, my radio still had tx light on and max mod bars and stayed that way for 3 seconds.......4. Thinking it was working, I keyed up again and aaauuuddddiiiioooooo radio check anyone? Same as before but this time when I let off the mic... smoke.. now no modulation..... basically did I ruin my radio by using two different batteries?

 

[kf4eyr]

just going to have to ask what was the swr on antenna with the amp out of line?

mounted on a atv is very questionable on if there is enough ground plane for swr to be decent,,, most i know that run atvs here use a no ground firestick antenna but they dont run amps with their setups,,,
if your swr was high it would blow fuse and the finals also,, what radio did you have mounted and the type of antenna?

 

[SCPD]

Yep. VSWR most likely is what killed your radio. At 4 watts or even 20 watts, a bad VSWR isn't going to be a big issue. Not add a couple hundred watts to that and things need to be almost perfect to operate correctly. Also make sure you have both batteries tied together in parallel. You can run a POS wire from the main battery to the secondary battery and then the NEG post of the secondary battery to the frame. This goes for the atv battery as well.
But like kf4eyr stated, you need to make sure your VSWR (SWR), is good. Meaning it should be at no more than 1.3:1 with the amp running. Anymore and things start creating heat and also like you see, will burn up radios and possibly the amp as well. You most likely just don't have a good ground plane under the antenna. You need metal under an antenna for them to work correctly. Even the no ground type antennas need some form of ground which is usually the coax outer shield. This would make a lot of sense as to why your radio blew. As your coax becomes the ground wire that connects to the radio from the antenna. If you are using a no ground plane type antenna like a firestick or similar.
You first need to tune the antenna without the amp in line. Then add the amp. Which on an ATV I just wouldn't suggest unless you have a good grasp on RF energy and how it works and also the other things that are involved with a properly tuned antenna besides a decent VSWR. There is more to tuning antennas than just the SWR. For now I would pull the amp put of line and just use a radio. I just don't think you will get a good enough match to allow an amp to be added to the ATV. JMHO's. Also you may have created a ground loop by not having both batteries going to the some ground. As in if the ATV battery is grounded to the frame, so should the secondary battery. The way your photo shows, both batteries are completely separate units. And like said, if you are using a NGP type antenna, you are just peeing in the wind. Read up on how to properly install 2 batteries into a vehicle or an ATV, and also how the no ground plane antennas actually work. If that is what you are using. If you have a 102" whip and your ATV body is plastic, I can about guarantee you didn't have a good VSWR or enough metal under the antenna to create a proper match for the antenna. Again, these are JMHO's. But I am pretty sure they are correct. Like I said, time to start reading about some things if it were me, that is what I would do. And check the ATV forums and see if anyone has added an amplifier to a CB radio on an ATV and how they did it and how well it worked. Lots of info out there. Just have to take the time to find it and read up on it. Hope you get your issues resolved, but IMO, I would not run an amp on an ATV unless I knew 110% for sure that I had plenty of metal under my antenna and also a good match. This will require more than just tuning for lowest SWR, you will need someone with an antenna analyzer to help you with this to do it properly. Best solution for now is just to leave the amp for something else and either get your radio repaired or get a new one. You didn't mention what type radio you have, but if it's not an expensive one, I wouldn't even worry about getting it fixed as it may end up costing you more than what you can buy a new radio for. Again. JMHO's. Hope this helps and hope you get your issue resolved. Have a good day and 73 and God Bless.

 

[greusome1]

Actually I was using a lil wil mag mount sitting on top of a peice of 4inx4in 1/4 inch plate steel bolted to front racks..... SWR WAS NOT CHECKED......I do know I'm lacking a lot of ground plane... never had a high swr to smoke a radio before.. but again never had 100+ watts to play with either..... batteries were not hooked parallel and were separate. I would say now my swr was like way high to begin with... ill have to find a meter....thanks guys... may have to find another antenna as well.... very good input.

 

[greusome1]

uniden 510xl and lil wil mag mount... and after doing some reading.... I only have like a 4x4 inch ground plane.... not considering the front racks which are actually directly beside my coil....

 

[SCPD]

No way no how would I run an amp with a lil wil antenna. Even with a good ground plane under it. They aren't made to handle much power. And don't believe what the package says, as far as wattage rating. They are a very narrow band antenna and are mediocre at best as far as antennas go. I would just use your radio and leave the amp out of the equation. That is JMHO.

 

[mmckenna]

An abnormally high SWR would cause issues in the amplifier, not the radio. The radio is only driving the amplifier, and isn't directly connected to the antenna.

I doubt high SWR was the cause of "smoking" your radio. If your radio blew a fuse on the power input leads, that means it was drawing too much current. What you need to figure out is why it was drawing too much current.

High SWR rarely "smokes" a radio, especially when we are talking about a 4 watt CB (OK, maybe 12 watt SSB). The radios will often lower their power. The heat generated by the mismatch can get soaked up by the heat sink. 4 watts isn't a lot of heat, especially if you only keyed up for a few seconds.
The urban legends about exploding finals are just that, legends.

I'd start looking at your power wiring closely. Since the radio ground and the amplifier chassis are likely connected via the outer shield of the coax, I'd start looking for something wired up bass-ackwards.

Either that, or is it possible you hooked the CB up to the amplifier output? Not sure that would cause this, though.

 

[SCPD]

So, why do people think they can blow up their rigs or linear amplifiers when there is a high SWR on the antenna?

Because that can happen, but it is not due to the reflected power!
There is a totally different reason.
A high SWR on an antenna probably means that the antenna is not tuned to the frequency that is being used. This, in turn, means that the antenna has some inductive or capacitive reactance that is de-tuning the final amplifier. De-tuned final amplifiers draw far too much current and can burn up. The rig or linear amplifier will have to be re-tuned to avoid creating too much heat.
Many linears and nearly all tube amplifiers have some tuning knobs that allow you to "dip the plate current" or adjust the SWR by adjusting something on the front of the device.
Transistor rigs usually do not have any tuning adjustments. To avoid the extra heat created when running a de-tuned amplifier, there is a protection circuit that will significantly reduce the output power if the SWR is high.
Hope this helps.

 

[gonefishn1]

An abnormally high SWR would cause issues in the amplifier, not the radio. The radio is only driving the amplifier, and isn't directly connected to the antenna.

I doubt high SWR was the cause of "smoking" your radio. If your radio blew a fuse on the power input leads, that means it was drawing too much current. What you need to figure out is why it was drawing too much current.

High SWR rarely "smokes" a radio, especially when we are talking about a 4 watt CB (OK, maybe 12 watt SSB). The radios will often lower their power. The heat generated by the mismatch can get soaked up by the heat sink. 4 watts isn't a lot of heat, especially if you only keyed up for a few seconds.
The urban legends about exploding finals are just that, legends.

I'd start looking at your power wiring closely. Since the radio ground and the amplifier chassis are likely connected via the outer shield of the coax, I'd start looking for something wired up bass-ackwards.

Either that, or is it possible you hooked the CB up to the amplifier output? Not sure that would cause this, though.

Correct- SWR did not cause this. The quality of the SWR match is determined by the transmission line and antenna. I doubt the SWR caused any problem in the radio itself, SWR would have messed up the amp. But in this case it seems the power and ground issues are the cause of the radio burning up.

 

[prcguy]

As I mentioned before, I will take any CB laying around my garage, transmit with no antenna (infinite VSWR) and key down for 5min, 10min, whatever, and nothing bad will happen. Its extremely rare a modern CB will be damaged from high VSWR. If the amplifier was turned on then the input of the amplifier probably had a reasonable match to the radio and the amp is what saw the high VSWR.

With that said, the OP stated he keyed up his radio, unkeyed and the transmit light was still on and the radio had max modulation bars. That sound like it has nothing to do with the radio transmitting into a bad VSWR. If he had the amplifier on and was in very close proximity to the antenna there could have been a lot of RF picked up by the mic cable and that damaged something.
prcguy

So, why do people think they can blow up their rigs or linear amplifiers when there is a high SWR on the antenna?

Because that can happen, but it is not due to the reflected power!
There is a totally different reason.
A high SWR on an antenna probably means that the antenna is not tuned to the frequency that is being used. This, in turn, means that the antenna has some inductive or capacitive reactance that is de-tuning the final amplifier. De-tuned final amplifiers draw far too much current and can burn up. The rig or linear amplifier will have to be re-tuned to avoid creating too much heat.
Many linears and nearly all tube amplifiers have some tuning knobs that allow you to "dip the plate current" or adjust the SWR by adjusting something on the front of the device.
Transistor rigs usually do not have any tuning adjustments. To avoid the extra heat created when running a de-tuned amplifier, there is a protection circuit that will significantly reduce the output power if the SWR is high.
Hope this helps.

 

[RFBOSS]

Problems happen when a transistor is asked to operate outside of its SOA (safe operating area). There are a number of parameters but lets just look at the voltage and current rating.

If a transmitter or amplifier is operated into an open antenna circuit the RF voltage will rise. If a transmitter is operated into a shorted antenna circuit, the RF current will rise.

If under either of these conditions the SOA of the transistor is exceeded, it will behave like an overloaded fuse. One and done.

Hopefully the radio and or the amplifier will utilize transistors that are robust enough to withstand these conditions and or have protection circuits that will protect the units.



Transmission line theory tells us that when there is a mismatched load at the end of a piece of transmission line there will be common mode RF currents on the "outside" of the shield of the coaxial cable. This can be a bad thing.

This common mode RF current can make it back to the input of the amplifier and the amplifier can go into oscillation (a bad thing). It may stay keyed when the radio is not unkeyed. This may cause damage to the amplifier.

This common mode RF may feed back into the output of the CB radio (a bad thing). The radio may think that it is still keyed because it is sees RF from the oscillation of the amplifier even when the radio is unkeyed.

The RF voltage being fed back into the CB may exceed the SOA of what ever transistor it encounters (not a good thing).

In this scenario, protection circuits may not be able to protect the equipment.



To be clear I have no first hand knowledge of what happened in this case. I offer some possible scenarios.

And I am sorry for your misfortune.

 

[greusome1]

Actually here was my setup... sitting in a shack on top of a hill..... metal roof....mag mount antenna sitting on roof, radio hooked up to atv battery, amp hooked up to 12volt marine battery (deep cycle)...antenna was sitting directly overhead about 4 feet above the setup... the tin roof wasn't grounded at all.. looking back i should have just hooked to the marine battery for both radio and amp for a check...if I ever use that shack again... think I need to bring a good battery,,, ground the roof to my - side... ...im only guessing my amp will only give me 100w max given the low drive of my radio....Personally I think using the two batteries the way I did fried my radio....any possibly the antenna too close to my goods...

 

[greusome1]

yup

Problems happen when a transistor is asked to operate outside of its SOA (safe operating area). There are a number of parameters but lets just look at the voltage and current rating.

If a transmitter or amplifier is operated into an open antenna circuit the RF voltage will rise. If a transmitter is operated into a shorted antenna circuit, the RF current will rise.

If under either of these conditions the SOA of the transistor is exceeded, it will behave like an overloaded fuse. One and done.

Hopefully the radio and or the amplifier will utilize transistors that are robust enough to withstand these conditions and or have protection circuits that will protect the units.



Transmission line theory tells us that when there is a mismatched load at the end of a piece of transmission line there will be common mode RF currents on the "outside" of the shield of the coaxial cable. This can be a bad thing.

This common mode RF current can make it back to the input of the amplifier and the amplifier can go into oscillation (a bad thing). It may stay keyed when the radio is not unkeyed. This may cause damage to the amplifier.

This common mode RF may feed back into the output of the CB radio (a bad thing). The radio may think that it is still keyed because it is sees RF from the oscillation of the amplifier even when the radio is unkeyed.

The RF voltage being fed back into the CB may exceed the SOA of what ever transistor it encounters (not a good thing).

In this scenario, protection circuits may not be able to protect the equipment.



To be clear I have no first hand knowledge of what happened in this case. I offer some possible scenarios.

And I am sorry for your misfortune.

sounds like oscillation to me.... something was sending power back through....funny how my + of my raido(connected to atv battery) blew... my tiny radio don't draw that much current.... using same wires as before im using a new radio.. no issues.. but nothing in-between them but a swr meter... working good so far!

 

[prcguy]

Most CB final transistors are very rugged and high VSWR will usually not exceed any of its safe operating parameters. They are designed this way because the radio mfrs have no control of how they are installed or used and they don't want any warranty issues with the millions of CB radios produced.

Take an older CB final transistor like the 2SC1306 which was one of the most common used from the 1970s through the 90s. Its designed as a 4watt device but its collector-emitter breakdown voltage is around 75V, peak collector current of 5A and its collector power dissipation is 10W and its rated for operation into an infinite VSWR. Its just not possible to exceed these ratings when used in a 12V environment.

It sounds like grusome1's radio has several problems and it would be very interesting to see what's actually wrong with it. Sometimes a post mortem diagnosis can point towards a cause of failure so he doesn't repeat the unfortunate incident with another good radio.
prcguy

Problems happen when a transistor is asked to operate outside of its SOA (safe operating area). There are a number of parameters but lets just look at the voltage and current rating.

If a transmitter or amplifier is operated into an open antenna circuit the RF voltage will rise. If a transmitter is operated into a shorted antenna circuit, the RF current will rise.

If under either of these conditions the SOA of the transistor is exceeded, it will behave like an overloaded fuse. One and done.

Hopefully the radio and or the amplifier will utilize transistors that are robust enough to withstand these conditions and or have protection circuits that will protect the units.



Transmission line theory tells us that when there is a mismatched load at the end of a piece of transmission line there will be common mode RF currents on the "outside" of the shield of the coaxial cable. This can be a bad thing.

This common mode RF current can make it back to the input of the amplifier and the amplifier can go into oscillation (a bad thing). It may stay keyed when the radio is not unkeyed. This may cause damage to the amplifier.

This common mode RF may feed back into the output of the CB radio (a bad thing). The radio may think that it is still keyed because it is sees RF from the oscillation of the amplifier even when the radio is unkeyed.

The RF voltage being fed back into the CB may exceed the SOA of what ever transistor it encounters (not a good thing).

In this scenario, protection circuits may not be able to protect the equipment.



To be clear I have no first hand knowledge of what happened in this case. I offer some possible scenarios.

And I am sorry for your misfortune.

 

[SCPD]

Don't want to argue about this. But proof is in the pudding. Please show some other solid info that says CB radios can be transmitted without any connection to the antenna port and transmitted for the 5 minutes you claim will not cause any type of failure. If you can do that, I'll leave this be. I know better, and wouldn't dare take one of my radios and try this. Maybe a video or some written proof from another source would help put my mind and many others at rest as to what you keep saying. Have a good day.

 

[greusome1]

actually yes it was....

An abnormally high SWR would cause issues in the amplifier, not the radio. The radio is only driving the amplifier, and isn't directly connected to the antenna.

I doubt high SWR was the cause of "smoking" your radio. If your radio blew a fuse on the power input leads, that means it was drawing too much current. What you need to figure out is why it was drawing too much current.

High SWR rarely "smokes" a radio, especially when we are talking about a 4 watt CB (OK, maybe 12 watt SSB). The radios will often lower their power. The heat generated by the mismatch can get soaked up by the heat sink. 4 watts isn't a lot of heat, especially if you only keyed up for a few seconds.
The urban legends about exploding finals are just that, legends.

I'd start looking at your power wiring closely. Since the radio ground and the amplifier chassis are likely connected via the outer shield of the coax, I'd start looking for something wired up bass-ackwards.

Either that, or is it possible you hooked the CB up to the amplifier output? Not sure that would cause this, though.

the amp when disassembled showed me they had the two outer rings of the jacks grounded together, that being said the amp/radio/antenna all three shared a common ground.. the shield of the coax was connecting all three devices.. never should I tried to use two different batteries unless I hooked them in series.... agreed that if anything smoked... amp was first in line to do so....if swr or ant was the prob...amp has 20 amp fuse.. radio 2 amp... so...guess the little one was the first to go...

 

[greusome1]

Most CB final transistors are very rugged and high VSWR will usually not exceed any of its safe operating parameters. They are designed this way because the radio mfrs have no control of how they are installed or used and they don't want any warranty issues with the millions of CB radios produced.

Take an older CB final transistor like the 2SC1306 which was one of the most common used from the 1970s through the 90s. Its designed as a 4watt device but its collector-emitter breakdown voltage is around 75V, peak collector current of 5A and its collector power dissipation is 10W and its rated for operation into an infinite VSWR. Its just not possible to exceed these ratings when used in a 12V environment.

It sounds like grusome1's radio has several problems and it would be very interesting to see what's actually wrong with it. Sometimes a post mortem diagnosis can point towards a cause of failure so he doesn't repeat the unfortunate incident with another good radio.
prcguy

I did take apart my smoked radio... here is a pic of what seperated, looked like it blew apart as some foil paper stuff just peeled off.. and heat sink goo (white in color) slid off with it... I didn't have to remove anything to see this....it was just sitting there..blew to heck... don't even know what that is... anyone?

 

[SCPD]

No you don't want to series your batteries. They need to be paralleled. By placing them in series you double the voltage. Parallel you double the amperage and voltage stays the same. Also having a bad VSWR/mismatch creates heat, which in turn causes parts to fail. Also you should always tune your antenna without any amp in line with a known good SWR meter. Then add the amp and recheck the VSWR. It shouldn't change much if at all. If it does that is a sign of an input/output mismatch. Just do some research into all of this. And do some reading on how RF energy works and affects things. It will help you to understand what is trying to be explained to you in a better way possibly. Also there are other forums you can visit and ask questions. Just some food for thought. Not saying that anyone is incorrect here, but it's always a good idea to get as much info as you can from different sources. Known reliable sources. Walt Maxwell and S. Ward and B. Cebik all have some great info published.
Hope this helps and I will not post anymore. Hope you get it all resolved. Good day.

 

[greusome1]

well.. i was sleep deprived.. i meant parallel... sry...

No you don't want to series your batteries. They need to be paralleled. By placing them in series you double the voltage. Parallel you double the amperage and voltage stays the same. Also having a bad VSWR/mismatch creates heat, which in turn causes parts to fail. Also you should always tune your antenna without any amp in line with a known good SWR meter. Then add the amp and recheck the VSWR. It shouldn't change much if at all. If it does that is a sign of an input/output mismatch. Just do some research into all of this. And do some reading on how RF energy works and affects things. It will help you to understand what is trying to be explained to you in a better way possibly. Also there are other forums you can visit and ask questions. Just some food for thought. Not saying that anyone is incorrect here, but it's always a good idea to get as much info as you can from different sources. Known reliable sources. Walt Maxwell and S. Ward and B. Cebik all have some great info published.
Hope this helps and I will not post anymore. Hope you get it all resolved. Good day.

.......ya parallel i mean

 

[greusome1]

here is what was smoking inside my radio

I did a an autopsy on my 510xl ... The Tx still lit up when keyed.. but no modulation bars at all.... ya this little white thing had some paper like material that had separated... it had white goo all over it... (heat sink stuff i guess)... it was toast.. this pic is of a good radio.. mine is identical except the circled thing-a-ma-jig is seperated/cracked/burned up....anyone know what this white bar shaped thing is???