RG-58 or RG 59 from radio to amp?

Trophyhusband · Jul 31, 2011

I want to install a radio with a small amp on my truck. I will be putting co-phased antennas on. The manufacturer (Firestik) says that the antennas need to be RG-59 for dual antennas and RG-58 for single antennas. Does this mean that from the transmitter to the amp also needs to be RG-59?

Where do I measure SWR, Out of the amp, out of the radio, or both?

Can I turn down or attenuate the output from the radio to the amp?

I'm using a Firestik stud mounts with Firering coax and mounting to the bed rails just behind the cab. Do I need to scrape the paint so that there is clean bare metal where the mount is?

Thanks.
KJ

LtDoc · Jul 31, 2011

The output impedance of your radio and the input impedance of a good amplifier is 50 ohms, so, use 50 ohm coax to connect them.
The only reason RG-59, 75 ohm coax, is used for phasing dual antennas is that it makes an impedance transforming system to connect two 25 ohm (approximate) antennas for a 50 ohm impedance output (approximate). That impedance transforming system won't work if 50 ohm coax is used instead of 75 ohm coax.
- 'Doc

gewecke · Jul 31, 2011

Trophyhusband said:
I want to install a radio with a small amp on my truck. I will be putting co-phased antennas on. The manufacturer (Firestik) says that the antennas need to be RG-59 for dual antennas and RG-58 for single antennas. Does this mean that from the transmitter to the amp also needs to be RG-59?

Where do I measure SWR, Out of the amp, out of the radio, or both?

Can I turn down or attenuate the output from the radio to the amp?

I'm using a Firestik stud mounts with Firering coax and mounting to the bed rails just behind the cab. Do I need to scrape the paint so that there is clean bare metal where the mount is?

Thanks.
KJ

Ditch the amp, and go with rg58 all the way to the antennas.

No you don't have to scrape any paint either.

73,
n9zas

Trophyhusband · Jul 31, 2011

Why ditch the amp and why rg-58 (50 ohm) over rg-59 (75 ohm)? I've already ordered the rg-59 as the manufacturer suggested, just curious.

kb2vxa · Aug 1, 2011

"Why ditch the amp and why rg-58 (50 ohm) over rg-59 (75 ohm)?"
1) Because of the "I almost got away with it" factor.
2) Because the system is 50 ohms throughout.

nonperson · Aug 1, 2011

Trophyhusband said:
Why ditch the amp and why rg-58 (50 ohm) over rg-59 (75 ohm)? I've already ordered the rg-59 as the manufacturer suggested, just curious.

Everything I've read on the subject matter is in line with what LtDoc said in his post. Never used an amp but depending on your set up I wouldn't mount the antennas in the corners, directly behind the cab. I currently have an 102" whip mounted there and all though I still have an excellent SWR reading, it's not as good as other mounting locations I've had in the past.

gewecke · Aug 1, 2011

Trophyhusband said:
Why ditch the amp and why rg-58 (50 ohm) over rg-59 (75 ohm)? I've already ordered the rg-59 as the manufacturer suggested, just curious.

RG59 is cheap cable tv line and 75 ohms at that. Your radio wants to see a 50-52 ohm impedance to your antennas, and as far as the amp goes? You create more interference to adjacent channels as well as being very inefficient and illegal on cb.

73,
n9zas

LtDoc · Aug 2, 2011

One reason I tend to agree with doing away with the dual antennas is that they are very seldom ever matched correctly, and do not offer the benefits that people seem to associate with them. The only benefit to using dual antennas is that they become directional if done correctly. That being directional in a mobile is only going to be the 'right' direction maybe 50% of the time (if that). The rest of the time they will be directional in the wrong direction. Lot's of myths associated with dual antennas. Most people who try them go back to a single antenna.
If you don't know what a phasing harness is and how it's constructed, and why, you are loosing from the start. So, do whatever you think you want to do.
- 'Doc

jhooten · Aug 2, 2011

Why ask if you have all ready ordered it?

Having run co-phased antennas on a Vega and a 1 ton dually I can tell you first hand, other than the cool factor, they simply do not give you more bang for the buck, and are not worth the hassle to keep them tuned and working correctly. And to work correctly they need to be a quarter wave apart. Is your truck 9 feet wide?

kb2vxa · Aug 2, 2011

"Twin Trucker" antennas started like everything else with an idea. Trouble is when thought out by the technically astute it becomes clear it was doomed to failure from the start. 18 wheel drivers soon found out that an antenna mounted on the cab is only omnidirectional when running bobtail, add a trailer and it becomes cardioid (heart shaped) with the major lobe to the rear and the minor one forward. The bulb comes on... dimly.

OK, theory has it if you feed two antennas in phase and place them 1/4 wave apart you have a bidirectional end-fire array but here's where practice departs from theory. What happens when you combine a figure 8 pattern with a cardioid at right angles? (I never did figure that one out, EZNec gets all confused.) Then that theoretical figure 8 only appears over an even ground plane surface so what happens when you put a truck cab in the middle with the antennas above ground? Are you sure those antennas are exactly 1/4 wave apart?

Now if someone could work out an equation full of complex unknown variables and reach a scientific conclusion please let us know, you deserve a prize of some sort and a place in history. Meanwhile I'll settle for a signal keeping to the road just where I want it... keep on truckin'.

I'm with you Jerry, "back in the day" I inherited dad's car with that cool factor and found out real quick how poorly that mess worked and what a pain in the butt too. As soon as I removed one antenna and the phasing harness I was amazed by the improvement. No, didn't care for an amp either. If you can't hear 'em you can't work 'em and anything more makes you the hated alligator, all mouth and no ears.

reedeb · Aug 2, 2011

Trophyhusband said:
Why ditch the amp and why rg-58 (50 ohm) over rg-59 (75 ohm)? I've already ordered the rg-59 as the manufacturer suggested, just curious.

WELL since you asked, use RG59, keep the amp, and remeber to put the black on + and red on - and everything will be great.

Trophyhusband · Aug 2, 2011

kb2vxa said:
"Why ditch the amp and why rg-58 (50 ohm) over rg-59 (75 ohm)?"
1) Because of the "I almost got away with it" factor.

2) Because the system is 50 ohms throughout.

1) Fair enough.

2 ) If it was a single antenna, yes, but with two antennas in parallel?

Trophyhusband · Aug 2, 2011

nonperson said:
depending on your set up I wouldn't mount the antennas in the corners, directly behind the cab.

I must admit that I'm putting form ahead of function, but I would like to maximize efficiency of the setup I'm choosing. This may mean switching to a single antenna setup.

Trophyhusband · Aug 2, 2011

gewecke said:
RG59 is cheap cable tv line and 75 ohms at that. Your radio wants to see a 50-52 ohm impedance to your antennas, and as far as the amp goes? You create more interference to adjacent channels as well as being very inefficient and illegal on cb.

73,
n9zas

I'm wavering on the amp right now. The one I want is only 35 watts, but it's the only one I can find and if the quality is poor and it's inefficient, I may well be better off without it.

Trophyhusband · Aug 2, 2011

LtDoc said:
One reason I tend to agree with doing away with the dual antennas is that they are very seldom ever matched correctly, and do not offer the benefits that people seem to associate with them. The only benefit to using dual antennas is that they become directional if done correctly. That being directional in a mobile is only going to be the 'right' direction maybe 50% of the time (if that). The rest of the time they will be directional in the wrong direction. Lot's of myths associated with dual antennas. Most people who try them go back to a single antenna.
If you don't know what a phasing harness is and how it's constructed, and why, you are loosing from the start. So, do whatever you think you want to do.
- 'Doc

Let me explain my situation a little. We currently live in Florida, but are "pencilled in" for orders to Alaska next summer. We will be driving with me pulling our 5th wheel and my wife driving her car either ahead or behind me. We also take quite a few trip throughout the year. Our last move was from Idaho to Florida and we used FRS radios to communicate and I was less than impressed with them. The kids rode with her and I rode alone. When someone had to pee, often she would speed up until she found an exit of pull off and quickly get out of range. When she got back on the road, she would have to almost catch back up to me before we would be back in range. I'm hoping to increase our range a little bit.

As I mentioned in another post, I'm making decisions with how it looks in mind. I like the way twin black fiberglass antennas mounted behind the cab look even though I know it's not the best setup, but I would like to maximize the mount I choose. Since I my communication will be mostly ahead and behind me not so much to the sides and I will have the big 5th wheel to tx/rx around, I'm hoping to see some benefit to the dual setup. That said, I'm not opposed to switching to a single setup if it turns out the duals just don't work out well.

I've ordered the phasing harness already constructed for dual antennas from the same manufacturer as the antenna. I've also ordered a SWR meter so I can properly tune the antennas. As I've said though, I will have no problem using only one of the antennas if it's not working for me. I want to try it this was first.

BTW, what's your screen name mean, do you happen to be a doctor in the military?

OCO · Aug 2, 2011

I agree with the sentiment against using an amplifier on CB, but the advise from Reedeb to

remeber (sp)to put the black on + and red on - and everything will be great.

is obviously incorrect and will destroy equipment and possibly cause a fire if not fused properly..

Trophyhusband · Aug 2, 2011

jhooten said:
Why ask if you have all ready ordered it?

Having run co-phased antennas on a Vega and a 1 ton dually I can tell you first hand, other than the cool factor, they simply do not give you more bang for the buck, and are not worth the hassle to keep them tuned and working correctly. And to work correctly they need to be a quarter wave apart. Is your truck 9 feet wide?

I wanted to order everything (except the amp) in one order so I needed to know what cable to order to go between the radio and amp. I was comfortable with the answer LtDoc gave so I placed the order. The question I asked was purely out of curiosity. I was an electronics tech in the Navy and had a job doing mostly marine and a little land mobile installs and repairs for about a year. At one time I learned the theory enough to regurgitate it on tests, but in reality I never used a lot of the info in the field. I've now been out of it for quite a few years so I'm pretty rusty on anything beyond Ohm's Law.

I'm interested in the hassle of keeping them tuned. How do they get out of tune? How often do you have to retune them?

The antennas would only be 70 inches apart. How does this effect the wave propagation?

Trophyhusband · Aug 2, 2011

kb2vxa said:
"Twin Trucker" antennas started like everything else with an idea. Trouble is when thought out by the technically astute it becomes clear it was doomed to failure from the start. 18 wheel drivers soon found out that an antenna mounted on the cab is only omnidirectional when running bobtail, add a trailer and it becomes cardioid (heart shaped) with the major lobe to the rear and the minor one forward. The bulb comes on... dimly.

OK, theory has it if you feed two antennas in phase and place them 1/4 wave apart you have a bidirectional end-fire array but here's where practice departs from theory. What happens when you combine a figure 8 pattern with a cardioid at right angles? (I never did figure that one out, EZNec gets all confused.) Then that theoretical figure 8 only appears over an even ground plane surface so what happens when you put a truck cab in the middle with the antennas above ground? Are you sure those antennas are exactly 1/4 wave apart?

Now if someone could work out an equation full of complex unknown variables and reach a scientific conclusion please let us know, you deserve a prize of some sort and a place in history. Meanwhile I'll settle for a signal keeping to the road just where I want it... keep on truckin'.

I'm with you Jerry, "back in the day" I inherited dad's car with that cool factor and found out real quick how poorly that mess worked and what a pain in the butt too. As soon as I removed one antenna and the phasing harness I was amazed by the improvement. No, didn't care for an amp either. If you can't hear 'em you can't work 'em and anything more makes you the hated alligator, all mouth and no ears.

Thank you for this explanation, something to keep in mind.

As far as the amp, I'm leaning pretty heavily against it at this point. I would have to get two of them (one for the wife's car) and I'm not sure I want to mess with that. Trust me, my goal isn't to blast a huge signal and make everyone listen to me, it's more to improve the range of communication between the wife's car and my truck.

Trophyhusband · Aug 2, 2011

old_CJDC_ops said:
I agree with the sentiment against using an amplifier on CB, but the advise from Reedeb to is obviously incorrect and will destroy equipment and possibly cause a fire if not fused properly..

Yeah, I think I had that part figured out so I wasn't too likely to make that mistake. (My dad, on the other hand, uses whatever color wire he can dig up to wire things. Black, red, green, who care? It's all copper on the inside.)

Confuzzled · Aug 2, 2011

Trophyhusband said:
I'm wavering on the amp right now. The one I want is only 35 watts, but it's the only one I can find and if the quality is poor and it's inefficient, I may well be better off without it.

Did you miss the part about it being ILLEGAL?

RG-58 or RG 59 from radio to amp?

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