RF Loss / Voltage Drop

[Time Keeper]

Can't figure out whats going on with my equip. Vehicle is a 2004 Freightliner Century. Galaxy33 set @ 2-6 watts deadkey, DaveMade 2x6 (2-2290 pushing 6-2879) both units hardwired to 6-1000cc bats. Predator Ant mounted on truck mirror using puck style mount using 213 coax, set @ <1.1 on chn 1, <1.1 on chn 20, 1.1 on chn 40, resonance on 27mhz, reflection @ 0.034%, wire mesh ground straps from mount to mirror door mount and door hing to truck body, and truck body to frame in front and back of cab. 270amp alternator set @ 14.7volts grnd to frame and starter. Excellent ga. wire and grnd straps. Grnds r as short as possible. Bench checked all equip and everything is working as advertised. Here's the problem. My system has gradually degraded from being a great setup to becoming really disappointing. The reception distance has dropped from 20-25mile to maybe 5-10mile, my transmit power is way down to where I get walked on everywhere I go. I have rf bouncing around inside my truck (stereo speakers, sting on the mike, led lights come on when I key with any power). Something has changed in the truck and not the equipment is my belief. Can anyone point me in another direction? Thanks

[drdx]

Is your transmit power down on an actual wattmeter or just how you feel it is getting out? When checking it, you mention bench checking, have you tested it in the truck with good meters? With any mobile setup running an amp you should always be running a meter unless you just like to roll the dice. Stuff can go wrong pretty fast in a mobile. You mentioned voltage drop. Are you seeing a drastic voltage drop when transmitting? Some of that RF sounds like a ground issue to me. Have you checked all of the connections? You mentioned excellent wire, is it #4 or larger for a setup that size? Do you have another radio you can try in there with your amp to see if you still have that rf issue?

I'm just trying to shoot out a few items for thought.

-drdx

[Time Keeper]

I don't run a power meter in line, but do have aftermarket voltage meter in line. The drop is from 14.7 to 14, more than half a volt and power drops significantly as well. With meter in line during transmit I will see anywhere from 1200-1500 watts in the truck. If you run power in a diesel wagon you will understand what I'm about to say. Most truckers will not spend the money to have a high power system and from day to day you pretty much know what your equipment will do. When you start noticing changes in your interactions on the road you know something is out of wack. There is always someone with more power and a better setup, but not all day everyday when u have a 2x6 under the bunk. Wire is 2ga. I cannot think of anything else to ground, but all the people I know into cb's say keep grounding until you see ur swr change. I keep grounding, but it doesn't change.

[silent1]

I don't run a power meter in line, but do have aftermarket voltage meter in line. The drop is from 14.7 to 14, more than half a volt and power drops significantly as well. With meter in line during transmit I will see anywhere from 1200-1500 watts in the truck. If you run power in a diesel wagon you will understand what I'm about to say. Most truckers will not spend the money to have a high power system and from day to day you pretty much know what your equipment will do. When you start noticing changes in your interactions on the road you know something is out of wack. There is always someone with more power and a better setup, but not all day everyday when u have a 2x6 under the bunk. Wire is 2ga. I cannot think of anything else to ground, but all the people I know into cb's say keep grounding until you see ur swr change. I keep grounding, but it doesn't change.

That's about right for a 2x6.
I was getting that with a cobra 29.
200amp alt and two 8d group battery's.
on a separate charging system.

[jessejamesdallas]

14.7 to 14v is not that drastic of a voltage drop...It could be just dropping after the alternator has got Hot from being driven all day...It could also be weather related. If the drop happens during extremely cold weather, that could also be part of the problem.

It could be your alternator has some age on it now too, and just not working as hard as it use to...Maybe the brushes are getting wore out...There's all sorts of reasons why the volts aren't what they use to be...Battery terminals may also need cleaning.

Now if the "Watts" aren't there anymore, like if you have dropped from 1200w's to under 1000w's, then maybe you may need to have someone look at your Amp. You could have a weak cap or even a blown pill...which may be why your having all the RF problems too...

I run basically the same set-up you have in my work Van.

General Lee (DK 2w's) and a 2x6 DM, with a Predator 10K...And on my little Radio Shack meter I see 1200w swing. So 1200w peak should be about right...I wouldn't go over a 3w DK into that box tho...No need to over-work it...

[sparky17]

That voltage drop seems reasonable.. I knew something was up when mine would drop from 13.8v to 7 volts. ..

At that much power, a tiny amount of resistance will add up very quick.. Clean all your connection points. Use deoxit gold or some type of contact cleaner..

Use some Penetrox (conductive anti-corrosion grease) at all your connection points.. I didn't know this stuff existed at the time, and used dielectric grease at all my connections..

[Time Keeper]

Thanks for the feedback so far. I have done all of the things suggested. The amp went back to NJ for bench check and came back with clean bill of health. I have tried different ants ( Fatboy, Monkeys, homemade by 727 out of paulsboro, nj )... dialing the ant in seems to be no problem. The problem is getting power in the air. I'm just guessing in the dark, but I think that the ground plane of the truck has changed somehow. If you go from a setup where people don't believe ur talking to who you r talking to ( u have to give them a landmark 15 mile down the road ) before they will believe... to a radio where people ask you what did you say and they r only 4-5 mile away or u can't get across the street to the other truck stop without being constantly walked on. My remote has 2 switches ( 1 for drive pills and 2nd for full power ), if I decide for some unknown reason to go to full power I can literally hear the rf from my external speaker and truck stereo speakers. The power it seems is being sucked back into the truck if that makes sense. It also makes my radio sound really bad...I'm told to throw it in the trash. My Century has four grounds. Alternator to frame , starter to frame, cab grnd to frame, and battery to frame. I have installed wire mesh grnds at all four points plus the doors and bottom of cab (front and rear). I can't think of anything else to grnd. Grndng the amp is useless, no help. Any ideas on the grnd plan? Thanks

[drdx]

Have you tried changing radios? Given a good antenna system, and you mentioned reception, the radio plays a big part.


Have you tried actual field tests with a base station that can give you actual results? To really know, you need constant test stations and noted distances so you can confirm performance. You know this more than most do, on the air with a bunch of guys on channel 19 is a poor way of judging performance. How often is a trucker in an area where he knows the exact distance, is telling you the truth, no messing with you, and is someone you can rely on?

Are your current radio checks from friendly sources? If you are listening to just general traffic and trying to guestimate range, you're lost. Much of your range depends on the systems of OTHERS, not yours, and their opinions of it. How much on the air do you really believe?


-drdx

[Time Keeper]

Yes, I have tried different radios. I have 2 Rangers ( 6900hp and 6300hp ), both have been modified to allow me to run high or low power amps with the flip of a switch installed to disable the internal amp. I get the same results with all my radios, amps, and antns. Also have a DaveMade 5 pill (1x2290 pushing 4x2879) and DaveMade 10 Pill (2x2879 pushing 8x2879). It doesn't make a difference which set up I have installed...performance is terrible. On a side note, both the Rangers have a water drop sound effect on key. I used to tell people I had to put some water on the line B4 keying so that I wouldn't burn the wire up. How arrogant of me!!! The good lord has definitely humbled this driver.

I do use 2 nearby base stations, 88 out of Wilmington,DE and 727 out of Paulsboro,NJ. They are 30 and 50 miles from where I park my truck in Middletown,DE. There was a time when I could talk to both of them with any of the above equipment, but not anymore. I can't even hear them transmitting. There is no doubt that my truck capability has diminished. I just can't figure out why and so far neither can they. I guess come spring and warm weather we will just have to go through the truck and see what we can find. Most people I know have 4 wheelers and are not familiar with issues found in a diesel wagon.

As far as chn 19 is concerned you are correct, there will always be the occasional gladfly but for the most part folks/drivers give you a certain measure of respect when you key up with a clean, strong, and lets face it DOMINANT signal. Player haters for sure, but also guys giving you props and wanting to know how they can get a system like yours. I would get requests for position checks all the time.

[drdx]

Well, from the sounds of it I'd look into the antenna system. Do you have another antenna, mount, and coax you can try, even if it is a cheapo one, just to see if it makes a difference? You've mentioned that you tried different equipment, but I didn't see mention of antenna, that's why I'm asking. Are you pulling a different trailer? Is the coax in good shape, as far as no water intrusion at the connectors? A good swr isn't always a sure indicator of an efficient system.

-drdx

[Radio 75]

Well, from the sounds of it I'd look into the antenna system. A good swr isn't always a sure indicator of an efficient system.

-drdx

Amen drdx!
Any chance you have a friend that has an antenna analyzer like the MFJ models? If not, maybe find a shop somewhere that could
do a quick check for you. Don't overlook commercial radio shops either, a lot of them have the MFJ analyzers....

[drdx]

Heck, just get a 20 foot jumper or whatever, use it as a test coax from the amp to the antenna. You could also have a bad jumper I guess but I'm leaning toward the coax. I bet the antenna is fine if there is not any visible damage but hey, it is a predator. Take it apart piece by piece and scotchbrite it all up like new while you're in the maintenance mode.

-drdx

[Time Keeper]

You guys r pointing directly to where my first thoughts were, the ants. I have three sets of ants lying on my bunk, (Fatboys, Monkeys, Pedators), have tried dual phase and single, have tried various brands of good coax (mini 8 thru 213).
One shop in Wildwood,Fl (beside chrome shop) sold me personally designed studs and coax and set my swr for $120.00. By the time I got to Ga and decided to go full power it wasn't long B4 I smelled something burning (3x2879's) in my 2x6. When I got home Pony Express (Chester,PA) who does maintenance on my equip checked my swr and found 1.7 swr, everyone knows u need 1.2 or better.
I currently run a design by 727 (Paulsboro,NJ) and it is a puck mount with direct pos feed and direct grnd to the mount using 213 coax. He checks everything with a computer based program...really comprehensive. The only good thing about Wildwood is that I bought 12ft of braided wire for $4.00 a ft. which everyone likes.

[Time Keeper]

Part of 727's computer based program test exactly what ur saying. Intially with an 18ft coax we were getting 1.1 or less swr but on 26mhz, so we shortened the coax to 15ft and got even better results but at 27mhz. Next we checked the flow rate from the radio to the amp and found that although the deadkey was set at 2-6 watts it was getting less than that rate. So we installed a longer coax (I believe 21ft) and found the amp getting what it was suppoed to. From there we checked the ant reflection, and then grnd. After adjusting all of these settings we tested everything again and this time with a byrd meter and ant anlzr...the whiz kids were happy. The only problem is it does nothing to stop the severe rf leakage.

[drdx]

I do my own stuff but if I went to a shop and they were tuning my antenna system with coax length I'd run away. Coax length doesn't matter unless you're doing some delay phasing or something along those lines.

The closest thing to tuning that way MAY be to hook an analyzer up to the coax itself with it shorted using a resistor to figure out for that particular piece of coax the length of a half wave. The value will repeat itself every half wave so that is something some do to get, in theory, the same reading at the end of that coax as you would get at the feedpoint. You'd check the antenna AT the feedpoint with the analyzer, with the doors shut, in the open, for that part. If you don't have an analyzer you can get close on the coax length by just figuring it with the published velocity factor. Make the jumpers from the radio to the amp whatever they need to be to get from point a to point b. An swr of 1.7 is fine, anything under 2:1 is fine but we all like nice low readings.

When you take your vehicle into the shop, often they recommend flushes. They do transmission flushes, radiator flushes, etc. In this case it sounds like a wallet flush.


-drdx

[Time Keeper]

I have been trying to figure out if I understand what ur last post means. RU saying that test we have done r bogus? Technically I understand that coax length doesn't actually change ur swr, but will give u different readings. Let me ask this. Is it possible to read an antenna resonance and if it is at something other than 27mhz change it?
My second question is if ur antenna swr is 1.7 and u key 1200 watts @ 14.5volts what then would be ur swr? This is the reason we check swr with power.
Personally I don't know alot of the technical stuff around CB and Amps, and believe me lessons learned can be quite expensive, but I do try to find people who do and pick their brains for anwsers. Some of these people u may have talked to in DX Land, Bombay out of Indianapolis, Monkey out of Chicago, 727 out of South Jersey, 88 in DE, Pony Express doesn't grab the mike anymore (he just builds AC boxes) now, but they all use the best meters available.
They all after checking my equipment and truck use the word GROUND, which leads me back to my original question. People like u and them know a lot more about this stuff than me, but I am a quick study. U point me in the right direction and I will get there.

[drdx]

Part of 727's computer based program test exactly what ur saying. Intially with an 18ft coax we were getting 1.1 or less swr but on 26mhz, so we shortened the coax to 15ft and got even better results but at 27mhz. Next we checked the flow rate from the radio to the amp and found that although the deadkey was set at 2-6 watts it was getting less than that rate. So we installed a longer coax (I believe 21ft) and found the amp getting what it was suppoed to. From there we checked the ant reflection, and then grnd. After adjusting all of these settings we tested everything again and this time with a byrd meter and ant anlzr...the whiz kids were happy. The only problem is it does nothing to stop the severe rf leakage.

From the above, it reads to me like they used coax to tune the system. In my short experience, that means that part of your coax is more part of the radiating portion of the mix than it should be, and that would explain the RF in the cab. Are you using any type of RF choke? Did he have 2 sensors so he could really see that it is "getting less than that rate"? The wattage has no bearing on swr anyway but I was just wondering. Nothing is 100%, so you're always going to be getting some loss but it should be negligible. If he could measure and see any reall loss at all, and loss there should be next to NOTHING at that short length, and we're talking unmeasureable amounts here, then there is an issue. I'm not sure what leakage has to do with it but if you have a bad piece of coax you can find out fast, just replace it. Your SWR is going to be the same at a half watt that it is at 2000 watts. I learn all the time too, so maybe those guys have something figured out. I've never heard of any of them but that means nothing. They could be fantastic. I'm in Tx, I do talk a lot of skip, but even hearing them in skipland doesn't mean anything to me as far as their skill.

Have you installed any other close by antennas close to that one? That was just a thought that came to mind.

Think about it. How many folks know absolutely nothing but how to plug stuff in and have great results? This isn't rocket science but there is some benefit to a good install. I was referring to the wallet flush on paying $120 for studs, coax, and setting swr. That's outrageous for $5 worth of coax and some "personalized studs". Even good coax (LMR, etc) full retail is less than a buck a foot. They should set SWR for free. It sounds like you're dropping a lot of cash in several places. I'd go back and get my money or have them fix it unless it worked fine for years and years. At this point, looking back, you've been to more than one place and done more than one thing, kind of like going to 3 doctors, getting 3 different treatments and now have a problem.

Good luck and maybe more will chime in with way more knowledge than me, and they're definitely out there. I'm just curious, what brand of coax is it?


-drdx

['Doc]

Just a few things I noticed in all of the above.

And SWR meter isn't very 'smart' at all. It can't distinguish between SWR and how that SWR is composed (resistance and reactances). So, it can't tell anything about resonance. Yes, it's certainly possible to make antennas resonant, but not with an SWR meter.

Using the feed line as a way of making SWR 'better' is only fooling that SWR meter. The same impedance mismatch is still there, that feed line length thingy doesn't 'cure' anything. The only time feed line length matters is with timing/phasing and total losses from resistance. It's a "feel good" way of hiding a problem, not 'curing' it.

One of the things not mentioned in the above about how one station hears another is propagation. That's the one thing that varies all the time and can make the biggest difference. Another thing that will make a difference in how you are heard is some kind of change in what you are using, and around where you are using it. Did someone build something near where you park? Other trucks around where you park? How about where the station who'z doing that listening to you? Huge variations in that.

Power output and the voltage of that output can tell you absolutely nothing about SWR, they are not closely related at all, there's no direct correspondence.

I seriously doubt if any of this will help you -directly-, but it's something to think about.
- 'Doc

[Time Keeper]

Being the novice that I am I think that when I talk to you guys with some technical knowledge I use the wrong words. That is totally my fault. Nothing other than a antenna analyzer has been used to set my swr on my truck since first installing amps. I use Belden Coax.
Pony Express once showed me a sliding scale chart that came with one of his byrd meters and how it worked in actual practice. On it were four fields (voltage, amperage, wattage output, and swr). Using any 3 fields u could calulate what the 4th would be. I'll never forget his words,"a lota guys will tell u that u can't do this,but watch". He had me change the parameters on the scale chart which has a wheel scale and a sliding bar scale and then dupilcated the changes on his test bench, GUESS WHAT.
I don't know the technical description for what happened after my Wildwood,FL experience, but I do know this. Pony told me to always set my antennas at 1.2-1.3 or less...I did...and I never burnt a pill. Wildwood set my Predator cophase at 1.7-1.9, I burnt 3 pills within hours. Muddy Waters who passed last year, a good friend of Pony's (people know him on the east coast) was against using Motor Mauls and influenced me to buy a 350amp alt as primary and a 270amp alt backup @ $900 and $700 ea. I'm sure there r people who have been using Motor Mauls for years with no problems. Who's right and who's wrong. They will be debating that after I'm dead and buried.
Back to my problem. I have replaced ALL pos and neg wire from the alt. back to the batteries including the jumper assy connecting the batteries and the grnds from the alt, starter, cab grnd, and battery to frame. Everything cleaned to metal and protected. Tried different antennas, studs, mounts, and coax. Installed braided wire everywhere I can think of. Nothing has worked...what else can I do?

[Time Keeper]

I forgot to mention that 727 is trying to fix the problem with the rf leak into the truck. It existed B4 he started working on my truck. In fact, he sees it as a challenge since he is an antenna man, and if what he does doesn't work, I don't have to pay him. There r 2 adapters which he uses that attach to his computer. He claims his program is better than any antenna analyzer on the market, but has one for people like me who feel better having one type confirm the other. He uses Belden coax, makes his own mounts and puck type studs, and of course his own antenna design.
I'm not sure but I think it was drdx that mentioned his procrdure may be part of the problem, but the problem existed B4 he touched my system. I also have ferrite chokes installed.
I was talking with another driver yesterday who runs a 22 pill setup in his Kenworth that he showed me who suggests that the problem may not be in my equipment at all, but rather generated by the ECM. He had a second alt to supply power to his amp that was isolated from the trucks electrical system. His point was that once the ECM became corrupted with RF all sorts of wacky things happened. He also had an RF shield made out of the same material in an xray room around that huge amp. His suggestion, have the ECM wiped and reprogrammed $500, and if that fails buy a new one $3000. Thats an expensive fix. Any ideas?

[drdx]

Hey, as long as you get it back going that's all that counts. Something else, on the rf ground part, you can try a grounded antenna on the mount aiming DOWN, forming sort of a dipole right at the mount. My local tech does that for difficult situations and it works in some applications depending on the truck.

Get that thing back going so we can hear you out there when we get some skip.

-drdx