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Updates: Oct 2004: finishing up the mobile antenna shootout July 2004: Added antenna testing and more photos June 2004: |
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[Mobile Station] [Antennas] [Mobile Power] [Noise Noise] [A Mobile History] [Sold Equipment] [Fixed] [Walkabout] [Other Hobbies] [Links] |
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I initially started with a 1994 F250 Gas (5.4L) truck and have since moved to a 2002 F250 Diesel (7.3L PowerStroke) Here is my story... thus far! (Mobile Links) |
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Noise Noise Noise Lets start diving in on the RFI issues. There are some really good web sites on this topic. The wiring underneath the radios is all a mess so I decided this is the time to clean that all up and wire the radios directly to battery. I put fuses on both sides and put inline filer on the radio. The RFI is coming in on the antenna line, going away when the antenna end is disconnected.One site pointed to the F250 fuel pump. I put an RF Choke on it (Radio Shack part) and it dramatically reduced the RFI. The web site points to replacing the spark plug wires as the next step. Where do you find good wires? I found one web site and sent them email asking which model I should buy and I am still waiting for a reply! (7/30) I gave up on them and now trying a different copany (Magneor) web site.. we shall see. Now about three weeks later... I received the wires much faster than I expected. I had understood they were custom made, but they arrived a few days after ordering. Instructions were included with hints on how to install the wires and reading these led me to think I should change the plugs when I was chaning the wires. I did cheat a bit:. I was going away for a few days and I asked a friend (who is a master mechanic) to install both new plugs and the new wires. Wow what a difference. First the change in engine performance was remarkable. No hesitation, no knocking and I belive the engine was running quieter! Really an unbelievable change. But, I suspect this was the result of something more than the wires alone. I had not changed the plugs since I boght the truck, 80K miles ago and I believe they were never changed before that (60K miles) Yep, some of the plugs were cracked and close inspection of the old wires showed some of them were cracked too. Ok, what about the noise? Also a remarkable difference! Across the HF bands there was 2-3db reduction, not alot but noticeable. I am pleased, this made a difference. The weird thing is that my VHF/UHF radio is working better all of a sudden. I am not sure why, but the audio noise that was there when unsquelched is gone and squelch does not mis gate as often. (This is also true of the scanner.) Overall this was a very worthwhile investment. The only remaining obvious source of noise (ie I can observe control/effect on) are the fans associated with heating and airconditioning. I am going to ignore these for now.. If I am in a good QSO then who cares about overheating! (or freezing!) I just dont seem to be able to get the SWR down. It isnt the radio itself. I connected it to a tuner and an endfed wire and made a couple of dozen contacts. I suspect the grounding of the antenna. (I really hope it was not damaged!) So I have it mounted to the toolkit. A friend of mine happened to find some beautiful tinned copper braid. But being silly I only took 3 feet of the 30+ he had. I ran 1’ of it from the grounding lug on the antenna mount to the pickup bed body. I put another 1’ between the kit and the bed body on the other side. (I need to connect the bed to the frame and the engine to frame) That did not seem to make a difference. I am testing with a MFJ 259 (more $) and nothing is making sense. The SWR bounces all around as I move thru the bands. I had done some reading at K2BJ’s site. I am sure grounding is the problem. Various articles on the ARRL site also suggested this was the first place to look. (Pretty obvious the tool kit itself was not much of a ground!) Crawling around the bottom of the truck, I decided to use the remaining braid to connect the bed to the cab and the frame to the exhaust. (I had connected the Tarheel mount to the bed already.) Under the cab there was a hole already there. So I sanded away the dirt and grime put a washer on the bolt to make a good contact and installed one end in the cab. I drilled a hole into a place out of the way under the bed and did the same. For the exhaust, I sanded away the rust on the pipe and used a pipe clamp to hold the braid. There was already a small hole in the frame to connect to. So I sanded there and bolted it in the other end. . I did not have enough braid to do as many places as I would like (the engine to the frame) but I am hoping this will be enough. I am hoping doing the places closest to the antenna first will help and that the exhaust will help for the engine a bit since they are well connected. I hooked up the 259 and wow: look at those SWRs: all in the 2:1 range. This is pretty good! Then the batteries died in the 259 (It does consume them and it is easy to leave it on) So stay tuned, I might be close to success! One small point. I initially used wire braid all over the truck. This is easy to find and install. But now that I have been using it for more than a year, I have notice that Braid does degrade. I have had to replace certain piece parts recently. While I was in the buying process for more I temporarily installed some large wire (#4) I noticed that there was not much difference in performance (noise, swr) between this and braid. (Other than it was bare copper which I did not want to use). In certain spots where there is alot of flexing or movement braid is the only choice. I did recently replace certain braids with 1.5” wide straps I picked up from Lowes. Grounding Grounding Grounding The first step was to ground together everything. I was lucky and in a dumpster at work there was alot of nice braid grounding strap. (But this can be purchased as well.) I just decided to go install without testing after each additional strap. Some of the key ones:
Actually I was not able to do this all in one sitting, so I was able to see if the grounding made any difference in the noise level. It did make some difference but not as much as I would have liked. ... But it did make a hugh difference in getting the antenna system to work well. I did some testing before the grounding and found that SWRs varied all over from test to test. (No need to post these results.) W8JI has some nice pictures of his grounding efforts. Noise Noise Noise This is a continuing battle. In this truck it is widely reported (see http://www.k2bj.com/) that the fuel pump creates lots of nose. I did put a filter on the leads in and out of the gas tank and there was some effect. The biggest source seems to be the computer and fuel injectors in the engine. I looked and looked what to do about these and there is no really good solution. I did put chokes everywhere but no one choke made a hugh difference. (Any hints out there?) What did work?
I tried to install chokes on the injector wires: it did not make any difference I could detect.I did finally find some sort of pump that was mounted right next to the transmission: I put some cores on this: SUCCESS!!! hugh difference.... Realize that there are limitations. There are going to be cars/trucks driving next to you that will be creating alot of noise. Not alot you can do about those vehicles! Remember to provide a DC grounding path for static discharge! If you dont have a inductive loading coil on your antenna put in a 10K resistor |
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[WB2EWB Ham Radio] [Mobile Station] [Fixed] [Walkabout] [Other Hobbies] [Links] |
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Copyright 2004 by Philip P. Thompson, All rights reserved. |