QRM,QRN Noise and Interference
G'Day. I thought I would start a story on installing some Radio gear in my new old truck . I'm going to be installing HF Radio in a petrol driven vehicle. This can be a real challenge in some vehicles that are full of electronics. Funny enough, it doesn't really matter whether the car is petrol or diesel. It just depends on how the electronics are set up and how good the noise suppression has been engineered into the vehicle. I am no expert in this field so it's going to be a process that I will share with you. at the moment I'm currently building the shell, which will house all the radio equipment. This will sit behind the backseat and between the fridge.
When I started this project, I knew it was going to be a challenge the reason why is that many four wheel drives have a Monoque chassis . This means that the manufacturer will bolt the body onto the chassis. One would assume that there would be no ground potential between either the body or the chassis. The trouble is in many cases there is this means that the voltage potential between the body and the chassis a different it may even mean that there is a separate circuit happening in the vehicle. This is the one main thing that I found with the last LandCruiser that I had HF Radio equipment installed. It's an easy fix and makes about 3 to 4S point difference on HF. All you need to do is put a 10 mil bolt into one of the rear tiedowns into the chassis job done. The next thing to do is to limit the amount of radio appliance that is anywhere near the engine, as there is a lot RF that comes from spark. Plugs leads injectors pumps. You name it? So this means that you need to think where the antennas are going to be placed and where the DC connection choose Radio is coming from. What I have found in the past? Is that if you isolate noise from the engine firstly, due to equipments proximity this helps enormously, probably about two S points. With regards to the antennas first off, do you want to drive looking at a fan park on the bull bar. Yes, some say it's pure art but that only goes for the first 50 km but the real reason is that the antenna is a great way to pick up our RF noise from the engine so relocating the antenna to the rear of the car can make a massive difference. I have a contact in South Australia which building a mount for me that bolts just over the rear tail light between the back window and the rear quarter panel. This takes away the antenna from near the engine and can safely stay by doing this. You will reduce the noise from anywhere up to 4S points serious. Just as a side track I had to do this on a land cruiser in 2007. I had it so called professionally, installed by a local Amateur radio dealer, power, distribution blocks were self, tapped into carpet the antenna base was put on the bull bar . So on and so on when I turn the radio on with the engine on the noise on 40 m was it 10/9 the radio was usable mobile when I turned the engine off the noise was still an S5. So I thought I'm a real technician I can fix this. myself. Just for doing the above. Three things pulled the noise level down so I could use 40 and 80 m mobile Yes there was a bit of noise about S2. Which I thought was a pretty good effort. I've been recently talking to a mate over in Wagga Wagga. John VK2YW. John has a diesel 2006 Lang cruiser. It has no noise and we have been swapping notes onto how to achieve zero noise level on the petrol version so let's see How the story unfolds. So at the moment we've only just started the project and I'm about to put the radio shell in the vehicle, permanently start working on mounting antennas, and then the most important thing start the process of bonding. This means creating a situation where everything in the vehicle is at the same ground potential and some parts in the car, fully grounded. Just another little sidenote. It really is a process to get a vehicle noise free. It is never just one thing that makes a car noise free. It is a formative project that many things will reduce noise in a vehicle it just means how far you want to go. I live in the country in the Riverina on always driving long distances when I go somewhere. In most cases, the minimum is an hour. So it's good to be able to talk to people in the car while on mobile. If I was just doing parks summits and silos on the air I wouldn't worry about it because I know the engine would be switched off, however, there's nothing quite like having the window down having the volume up and talking to somebody on the other side of Australia. Anyway, I'll leave a photo of the shell and I'll give an update in one week. Amateur radio is all about having fun and building. I'll be back.
