Fossicker
Hi All
Probably a strange question, but I'm experiencing some interference noises on my UHF CB, has anyone had this happen? It's a ignition buzz that varies with RPM
I have traced it down to ignition caused noise-HT spark. The car has new leads/new rotor/new cap and new spark plugs. Plugs Bosch, Cap and rotor OEM lucas. Leads I'm not sure at the present.
UHF antenna isn't mounted in the ideal location on LHS close to IGN coil and module (they were moved for a dual battery install by previous owner). Earth strap is there from engine to module heat sink as is the suppressor capacitor. The plug leads and plugs are resistor types for suppression etc. I switched standard OEM car radio to AM band and there is a fair bit of buzz there too that disappears when engine isn't running? The open door "binger" also comes through on the AM radio too with door open? I have checked earths under bonnet and they all appear ok. Weird but was wondering if anyone has experienced that kind of thing?
Regards,
David
Swaggie
SubscriberSometimes the interference can be picked up by the power lead, and chokes can be bought from jaycar.
However , has the AM interference always been there or is it new?
You should also check whether you have good earths both ends of the coax. Sometimes if fitted to a bullbar you have to have a separate earth to a good body earth.
You have to be sure the UHF is earthed properly also, as it may be earthing via the coax.
Regards Philip A
Fossicker
Thanks for reply Philip A
Has it always been there? Good question. I have only had the vehicle for 4 months and got it on the road 3 weeks ago. UHF still suffers interference if the antenna is isolated from body earth (its an independent ground plane so no issue with that test) and the UHF is powered by a gel cell battery, so no earth connection at all. Hand held UHF also picks it up if close/ish to ignition components.
I'm still trying to iron out some of the bugs in the disco, I suspect I will be for a while yet.
Off topic but did I read somewhere on the forums that you did a conversion with lambda sensors for the 14CUX?
Swaggie
SubscriberUHF still suffers interference if the antenna is isolated from body earth (its an independent ground plane so no issue with that test) and the UHF is powered by a gel cell battery.
I don't understand what you mean by no earth. Any circuit has to have an earth to complete the circuit. If you have not earthed your Gel battery to the body and have a direct and only earth from the UHF to the gel cell battery , that is most probably the source of your problem.
You should earth your gel cell to the body and the UHF to the body as the antenna is earthed to the body.
I may have misunderstood what you intended but the earth must be good in both cases, as well as the coax to the body of the UHF radio.
Added later (its an independent ground plane so no issue with that test) . This has nothing to do with interference and earthing . The independent ground plane takes the place of a reflective surface for the transmitted signal and is not earthed, it is part of the isolated antenna .
Re the O2 sensor . I still have the project Pdf in my computer . If you want a copy PM me your email address.
Regards Philip A
Last edited by PhilipA; 5th November 2014 at 08:09 AM. Reason: more info
Fossicker
Yeah it probably does read strange, I'm a Broadcast/Electronics Technician by trade so you would think that I wouldn't have these kind of issues. The way I have the UHF installed is the +12V and earth return power for the UHF is being supplied via the wiring to the cigar lighter plug. I have often done this as you know the cigar lighter is a high current circuit and don't have to worry about overloading the circuit. I used the GEL cell as a test directly powering the UHF with clip leads POS and NEG to complete the circuit but to isolate from the car chassis/body to see if this made interference better or worse. Long and the short of it, no change of state.
The antenna is mounted on a "Z" style bracket on the RH guard (well is now, was on LH guard close to IGN coil and module (its been moved due to a dual battery installation at some stage-previous owners). What I meant regarding the independent ground plane is even though the antenna is an independent ground plane type the base (SO239/UHF) and "Z" bracket effectively ground the outer/shield of the coax and for testing purposes I unscrewed the bracket and had it in mid air, this poses no issue to the UHF as the antenna doesn't require the car body as ground plane (as you said). This also made no difference.
Hopefully that explains it a bit better :-)
Regards,
David
Swaggie
SubscriberJust a suggestion.
I now fit my antenna well away from interference sources, either in the middle of the roof or in the gutter.
I have a folding gutter mount at the B pillar on the driver's side on my D2.
I have drilled a small hole in the very corner of the door aperture to run the coax, and have shortened the lead to about 1.5 metres. I have my UHF in the overhead glove compartment next to the mirror, and powered from the redundant sunroof wires that are still in place behind the mirror.
No interference at all, even with no real attention to the earth at the antenna base. In fact I don't have an earth there and still no problems.
AND you Do NOT need to have the antenna coax at a set length for UHF. The shorter the better. If you don't believe me read the Mobile 1 site.
Regards Philip A
Fossicker
Just a quick thought, my CB and Stereo both had a rpm whine to them, turned out to be my iPad charger off the cigaret lighter...
TopicToaster
All wires make antennas if you need them or not. Therefore all wires/cables entering the case of your cb or broadcast receiver have the potential to bring in the signals that have been radiated. Stronger interference is likely due to conducted interference, power supply lines should be filtered.
You should try and reduce the amount of interference generated by use of chokes and capacitors in the usual places. Good earthing helps.
Originally Posted by benji
........
Maybe we're expecting too much out of what really is a smallish motor allready pushing 2 tonnes. Just because it's a v8 doesn't mean it's powerfull.
One answer REV IT BABY REV IT!!!
ForumSage
Do you have a dummy load you can try on the effected UHF radio's aerial socket ? No noise with a dummy load fitted would also mean the Radio frequency interference (RFI) is radiated.
Noise heard with a dummy load fitted would indicate a strong interfering signal is present on the power wiring and /or the chassis of the effected radio.
Is the interference picked up by another cars UHF when parked nearby?
If so that would rule out any earthing problems within your UHF aerial, to double check, you should be recording a low VSWR on the channel most effected by the interference regardless if the aerial base is coupled to the body of the car or uncoupled and free from any electrical coupling to the vehicle which is generating the noise, as you have already stated your aerial is a ground independent.
Treat the RFI at it's source.
From what is written, I can gather you must have a ignition module that is poorly shielded or suppressed, study the casing and wiring of your module and try a couple of ways of suppressing the interference at that point.
To positively identify that is the source, make yourself a sniffer coil, a two turn coil coupled across the centre conductor and the braid of a length of 50 ohm coax, sufficient to reach the aerial socket of the UHF radio effected by the RFI, using a attenuator in line with the sniffer coil, can further reduce the noise so the pickup can be move closer to the exact RFI source.
Start with your UHF radio then as you find a way of reducing the RFI, the noise will diminish to the point it will be difficult to hear. Then try the same process with a lower frequency radio, such as a SSB 27 meg CB.
Frequency modulated signals ( UHF ) are as a rule free of RFI only the sensitivity diminishes as the RFI increases. Where as Single Side Band is the most prone to RFI .
Please be mindful I am writing this way as most readers don't have any radio theory training.
Posting Permissions
| Search AULRO.com ONLY! |
Search All the Web! |
|---|
|
|
|
Reply With Quote
Bookmarks