Is there anything filter wise I could do so that all the clutter from a house is not added to a long cable to a small garden building to help me get better radio reception while away from the nearest houses. some tests I did with a long cable like those used for a lawn mower suggest to me that the mere act of putting the cable down the garden to the vicinitof the radio is just going to make it just as bad as trying to run it in the house. Brian
Would putting a low pass or some other filter help?
Dunno which make is best, but something like this?
A mix of the following.
- Isolation transformer
- Filter
- local ground spike?
Or charge up a car battery on a timer. How long are you out there?
feed it through ferrite cokes and or mains filters in an earthed metal conduit.
Put a ferrite bead or two on the cable. Buy a better radio. Use internet radio.
In order of cost and reverse order of what would probably work best.
If you use armoured cable to the shed, the steel outer on that which should be earthed will help contain any radiated interference. Lawn mower cable isn't screened.
Radio waves have fairly long wavelengths so apart from inverse square law you don't gain much from being a modest distance away. Interference filters are available from the likes of RadioSpares and RapidOnline (or for HiFi buffs who enjoy being price gouged Russ Andrews). eg
Assuming here you are happy to make your own enclosure. The two stage ones give better rejection and attenuation. You probably want to use a filter for the lowest current you can get away with - see datasheets.
Most kit is already filtered on its mains inlet so I'd be surprised if filtering the mains made much difference unless you do something silly. You are surrounded by phone lines broadcasting ADSL and domestic Wifi.
Depending on how sensitive your receiver is you are pretty much down to avoiding those frequencies where interference dominates. A battery powered scanner will allow you to check how much is coming down the mains - my suspicion is not that much unless you are using ethernet over mains (which would not be ideal for a radio HAM).
*Some* radio waves ...
Important thing is to site the aerial(s) as far from any interference as possible, and use properly screened and or balanced feeders. A decent receiver should cope with any interference on its power supply.
Wrong. At low to medium frequencies the effect is down to coupling via inductance and capacitance. See near field versus far field
"Far-field E and B field strength decreases inversely with distance from the source, resulting in an inverse-square law for the radiated power intensity of electromagnetic radiation. By contrast, near-field E and B strength decrease more rapidly with distance (with inverse-distance squared or cubed), resulting in relative lack of near-field effects within a few wavelengths of the radiator."
Phone lines fall off rapidly as they are twisted pair.
Yoiu get broadband crud from switched mode power supplies. They are suppose to be suppressed of course...
also fluorescent lights running on trad AC ballasts etc pump broad spectrum crap back in to the mains. And the run from the local substation will pick up anything in the area
Best is to use armoured cable and earth the armour to mains earth and or the ground. Or run T & E in earthed metal conduit
Lots of scrap electronics has the necessary common mode choke, capacitors etc to clean up a mains feed.
NT
Brian Gaff used his keyboard to write :
Are you certain it is mains bourn interference?
See if you can set up a battery powered radio, to check if that also suffers. Usually you will find most similar problems are due to inadequate antennas, not high enough, not tuned to the band in use etc..
Well Its hard to say. The problem I imagine is stuff like switch mode supplies, whether in lighting or domestic appliances, and over the mains network adaptors that put ticking and whining sounds all over the short wave bands. Its interesting that running a battery radio at the bottom of my garden does reduce this as long as any aerial does not go near telephone cables or mains cables or too close to the houses. I suspect though that increasingly I am going to just lose my hobby unless I can get a remote site in the middle of dartmoor or something connected via the web under remote control, but that is a little bit like cheating, and SDRs already exist in all countries.
I'm thinking maby isolation transformer and local earthing of the secondary, but that would restrict the current somewhat.
Brian
I would have thought it can only enter the radio through mains and aeria= l. Run it off batteries, and put some filters on the aerial so it only = allows the frequencies through you're trying to receive. Of course if t= he interference is around those frequencies, then you're f***ed. Presum= ably the radio already only lets through those frequencies though.
-- =
Los Angeles's full name is =E2=80=9CEl Pueblo de Nuestra Senora la Reina de los Angeles de Porciuncula=E2=80=9D and can be abbreviated to 3.63% of its size, =E2=80=9CL.A.=E2=80=9D
Are you using an ATU, Brian? Those can help a lot if the notch is steep enough. It wouldn't be perfect, but it might make a big difference.
For mains filtering I'd initially try several turns of the incoming mains through a decent size toroid core. You could also add a class X capacitor across the mains and class Y capacitors from both live and neutral to a local earth. That should probably be an earth rod.
Your RF earth could be a ground plane at VHF or UHF but it's not so easy at lower frequencies.
Any chance of using a dipole? With an ATU and a proper 300 ohm feeder something like a G5RV (even half size) might be better for interference rejection. It depends what bands you want.
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