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Radio reception in the kitchen - problem

-alan-

-alan-

pfm Member
After a bit of effort (and a steer or two from here) on rigging up a kitchen-based tuner/amp/top of the cupboards mounted speaker and aerial system, (and refurbing my old Mission 700s with new rubber seals along the way) I though I'd nearly got it cracked. But there's still something not quite right.

For long period of time the set-up works perfectly, good reception and sound, but every so-often the sound volume drops to the point where I have to shift the volume control from 3ish to over 7 on a ten point scale to restore the sound - and then almost get deafened when the problem disappears anywhere from 30secs to 10 minutes later and max volume comes blasting in again.

Current set-up is the aforementioned Mission 700s driven by a Nytech 202 amp and a Linn Kudos tuner. The aerial is a little twin telescopic arm device pinched from a neighbouring tv. I know the aerial isn't wonderful - but the sound when everything is working well is perfectly acceptable.

I've swopped amps in and out to no avail, and soldered up a break where the co-ax cable meets the base of the telescopic arms - but the problem remains. I thought it might be due to the equipment and aerial sitting close to some of the main power cables running round the house - and can sometimes recreate the problem by switching on some of the heavier duty electrical equipment in the area like the cooker or the dishwasher - but not on a repeatable basis.

I'm flummoxed because I can't tell if it's a reception or an equipment problem. I was wondering if somebody could shed any light on the topic before I have to concede to the missus' request and remove the whole set up from 'her' kitchen ?

Any thoughts much appreciated.
 
It's not reception. If it were you'd get hiss and interference but not drastic volume reduction without other ill effects.
 
Could be a faulty component or a dry joint/broken wire in the tuner.

Open it up and gently touch joints with a plastic tool starting at the output socket and working forwards towards the tuner head.

Cheers,

DV
 
Darth Vader said:
Could be a faulty component or a dry joint/broken wire in the tuner.

Open it up and gently touch joints with a plastic tool starting at the output socket and working forwards towards the tuner head.

Cheers,

DV
Click to expand...

I wondered about that DV. What threw me off was the fact that I can sometimes recreate the massive drop in volume levels by turning the oven thermostat to the point where it feeds power to the grill element - even though the two pieces of equipment are at opposite sides of the kitchen. Similarly, switching on the tumble drier which lives in an adjacent utility room seems to trigger the problem as well :confused:
 
Are all these devices on the same ring main? If so there may be a loose and/or tarnished connection.

Check inside the tuner first or try the tuner on another ring circuit using headphones.

If it is the ring you'll need to disconnect it at the fuse box and open up each wall socket and examine the connections. Its usually crap solid copper wire held down by a screw.

Cheers,

DV
 
FM signal strength can vary quite a bit at the point of reception, depending on time of day and amount of whatever might be interfering/getting in the way that happens to be about at the time.

I'd start by swapping the antenna for a something more suitable, a proper dipole of five feet wide across the arms. You can make one from a spare piece of two-core cable, just split it down to a distance of 30" and spread the resulting arms wide apart, and fix somehow to something suitable. See if that helps.
 
Darth Vader said:
Are all these devices on the same ring main? If so there may be a loose and/or tarnished connection.

Check inside the tuner first or try the tuner on another ring circuit using headphones.

If it is the ring you'll need to disconnect it at the fuse box and open up each wall socket and examine the connections. Its usually crap solid copper wire held down by a screw.

Cheers,

DV
Click to expand...

They are indeed on the same ring circuit - and now that you mention it I have indeed had a similar experience with a temperamental socket in a neighbouring room :mad: Given there seems to be at least some correlation between other appliances in the room being switched on and off (manually or of their own accord) I'll test the effects of with relocating the kit to different sockets first.

(Just totting up here - and there are potentially six thermostatically controlled suspect devices in the vicinity - oven/grill/fridge/tumble-drier/deep-fat frier/freezer in the utility room :rolleyes:)
 
Michael J said:
FM signal strength can vary quite a bit at the point of reception, depending on time of day and amount of whatever might be interfering/getting in the way that happens to be about at the time.

I'd start by swapping the antenna for a something more suitable, a proper dipole of five feet wide across the arms. You can make one from a spare piece of two-core cable, just split it down to a distance of 30" and spread the resulting arms wide apart, and fix somehow to something suitable. See if that helps.
Click to expand...

Might try that as well.

(Michael - for clarity, that's taking approximately a 90"/7.5ft length of 2-core, splitting it into a T with two single-core arms of approx 30" length each spread out to form the top of the T, and the last 30" being the original 2-core which simply connects to the standard coax plug ?)
 
It doesn't matter about the length of the cable, the longer the better really as it makes it easier to route to wherever your tuner is situated. Think of the length of coax that runs down from proper roof aerials, it's essentially the same thing. All that matters is that the tee formed at the end is approx. 60 inches (1.5m) across.

Ed: and in your scenario you would end up with a five foot (60 inch) length from the coax plug with a pair of 2.5 foot (30 inch) arms on the end. Haven't you got a longer piece of wire? Some old speaker lead would be fine, or a length of lamp cord, or an old extension cable, anything. A simple dipole such as this has an inherent impedance of about 72 ohms, a near perfect match for "75 ohm" inputs.
 
Michael J said:
Ed: and in your scenario you would end up with a five foot (60 inch) length from the coax plug with a pair of 2.5 foot (30 inch) arms on the end.
Click to expand...

Apologies, I didnt describe it too clearly - but what I envisaged was the other way round - a 30" length from the co-ax plug, with two 60" single core arms spread out at the top. Was this what you meant ?
 
2 x 60 = 120, or ten feet, which might work in some areas for VHF television... ;)

The arms are 30 inches each, total 60 inches (five feet, or 1.5m) across the T.

http://www.aerialsandtv.com/fmanddabradio.html

You will be making a half-wave dipole. Speed of light is 300 million metres per second, centre of FM waveband is around 100 MHz, and velocity = frequency x wavelength.

(300 million m/s) = (100 million /s) x (3 m)

and we only want half of that 3 metres.
 
Got it - thanks!



(btw - This bit took me back years to struggling through A-level maths and physics: depressed the h*ll out of me again, and reminded me why I loathed the last couple of years in school so much..)

halfwaveFields.jpg
 
Then ignore it. :D

The relevant part is this:

halfwavecurrent.jpg


Each arm covers a quarter of a wavelength (total is a half wave as there are two arms), and the result is max. current at the centre of the dipole.
 
Slight update. My brother brought a multi-meter down and stuck it across the terminals on the socket used to power the tuner. Standard voltage this part of the world is closer to 220V than 240V. At this socket particular ring circuit, depending on what else is drawing current, the voltage can drop to 208V-210V. Little wonder the tuner and amp have been cutting out intermittently.
 
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