Braun RC61 Radiogram MW problems

[sobell1980]

Here is the diagram of the aerial set up as standard for my radiogram. I have already extended the single aerial socket to my curtain pole which has improved LW MW tremendously. I just have this slight hiss on FM. Standing in front of the gram it goes away. It is slightly there in daytime but worse at night. A loud song you don't hear it so much but on commentary etc you can. Many thanks.
Dave.

[sobell1980]

Here is a photo of the magic eye . This is the best I can achieve on tuning for radio 2. Where as radio 1 and classic fm completely closes up the black space on the magic eye. But even on those stations at night I can get some out of tune hiss.
Dave.

[TrevorG3VLF]

An FM receiver will produce lots of hiss between stations, this is objectional and some circuitry is often added to suppress it.

The bow tie aerial is too small to tune to the FM band and there is a capacitor in the set to drop the resonant frequency. This makes it difficult to properly match an external aerial. If you have nothing better to do, you could try inductive coupling to the loop.

An aerial used for transmitting needs to be optimised so that expensive power is not needlessly lost. For reception, an optimised aerial is a good thing but if it is inefficient, interference is reduced similarly to the wanted signal so it may not be too bad.

Any bit of wire can in theory can be tuned to any frequency but it practise losses can be severe. The dipole, whether simple or folded can be made to resonate with very little loss. As the frequency is shifted away from resonance it deviates from optimum so the aerial will be less efficient at the edges of the band.

If the signal changes when walking by the set, then that is an indication that a better aerial remote from the yokels would be advantageous.

The feeder is a way to connect the aerial to the set, it will have minimum loss if the impedance is matched at each end.

[sobell1980]

The thing is I don't mind having a go at this but if it's going to give little improvement I will leave as is. I don't want to spend an age rigging up all various types of aerial for little or no improvement. Today it's performing faultlessly. It's almost as it could be interference when something is switched on in the evening. There is a chap as the crow flies about 200 metres away with a huge aerial. Probably used for transmitting etc. All new territory to me though.

I could try looping wire around the circumference of the back panel inside attaching it to the feeder of the bow tie aerial? See if this helped?

My wife also won't take kindly to wires all around our living room. Again thanks for all your time and great advice on this. Any further help gratefully received.
Dave.

[Nickthedentist]

My Ekco VHF set was misbehaving in a similar way every evening, which was disappointing as it had been trouble-free up until now. It turned out that my wife was charging a new phone from work a couple of feet away, and when the charger was switched off, normal service resumed

[Herald1360]

It does sound as though for good FM results, your set will need a better aerial than its internal one, maybe even than a passable indoor one. This isn't unusual for older FM receivers- they are generally less sensitive than modern portable sets and in any case it wasn't thought unreasonable to get another dipole or array up on the chimney stack along with the telly aerials already up there. A diplexer (tuned combiner / splitter unit) at the top and bottom of the existing aerial coax enabled the same feeder to be used for both signals.

The symptoms you describe of how walking away from the set can change the signal are classic signs that the signal level near the set isn't brilliantly strong. Try an indoor dipole first or if the room happens to have a window conveniently facing towards the transmitter there are some cunning "slot" aerial configurations that can be tried taped to the window. Have a google! Otherwise, a dipole in the loft (I get away with a vertical quarter wave whip on an old magnetic mount car roof aerial base) is the next upgrade in signal gathering.

Big aerials 200m away.... if you can estimate the length of the elements it will give a good idea of operating frequency- and hence whether they're likely to be used for transmitting.

It's all good fun (or a right royal PITA)

[sobell1980]

It's so frustrating Nick. I love my music and it can really spoil folk night on radio 2. If I turn the volume up and listen to it from other rooms it's fine, I can cope with it as you cant hear the hiss. However if I want to sit and listen to it in the same room it is quite irritating. I have taken some photos of the user manual which quotes about fitting an extra dipole aerial. Also it has an adjustable ferrite rod aerial . This makes no difference either. Perhaps fitting an earth to the earth socket may improve things? Please find attatched pictures of the manual about adding an aerial that may help you to help me. Many thanks.
Dave

[Nuvistor]

It is not just old radios that are perhaps not as sensitive as later ones, the problem of walking near a VHF radio can cause the signal to change on any set depending on how strong the signal is.
If external cables for an aerial running around the room are not acceptable, do the best you can making a dipole on the back of the cabinet then perhaps try a transistor aerial amplifier.
Frank

[sobell1980]

This sounds like a great plan. I'm definately thinking it's poor signal as you all have said. Radio 2 only about 3 quarter fills the tuning eye and is regularly plagued with out of tune hiss. If I tune into classic FM the signal fills the tuning eye with the thicker green lines to show each section of the tuning eye is filled. The hiss is much more less apparant with this stronger signal although there ever so slightly.
If you look at my post #67, the photo of the user manual quotes an additional dipole aerial can be used of 240 ohms. So if I can construct one of these or buy one and build an amplifier as suggested, but for this I must again ask for your kind help. This is my first time at delving into the realms of FM aerials . Many thanks.
Dave.

[Nickthedentist]

Another thing, Dave. Have you got any valves you could substitute as a test? I have some Bush VHF sets, and tired valves in these often give similar symptoms too.

[sobell1980]

I'm afraid I do not, Nick. I have many spare valves but not this line up. Thankyou for the thought though. I feel like I'm being a fuss pot over this as my wife says. If I have gone to all this trouble of this large restoration and many hours of labour of love I like things to work just so. I'm just about to try the earth lead connection before we all go too far with this. Many thanks for all your time with this.
Going to play with my Decca for a bit whilst the gram is on test with this additional earth lead to the earth of my house.
Dave.

[sobell1980]

Well good news. I attatched an earth wire from the sets earth connection to my living room ceiling lamp unit of which is on the houses earth system. Been playing Radio 2 for 3 hours with no hissing, interference or sounding out of tune. Will try it again in the morning, same thing with the earth lead. If all ok would it be ok to use the earth pin in the mains plug? This means the wiring will be more or less hidden. The mains plug for the unit only has two core flex fitted so the earth pin in the mains plug is not used . Many thanks.
Dave.

[Herald1360]

Try it and see, though the earth to the light may be looking more like an aerial at VHF, giving the improvement in signal you found. A short lead down to the mains plug may not be the same.

[G6Tanuki]

I'd definitely look at fitting a proper external [up on the roof/in the attic] FM antenna - but *not* one of the stupid 'halo' things.

As others have mentioned - older VHF/FM radios are nowhere near as sensitive as modern ones; equally, their detector-stages were often ill-equipped to handle 'multipath' signals, causing odd sibilance and hissy-rattly-noises (as you've found when the signal varies as you move around - your body is acting as a reflector of the signal and causing local multipath-reception!)

Whatever the radio, it can only reproduce the signal it's presented with. A simple dipole fitted in the loft/attic and fed to your radio with 75-ohm coax would be a good way to go.

See here:

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

for ideas.

[sobell1980]

Good morning, Chris. I tried running a length of wire from the single pole aerial socket for LW, MW out of my patio doors to my hanging basket bracket, this made no difference. However, may I point out this was to the single aerial pole extension socket and not the earth socket. You would have thought though that this would have made a difference. I will let you know my findings.

Many thanks G6Tanuki, I've had a look at the link and this seems a very good idea for the loft. Even if my earth connection works I'd like to do this in my loft so I'm getting the best possible signals possible. How do I know which one would suit best to cover the VHF wave band, with the half signal length maths to work out it can all get a bit confusing. Also why is it that VHF has a resistive aerial connection to a dipole but for the other wave bands a simple length of wire will do?
Many thanks.
Dave.

[Nuvistor]

It all about impedance matching and affects the AM bands just like VHF but in a simple set up with a relatively high impeadance aerial input you can get away with a bit more on the AM bands. The relatively low impeadance on VHF, below 300 ohms allows a good match to a dipole type aerial and either coax cable for screening the down lead or balanced twin cable that balances out interference picked up on the downlead.

see http://m.electronicdesign.com/commun...atching-part-1 for info on impeadance matching and why.

Note the VHF. aerial is impeadance not resistive although it us uses the same term they are different. see http://www.physlink.com/Education/AskExperts/ae517.cfm

Frank

[Herald1360]

Originally Posted by Nuvistor

Note the VHF. aerial is impeadance not resistive although it us uses the same term they are different. see http://www.physlink.com/Education/AskExperts/ae517.cfm

That's strictly impedance not resistance. For a dipole precisely at its resonant frequency, its impedance is resistive- about 75 ohms. As you move away from resonance, the impedance contains reactive components as well.

For Dave- if a dipole is made to the dimensions suggested its change in impedance across the FM band will be small enough not to matter.

[Nuvistor]

Yes you are correct, Dave was asking a question, I tried to answer it but I could have done better.
Frank

[sobell1980]

Thanks Frank, Chris,G6Tanuki and all who have inputted on this lengthy thread.
The set has been working well the last few weeks with the aerial earth fitted to the earth pin of my mains plug. It has now got zero interference and the tuning indicator (magic eye) is completely filled. I think also supplying a pemanent length of wire for the aerial for the other bands has also improved matters. However I will be looking into experimenting with a loft dipole aerial after reading the various links you have provided to improve things further snd for use on my other sets.
Many thanks to all who have helped. It's been a most enjoyable project. It is now being used everyday and will also be used to play some 78s and christmas vinyl over the festive period.
Kind regards
Dave.

[sobell1980]

This thread can now be closed.