Connecting external aerials to FM radios without one

[Old Sparky]

Specifically those with only lengths of wire as aerials-is there any reason why a teelescopic, indoor dipole or even external aerial shouldn't be connected to these, as reception in some places is poor with just the length of wire fitted.  AFAIK, the input circuit of most of these is a fairly standard VHF type which could be connected to either a 75 ohm unbalanced or 300 ohm balanced aerial, yet at least one manufacturer's instruction booklet states 'do not connect any external aerial to this receiver'  What , apart from maybe overloading the front end with too strong a signal (unlikely I would have thought), harm could result from connecting a better aerial?

[pwdrive]

Safety/Lack of isolation?

Lawrence.

[Murphyv310]

Safety/Lack of isolation?

Lawrence.

Hi.
Very unlikely Lawrence as the telescopic or wire aerial is exposed anyway (these wire aerials have very thin insulation) and of course portables are often battery only.

I have on many occasions fitted a coax socket to portables with greatly differing results with a 3 element beam or dipole. Some work fine but a lot get terrible flooding with stations repeating all over the band. A lot of these sets don't have a tuned front end to cut costs so they flood with strong signals. Sony in particular are bad on this respect. Matching will never be right as they are "matched" (in the loosest possible way) to a random length of wire so a 75 or 300 ohm feeder will not be a match but often it will work OK. Usually the outer of the coax will just be tied to an RF ground.
All I can say is give it a go, you may be lucky or get a lot of flooding, a 10pf cap in series with inner and another on the earthy side to the coax socket if your fitting one certainly wont go amiss.

[pwdrive]

""Specifically those with only lengths of wire as aerials""

Wire fitted inside receiver, outside receiver?

Need more info such as make/model/schematic.

Lawrence.

[Murphyv310]

""Specifically those with only lengths of wire as aerials""

Wire fitted inside receiver, outside receiver?

Need more info such as make/model/schematic.

Lawrence.

Hi.
Yes a diagram would be of help, TBH any I have done are fed from an internal transformer or battery which will be isolated from the mains, the addition of the 10pf caps suitably rated will alleviate any fears of isolation, this though should be handled by the mains TX.

[Old Sparky]

The set in question is a Steepletone 'Edinburgh', which is a wooden cased mains only (double wound transformer) stereo with CD Recorder, etc. It isn't mine, but belongs to someone who has just moved to Chipping Norton from Charlbury, which is about 9 miles SE of here. Their new home is down a slope so not in a very good signal area. There is a specific instruction in the user manual stating 'do not connect an external aerial'. The aerial wire, as is often the case, protrudes through a hole in the back of the cabinet. I know that Steepletone and other similar brands, don't have a good reputation, but as this is one of their better products it's probably worth adding some kind of 'proper' aerial to it.

[Refugee]

The answer to that is to get a longer aerial wire and without a direct connection twist it together so that there is enough coupling between the two wires. The new wire could even be driven from an out door aerial.
You may need a couple of tywraps to keep the wires together.

[Old Sparky]

I do,in fact, sometimes use a temporary connection of that kind in my workshop, which is in a cellar, but haven't yet tried it with the Steepletone. Might be worth suggesting this to the owners of the radio.