Hi people just wondering what the most used or best replacement antenna wire I should use , to be used on cabinet radios. Some of my collection has short bits of copper wire while others have have it stapled around the full length of the cabinet, Regards Rob.

The best wire is either a similar insulated wire to the original used or a length of speaker wire.

The length of the wire and where you put it will depend on where you are and what station(s) you'd like to receive.

In most cases, local stations can be picked up by a well-tuned radio with only a few inches of wire hanging out the back of the chassis. If you'd like to pick up some stations in adjacent areas, connecting about two metres of aerial wire may suffice. If you want to listen in long distance at night, perhaps to interstate stations, then you will need to run a long aerial wire outside the house, usually into a large tree or other tall structure.

Most of the radios, where an external antenna was required, were designed for a wire length of 25feet. Internal loop antennas are often unique to the particular set but, may have provision for an external antenna, so that more distant stations could be recieved.

It is preferable, where their is risk of shorting (bearing in mind the copper winding wire is actually insulated), to have insulated wire within the set or transiting to the main body of the external antenna. The long wire was the most common external type. If you damage the coating on the copper wire, recoat it and any joints to reduce corrosion.

Internal antenna's have a bad (and unavoidable) tendency to pick up elecrtrical noise from switching, or have their signal drowned from the hash & buzz from Compact Flourescent Tubes that generate massive RFI & should never have be allowed to be sold because of it. Then there are the switchmode power supplies.

As Brad said, what you can get away with in your location is governed by the space available. I am rural so space is not a major issue. Albeit I have moved location and have to refurbish what is here; The comms receiver had a longwire of around 50m (approx 100 cubits). The main lenght of that (pole at 25m) was 2.5mm fencing wire on electric fence porcelain insulators.

Marc

Just curious -

Is there any difference in signal performance between say a solid single-strand copper wire and a multi-strand twisted cable?

How significant is the gauge of the wire?

Is signal strength just a simple product of antenna length x total diameter?

Maven

The gauge of the wire in an antenna is more to do with mechanical strength. There is significance in the strands and many RF coils are wound with multistrand wire (as fine as it is).

Signal strength is related to the distance the transmitter is from the radio and atmospheric conditions. Losses in badly designed antennas contribute

When you get into higher frequency stuff, the lenght of the antenna gets more critical.

Marc

Thank you for your reply`s very interesting indeed,
Regards Rob.

Hi Nugget, most of my radios are from late 30's to mid fifties & I have found (I am in the city) that adding an antenna wire longer than about 2 or 3 meters can be a problem as the stations just seem to interfere with each other & the strong locals seem to bleed out wider across the dial...i guess its a selectivity issue or similar?
Best results for me to date have been from installing a separate radio earth stake...standard earth stake from middy's etc as close to the radio as possible & using a shorter antenna....I am in Melbourne & quite easily listen to 2CA with the earth stake attached but if I use a longer antenna & no earth the locals seem more prone to interfere. This is just my experience & may be something to experiment with. Also as a plus I noted the reduction of background "hum" when the earth stake is connected....I been told this may be due the AGC or equiv not having to work so hard & therefore less filament hum is amplified through the radio stages as you try to suck in those distant stations.....I will leave that to the experts to ponder & explain however!

Cheers Paul

Aerial systems are a subject on their own. What must be appreciated, is that the vast majority of built & surviving radio sets here, are transformer type.

Most of these were fitted with just a two wire mains cable. The aerial coil in these tended to be connected to the chassis. With a two wire cable there is no direct earth return to mains, or physical ground for the coil: It has to rely on induction.

Some sets also have "shielded" transformers, albiet that best practice now is to retrofit Three wire earthed cables, this type bleeds an AC charge onto the chassis. These are best mains grounded to avoid issues (zap).

AGC is a cart before the horse. AGC / AVC is a voltage developed, in most cases, at the diode plates of the detector. On a strong station the (neg) voltage is fed to the control grid of one, or more of the front end tubes (converter / mixer). It desensitises the valve (shuts it down). So no AGC voltage allows the valve to run at it's circuit's designed maximum.

Marc

This topic is good timing for me actually.
I am restoring a 1935 vintage 5 valve console for my brother in law as a chrissy present. Up where I am theres only a few stations around, so the workbench has an aerial about 30 metres long which seems to provide good signal.
Brother inlaw lives in inner sydney and I was wondering what I could do for an aerial.
Would 2 or 3 turns of wire fixed to the back of the console to form a loop aerial suffice in this instance


ben

This may be stating the obvious, but when considering erecting a long line external aerial keep lightning in mind. Here are some articles on the subject:

http://www.arrl.org/lightning-protection

Normal practice, with the big long wires is to have a knife switch on them which ties them to ground during lightning events.

I am in a lightning prone area and over the years here has split a couple of trees, damaged a telephone exchange, burnt the contacts off a contactor here, took out an SP Ausnet transformer, destroyed a lot of electrical stuff in my brothers house (after lightning arrrestors were removed?), started the odd few fires and killed a person.

Tying the long antenna to ground can actually act as an "Umbrella" & help to discharge some lightning, stopping it from ground striking.

The also look fascinating on some occassions as "St Elmo's Fire trails off of it. (Seen power lines also doing that.)

Marc

When earthing the chassis to the mains earth I have noted with several sets that reception of distant stations is sacrificed somewhat. Does this indicate the radio should be re-aligned to suit? Is this possible or just a trade off? my HMV881, AWA R82,449,469MA are ones I noted it on to varying degrees. As a result I have left them unearthed & only tinker when removed from the mains even though my volt stick shows them safe anyway.
This is what motivated me to install the radio earth stake in the first place with surprising results but has since left me wondering why??? I would much rather just earth the chassis so reception is at its best anywhere the radio is plugged in..,...has anyone else noted this or is just me & my house!!

I recommend always using test lamps or a multimeter to test for zero volts. Voltsticks and even neon screwdrivers are not reliable test methods for most applications and may not only fail to diagnose a fault but may also give false positives.

I'd agree in the case of earthing a chassis to the mains. The only reason I do this is because most double-insulated flex is three core so all three wires may as well be connected. That said, the earth wire only protects against faults on the primary side of the transformer.

Duconbuster,

My 'simplistic' understanding of the signal strength - earthing issue ......
the aerial circuit is a closed loop with resistance, inductance and capacitance ... assume R is low, L is provided by the aerial coil, and capacitance is provided by the long wire (one capacitor plate) and Earth (the other plate). If the L and C are about right, the aerial is resonant and provides your radio with a reasonable voltage across L etc etc..

I would suspect that a good radio earth would provide a better capacitance as it is closer to your long wire rather than where the Mains Earth is located, is more efficient due to less cabling and connections, less chance of picking up interference from other house wiring etc..

But don't forget Brads safety advice.

Cheers,
Ian

If you add an earth you will invariably alter the loading on the aerial and change the way it performs. Re-trimming the caps on it, would be desirable.

Also note that some mains transformers are of a shielded type. The shield bleeds an AC charge onto the chassis which can be several hundred volts.

It is desirable to earth the set to get rid of the charge.

Marc