Obtained a nice Proton 320 clock radio (it’s a classic as clock radios go) that cleaned up very nicely the other day. The antenna wire is not a “T” dipole, but just a single strand, relatively thin insulated copper wire. I need to replace this FM antenna wire as it was cut iff right at the edge of the chassis. How long should I make this wire for best average FM reception?
basically, the longer the better, but anything over ~50cm
should work.
A multiple of 1/2 wave would be ideal. For the center of the FM band, that works out to about 16 cm.
Hmm…interesting. I would thought it would have been longer given the normal size of a T dipole. I’ll find some scissors and a ruler later on this afternoon and give it a trim.
Thanks QED!
STOP!! Put down those scissors and back away slowly!!
A half wave at the center of the FM band would be closer to 160 cm. A full half wave antenna is not practical for most people (if it’s indoors) so the usual approach is a quarter wave antenna. This would be around 75 cm or about 30 inches. If you notice, automobile fixed antennas are standardized at around 30 inches (actually 30.5 if I remember correctly).
Oops. I inverted the equation. :smack:
That’ll learn me to do math before I’ve had my coffee.
Try placing a glass on th radio…Sounds dumb…
I never got around to it this afternoon so the wire will be trimmed to the correct spec. tomorrow.
I was just starting to research this as well. I just got this used JDK two speaker boombox and I think I’m in love, but I could use better reception. I’ll research this more in time, but a quick think seems a quarter wavelength single wire antenna was it’s base. I will learn about this more as I figure two different ways I will use this. In my house, where I can probably create a longer more elaborate antenna, but also outside where I expect it has to be more quick and simple.
I think a quarter wavelength is about 5 ft (60") - that would be a rough center as each frequency will be a bit different. So if you are more interested in higher frequencies, the wavelengths will be a bit shorter, and vice versa for the lower frequencies.
You could make a length of wire a little longer than that and trim it a little at a time until you get the best you can. Then if you want better than that, you can double the length for half wavelength, etc.
Longer is not better but worse, unless it is the right length of longer.
For FM radio, around 100 MHz, a wavelength is about 10 feet, so a quarter wavelength would be 2.5 feet, or 30 inches, as mentioned upthread. For other frequencies, it will vary like 1/frequency.
If you feel like playing around with different antenna lengths, you could try adding a 3/4 wavelength wire in the opposite direction. Crudely, with the vertical line representing the radio attachment point:
_____ _______________
30" V 90"
|
Note that this is one wire, like for a radio with a telescoping antenna. i.e., point the telescoping part in one direction, and attach the 90" wire to the base of that, and string it in the other direction.
If you have two antenna inputs, then a folded dipole made from 300 Ohm twin lead wire would indeed be about 5 feet across.
zombie or no
single wire FM antennas coming out of the radio (not detachable, not a terminal point) are about 36 inches. these are on table or clock radios and can perform poorly.
a boombox would likely have a telescoping whip antenna.
You’ll need the antenna as long as you own the radio. Duh.
Notice that many modern cell phones work as FM receivers, but only if you have headphones plugged in. They use one of the lines in the headphone as the antenna.
As far as I can tell, there is no standardized length for this.
So while there is probably an optimal answer, I’ve found that practically speaking, “about this long” usually works.
Hmmmm. As long as we’ve dragged this thing out of the graveyard. . .
Could somebody elaborate a bit for the “knows nothing at all about small radio antennas, but the Celting knocked my boombox off the counter yesterday and the antenna broke, so I missed ‘Wait, Wait, Don’t Tell Me’ today” demographic?
tl:dr. How exactly do I go about removing the old antenna and attaching the wire, and what kind of wire do I need? And if I choose the longer length can I coil it up a bit or should it be straight?
If you look close at the antenna pivot point, there should be a screw there. You can buy replacement telescope antennas. I did this once, and it worked, but there wasn’t enough friction at the pivot point, so I had to have the antenna leaning against something. It wouldn’t just stand up on its own.
Until you do this, or if you can’t find a replacement, if you remove that screw, you can remove the broken bit of antenna and replace the screw. This will give you somewhere to firmly attach the wire. Just poke it through below the screw, and twist it tightly around the screw. Any wire will do, but thin stranded wire will be easier to work with. You want it straightish, but it doesn’t have to be perfect. You could tape it to a wooden or plastic stick to make it behave more like the original, if that helps.
If you use two conductor wire, like speaker wire, either split the wires apart and only use one conductor, or twist the ends together. You don’t want one of the two wires attached, and the other not.
Save any washers that may fall out or be stuck to to broken bit. Those can be used as spacers if you have the same loose antenna problem I had.
Too late to edit: if by “longer length”, you mean that 90" section in my previous post, the 30" of the loner section closest to radio could be coiled, but the outer 60" should be straight (ish). But I wouldn’t bother with that unless you’re getting marginal reception with drop-outs. If your reception is OK, you don’t need it, and if you’re trying to get a station you can’t otherwise get, it probably won’t help enough.
if there is a hollow remainder of tube then before replacement you can stuff the end of a wire there. like a piece of doorbell wire (easily purchased by the foot at a home improvement store) and take the insulation off an inch at the end, bend a U in that inch and stuff in. the antenna won’t be self supporting.
if the antenna retracts into the radio totally or is on a pivot then you need to find a replacement. an exact replacement isn’t needed just the length and the same size at the attachment point. if it is a pivoting antenna then just replace the rod and attach the new to the pivot point.
you will need to solder a connection inside the radio if the inside portion needs replacement.
a make-do wire can last for a long time if you don’t need to move the radio. you will need to aim the wire if the signal isn’t huge strong.