Wanted: single wire FM antenna thingy.

[97tbird]

I'm talking about the little push-in single wire indoor FM antenna thingies that normally comes in the box when one buys a receiver or a tuner..
(basically a wire attached to a part that screws/pushes into the 75 ohm FM antenna receptacle in the back of a receiver/tuner)

I have damaged mine that came with the mini onkyo receiver, and I looked online but couldn't find a place that has those for sale...(i could only find real indoor antennas, but all I want is one of those push-in ones, which work great in my area).

onkyo wants $10 or so for one, i think it's probably worth about $2.00, so i thought i'd look here.

If someone has one that's not in use, I would be willing to buy it), or if you're willing to give it away, I would pay postage to ship...

OR: if someone has an idea where to find one, please let me know.

Thanks a lot.

 

[XS650]

Originally Posted By: 97tbird
I'm talking about the little push-in single wire indoor FM antenna thingies that normally comes in the box when one buys a receiver or a tuner..
(basically a wire attached to a part that screws/pushes into the 75 ohm FM antenna receptacle in the back of a receiver/tuner)

I have damaged mine that came with the mini onkyo receiver, and I looked online but couldn't find a place that has those for sale...(i could only find real indoor antennas, but all I want is one of those push-in ones, which work great in my area).

onkyo wants $10 or so for one, i think it's probably worth about $2.00, so i thought i'd look here.

If someone has one that's not in use, I would be willing to buy it), or if you're willing to give it away, I would pay postage to ship...

OR: if someone has an idea where to find one, please let me know.

Thanks a lot.


Have you tried Radio Shack?

 

[97tbird]

yep. don't anything quite like it (at least not on the website)

 

[oilyriser]

Why would you have to buy a little scrap of wire? You can probably find one lying around.

 

[97tbird]

how do i connect it to the 75 ohm jack though?

 

[brianl703]

Is it a threaded 75-ohm jack like what you'd find on the back of a TV set?

If so just get a scrap piece of cable TV coax with a connector on one end and strip back the outer jacket and shield on all but the last 3 feet. That last 3 feet becomes your antenna. (You can leave the white foam stuff around the center conductor).

 

[97tbird]

Thanks...i might be able to try that.

so that means going from the receiver end, where it is connected to the 75 ohm jack (yeah, it is just like a TV jack):
3 feet of insulation still there, then stripped wire how many feet?

(or did you mean the other way around? as in:
receiver end bare to some length, then 3 feet of insulation intact??)

 

[brianl703]

Sorry..I meant to say strip only the outer jacket and braid/foil from the last 3 feet.

To rephrase:

From the receiver end, however many feet of intact cable you want (so you can place the antenna where you want in a place that gets good reception), then strip the braid/foil shield and outer jacket for about 3 feet. Cut off the rest of the cable, so that the end of the cable is 3 feet of exposed center conductor. (It's best to leave the foam insulation around the center conductor--the shield, and not this foam insulation, is what blocks radio signals. If you do strip the foam insulation off the center conductor, make sure that the foil/braid shield does not contact the center conductor).


This 3 feet of exposed center conductor becomes the actual antenna. The rest of the cable is just a feed.

Note: Some very cheap cables may not have a foil shield, just a braid. Anything you got from the cable company will have both a foil and braid shield, sometimes two of each.

Note: By "exposed center conductor" I mean the center conductor is no longer covered by the braid/foil shield, hence exposed to radio signals so it can act as an antenna.

 

[oilyriser]

a scrap of telephone wire can be poked into the centre hole of the 75 ohm connector and itll work pretty good. strip insulation off 1/2" first

 

[brianl703]

I've done that before..it's not real secure. Move the receiver and it pops right back out of the connector. Guess you could wire-tie it somehow.

 

[The_Jeff]

coincidentally the length of wire tunes it, if you get it close to right you'll get pretty good reception.

75 cm should be about good.

 

[Papa Bear]

1/4 wave length .... 300/ freq. in MHz measured in meters if I remember correctly. Center of the FM dial ia about 100 MHz so it's 300/100 = 3 meters, 1/4 of that is 3/4 meters or 28" or so.

Could be wrong though...

 

[97tbird]

Thanks for all the suggestions, guys. I learned a lot here, but before I could put it to work, a guy from another forum said he has one extra that came with his receiver, and he is sending it to me free of cost, so I guess it all worked out, but:
thanks SO much for your time, and info: if this need ever arises again, I know how to solve the problem now!

 

[Oldmoparguy1]

Originally Posted By: Papa Bear
1/4 wave length .... 300/ freq. in MHz measured in meters if I remember correctly. Center of the FM dial ia about 100 MHz so it's 300/100 = 3 meters, 1/4 of that is 3/4 meters or 28" or so.

Could be wrong though...

That sounds about right. I was going to post directions for making a neat little 1/4 wave center feed coaxial dipole antenna from a piece of coax, but I guess there's no point now.

 

[97tbird]

go ahead...I like to learn anyway

 

[1sttruck]

Does it make sense to design it for the middle of the dial, or at a larger or smaller value ? As I recall a larger one than average will handle a wider range of signals over a given range better than a smaller one will, but it's worth checking into.

Years back I made a 'folded dipole' I think it's called, which was 300 ohm twin lead wrapped around a specific length of 1x4 with rounded ends, terminated into 75 ohm coax for connecting. It had the advantage of being directional and being a bit more sensitive than the typical vertical or rabbit ears. An ultimate at the time was a 'rhombic fm', also built using 300 ohm twin lead, but the sizes warranted building them in the attic.

 

[Oldmoparguy1]

Originally Posted By: 97tbird
go ahead...I like to learn anyway


Ok, here goes,

Keep in mind that this is a "quick and dirty" way to build an
antenna, but I've used something like this on my hand held
aircraft band transceiver and it worked well, much better then
that little rubber stick.
[*]

1. buy a cheap piece of TV coax 6' to 8' long at chinamart or
your favorite junk retailer. Even better if you have a
well stocked junk box. Make sure it has a standard TV
connector on one end.

2. Cut off the connector on the other end, if present.

3. Measure from the cut end for the first cut. Use this table
to get the measurement for this cut.

.98Mhz. = 2.39'--(28 11/16"). Center of the FM band.

.93Mhz. = 2.515'-(30 3/16"). Center of the lower half of the
FM band.

.103Mhz. = 2.27'-(27 1/4"). Center of the upper half of the
FM band.

4. Carefully cut through the outer cover and the shield.

5. Carefully remove the cover and shield, while saving the
center insulation.

6. Now you want to connect the shield braid to the center
wire. Remove about 3/4" of cover at the cut.

7. push the braid back and remove any foil under it, exposing
the center insulation.

8. Carefully cut through the center insulation without
damaging the center wire. Now make another cut through the
center insulation about 1/4" back from the first. Remove
this small piece of insulation, exposing the wire.

9. Stretch the braid out, pull and twist it into a small
pigtail.

10. Carefully solder this pigtail to the bare center wire.

11. Now, measure back from the first cut to make the 2nd. element,
and cut the cover and shild. Measure and cut, then 1" further cut
again creating a gap in the shild, being careful not to damage
the center wire. Remove the outer cover, the braid, and the
foil, while leaving the center insulation.

12. For use outdoors, wrap the gap area with electrical tape
and cover with shrink tubing. Optionally, cover the outer
end with shrink tubing.

From the gap forward to the end of the wire is your
antenna. From the vent back to the receiver is the feed
line. The feed line can be as long as you wish, but the
longer it is, the more signal is lost, so you want it to
be as short as practicable.

A FM signal is vertically polarized, so the antenna should be
mounted vertically for best effect.

You could extend the length of the first piece about 1/2" and
bend a small hook on the end of the wire to hang the antenna
from.

I've included the 2nd. and 3rd. measurements in the case that
you want to pull in a weak station at one end of the FM band.
Keep in mind that this antenna will only give something like
2DB gain over a standard 1/4 wave wire, maybe a little more
then those little push on antennas that you were asking
about.

Anyway, have fun.

Wayne

 

[97tbird]

Thanks a LOT for your time. I saved this info for future reference.
Great write up!