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Extra long basic FM T Shaped Dipole Antenna?

R

red888

Active Member
I bought this for my vintage receiver:
1739896182715.png
Works great, but I have it pinned to the back of my stereo cabinet. I want to get a longer one so I can tape it to a big window nearby. I know I'll probably get minimal increase in reception but I figured why not.

Problem is I can only find them with a 5ft length. I need something closer to probably 20ft. Does that exist? Is there a reason why I can't find them longer then 5ft? I was hoping I could just get another cheapo one like this with a really long length.
 
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5' 9" seems to be a common lead length for these so I'd mount it where you want it and use some cheap speaker wire as an extension cord. The radials should be 60" in total (30" each side) for FM reception so no benefit is gained by extending them.
 
I wouldn't use speaker wire for extending it; that will result in an impedance mismatch. If you don't have any 300Ω twin lead (likely, since hardly anyone uses it any more), you can extend the antenna by attaching a 75Ω-300Ω balun and attaching some RG6 or RG59 (if your receiver doesn't have a 75Ω antenna connector, you can use a second balun). However, if you're going to go through the effort, you might want to start with an antenna better than a simple dipole.
 
@swechsler what would you recommend? I don't need anything too crazy I just need something with 20-25ft length so I can string up and stick it across my window. I keep reading the dipoles are still very effective and I have a really wide window too so I can stretch it the full 60"s across.
 
I was thinking I could get one of those 75Ω-300Ω balun adapters, then a coax cable, then another adapter that would connect the coax back to the dipole antenna :D but is that stupid hahaha
 
Can you temporarily move your receiver to where the antenna would go and make sure you can still get all the stations you want? If so, sure, just go with the dipole.
 
Not really but I don't care. I'm not too worried about wasting a couple bucks if I set it up and the one station I'm longing for still doesn't come in great. If that setup of connections makes sense could you recommend which ones so everything connects correctly?

Would this work?

Connect receiver to coax cable:
1739902543284.png


Then I would get a UFH Coax cable?
1739902573843.png

And then finally one of these to connect the female end of the UHF cable to back to the dipole right?
1739902641375.png
 
No, you can't use RG58, that's the wrong impedance. It needs to be RG6 or RG59. It's the same wire that your cable company uses (if you have a cable company), so you might have some cables lying around already.

What receiver are you using?
 
You could get another one or two of the same antenna, and cut/solder it into a straight length to connect to the dipole antenna.

Dipole antennas can be very orientation specific, will the antenna on the window face the same way as the antenna does at the back of the stereo cabinet?

Do you have access to an attic space?, that is a good place to put either an omnidirectional, or directional antenna, Stellar labs sells them for $20-30, they require a RG6 cable.
 
So what I'd get is a pair of baluns like I linked to earlier and a 25' RG6 cable. You can connect the balun's leads to the antenna leads using some short screws, washers and nuts, then tape everything over to prevent them shorting together. Or you can cut off the clips, then strip, solder and tape, but I'm not 100% sure that the wire coming out of the balun will take solder (could be aluminum). Ideally you should keep the 300Ω conductors at the same distance from one another (that's why twin-lead is like that - some RF reason), although it's only a couple of inches so probably won't make too much of a difference. Also, the signal running through 300Ω wire can be sensitive to metal and other wires, so you want to keep it a few inches away, if possible. 75Ω doesn't matter because it's shielded.
 
ohhh this could be a great excuse to get a soldering iron haha. I already bought all of those components in my previous post (save for an RG6 instead of the UFH cable). If that Push-On "F" Type Balun doesn't work I'll find some screws/nuts. Almost $10 for that dumb thing, but whatever if it provides a secure connection. That _will_ work right?
 
oh wait no, its not just extending the wire its transforming it oops. So yeah I guess I'll have to screw it together
 
You can still find 300 ohm antenna wire. I used to have a roll of ladder wire.
It consisted of two copper wires with plastic spacers between the two wires Spaced out around 6" or so if I remember right. It was used to connect TV antennas. I used some once for FM and it worked pretty well.
 
You might be able to find it at an electronics store (are there any left?) but I couldn't find it on Amazon. I don't think it's being manufactured any more.
 
OMG, OBMG. $10 for 10'? What a steal. I suppose that doesn't include shipping or "insurance". o_O

Sometimes twinlead shows up in thrift or "Christian" stores.
 
Antenna theory is great but IMO it's near useless in the real world. The antenna is never high enough off the ground and there are always obstacles that affect the pattern. 75 and 300 ohm receiver antenna terminals are often not what they're labeled. Given all that, aim for something sensible but don't get too hung up on precise tuning and matching. You can make a good dipole out of plain wire if you can't get twin-lead. I've always found cheap twin-lead to be readily available when I didn't need it, but rare as gold and just as expensive when I did. You'll find lots of good test results, DIY designs and other stuff here- http://ham-radio.com/k6sti/
 
Mumbles said:
5' 9" seems to be a common lead length for these so I'd mount it where you want it and use some cheap speaker wire as an extension cord. The radials should be 60" in total (30" each side) for FM reception so no benefit is gained by extending them.
Click to expand...
The overall length should be some whole fraction of the wavelength. For 100mHz, the wavelength is 3 meters. One-quarter length for each dipole is typical — for a total of 1.5 meters, for both dipoles.

:)
 
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