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Suggestions for a DIY AM Antenna?

Homebrook

Homebrook

Member
I have a Kenwood KT-8300, but I with the built-in antenna I get no stations at all. I can get plenty of AM stations on my car radio, so even though I do live out in the "boonies" here in Northern California, it should be possible to tune in a decent number of stations. I would like to get some use out of my KT-8300 AM tuner.
I have read online about AM loop antennas. It seems I should be able to build one fairly easily to use with my KT-8300, but I am a little confused. Do I need a tunable AM antenna, or is that intended with simple AM radios that have no antenna hookup? It seems I should be able to use my AM tuner to tune the antenna, no?
Have any of you built a high performance AM antenna to use with your tuners? If so, could you clue me in on a good design I could build one and get full functionality out of my really cool Kenwood KT-8300?
 
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Um, it depends on your target station(s).

A small tuned loop like the Grundig AN200 might be enough.
Put it close to the factory AM antenna on the back of your
Kenwood, tune away. Quality of reception depends on noise
sources close to your tuner. If it's not good enough, you may
have to run a wire outside. This is more complicated, because
it really needs to be grounded through a grounding block, and
ideally, run through coax in the house to your tuner. The
upside is that it lowers noise and raises signal considerably.
 
Thank you RxDx! Yes, I understand that I can make or buy a tuned loop antenna and place it near the factory AM antenna, but I would like to understand it all better. Obviously I already have a tuner in my tuner, why do I need to have another tuner in my antenna? Would I need to tune in a station twice - on the antenna, and on the turner too? It seems I would be twiddling knobs all day long trying to get a particular station. Am I missing something?
Also I'm not clear on where the wires connect. If I have a loop, where do I connect each end, to each other? Where does a ground come in?
 
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Think of a tunable antenna as a preselector/filter. You tune it so it resonates at the station frequency, improving the signal to noise ratio and making the job of the similar circuits in the tuner easier. The first thing I'd try is just a long wire indoors. If that doesn't bring in a good collection of signals at night, I'd be suspicious of something else being a problem. Interference from things in the house, any dimmer, florescent lights, LED lights and motor controls can play havoc with AM. If you have noise, start turning things off! A long wire (search long wire antenna) outdoors will be even better.
 
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A passive tuned antenna increases the capture aperture area of the oem antenna, with a sharply tuned efficiency.
 
Homebrook said:
Thank you RxDx! Yes, I understand that I can make or buy a tuned loop antenna and place it near the factory AM antenna, but I would like to understand it all better. Obviously I already have a tuner in my tuner, why do I need to have another tuner in my antenna? Would I need to tune in a station twice - on the antenna, and on the turner too? It seems I would be twiddling knobs all day long trying to get a particular station. Am I missing something?
Also I'm not clear on where the wires connect. If I have a loop, where do I connect each end, to each other? Where does a ground come in?
Click to expand...

Right, I did leave out a few details.

With the little loop, it's called inductive coupling. The AN200 sits next to the tuner's
antenna, which gets a signal boost just being next to the AN200.

Yes, you're tuning twice, but you'll get used to it. When the AN200 is 'tuned' to the
frequency you're listening to, it's like an extra signal amp stage in your tuner. It
can/should? give you the range you're looking for. If not, you may have to consider
an outside antenna. But I have really good results with this loop. A piece of long
wire inside can work, too. You need to figure out what works best for your
situation.

Grounding comes in if you put a wire outside. That's a whole other conversation.
 
The best thing about an AM loop is that there is a sharp null broadside to the antenna and you can eliminate single sources of interference by rotating the antenna and nulling them out. Here's mine:

index.php


It's tuned with a tuning capacitor taken from an old junk AM radio:

index.php


I have better luck coupling this to the OEM AM antenna than using the input AM antenna terminals. OEM bar:

index.php


Or OEM loop:

index.php


edit - when I'm not logged in these look like
 
loopstick said:
The best thing about an AM loop is that there is a sharp null broadside to the antenna and you can eliminate single sources of interference by rotating the antenna and nulling them out. Here's mine:

index.php


It's tuned with a tuning capacitor taken from an old junk AM radio:

index.php


I have better luck coupling this to the OEM AM antenna than using the input AM antenna terminals. OEM bar:



Or OEM loop:



edit - when I'm not logged in these look like
Click to expand...

Really like your loop. Did you build it?

Cheers
Hermit
 
loopstick said:
The best thing about an AM loop is that there is a sharp null broadside to the antenna and you can eliminate single sources of interference by rotating the antenna and nulling them out. Here's mine:
It's tuned with a tuning capacitor taken from an old junk AM radio:
I have better luck coupling this to the OEM AM antenna than using the input AM antenna terminals. OEM bar: Or OEM loop:
Click to expand...
Thanks for the information! I do have a couple questions on the details:
1. How did you decide on the dimension of the loop? I see small ones where the loop is about a foot, and then yours which is much larger. Does it matter?
2. How did you decide on how many loops to make? Does it matter? How do the number of loops affect performance?
3. What was the capacitance range of the air capacitor you used? I see all kind of old tuning capacitors on sale. What criteria should I use to select one?

I know, so many questions...! But I do want to understand what I'm doing otherwise I am just shooting in the dark and hoping for the best.
 
A really long piece of wire ... <G>

I use a couple brass slinkies myself ...

slinky.jpg


Those are just strung on heavy trimmer line stretched between a couple other masts. Long effective length in a small area ... works nice!

These also work surprisingly well ... passive, so all you do is place it next to the radio ...

512wqnC2GkL.jpg

I think I paid $4 for mine at a garage sale.
 
Homebrook said:
Thanks for the information! I do have a couple questions on the details:
1. How did you decide on the dimension of the loop? I see small ones where the loop is about a foot, and then yours which is much larger. Does it matter?
2. How did you decide on how many loops to make? Does it matter? How do the number of loops affect performance?
3. What was the capacitance range of the air capacitor you used? I see all kind of old tuning capacitors on sale. What criteria should I use to select one?

I know, so many questions...! But I do want to understand what I'm doing otherwise I am just shooting in the dark and hoping for the best.
Click to expand...

It's the capacitor that really determines the number of turns. I used what I believe is a typical 360 (?) pF (max - I assume) variable cap common in old radios. I made the loop as large as practically possible. Then adjusted the number of turns so that the loop would resonate across the AM band as you tuned the cap from minimum to maximum. The thing you want is the sharpest resonant peaks - and that means keeping the stray inter-winding capacitance to a minimum. So I suppose that a design with fewer turns might be better in that regard than one with many. But I kept my turns away from each other. The one in the pic has six turns - smaller diameters will have more.

There are a few AM loops sprinkled throughout this thread (the attachments got unlinked with the new forum software - but you can still click on them to make them big).

Antenna Pix: DIY and Store Bought
.
 
I generally use a small shunt capacitance across variable caps without tunable padders to limit the top end and spread useful bcb tuning across the tuning range without a dead space to the top.
 
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[QUOTE="Yes - it's a couple of 8 ft. 1x2's notched and glued at the center of the cross with wires threaded through holes drilled in the arms.[/QUOTE]
Great Job!!

I have done a few loops over the years usually finding the typical 365pF variable capacitor is the easiest to find available. You can use a larger cap but most folks like to keep it simple and cost effective. I even tried using some of the antenna tuners that are typically used in Amateur Radio but those can get a bit over the top in configuring a low enough impedance to work the MW band. If the tuner will cover 160 meters 1.8-2.0 mHz you can sometimes make it work a bit lower into the 540 kHz - 1600 kHz (0.540 -1.6 mHz) areas but then again it can work out to require a lot of trial and error to get the length of the finish loop becoming much more involved.

If you do some internet searching you can find some old pics of receiving sets from the 1920s through the late 1930s showing a set with a loop on the top with some of the them getting to be quite elaborate. The capture effect due to the larger size of your loop must be great. Using the same amount of wire on a smaller fixture could work too if you get the inkling to try building another for set top placement. I have had some success with 4 foot crosses and then building a suitable base to hold it in place. Weighting it down along with being able to move it to find the sweet spot of reception is another approach in building a smaller loop and being able to rotate it allows it to serve in some rejection of more local signals to obtain DX or distant stations.

I like yours because it simple, has the totally home brew look and of course it works which is always the best result.

Again simply love the loop you made.Thanks for posting pics and perhaps it might inspire a few others to take on a project like yours.

Cheers
Hermit
 
Thanks Hermit - in a weird sort of way that antenna led to me becoming an AK'er. I could get this ethnic station in Toronto that played pop music from India but it was weak. So I bought a Panasonic RF-2200 off ebay and made the loop. The RF-2200 (and other portables like the GE Superadio III and the Sangean ATS-803A) picked up a neighbor's pulsing electric horse fence.

I saw a vintage Olson receiver at GW and bought it and recapped it because of hum. I hooked it up to the antenna and the clicking of the horse fence was gone. Maybe because the receiver had a better ground plane in the bulky chassis. Dunno but I got into vintage receivers and the rest is history.
 
If you are talking about MW band, best antenna is a REALLY LONG wire. These waves are in hundreds of meters. Optimal antenna is between 1/4 and 1/2 of wave length. Now do your calculation. Anything of small size is a poor compromise.
 
The advantages of a large loop include directional control for specific selection/rejection, hi- 'Q' tunability, and excellent static interference immunity.
 
Pio1980 said:
The advantages of a large loop include directional control for specific selection/rejection, hi- 'Q' tunability, and excellent static interference immunity.
Click to expand...

Very true Pio but I've read of extreme DX'ers on the West Coast who string out these mega-long wire antennas on some bluff over the Pacific and basically bore-sight commercial MW in Japan, etc., "ground" wave IIRC. That's hard core.
 
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