AM loop antenna for my receiver

[MorrisSWL]

New here and hope I can get some help from folks versed in AM radio.  We have an Onkyo TX-8011 receiver in the bedroom for several years for TV and CD listening.  My wife wants to listen to AM radio now. The TX-8011's user guide says that the supplied AM loop antenna should be connected to receive AM radio stations and should be left connected even if an external antenna is connected.   But I lost the supplied external AM loop antenna.  

I tried an AM loop antenna from a Teak AG-780 receiver and also tried a tunable AM ring antenna from Radio Shack that works on a Panasonic mini-receiver.  Neither work with the TX-8011 receiver.  All I get is static with no AM reception at all, even if I tune the RS ring antenna.

I tried a quick build 4 loops of wire on a square box that is about 14 inches on each side.  Connected the two ends to the two antenna connectors on the TX-8011 and that at least picks up strong AM stations but there's a lot of static on weaker (but not that weak) AM stations.

1. Do receivers need a specific AM loop antenna to match their internal circuitry?  (I wonder why the Teak AM loop antenna and RS tunable ring AM antenna wouldn't receive any AM stations at all?)

2. Any suggestions on how to get the Onkyo TX-8011 to receive AM radio stations?

Thanks,
MorrisSWL

[w5kcm]

Hi Morris, one old trick is to run a long peice of wire out the window and raise it at the far end, like in a tree or other support. use an insulator at this far end. Now on the end back at the radio, wind the same wire around the outside of the radio cabinet about 5 or 6 turns. now check your AM reception and it should be much improved. Also, try and ground your radio properly to a good earth ground. Good Luck with that and 73. 

[Opcom]

could the old antenna have been a "loopstick"? a ferrite rod with many turns of wire, even some taps on it? there might be more than meets the eye going on.

[W4AMV]

I looked at you manual. I suspect your input is 75 ohms and not a high impedance and not equipped with a ferrite loopstick antenna. Your manual says 35 uV sensitivity for 40 dB SNR in the broadcast band and this is typical for AM sets. This is usually specified again across a 75 ohm impedance. So the challenge in putting up a simple AM antenna is to generate as much signal voltage across this challenging low resistance. There is a solution and it is known as impedance matching... Not going to go there! However, the prior suggestions outside long wire or place your  loop as high and as close to a window or possibly outside is a good start. You mention building a loop on a card board box or frame. Great.... you just cannot hook it directly to that radio input.... its that impedance matching thing! However, if you provide the ability to TAP the loop along its perimeter that will assist you increasing the receive signal. You also need to "resonate" the loop and again just connecting across the AM terminals will destroy that ability to resonate...See...

http://www.youtube.com/watch?v=VPALB-ZZGbY

This is a neat video. I built a much smaller one that sits on a table 8 inches on a side.

Your manual is a little confusing by the way... it states you can hook up their loop and a long one together on the same set of terminals. I think what they mean is when the loop is in use remove the ground tab from the AM antenna terminals. When the long wire is used, you should then find a ground point and connect this tab back. I hope this helps. Good luck.  

[Pete, WA2CWA]

Typically, this receiver, along with many others, comes with this type of AM loop antenna.



The loop is generally tailored (specific inductance)  to work well with the receiver it comes with. Sometimes the inductance is even marked on the loop. If you're not using the loop that came with the receiver, you most likely at the very least, would have to adjust the internal AM front end to increase the usefulness of the loop you are using.

[MorrisSWL]

Hi Morris, one old trick is to run a long peice of wire out the window and raise it at the far end, like in a tree or other support. use an insulator at this far end. Now on the end back at the radio, wind the same wire around the outside of the radio cabinet about 5 or 6 turns. now check your AM reception and it should be much improved. Also, try and ground your radio properly to a good earth ground. Good Luck with that and 73. 

Sounds like a good trick.  However, I think that would work with an AM radio that has a built-in ferrite core antenna and can already receive AM broadcasts.  In my case, the TX-8011 receiver can't receive any AM stations at all without an external antenna connected.  I'm thinking that it might need an external AM loop antenna connected to complete the internal circuitry.

I'll certainly check out your suggestion once I get the TX-8011 receiving AM stations.

Thanks for taking the time,
MorrisSWL

[MorrisSWL]

could the old antenna have been a "loopstick"? a ferrite rod with many turns of wire, even some taps on it? there might be more than meets the eye going on.

The user manual for the TX-8011 shows a loop antenna like the one that Pete posted a picture of.  So I don't think it's a ferrite rod type antenna.

Thanks for taking the time,
MorrrisSWL

[MorrisSWL]

I looked at you manual. I suspect your input is 75 ohms and not a high impedance and not equipped with a ferrite loopstick antenna. Your manual says 35 uV sensitivity for 40 dB SNR in the broadcast band and this is typical for AM sets. This is usually specified again across a 75 ohm impedance. So the challenge in putting up a simple AM antenna is to generate as much signal voltage across this challenging low resistance. There is a solution and it is known as impedance matching... Not going to go there! However, the prior suggestions outside long wire or place your  loop as high and as close to a window or possibly outside is a good start. You mention building a loop on a card board box or frame. Great.... you just cannot hook it directly to that radio input.... its that impedance matching thing! However, if you provide the ability to TAP the loop along its perimeter that will assist you increasing the receive signal. You also need to "resonate" the loop and again just connecting across the AM terminals will destroy that ability to resonate...See...

http://www.youtube.com/watch?v=VPALB-ZZGbY

This is a neat video. I built a much smaller one that sits on a table 8 inches on a side.

Your manual is a little confusing by the way... it states you can hook up their loop and a long one together on the same set of terminals. I think what they mean is when the loop is in use remove the ground tab from the AM antenna terminals. When the long wire is used, you should then find a ground point and connect this tab back. I hope this helps. Good luck.  

Sounds like the type of info that I need.  Especially the 75 ohms impedance part.  I'm downloading the youtube video now and will view it later since it keeps stopping to buffer when I try to view it live.  I'll reference the info you posted as I progress.

Thanks for taking the time,
MorrisSWL

[MorrisSWL]

Typically, this receiver, along with many others, comes with this type of AM loop antenna.



The loop is generally tailored (specific inductance)  to work well with the receiver it comes with. Sometimes the inductance is even marked on the loop. If you're not using the loop that came with the receiver, you most likely at the very least, would have to adjust the internal AM front end to increase the usefulness of the loop you are using.

Yes, the AM loop antenna in your picture is what's shown in the TX-8011's user guide.  I'm apprehensive that what you said about a specific inductance being needed for the receiver to work well might be the case.

The TX-8011 has a digital tuner and the station that my wife wants to listen to is 1460.  I don't know how to adjust the internal AM front end so I'm hoping to get it working by building a custom antenna.  The simple 4 loop antenna that I threw together at least receives strong AM stations so I'm getting close.  Help from folks here might be enough to get me over the hump.

Thanks for taking the time,
MorrisSWL

[Pete, WA2CWA]

Using the same type of AM loop (sitting in the basement roughly 2 feet below ground level) connected to my Sangean HD-1X AM/FM tuner (it came with the tuner); I can easily pick up Toronto, Canada stations from central Jersey (roughly 340 miles) from late afternoon through the late evenings. Trying a similar one from a Sony receiver worked OK, but the perception was not quite as good. Why the other two that you have did not work at all seems to be a mystery. Make sure the wire leads were making good contact in the antenna terminals of the receiver.

[MorrisSWL]

Using the same type of AM loop (sitting in the basement roughly 2 feet below ground level) connected to my Sangean HD-1X AM/FM tuner (it came with the tuner); I can easily pick up Toronto, Canada stations from central Jersey (roughly 340 miles) from late afternoon through the late evenings. Trying a similar one from a Sony receiver worked OK, but the perception was not quite as good. Why the other two that you have did not work at all seems to be a mystery. Make sure the wire leads were making good contact in the antenna terminals of the receiver.

Yes, did insure that wire leads were making good contact in the receiver's antenna terminals.

Thanks,
MorrisSWL

[MorrisSWL]

Hi folks,

I'll be tied up for about 2 weeks so putting this project on hold.  I will post again in about two weeks at which time I'll have time to build some loop antennas and try to get this sorted out.  Will probably have to buy a variable capacitor from ebay unless I can make one that will be reliable and last a long time.

See you in about two weeks.  Thanks for the help so far,
MorrisSWL

[Sam KS2AM]

Any suggestions on how to get the Onkyo TX-8011 to receive AM radio stations?

Thanks,
MorrisSWL

Most stereo receivers are notorious for having a lame AM section.  i.e. poor sensitivity and lousy audio.  I've never run into one that I thought was very good although I think that there are some decent high-end ones out there.
For casual AM listening I usually use my Sony XDR-S3HD radio and also an old Panasonic "walkman" that is suprisingly sensitive and has good audio on AM.  The Panasonic is also quiet and directional due to the internal ferrite loop.

If the Onkyo doesn't work out, keep in mind that you can get another stereo receiver cheap/free on craigslist or a local yard sale that may have a better AM section.

Sam

[W4AMV]

Hi folks,

I'll be tied up for about 2 weeks so putting this project on hold.  I will post again in about two weeks at which time I'll have time to build some loop antennas and try to get this sorted out.  Will probably have to buy a variable capacitor from ebay unless I can make one that will be reliable and last a long time.

See you in about two weeks.  Thanks for the help so far,
MorrisSWL

The variable cap implemented in the video used a mailing envelope and tin foil. Very clever! Nothing to buy.

[MorrisSWL]

If the Onkyo doesn't work out, keep in mind that you can get another stereo receiver cheap/free on craigslist or a local yard sale that may have a better AM section.

If I can't build a loop  antenna that works, I'll keep your suggestion in mind. 

Thanks,
MorrisSWL

[MorrisSWL]

The variable cap implemented in the video used a mailing envelope and tin foil. Very clever! Nothing to buy.

Do you think that making a variable cap out of aluminum foil and using alligator clips to make the electrical contacts will work as a long term solution?  If I get a loop antenna to work with the Onkyo, I want it to work reliably for many years.

Thanks,
MorrisSWL

[Steve - K4HX]

Answer your own question.   

Do you think that making a variable cap out of aluminum foil and using alligator clips to make the electrical contacts will work as a long term solution?

[MorrisSWL]

Answer your own question.   

Do you think that making a variable cap out of aluminum foil and using alligator clips to make the electrical contacts will work as a long term solution?

Gosh, I thought this forum was for knowledgeable folks with experience to help people who don't know the answer.  Your response doesn't help me at all.

Best regards,
MorrisSWL

[Steve - K4HX]

Come now. Do you really think using aluminum foil and alligator clips are a long term solution?

We're here to help but meet us half way.

[W4AMV]

Good day Morris.

Sorry for the mis understanding. The video and the intention I had in directing you to it was to show some very clever solution to a problem in hand. Namely... I don't have a broadcast variable capacitor of 365 pF.  This fellow provides a very neat answer and it works. And if you are really motivated, clean up your algebra book, and calculate the resulting C that you get! Quite alot of FUN.

No, you are probably right, it will not last for more than a year... But what the heck, if it works, WOW. In the meantime you can save up the dollars and go buy a real cap while your looking at this one made out of a paper envelope in AWE. In addition you get to see if the loop works. However, you will have to provide the wire! 

[MorrisSWL]

I tried a quick build 4 loops of wire on a square box that is about 14 inches on each side.  Connected the two ends to the two antenna connectors on the TX-8011 and that at least picks up strong AM stations but there's a lot of static on weaker (but not that weak) AM stations.

Hello,

Cleared up my backlog so ready to resume working on this project.

I had previously connected a Radio Shack tunable am loop antenna directly to the Onkyo TX-8011 am antenna input and only heard static regardless of the tuning.  While doing more googling, I saw where some folks used a separate loop to inductively couple their loop antenna to their radio.  The 4 loop antenna that I made (see original post) "sorta" worked but had a lot of static on the station my wife wants to listen to.  I tried holding the Radio Shack tunable antenna next to the 4 loop antenna to inductively couple it.   Tuned the loop antenna and wow, the station was received clearly without any static!

So now here's my next question:
I bought a 365pf variable cap from ebay today and hope to receive it in about a week.  I'm going to build a new tunable loop antenna and will inductively couple it to the TX-8011.  The loop antenna will be mounted on a closet wall with proper orientation to pick up the am station.  But I want to mount the variable cap in a box that's placed next to the TX-8011 receiver.  This means that the loop antenna will be about 5 or 6 feet away from the variable capacitor.  Do you think placing the variable cap 6 feet away from the loop antenna, connected by a pair of wires (either twisted or flat adjacent wires) will still allow the loop antenna to work properly?

I know I can just try it and find out but thought it might be interesting and helpful to get your opinions while I'm waiting for the cap to arrive.  Also, I wanted to post how it can work in case it might help others.

Thanks,
MorrisSWL

[kb3ouk]

Come now. Do you really think using aluminum foil and alligator clips are a long term solution?

Yes.

Now as far as mounting the variable cap, you want it as close to the loop as posible, and you want that loop as close to what you as coupling it to. I have a recevier here that has a large loop mounted on the back with an adjustable cap on it. Inside that loop is a single loop of wire that couples the antenna to the receiver inductively.

[W4AMV]

So Morris, what you built that worked was an impedance transforming network. Again, hooking any loop directly across the receiver inputs will degrade its performace as the input on your receiver is 75 ohms as I recall. Keeping a similar configuration as you outlined that worked, try using 75 ohm coax routed from the Rx AM terminals to the tuned loop-coupled loop configuration (TL-CL). Keep the TL-CL as mentioned in the prior reply compact and together. And route the CL via 75 ohm cable to your Rx. Hopefully a tweak in the variable C value will be all you need to compensate for the 75 ohm line. Finally you may try experimenting with the number of main loop turns while adjusting the coupled loop turns between say 1-4 turns. The main loop I assume has more turns than that. GL

[MorrisSWL]

Now as far as mounting the variable cap, you want it as close to the loop as posible, and you want that loop as close to what you as coupling it to. I have a recevier here that has a large loop mounted on the back with an adjustable cap on it. Inside that loop is a single loop of wire that couples the antenna to the receiver inductively.

Regarding the loop connected to the receiver, I'll try different number of loops, starting from one loop, to see what works best.

Thanks,
MorrisSWL

[MorrisSWL]

So Morris, what you built that worked was an impedance transforming network. Again, hooking any loop directly across the receiver inputs will degrade its performace as the input on your receiver is 75 ohms as I recall. Keeping a similar configuration as you outlined that worked, try using 75 ohm coax routed from the Rx AM terminals to the tuned loop-coupled loop configuration (TL-CL). Keep the TL-CL as mentioned in the prior reply compact and together. And route the CL via 75 ohm cable to your Rx. Hopefully a tweak in the variable C value will be all you need to compensate for the 75 ohm line. Finally you may try experimenting with the number of main loop turns while adjusting the coupled loop turns between say 1-4 turns. The main loop I assume has more turns than that. GL

I'll try 1-4 turns for the coupled loop and use 75 ohm coax to the receiver AM antenna inputs.

The tuned main loop will be square, 14 inches per side and will have 17 turns.  This is per a chart I found while googling.  The loop will be mounted in a closet and I really want to have the variable cap in a box next to the receiver so my wife can adjust the tuning since there's actually two stations she wants to receive.  Any insights from anyone as to how adding 5-6 feet of wire from the main loop to the variable cap will affect affect the resonance, will be much appreciated.

Also, when constructing the tuned main loop, does it make a difference whether the wires are precisely wound so that they are all in the same plane (like winding carefully around a box so the turns don't actually touch each other) or does a loop antenna work equally as well if i just randomly wind 17 turns with the wires touching each other?  The wire will be 22 gauge insulated telephone wire since that's what I have lying around.

Thanks,
MorrisSWL