The AM Forum

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

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.  :)

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.

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.  

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

(http://images.amazon.com/images/G/01/electronics/detail-page2/RTB1100_accessories.jpg)

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.

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

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

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

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

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

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

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

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

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

Thanks,
MorrisSWL

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

Answer your own question.   ;)

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

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.

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! 

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

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.

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

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

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

Hello!

Just throwing out another idea. You could use an  NTE618  varactor diode and a simple variable dc supply to control the capacitance of the tuned loop. This way you would eliminate the problems of a remotely mounted mechanical capacitor.

I don't have the particulars of exactly how to do this, but, someone else here might be able to shed more light.

Roland............

Lay them out neatly side by side with say a spacing of several wire diameters. The space between windings is not to critical... but scramble winding unless precisely done, increases the capacitance per turn and lowers the resonant frequency of the loop. Taken to far, your loop will never resonant as it will appear as a capacitive element.

One problem with varactors outside is thermal stability.  If your resonated Q is high enough to get good output, you're going to have to stay on top of the tuning.

Chris

Thanks for that info.  I'll wind the wire neatly in a flat plane.

MorrisSWL

Already ordered the mechanical variable capacitor and want to keep it as simple as possible.  Thanks for the thought though.

MorrisSWL

Finally completed the AM loop antenna for our Onkyo TX-8011 receiver.

The frame is made out of two pieces of 3/16" x 1-1/2" x 20" wood, ripped off a clear 2x4.  I notched the center of the strips half way to form an X.  This made the four sides of the square 14" long.  

The 365 pf variable cap that I bought from ebay has 3 threaded machine screw holes on the shaft side.  That allows mounting the cap to the frame of a radio with the shaft sticking out.  The problem with this setup is that the threads appear to be metric and I only have US standard screws in my junk box.  Also, the screws have to be a precise length.  Too long and they will hit the capacitor plates. --- My fix was to cut a piece of sheet metal and epoxy the "bottom" of the cap to it.  The sheet metal has two holes which I can then bolt to one leg of the wooden X frame using machine screws and nuts.  A much better mounting method with no chance of a screw hitting the capacitor plates.

VERSION-1:
I used a flat ribbon cable and soldered the ends to form a loop with 18 turns, then mounted the loop on the X frame which was a perfect fit.  Soldered the ends of the loop to a 365pf variable capacitor that I bought from ebay.

I positioned the loop next to a battery powered portable radio tuned to 1460 which is the main station my wife wants to listen to.  The loop would not resonate at 1460.  I moved one lead from the cap to the different turns and found that 7 to 8 turns would allow comfortable tuning of the loop to 1460 and another station at 1540 that my wife also wants to listen to.  I was not interested in tuning lower frequency stations.

The ribbon cable that I used had a tiny gauge wire that looked smaller than 30 gauge wire.  The soldered ends broke a couple of times so I gave up on using the ribbon cable.

VERSION-2:
I used the same wood frame and cut 1/8" deep notches on the ends.  The notches are spaced 1/8" apart and I cut the notches using a hacksaw.  There was room for 10 notches since the wood is actually 1-7/16" wide.  I wound 10 loops using 22 gauge wire and connected the ends to the 365pf cap.  I used 10 loops since the loops were spaced 1/8" apart as opposed to being very tightly spaced when using the ribbon cable.  I turned out that the 10 loops are just about right.

I had also drilled 5 holes 5/8" below the tuned loop on each leg of the frame.  These holes are spaced 1/4" apart.  I threaded 22 gauge wire through these holes and had a 5 turn coupled loop.

Connected the coupled loop to the TX-8011 and adjusted the cap so that station 1460 came in fairly clearly.  But there was still just a hint of static.  I tried using 1, 2, 3 and 4 turns for the coupled loop.  One turn yielded nothing and the signal got stronger as I added more turns up to 5 turns.  So I drilled one more hole in each leg of the frame below the coupled loop and added a sixth loop.  Now station 1460 came in clearly without any static.

I tuned the receiver to station 1540 and there was a small amount of static.  I adjusted the variable cap and 1540 came in clearly.  

So now I'm able to receive stations 1460 and 1540 clearly but I have to adjust the cap to do so.  I tried placing the cap next to the receiver using about 6 feet of coax but all I heard was static and adjusting the cap did nothing.  So having a remotely adjustable cap was a failure.

Currently, my wife can only listen to station 1460 and she doesn't want to get out of bed to adjust the cap to hear station 1540.  Besides, the cap adjustment is pretty fine to obtain resonance on either station so it would be too much for her to do every time.

I'm wondering if removing one loop from the tuned loop will allow receiving station 1540 clearly without having to adjust the cap.  But even if it does, I would have to run 3 wires from the tuned loop to the receiver so my wife can throw the switch when she changes stations.  Do you think there's a possibility that this would work?  I'm guessing it won't so no sense even trying but thought I'd ask what you think.

What I documented is only a small part of all of the tests I did to get my loop to work.  I spun my wheels trying all kinds of things over two days to get it to ultimately work.  I heard a lot of static over those two days  :).   So I hope the info above will help someone to get their receiver to receive weak AM stations.  

MorrisSWL

What Fun Morris. The battle you are up against is achieving high sensitivity and hence high Q in the main coil. Hence it must be tuned. The fact that many of your tries did not work out is due to the inductnace value of the main loop being incorrect and the difficulty of resonating. I suspect the value of L is 300-600 uH, quite large. Need to think about how to solve your problem without re tuning the loop C. It may be that a better solution is to go with a long wire outside as high and as long as possible. Cannot recall but I assume there are reasons you dismissed that idea. Again, the problem with the loop is it is a small capture area, must have high Q, and therefore the need to resonant it to the desired frequency. 

2 seperate loops with fixed caps??

klc

Morris,

I was facing a similar problem with a bedside radio in my house. I like to listen to two non-local AM broadcast stations, one in New York City and the other in Boston. Living in the north central part of Connecticut put me out of their listening areas with the usual little loops that come with radios these days. I've played with high Q tuned loops and they work very well but installing one next to the bed would have brought howls of protest from my wife. I also determined that the biggest problem I had with the bedside radio was digital noise from the cordless phone that shares the table the radio is on. Because I still wanted the phone nearby, the solution was to move the antenna out of the interference.

I've had very good success using PVC pipe to build an 18" x 18" frame to wind 6 turns of wire onto, using electrical tape at the corners to hold the wire to the frame. The loop is un-tuned, covers the entire BCB and is fed with about 25 feet of twisted wire that runs from the radio, under the carpet, and over to a closet where the loop is oriented for best reception of the two stations. For even better reception I've also placed the loop in a window across the room, but the closet location works fine for my purposes. There's nothing magical about the 18" frame size, that was just a convenient size that could be concealed. You could make it bigger or smaller, but I imagine the greater the capture area is the better it will work. I didn't experiment much with the number of turns on the loop, but again, more turns may work better on the lower end of the BCB but since you are primarily interested with the top end of the band it probably won't help much.

If an outdoor antenna is possible at your location, you might want to try a broadband 85 foot loop. What I built is a pair of simple K9AY type bi-directional loops. There's no terminating resistor, so one loop receives north-south and the other receives east-west. They work beautifully on the AM BCB and in fact they do an excellent job below the AM BCB and as high as 40 meters. They're quiet and hear quite well. This past week I built and installed a 2N5109 broadband preamp at the feedpoint of one of the loops and that has added a whole new level of performance across the spectrum. I'm adding another preamp to the other loop as soon as I scrape together the parts. Details for building the outdoor loop as well as a few YouTube videos of the loops in action can be seen here:    

http://www.w1aex.com/loop/loop.html

The only deviation from the plans on that page would be that you would need to wind a transformer for the feedpoint of the radio to transition from the balanced high impedance terminals to the unbalanced RG-6 feedline. That's easily done but it does add one more step.

Good luck with your project,

Rob W1AEX

Yup, it was frustrating at times but fun and satisfying after it started to work.  The reason I didn't try a long wire is that I lost the loop antenna that came with the TX-8011, and the user manual says that the supplied loop antenna should be connected in addition to a long wire antenna.  So I had to build a loop antenna regardless.

Thanks,
Morris

Now that would be a "real" challange!  The tuning of the variable cap needs to be so precise that I can't imagine how getting the proper values of two fixed caps would work.

Thanks for the thought though,
Morris

That's a very interesting PVC AM loop antenna.  Just what I was wondering if it would work without all of the turns being in a flat plane.  I have a few questions:

1. I see you used 25 feet of twisted pair from the loop to your receiver.  When I tried about 7 feet of twisted pair from my loop, all I got was loud static.  Luckily I had about 7 feet of small diameter coax (like about 1/8" diameter) and when I used that, my loop started working.  Any secret to using twisted pair?

2. How is that loop connected to your receiver?  Do you have a factory supplied loop antenna at the input terminals?  If you don't have any external antenna connected, will your receiver receive any AM stations at all?  I ask since our TX-8011 won't receive any AM stations at all without an external loop antenna connected.  I lost the one that came with the TX-8011.


Very interesting info!  Thanks for sharing that.  I want to try building an untuned PVC loop like you did before I try any external antenna.  My goal is to receive AM 1460 and 1540 static free just using the digital tuner in the TX-8011 without my wife having to adjust the variable cap.

Thanks much for all of your info,
Morris

1. Nope, no secret at all. I grabbed 50 feet of wire, folded it back on itself to make a pair of 25 foot leads and then used my drill to create the twist. The twisted pair feedline seems to work quite well and ignores the noise from the phone while doing a decent job of carrying signals from the loop back to the receiver. In fact, if I disconnect the loop and leave the feedline connected the receiver doesn't hear much at all, which tells me that the twisted pair is doing a decent job of not acting like an antenna.

2. My receiver has two push terminals on the back for a balanced feed loop just like the picture of the one that Pete provided in the thread. The receiver has no internal antenna at all, so whatever you hook up to those terminals is all you've got for reception on the AM broadcast band. The little plastic loop they provided worked fine for strong local signals, but the feedline was too short to allow it to be placed far enough away from the noise field created by the phone. My first attempt involved lengthening the feedline to the little stock loop, and that did work, but the larger PVC frame loop is far superior and captures much more signal making reception of the distant stations more reliable.

Rob W1AEX

" Thanks for the thought "

Well, it was a 'duh' moment on my part.  

A bit better idea. Some trimmer caps after you find the sweet spot.

FWIW, RG8X has 25pf per foot.......  ya could just cut and cut untill you find the right spot.


klc

Success!  Now able to receive the two AM stations (1460 and 1540) that my wife wants to listen to, static free.  This is a long post but thought that it might be interesting reading for folks who love radio.

Since having the loop antenna on the wall and placing the variable capacitor by the receiver didn't work, I tried varying the amount of inductance instead.  Basically I have a spdt switch at the receiver which selects the amount of the wire loop used.  Here's what I did:

I decided to mount the loop antenna on the bedroom wall close to the TX-8011 receiver, instead of inside of the closet.  I wanted the antenna as close to receiver as possible.  The antenna is mounted with the X frame vertical and horizontal which makes it look like a diamond on the wall.  Two 6 penny finishing nails in the wall support the horizontal frame.  With the closet bi-fold door open and the window curtain, the antenna is not visible.  With the bi-fold door closed, the antenna is visible but looks rather "neat" on the wall. (to electronics folks anyway)  ;)

I took 3 five foot lengths of 22 gauge wire and twisted them together.  Connected one end of the twisted wires to a small spdt toggle switch with black in the center, purple and gray on the outside terminals.  I looked around for a small plastic project box to mount the switch but didn't have any.  Before making a trip to Radio Shack, a thought hit.  I scrounged through the grandchildren's toy box and found a small plastic car just the right size.  Removed the bottom of the car to remove the wheels.  Drilled a 1/4" hole through the roof for the spdt switch and another small hole through the rear license plate for the wires.  Mounted the switch in the car and it looks rather neat with a small toy car on top of the CD/DVD player (which is on top of the receiver).

Drilled 2 small holes about 1/4 inch apart in the bottom portion of the antenna frame and strung the 3 twisted wires through the holes for strain relief.  The wires continue up to the horizontal leg where the variable cap is mounted.  The black wire connects to one terminal of the variable cap, the purple wire to the 10th turn of wire (the full loop).  This allows tuning AM station 1460.

Now connecting the gray wire to the correct place on the loop to optimally receive station 1540 was a challenge.  Remember that there are 10 turns.  First I stripped a small portion of the insulation off at loop 9 and connected the gray wire to it.

With the switch set to loop 10, I adjusted the variable cap to receive 1460 clearly.  Then set the receiver to station 1540 and there was some static.  Flipped the switch to select loop 9 and most of the static cleared but there was still a little static.  By playing with the variable cap, I determined that a little more inductance was needed to receive 1540 clearly.  Judging from how much I had to turn the variable cap, I estimated that maybe 1/4 turn more was needed.  So I stripped a small portion of insulation to obtain 9-1/4 loop.  Connected the gray wire to that point.  And wow, 1540 came in clearly!

To recap, I set the switch for turn 10 and adjusted the variable cap for clear reception on 1460.  Then I tuned the receiver to 1540 and I heard a little static.  I flipped the switch and 1540 came in clearly.  That's so sweet  :).

The moral of this story is that even if I managed to get the remote capacitor to work, it would have been a royal pain for my wife to fine tune it every time she switched from 1460 to 1540.  It's a good thing that the remote cap method didn't work.  Switching inductance in and out works and a remote switch is so much easier to use.  Just flip the switch without fiddling with a variable cap.  If one strips the insulation off the entire last turn of the loop, it would then be possible to use a small clip to slide on the wire to really fine tune a second station.  If one used a multi-position switch, I guess it would be possible to have a position for every station one wants to receive.

Hope you enjoyed the read and hope it helps someone,
MorrisSWL

Nicely done!

Great job!! Its nice to see a bit 'o construction.

Now we have to shame you into getting licensed.


klc

Hi W1AEX and klc,

Thank you very much for your kind words.  
Also, I appreciate every post that everyone made to offer help and suggestions.  So thanks to each and everyone of you too.
Very nice forum here with nice folks.

Best regards,
Morris

These receiving loop construction accounts are encouraging. Thanks for sharing the particulars!


Well, the old timers used to tune their TRF receivers.. I worked with a 3-stage one at an antique radio show and with no mechanical coupling between capacitor shafts and no calibration it would have been difficult if not for 50KW AM stations. Maybe that's why old people were perceived as cranky!! It musta drove them nuts.

Welcome.  Do post details of your setup if you build a loop (or already built one).

I'm just reading and learning from examples at this point. I'm beset by noise in the city.

In the late 1970s I built a square loop from wood. It was about 3 feet across and had 4-6 turns of litz wire. A 365 pf meat slicer was in series. Alongside it, i had a second single turn loop of RG174, with the center cond soldered to the shield and a cut in the shield. It worked fantastic, with my old Scott receiver at the time. Hi Q so it had to be tweaked for each station, but I did a lot of DXing before I got rid of it. It covered the entire BC band. Now I wish I hadn't tossed it.