160 METER
BALANCED COAXIAL RECEIVING LOOP ANTENNA

Article and Website By KN4LF

I decided to publish this website in order to pass on some insights about this antenna that I've garnered through extensive experimentation. A warning though, very recently an arrogant 1 x 2 callsign Extra Class ham who can't think outside the box said that I don't know jack about antenna theory and that this antenna won't hear DX.

As follows is an explanation of the 160 meter balanced coaxial receiving loop antenna that I recently built. You can also make an 80 or 40 meter version of this antenna that works very well. I make no claim to have invented or even improved the antenna in any way. I'm simply passing along information about it because it works very well for low band DXing. I was advised in advance that this receive loop antenna design would not work on low angle DX on the low bands but years of personal practical experience with MF AM broadcast band receive loops told me otherwise. I must say though that it's not a replacement performance wise for a properly installed beverage antenna but HB9AMO earned the first WAZ on 160 meters with this receive loop!!!

My 160 meter receive loop antenna has a diameter of approximately eight feet, with the bottom of the loop mounted approximately two feet above ground on a HY-Gain AR-35 light duty rotator. The support system is made up of 2" OD schedule 40 PVC pipe. The preamp is made by Gary Nichols KD9SV and is sold by Radio Ware Radio & Bookstore. The preamp provides up to 22 db of amplification with a high dynamic range and has tuned broadcast band station filtering on the input and output!

As far as feedline I used RG-8U coax which is of course overkill on 160 meters but it is what I had on hand. At the feedpoint of the antenna and also at the entrance to the radio shack I have two home brewed common mode choke baluns in place to knock down any near field common mode noise The feedline is direct buried to also prevent pick up of local noise. The rig here is a Yaesu FT-1000MP Mark V Field. Also if you would rather have someone build you a balanced coaxial receiving loop contact KC2TX.

NOTE!!! It's not necessary to elevate this antenna for optimum receive performance, as it retains it's receive pattern whether near the ground or mounted well above. If anything, elevating it can the degrade noise reduction capabilities as the elevated coaxial feedline will pick up noise if any amount is in the vertical plane.

As I own a slightly smaller than 1/2 acre lot in a "NON CC&R HOA" suburban housing development, I have little room for receive antennas. My receive loop is mounted in the NE corner of my backyard, approximately 70 feet from my 160 meter inverted L transmit antenna and 50 feet from my radio shack. It is also approximately 100 feet from the nearest neighbor located to the NE of the antenna.

Even with space at a premium and both transmit antenna and receive loop antenna pretty close together I'm able to null local vertical polarized noise up to 12 S units/72 db, versus the transmit antenna on receive. F/S on the receive loop is approximately 10 S units/60 db. Also as I rotate the receive loop I'm able to peak low angle DX stations of the end and peak close in high angle signals broadside to the loop. Remember though that every QTH is different and you may get different results to an extent than I do.

This receive antenna is subject to misinformation concerning performance as allot of experienced 160 meter DX'ers will say that the antenna can't here DX BUT THAT'S NOT TRUE. Here is an example of how well the antenna works:

Material for construction of the loop is as follows:

1.) Three sections four feet long and one section five feet long of 1.5" OD schedule 40 PVC pipe. One section five feet long of 2" schedule 40 PVC pipe. The five foot 1.5" OD section seats into the rotator and allows for clearance. The five foot 2" OD section goes into the ground as a support.

2.) Three PVC end caps to keep insects from setting up shop inside the PVC piping. One four way PVC pipe coupler/combiner to attach the four arm spokes together.

3.) 20 feet of black UV resistant 75 ohm CATV coaxial cable, also two male F connector plugs.

4.) Two female F connecter jacks and one female SO-238 jack.

5.) Once variable capacitor with a value of 300-400 pf's for 160 meters. The capacitor can be the typical 100 watt antenna tuner types with some padding added in parallel or even the real small ones out of a analog transistor AM radio.

6.) One small plastic or metal box enclosure to house the tuning capacitor and connections. Two 3" nuts and bolts to attach the box to the loop.

7.) Appropriate run of 50 ohm coaxial cable feedline. I used 100 feet of RG-213 which is of course overkill on 160 meters but it is what I had on hand.

8.) Two sections of  33 feet of 50 ohm RG-8X coax. Also two pieces of schedule 40 white PVC pipe 3" in diameter by 5" in length. These materials are for the two common mode near field noise reducing choke baluns.

9.) 50-100 feet of three wire rotator cable.

10.) Silicone RTV or Borden Stix All or Liquid Electric Tape and PVC pipe glue.

11.) Optional high quality spray paint for the PVC piping. I used the type that bonds to PVC piping. At first I used silver but then changed it to brown to blend in with the natural surroundings.

12.) Hy-Gain AR-35 light duty rotator.


Construction tips:

1.) Take 20 feet of 75 ohm RG-59 cable TV type coaxial cable. Find the exact middle and remove 2" of the outer PVC casing. Then remove the outer braid while keeping the inner conductor unscathed. Then place a piece of heat shrink tubing across the 1" gap overlapping and of course heat it up and shrink it for physical wear and tear protection and water proofing.

2.) Attach the four PVC pipe spokes to the four way pipe coupler/combiner and also add the end caps. Don't forget to glue the pieces together with PVC pipe cement.

3.) Drill one hole in each of the three four foot long arm spokes 3" in from the end cap. You will run your RG-59 coaxial cable through these holes. Then run the 20 feet of RG-59 coaxial cable through the holes making sure that the 2" gap sits in the middle of the top four foot long vertical spoke. Seal this area too. Then prepare the coax and then crimp the two male F connectors on.

4.) Build your tuning capacitor box. That means one female F connector jack on each side of the box, one female SO-238 jack on the bottom and the tuning capacitor inside. If you use a metal box then the ground side of the jacks are already grounded RF path wise. If you use a plastic box then you will have to wire in the ground side paths between the three connector jacks. I personally used a black plastic box purchased from my local under stocked Radio Shack and added copper foil for the ground plain. It's dimensions are 3 1/2" tall, 2 1/4" wide and is mounted vertically. I drilled a small hole in the bottom of my box to allow for condensation to drain out.

5.) Then of course bolt the box to the same five foot long bottom vertical spoke that will bolt into the rotator housing. The center of my box is mounted approximately 18" up from the end of the five foot long PVC pipe spoke.

6.) Screw in the RG-59 cable male F connectors into the female F connector jacks on the side of the box and seal with Silicone RTV or Borden Stix All or Liquid Electric Tape. Personally I used the Liquid Electrical Tape purchased that I purchased from Lowes.

7.) Roll two common mode near field noise reducing chokes. I used 33 feet of 50 ohm RG-8X for each. I wound a single layer on a piece of schedule 40 white PVC pipe 3" in diameter by 5" in length and held the end turns in place with black plastic UV resistant wire ties. One goes at the feedpoint of the loop and the second one at the antenna service entrance to your radio shack.

8) Bury the five foot long 2" OD PVC pipe in the ground three feet. Bolt the rotator onto it and then bolt the receive loop onto the rotator. You will want to attach the three wire cable to the rotator before mounting the rotator to the pipe.

9.) Now it's time to tune the receive loop antenna for resonance with your MFJ-259B analyzer or equivalent, to your frequency of choice. I used 1830 kc. An alternate method would be to tune the receive antenna for maximum signal on the rig S meter.

10.) Then attach the 50 ohm RG-8/8X/58 coaxial feedline to the SO-238 jack on the bottom of the box and seal it with liquid electrical tape.

11.) Hook the incoming coaxial feedline to your rig and the rotator control cable to your rotator control box and you are in business.

12.) Now tune around the band and be stunned at the terrific S/N ratio that you will hear with this antenna. At times I use up to 6 db of amplification and receive signals pop up at full quieting, while the same signals on the transmit antenna are completely buried in local QRN. This receive loop antenna hears DX and I mean like Europe and Asia not just the Caribbean.


Tuning Tips:

1.) Tuning the loop for resonance can be done by attaching an MFJ-259B antenna analyzer and tuning for the lowest SWR at the antenna. A second option would be to have one person tuning the capacitor outside while someone else in the shack watches for a peak on the rig S meter.

As I mentioned previously I tuned mine to 1830 kc and got a 1.2:1 SWR with a feedpoint impedance of 58 ohms. The bandwidth is very narrow as would be expected with a high Q resonant circuit. Mine covers 5 kc at the 1.2:1 points, 7 kc at the 1.5:1 points and 9 kc at the 2:1 points. However the KD9SV preamp will provide you with a usable S/N ratio across the entire 160 meter band.

An added bonus with this high Q receive antenna loop is the reduction of IMD and improvement in the dynamic range of your receiver. I have the INRAD 70 mhz roofing filter in my Mark V Field for the main receiver. What I have found is that this loop antenna knocks down IMD from local broadcast band stations on the second receiver comparable to the first receiver!!!!!


Below are some not to scale diagrams of the antenna. Excuse the marginal artistry, it's the best I can do with nerve damage in the hands.

DIAGRAM #1 BROADSIDE PHOTO OF LOOP ANTENNA
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DIAGRAM #2 ELECTRICAL LAYOUT OF LOOP
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DIAGRAM #3 RECEIVE LOOP SUPPORT SYSTEM
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DIAGRAM #4 RECEIVE LOOP TUNING CAPACITOR
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