My New 160 receiving Loop antenna on the 6500

Ken - NM9P

I got this antenna built just in time for the CQ 160 SSB contest last night.  Actually an hour late, but the band stinks for the first two hours, so I didn't miss anything.

Plans were based upon this great article:

http://www.n6rk.com/loopantennas/pacificon.pdf

I bodged it together using a small rectangular gourmet coffee tin for the antenna junction box.
I couldn't find my RG-11, so I used 20 feet of RG-213 for the shielded loop.
I quickly taped some pvc pipes and tubing together for the support cross.
using the dual NTE-618 Varactor diodes to remote tune it and a variable resister and 9 volt battery in an isolator box inside the shack.

I didn't have the FT82-61 torroid for the matching transformer, so I substituded a "hamfest special" that is probably closer to an FT-37-43.  Instead of 50 turns, I could only get 40 on the primary so I only put 4 on the secondary to get a close match to the 5000 Ohm impedance of the loop.

When I connected it to a RigExpert AA-54 antenna analyzer before connecting it to my rig, I was disappointed because it didn't show any change in the resonance or SWR with adjustment of the tuning control.

But After double testing to make sure I had no voltage on the receiver side of the coax (I have already paid the "**** tax" once!)  I was amazed to see the loop's receive response sliding up and down the band.

I can tune it from about 1350 KHz to about 4460 Khz from inside the shack!  And it made a noticeable difference on signals on 160 last night. I have posted some pictures of the response peaks below.

With it, and my 160 Meter Offset Fed Dipole at 38 ft, I was able to make 201 contacts, 45 states/Provinces and 3 DX multipliers for a total of 21024 points in about 9 hours on Friday night alone.  Running Barefoot with the dipole and the receive loop.
The loop would be more effective if I had my Radio Shack TV rotator on it, because it has a substantial null to its broadside.  But It is making a difference so far.  I was going to put up my Inverted 'L' this afternoon and try some more DX but I woke up with a sore throat this morning and didn't want to get out.  
Here are some pictures of the loop peaked at different frequencies:

The peak control makes about 15-20 dB difference, depending upon the frequency.

I recommend this as a poor man's alternative to the $500 loops discussed elsewhere... at least until I can afford one!

Ken - NM9P

Jim Bryce W5HFS

Please give details of your 160 OCF transmitting antenna. Thanks.

MH_Flexer

Ken,

Have you seen this link?

 http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm

I am in the process of building one of these magnetic loops.  I have a fried that has a really nice tubing bender so I am going with a 6.5 diameter 3/4" copper tubing loop.  I am collecting build materials and am waiting for a stepper USB control module to automate the tuning.

Frank's web page has a wealth of information, there is an especially intriguing link to Loop efficiency using thermal imaging.

dmr

N6DMR

Ken - NM9P

Homemade, using a Balundesigns.com 4:1 balun.  about 90 ft. on the short leg and about twice that on the long leg.  Exact dimensions were lost in the pruning.  (When tuning, prune twice as much from the long end s you take from the short end.)  

Feed point is in a tree about 35-38 ft up.  The short leg goes over the house to a pole in the front yard about 18 ft. high.  The long leg goes to the back yard about 65 ft. away to a pole 8 ft. off the ground so I can get under the 220V drop to the house, then it makes a LH turn about 90 degrees to a tree at about 15-20 ft. high, then another LF bend of about 45 degrees to a pole about 18 ft. up.  sort of a lazy 'U' shape.

The short side wire is black telephone twinlead (the stuff they bring from the pole to the house) split down the middle to give a single conductor and save weight.  The long side is 14 guage stranded THNN.  It is what I had!

Don't build one without the 4:1 balun.  it won't tune right.  As is, I can tune it on all bands 160-6 meters, except 15 meters, with reasonable performance.  It will do until my Tower and T-11 LP goes up, (I pray this spring!)  Then I will also hang a 50 up and 80 ft out Inverted 'L' with elevated radials and probably a parallel element for 80 meters.

With antennas, it doesn't have to be pretty or perfect to work.  There are much better antennas, but this is "temporary" until the tower.  and it was inexpensive.  The biggest expense was the balun.  But you need to use quality, low-loss coax.  

Hope this helps.

Ken - NM9P

Ken - NM9P

Yes, I looked at that a few months ago, but I was just looking for a receive antenna for the low bands and it looked like a lot more hassle.

Ken - NM9P

Pictures of the antenna and junction box.

Ken - NM9P

This afternoon, I cut the mast and inserted the rotator. Works a champ, now!

k0eoo

Hello all,

I built the same N6RK magnetic loop several months ago and use it all the time on 160m.  I usually get a 10dB or more improvement in SNR over my 90' shunt fed tower with the loop...  I have mine 4' high and on a rotor and can get better than  40dB null broadside to the plane of the loop.  I used the recommended toroid core and my AIM4170C showed a good match to the 75 ohm feed line on 160m but not so good up at 80m...  It works OK on 80m but it definately works good on 160m...

MH_Flexer

K0EOO What diameter loop did you build for 160m? I am limited to about 6.5 foot diameter loop, I can' carry anything larger on the roof of the motor home. The article link I posted earlier is really great, a lot of depth of content and well written. Dmr

Ken - NM9P

20 ft total loop length, which gives 5 ft on a side.  In a diamond shape it is a little over 7 feet across and the same high.

k0eoo

I bought a ready made 25' piece of CATV coax at Home Depot with connectors and scaled the spreaders to accommodate....

Pat Garrett

I built this one some years ago. It's the 160/80 version.

http://www.qsl.net/kc2tx/

It's very directional and really improves S/N ratios. I still have it around here somewhere. I'll have to dig it out.

km9r.mike

Did you utilize the transverter input for this receive antenna or ant #2 ?

Ken - NM9P

I used the RX A input on the 6500.

km9r.mike

Ok I am not familiar with that. Thanks for the reply. I will read up on the 6500's manual.

k0eoo

I used the ANT2 input...

Ken - NM9P

For the 6500 and 6700 I would prefer the RXA input because there is no danger of transmitting Into the antenna. If that is already taken, use the transverter input. On the 6300, I would suggest using the transverter input.

km9r.mike

That is what I understood wrt the 6300 that the xverter input should be utilized. Regardless utilizing the separate receive ant in general appeared to be very beneficial for you. Good job.