Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Mar Sat 28, 2020 9:22 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 22 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Another Tuned Loop Antenna
PostPosted: Dec Thu 12, 2019 7:20 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 181
My outside 50' antenna works well for DX'ing the MW broadcast band, except for 600 to 750kHz. There is something causing RF noise on those frequencies 24x7 a street north of me. So, I thought I would try building a 36" tuned loop antenna that I could point to a station, while nulling out noise coming from other directions. I based it, more or less, on Don Moman's 1980s design. I put the frame together with wood dowel pins and glue - no metal screws or nails.

It has (12) loops of 20 gauge magnet wire connected to a 10-365pf variable capacitor I took from an unused RF signal generator. I used it, because it has a vernier dial. The pickup is a single loop of the same wire placed as the 13th loop but not connected to the first 12 loops. For now I'm just connecting Ant and Gnd from my radio to the pickup loop without any coax. I found I still have to ground the radio's Gnd connection to my outside ground rod due to noise inside the house.

Its tuning range is 580 to 1760kHz. I would have to either add another loop to the 1st 12 loops or reduce the range of my variable capacitor to get it to 530 to 1710kHz. I may or may not do that, because there is more activity at the high end where I live.

As you can see, it's pretty bulky. But it definitely works! A small transistor radio placed on the crossbeam at a right angle to the loop also works well without any connections.


Attachments:
tuned_loop_1.jpg
tuned_loop_1.jpg [ 247.08 KiB | Viewed 1002 times ]
tuned_loop_2.jpg
tuned_loop_2.jpg [ 286.07 KiB | Viewed 1002 times ]

_________________
KC1LML
Peterborough, New Hampshire USA
Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Thu 12, 2019 8:46 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14990
Location: S. Dartmouth MA 02748-1225 USA
Very nice...

The sense loop is balanced, coax will not match the impedance nor that of the radio. The pf/ft will simply kill the signal. I use "floppy, soggy" tinsel cord, single conductor, when I connect loops and let the cord lay about like a shoe string. No more than 4' long...

Quote:
something causing RF noise on those frequencies 24x7 a street north of me.
Grow lights for hydroponic agriculture :?

Radios operated with loops are not usually grounded. If the radio has a ground via the power cord noise will still get in.

Will need a "Lazy Susan" :D

Chas

_________________
I'll admit to agreeing only to what I know is true.


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Thu 12, 2019 9:15 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 181
Chas wrote:
Grow lights for hydroponic agriculture :?

hmm... hadn't thought about that. Maybe I should complain to an organization that might find that interesting.

Chas wrote:
Radios operated with loops are not usually grounded. If the radio has a ground via the power cord noise will still get in.

I usually run my DX radios on an isolation transformer, and the radio's ground to my outside ground rod. I only do that after checking the radio's wiring and schematic. No one should do that unless they understand the risks.

Chas wrote:
Will need a "Lazy Susan" :D

I've seen lightweight ones that are all plastic. Some mount their loops on an umbrella type stand to get both rotation and tilt. I haven't seen much difference by tilting, but yes, this does require a lot of rotating.

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Fri 13, 2019 5:55 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34389
Location: SoCal, 91387
moallen wrote:

Its tuning range is 580 to 1760kHz. I would have to either add another loop to the 1st 12 loops or reduce the range of my variable capacitor to get it to 530 to 1710kHz. I may or may not do that, because there is more activity at the high end where I live.

Nice build! I built a 23" loop using a quilting hoop, a 405 uF tuner from an AA5, and 12 turns to get a 540-1600 range. I would suggest actually removing one turn on yours, in order to get the range lowered to cover the BCB.
To get mine to rotate, I used a small round metal gimbal, mounted between the base plates.


Attachments:
5A.JPG
5A.JPG [ 712.07 KiB | Viewed 933 times ]

_________________
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins/////////////////////////
Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Fri 13, 2019 7:08 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13446
Location: Omak,wa,usa
Hello,
Nice antenna I need to finish mine and I also ran a wire outside to the grounding rod .

Sincerely Rich


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Fri 13, 2019 3:21 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 181
fifties wrote:
Nice build! I built a 23" loop using a quilting hoop, a 405 uF tuner from an AA5, and 12 turns to get a 540-1600 range. I would suggest actually removing one turn on yours, in order to get the range lowered to cover the BCB.


Out of curiosity, I just now removed 1 turn, because it was easy to do. This actually raised my coverage from about 620kHz at the low end to something out of range at the top end. I have looked at several configurations people have built. Some say removing a turn lowers the coverage, some say removing a turn raises the coverage. I thought some were typos, but maybe not. I may have a ham radio license, but I'm no antenna expert! Could there be some other factor[s] involved?

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Fri 13, 2019 3:56 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 8883
Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
moallen wrote:
fifties wrote:
Nice build! I built a 23" loop using a quilting hoop, a 405 uF tuner from an AA5, and 12 turns to get a 540-1600 range. I would suggest actually removing one turn on yours, in order to get the range lowered to cover the BCB.


Out of curiosity, I just now removed 1 turn, because it was easy to do. This actually raised my coverage from about 620kHz at the low end to something out of range at the top end. I have looked at several configurations people have built. Some say removing a turn lowers the coverage, some say removing a turn raises the coverage. I thought some were typos, but maybe not. I may have a ham radio license, but I'm no antenna expert! Could there be some other factor[s] involved?


To lower the frequency range that you are able to tune you need to increase the inductance or capacitance or both. So add a turn to the coil or parallel a small cap across the tuning cap.


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Fri 13, 2019 5:33 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 181
John Bartley wrote:
To lower the frequency range that you are able to tune you need to increase the inductance or capacitance or both. So add a turn to the coil or parallel a small cap across the tuning cap.

I just did some more experimenting and definitely don't understand all the results. First of all, you were correct that adding a turn (in this case, putting it back to 12 turns) lowered the range back to 580 from 620 at the low end. Then I paralleled the tuning cap with a 100pf cap and furthered lowered it to 520. So far, so good.

However, I found that this wasn't really doing anything for the high end. The high end was presumably so far past 1730 I couldn't reach it. Then I discovered removing the 100pf cap and using a 20pf cap brought the high end down to 1720. The problem with that, though, is that puts the low end back up to 620.

Just to summarize - I can get the low end down to 520 by paralleling the tuner with only a 100pf cap, and I can get the high end down to 1710 by paralleling the tuner with only a 20pf cap. How would I lower both ends down at the same time? I assume this involves doing something different with the inductance side of this tuned circuit? Maybe adding a 13th turn?

BTW, the tuner I'm using is supposed to be a 365pf according to the parts list of the signal generator I salvaged it from. My cap tester agrees and says it ranges from 10 to 360pf. To get 20pf, I used a trimmer from the same generator. It ranges from 5 to 35pf.

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Fri 13, 2019 10:07 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2384
Location: Saskatoon
I ran your numbers through a spreadsheet and a couple of online calculators, and for those combinations of capacitance and tuned frequency, it comes up with an inductance value of 197.71µH for your loop, and a self/stray capacitance of 13.86pF. Your inductance value is a bit low for the AM band and your tuning cap.

With those values, there's no way to add any fixed value of capacitor to get it to tune across the AM band. If you add a 13th turn to the loop, it would increase the inductance 224.14µH. Then adding a 15pF fixed cap in parallel would give a range of 540 to 1700 kHz which just barely covers the band (if you exclude 530 kHz).

It looks as if your turns are spaced about 1/2 inch apart which is more than necessary. If you move them closer together, you can increase the inductance to a better value. For example, a spacing of 1/4 inch would give you about 227µH which would be easier to configure for the AM band. Even better, use a spacing of 1/4 inch and add a 13th turn, which would give you 260µH, and would easily cover the AM band with a fixed 10pF cap in parallel with the tuning cap.

http://electronbunker.ca/eb/InductanceCalcRc.html
http://electronbunker.ca/eb/BandspreadCalc.html


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Fri 13, 2019 11:19 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 181
BobWeaver wrote:
I ran your numbers through a spreadsheet and a couple of online calculators, and for those combinations of capacitance and tuned frequency, it comes up with an inductance value of 197.71µH for your loop, and a self/stray capacitance of 13.86pF. Your inductance value is a bit low for the AM band and your tuning cap.

With those values, there's no way to add any fixed value of capacitor to get it to tune across the AM band. If you add a 13th turn to the loop, it would increase the inductance 224.14µH. Then adding a 15pF fixed cap in parallel would give a range of 540 to 1700 kHz which just barely covers the band (if you exclude 530 kHz).

It looks as if your turns are spaced about 1/2 inch apart which is more than necessary. If you move them closer together, you can increase the inductance to a better value. For example, a spacing of 1/4 inch would give you about 227µH which would be easier to configure for the AM band. Even better, use a spacing of 1/4 inch and add a 13th turn, which would give you 260µH, and would easily cover the AM band with a fixed 10pF cap in parallel with the tuning cap.

http://electronbunker.ca/eb/InductanceCalcRc.html
http://electronbunker.ca/eb/BandspreadCalc.html

Thanks Bob. That's very informative. You went to a lot of trouble, and I appreciate it! Since I do have the loops 1/2" apart, I will take your advice and cut slots in between them and go for 13 loops with 1/4" spacing.

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Fri 13, 2019 11:28 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 8402
Location: Beautiful Downtown Burbank CA
...and would easily cover the AM band with a fixed 10pF cap in parallel with the tuning cap.

Is there a "built in" trimmer that could tightened?


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Sat 14, 2019 12:27 am 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 181
Mike Toon wrote:
...and would easily cover the AM band with a fixed 10pF cap in parallel with the tuning cap.

Is there a "built in" trimmer that could tightened?

No trimmers on the tuner, but the generator had a small 5-35pf variable tuner in parallel with the main 365pf one. I've been using that smaller one to experiment with more capacitance. Just got done tearing the frame apart and cutting slots every 1/4".

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Sat 14, 2019 2:36 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34389
Location: SoCal, 91387
Here's a link to a thread I did about making my loop;
viewtopic.php?f=12&t=241661&p=2024254#p2024254

The first post gives a link for the gimbal, and has scans showing how close the wiring is (right next to each other. The 7th post displays my experimentation with the different number of loops. I did make a mistake in this thread, stating that the tuner had a 405 pF maximum capacitance. Rather, it has 525, going down to 23 pF.

Now the ways to change the frequency range would be to either swap the tuner, or change the number of turns on your loop. Since it's larger than mine, it would seem to require fewer turns. I base that on the fact that my Grundig AN-200 has a smaller loop, with more turns, than my home brew which is larger in size, with less turns.

You might consider 11 turns, and trying a different tuner.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins/////////////////////////


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Sat 14, 2019 4:36 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 8402
Location: Beautiful Downtown Burbank CA
Doesn't more L and less C equal better reception?

Our transmitters should have as much L as not to waste power in the C air.

Or doesn't it matter for receiving.

I know we are talking about his total band coverage.


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Sat 14, 2019 4:58 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 14990
Location: S. Dartmouth MA 02748-1225 USA
moallen wrote:
Mike Toon wrote:
...and would easily cover the AM band with a fixed 10pF cap in parallel with the tuning cap. Is there a "built in" trimmer that could tightened?
No trimmers on the tuner, but the generator had a small 5-35pf variable tuner in parallel with the main 365pf one. I've been using that smaller one to experiment with more capacitance. Just got done tearing the frame apart and cutting slots every 1/4".


Many 20's era loops had taps for the turns and were often either OEM or added a resonating condenser 400-500pf maximum.

Current experimenter trend is to use a dual/quad 500pf variable or greater, float the rotor and place one or 2 stator sections on each side of the main loop windings. Using SLF cut plate variable is a definite advantage at the higher end of the BC band...

There are a couple of loop projects running on the Radio Board. Experimenter slogging through ideas, often finding that the loop calculators give results under ideal conditions. Loops built with the software calcs, are not performing as anticipated...

Chas

_________________
I'll admit to agreeing only to what I know is true.


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Sat 14, 2019 6:39 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2384
Location: Saskatoon
Chas wrote:
...often finding that the loop calculators give results under ideal conditions...


It's not so much that the calculators assume ideal conditions, but that the calculators are only suitable for a certain range of coil length/diameter ratios, and people try to use them outside of their usable range. For the calculators on my website, I've been very careful to point out what range they're accurate over.


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Sat 14, 2019 2:54 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 8883
Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
BobWeaver wrote:
Chas wrote:
...often finding that the loop calculators give results under ideal conditions...


It's not so much that the calculators assume ideal conditions, but that the calculators are only suitable for a certain range of coil length/diameter ratios, and people try to use them outside of their usable range. For the calculators on my website, I've been very careful to point out what range they're accurate over.


Agreed. Several years ago I was experimenting with home built transmitters for AM use and I found that winding coils according to the "formulas" (formulae?) was not getting me spot on. I bought a General 650 bridge and soon found that I needed to wind some allowance into my coils, the allowance being windings that I could remove to fine-tune the coils.


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Sat 14, 2019 3:52 pm 
Member

Joined: Sep Thu 26, 2019 1:56 am
Posts: 181
Ok - I've rebuilt my 36" tuned loop antenna according to Bob's suggestion of 13 loops 1/4" apart. I placed my single pickup loop 1/4" outside the 13 loops. This configuration yields a range that is a close match to the range of my old radios. The high end is 1690kHz, and the low end goes a bit below 520kHz. Of course. that isn't high enough for the newer stations above 1700, but my old radios can't get them anyway.

I plan to spend more time on Bob's website. Lots of good information there!

_________________
KC1LML
Peterborough, New Hampshire USA


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Sat 14, 2019 7:03 pm 
Member

Joined: Feb Sat 08, 2014 7:43 pm
Posts: 76
Location: Denver, CO
Nice job, moallen. Very neatly done.


Top
 Profile  
 
 Post subject: Re: Another Tuned Loop Antenna
PostPosted: Dec Sat 14, 2019 10:05 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2384
Location: Saskatoon
moallen wrote:
The high end is 1690kHz, and the low end goes a bit below 520kHz.


Not bad at all. Is that with a fixed cap in parallel, or without?

You could probably bring the range up just a touch by putting a 0.0068µF padder cap in series with the variable cap.


Top
 Profile  
 
Post New Topic Post Reply  [ 22 posts ]  Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 4 guests



Search for:
Jump to:  






























-->


Privacy Policy :: Powered by phpBB