Box Loop Update

[crainbebo]

I did a scan of 1280-1700 today at noontime. Antenna pointing E/W to avoid KIXI bleed.

1280-KLDY Lacey good
1300-KKOL Seattle
1320-KXRO Aberdeen very good
1330-KGRG Enumclaw excellent
1340-various stations (KWLE/KUOW/etc)
1360-KKMO Seattle
1380-KRKO Everett
1400-KITZ Silverdale pegging S-meter
1410-CFTE?
1420-KRIZ excellent
1430-KBRC Mt. Vernon poor-fair, but should point N
1440-UNID carrier (CKJR?)
1450-KSUH Puyallup very good
1460-KARR Kirkland
1470-KELA Centralia very poor (but should point S)
1480-KNTB Tacoma fair
1490-KBRO Bremerton pegs S-meter now.
1520-KKXA Snohomish
1540-KXPA monster
1560-KZIZ Sumner pegging S-meter
1580-unid carrier (Lahar TIS Puyallup?)
1590-KLFE Seattle
1600-UNID (KVRI?)
1610-Naval Kitsap Bremerton emergency TIS
1620-KYIZ Seattle
1640-KDZR barely from OR
1650-Redmond TIS + maybe Vashon
1660-unid carrier (KXOL?)
1680-KNTS Seattle
1700-Issaquah TIS (sounded like I was in town!)

-crainbebo

 

[crainbebo]

1650 is confirmed as WQHK904 Vashon Island. New #466 at 10w.

-crainbebo

 

[boombox]

That Vashon one on 1650 gets out pretty well at night. Seems to be a regular here at my QTH.

 

[boombox]

The box loop is finished! Highlights around 4:30PM

1700-Issaquah TIS went from nothing to a 35dbu, very good signal!
1670-KNRO Redding, CA went from threshold to 39dbu (1000w)

Unfortunately I do hear a LOT of 880 and 1150 bleed all over the band. East is the only direction to point. Nighttime is better (from 50kw-880/10kw-1150 to 10kw-880/6kw-1150). Anyway to help this? Or is the only option to go up in the Cascades? I live two miles from 880 and 1150.

-crainbebo

Try placing the radio farther away from the loop. You'll have to retune the loop a bit. You'll also lose a slight bit of sensitivity, but the overall setup will probably be more selective. It may reduce the overload from 880 khz.

Then again, it's possible that the RF from KIXI can't be defeated that way, because it's so strong.

But it's worth a try.

You can add some wire to the loop if you want to tune lower in the band with that capacitor. You could 'switch' it in and out with an alligator clip. With my (presently unused) 4 ft. spiral loop I had to use an extra capacitor to tune up past 1300, because I put too much wire on the frame. With the extra capacitor it would tune from the high longwaves to the top of the MW (don't recall how high).

 

[Schroedingers Cat]

The loop I built was actually from plans from an electronics hobby magazine, and was actually plans for a one transistor radio. It had a tap about 2/3 of the way through the windings. I didn't build the transistor radio, since I figured it was a decent antenna. I wonder if more windings and a tap would be a good solution. Remember that a switch becomes a capacitor when shut off, and may do unpredictable things if you switch taps with an actual switch. The alligator clip may be better because it avoids this.

Inductors also have a property called self resonance which has to do with the capacitance of the coil windings to each other.

In fact, many components have two or more significant electrical properties-coils have resistance as well as inductance and even capacitance. Switches have capacitance in the off position, and inductance in the on position, and different resistance in the on and off position. Resistors have inductance, more of course with wirewound than carbon. Capacitors have a less than infinite resistance.

All of these things have the ability to throw off your calculations, and can cause unpredictable behavior of a loop. That's why I prefer to have some plans and a good idea of the inductance of the loop and the capactitance needed. It's fun to experiment with these things, but the main thing is do your experimenting BEFORE getting things too invested in being permanent. You may want to build a prototype and improve on it, and build it more permanently later.

It's just an extension of "measure twice, cut once".

In another installment, I'll discuss some suggestions about building FM antennas.

 

[crainbebo]

I'd also love to get some NDB action here. When I lived in Bothell, I could get YCD-251 from Nanaimo, BC with ease. Very strong in the daytime. Used to be PA on 396 from Everett but it went silent last night.

-crainbebo

 

[crainbebo]

We built the antenna, but the capacitor does not work below 600 khz. Can we add a fixed capacitor in parallel to bring the frequency down, so I can get the 530-600 and NDB bands? Maybe R. Fry or Schroedingers Cat could help me out.

P.S. I had some great daytime DX today, and skywave is excellent tonight.
2:45PM observations
1270-KAJO Grants Pass, OR
1060-KBGN CALDWELL, ID
1280-KZNS Salt Lake City, UT
1290-KOUU Pocatello, ID
1320-KCTC Sacramento
1640/1660 Utah, all with the box loop.

Tonight, I can get KSTP to *PEG* the S-meter!!! WBBM is showing up fair under KKOH as well, and a DXer in NJ had CFAC tonight as well. So, great loop!

-crainbebo

 

[Schroedingers Cat]

R. Fry can check my math, but to bring the resonant frequency down to 530, it would require another 102.8 pF in parallel with a 365 pF capacitor, or about .0001 uF. Or add another 30 percent to the number of turns identically spaced to the rest. The resonance formula in general is f=1/2*PI*SQRT(L*C). So for a given frequency ratio of change, you have to square it to get the capacitance ratio or inductance ratio to achieve it. L is in henries and C is in farads. Most practical components use much smaller units of L and C, milli-, micro-, and pico-.

 

[crainbebo]

Thanks Schroedingers Cat.

And I made a mistake-PA 396 Everett went silent last YEAR, not last night...

-crainbebo

 

[rbrucecarter5]

We built the antenna, but the capacitor does not work below 600 khz. Can we add a fixed capacitor in parallel to bring the frequency down, so I can get the 530-600 and NDB bands? Maybe R. Fry or Schroedingers Cat could help me out.

P.S. I had some great daytime DX today, and skywave is excellent tonight.
2:45PM observations
1270-KAJO Grants Pass, OR
1060-KBGN CALDWELL, ID
1280-KZNS Salt Lake City, UT
1290-KOUU Pocatello, ID
1320-KCTC Sacramento
1640/1660 Utah, all with the box loop.

Tonight, I can get KSTP to *PEG* the S-meter!!! WBBM is showing up fair under KKOH as well, and a DXer in NJ had CFAC tonight as well. So, great loop!

-crainbebo

Fixed capacitor or more turns, probably only one or two. Be aware that you may need to switch the turns or capacitor in and out to cover 530 to 1700 - it is tough to do. If you add a fixed capacitor, be sure it is NPO ceramic or silver mica. If your tuning cap has another section, you can also use that.

 

[Schroedingers Cat]

Remember that to tune 530-1700 with a single variable capacitor without trimmers, the ratio of the maximum to minimum capacitance has to be (1700/530)^2=10.288+ or about 10.3 to 1. This means that the minimum capacitance of a 365 pF variable would have to be less than about 35.5 pF. Adding a trimmer in parallel would lessen the ratio, making switching necessary. I don't know what the typical capacitance would be of the switch in the off position, probably really small, so it would probably be negligible in the off position, and the series switch and trimmer would be less than the trimmer. Perhaps you could find a value for the switch capacitance online. It would probably be on the order of variation as when you put your hand on the shaft of the capacitor. Maybe someone here knows an approximate value.

 

[crainbebo]

12:45PM observations 12/05
1640-KDZR Lake Oswego
1510-KGA Spokane 220 miles
1440-KMED Medford, OR 380 miles

Pretty good results at day, even with the "Bellevue Trio" close (KXPA/KKNW/KIXI).

-crainbebo

 

[Tom Wells]

Remember that to tune 530-1700 with a single variable capacitor without trimmers, the ratio of the maximum to minimum capacitance has to be (1700/530)^2=10.288+ or about 10.3 to 1. This means that the minimum capacitance of a 365 pF variable would have to be less than about 35.5 pF. Adding a trimmer in parallel would lessen the ratio, making switching necessary. I don't know what the typical capacitance would be of the switch in the off position, probably really small, so it would probably be negligible in the off position, and the series switch and trimmer would be less than the trimmer. Perhaps you could find a value for the switch capacitance online. It would probably be on the order of variation as when you put your hand on the shaft of the capacitor. Maybe someone here knows an approximate value.

In order to get the high-to-low ratio high enough to tune the entire band, it is essential to keep stray capacities to a minimum.
This is why there needs to be space between each and every turn on a loop.
Closely wound turns touching each other results in a coil with too much self capacity.
It's also helpful to keep the 2 wires feeding the loop spaced at least an inch apart, or otherwise seperated.

Any place where the spacing gets close between wire increases the minimum capacity, decreasing the min/max ratio.
It also helps to use a >loosely< coupled pickup loop, rather than connect the loop directly.

Use or MAKE a wooden knob on the variable cap shaft, and/or extend the shaft with plastic/wood etc so there isn't any detuning from body proximity.

I built a superhet about 2000, and was lucky enough to score an old Zenith radio tuning cap with about 500 pf
in the max position, so it was able to tune a wide range without too much special consideration to minimize stray capacitances.

The less one has minimized stray capacity, the more likely it will be necessary to use switched capacitances to
tune the entire AM band.

I'd prefer to use a two pole switch to switch in/out additonal turns on the loop, or to short out turns selectivley
to change the inductance.

 

[crainbebo]

Well I tried the loop again tonight, and conditions are good to the East.

730-CKDM on top
740-CFZM Toronto, ON-this was on top with standards. Fair-good signal!!
780-WBBM right under KKOH
1500-KSTP huge
1690-KDDZ Denver under KFSG

-crainbebo

 

[radioman148]

Well I tried the loop again tonight, and conditions are good to the East.

730-CKDM on top
740-CFZM Toronto, ON-this was on top with standards. Fair-good signal!!
780-WBBM right under KKOH
1500-KSTP huge
1690-KDDZ Denver under KFSG

-crainbebo

Any sign of WLS? I would think the loop would help dig it out.

 

[cd637299]

Well I tried the loop again tonight, and conditions are good to the East.

730-CKDM on top
740-CFZM Toronto, ON-this was on top with standards. Fair-good signal!!
780-WBBM right under KKOH
1500-KSTP huge
1690-KDDZ Denver under KFSG

-crainbebo

It could be "880 trouble" for him....

cd

Any sign of WLS? I would think the loop would help dig it out.

 

[pianoplayer88key]

Well I tried the loop again tonight, and conditions are good to the East.

730-CKDM on top
740-CFZM Toronto, ON-this was on top with standards. Fair-good signal!!
780-WBBM right under KKOH
1500-KSTP huge
1690-KDDZ Denver under KFSG

-crainbebo

It could be "880 trouble" for him....

cd

Any sign of WLS? I would think the loop would help dig it out.

I would have thought that would have made it a bit less than easy to get WCBS....that is, if his local 880 is within 0°0'0.000001" of the same heading from where he's DXing...

 

[crainbebo]

I'm moving to Monroe, WA in a couple weeks (about 20 mi NE from here), so KIXI is not going to be as much as a problem there as it is here. I live currently two miles from the 50kw-D/10kw-N monster. WLS is out of the picture unless I go barefoot and find the right spot. There is one spot in the backyard where I can null KIXI down to regular "local" strength, and get mostly CJDC on 890. I logged WWL 870 due to that null!

Now, with the move I've hit another "whammy" again-apartment interference and noise. There is a balcony deck looking South however. However, I'm worried about noise from the new apartment, and from the hospital next door...

-crainbebo

 

[cyberdad]

Just tell the doctors to turn off all of their diagnostic equipment. You'll be fine. The patients? Tell them to take 2 aspirins and send you a DX-440 in the morning!

 

[kenglish]

OMG! Not an APARTMENT!!

Funny, but I got a reception report from a guy in Japan a couple of Christmases ago, He was listening to KSL (1160) with a loop on his apartment balcony! I don't know if he was just lucky, or he bribes his neighbors to turn off the TV's and computers. I should have asked him.