Using the shortwave transmitter designed by members of part15.us and named “Big Talker,” KDX-SW in the center of north america has been transmitting daily at 13.560mHz in the 21-meter band.
Using the shortwave transmitter designed by members of part15.us and named “Big Talker,” KDX-SW in the center of north america has been transmitting daily at 13.560mHz in the 21-meter band.
The 21-meter band spans from 13.500 to 13.870mHz and is usually fairly inactive from our location, but over a period of months we have scanned the band and found international stations operating on 18 different frequencies.
Most of the stations we hear are broadcasting in the Spanish language, suggesting they are active in the south american region, but the occasional English speaking station is heard.
This morning between 10:30 and 10:40 AM CST we monitored WWCR from Nashville, Tennessee on 13.845 operating with 100kW on their Transmitter # 3. The program in progress was from libertylive.com. According to the station website at wwcr.com the station also carries the popular GCN Network, home of The Alex Jones Show and Free Talk Live, two syndicated U.S. shows carried by many AM & FM stations and webcasters.
As of the present time we have not overheard any other broadcasts on our own frequency at 13.560mHz.
Life is grand on the 21-meter band.
Band Of Silence
The 21 meter band is inactive around here. Just the rare skip that moves in now and then.
RFB
21 Meter ISM Band Signals
I checked this band at 2:23 EST here in Central Ohio and found the noise level abruptly rose from S1 to S7 at 13.553 tuning up from below this frequency. The noise continued up to 13.56570 where splatter from a broadcast station was heard. The station was a religious program on 13.57000 where the signal was 5 over S9.
The abrupt appearance of noise in the ISM band makes me wonder if there is a bit of ISM activity here. It covered the whole band up to where the splatter was heard.
Do shortwave stations run IBOC?
Neil
logging contacts
I turned off my 13.560000 AM and logged the following stations:
GNK on 13.563 CW,
IH on 13.555 CW,
big AM broadcaster on 13.570.
Carl,its actually 22meters!
If you dont hear any activity,you need a better antenna!
Check out this link: http://www.lwca.org/sitepage/part15/
Meter Measure
Thanks for that new link, WILCOM.
My Sangeon ATS 505 has an imprint that lists the bands by meters and frequency, and it says: 21-Meter Band 13.500 to 13.870mHz.
Now that it is the 22 Meter Band, I need to change my announcements and website mentions.
WILCOM, do you mean you turned yours off momentarily, or permanently?
Good question, Neil: does SW have IBOC so-called HD-radio?
Part 15 neither has IBOC nor any interest in ever having it.
21 Meters Quiet? – 20 Meters Hot!
I mentioned my MFJ Cub 20 meter QRP transceiver in the Big Talker post. The thought was that I would retune it from 14 mHz down to 13.55 mhz.
I haven’t tried that yet because when I got it out I started using it on 20 meters.
The band is good! With only 1.2 watts into 100 feet of old RG-58 to a loaded dipole at 30 feet, I was able to QSO with North Carolina and New Jersey. I’m close to Akron, Ohio so they’re a fair distance away.
That said, Carl, I’ll be listening for you on my short wave. Do you have a schedule?
Schedule Yes
Great MRAM, my schedule is here
http://www.kdxradio.com/schedule.html
The 13.560 is always on during the whole schedule.
I still have the antenna indoors.
Trying to plan an outdoor antenna has to be juggled with also planning two 3-meter poles and the long wave 50-foot antenna.
I may just slap an outdoor 13.56mHz antenna out there in a temporary location.
Have Schedule – Will Listen
Simul-Casting, OK!
I’m thinking when you get that antenna out and up I may have a chance to hear your signal.
The END FED DIPOLE looks like an easy to make and install antenna.
The typical dipole is center fed making it a little harder to install.
I bought the torroid cores to make one. Hope to get it up before the snow flies.
Not End the Fed
We are not talking about “end the fed.” No. This has to do with the End Fed Dipole, and I love it! Thanks MRAM.
Indeed, I was hanging up on trying to figure out where the center would be and where the two ends would be. I was thinking “inverted vee.”
But right now, no deliberation, it’s going to be End Fed!
I’d go out there right now if it wasn’t after dark.
Strange activity as man works in the dark doing something in his yard.
All Wound Up…
The article mentions the original design used coiled up coax to form the RF choke (balun.)
Might be worth a try to save a few bucks. The torroid cores cost $26 with shipping.
Also Mention
During the design of Big Talker the part 15 shortwave transmitter PhilB ran some simulations and determined that a half-wave (or was it quarter wave) vertical with ground radials would be very efficient, and that may be tried sometime.
But for a first outdoor venture on shortwave it will be END FED DIPOLE.
The $26 will be no obstacle.
Get ready.
Article
Is that an information publication or an advertisement flyer?
LOL!!
Replace that massive boat anchor balun and all that coax and put the TX right at the feed point with an output tank built for a long wire. With the power limitations to Part 15 for this frequency, all that coax and huge choke will absorb so much of that signal it would be lucky to get a tenth of the tenth watt out of it!
And do not forget to put relief springs at the end of your long wires and support ropes!! A light wind will snap this thing apart like as if two trees were playing tug of war with your new end fed dipole!
RFB
Dizzy in the Head
I am feeling dizzy and might fall down.
From down here I can look up at the sky and see where the antenna was.
So, ah, now what?
Oh you may have said something about that. Dizzy. Busy.
See you later.
Objects Are Closer Than They Appear In The Mirror…
Massive? The balun core only measures 1″ X 2″ and the RG-174 is very light-weight.
What’s the point in going to the extreme of placing the TX at the antenna when you’re not limited by TX power output? Rather, the limit is on field strength.
So run out cable and adjust for field strength from the comfort of your arm chair. Much easier.
By the way, most publications include advertisements to cover the cost of publishing.
Out In The Open
“Massive? The balun core only measures 1″ X 2″ and the RG-174 is very light-weight.”
Anything sticking out in the wind like that poses wind loading as well as being subject to the elements. At the very least, wrap it up in household shrink wrap.
“What’s the point in going to the extreme of placing the TX at the antenna when you’re not limited by TX power output? Rather, the limit is on field strength.”
Because just like the field strength limitations on the FM band, having the TX right at the antenna equals better signal transfer efficiency. Having all that coax length and balun only means you have to crank up the TX power to compensate for their inherent looses, even if those looses barely hit a half pint db above negative 1. At Part 15 flea levels getting the most efficiency is part of the effort isn’t it?
Just tossing out there what I would do if I wanted that 13.56Mhz signal to really make some serious as possible DX range.
RFB
simple and cheap
Hey fellas,do the basic dipole,no choke needed,works better than an end fed too. And do put your transmitter indoors,there are so many advantages to this as well. Cable loss will be pretty low at 13 mhz,dont worry so much about that. Worry more about the required frequency stability that you need the indoor stable temps to accomplish. And you can work and tweak away all winter,cozy and warm! Something happened to my antenna in this latest windstorm,so my 13.56AM is down for now,,,
Missing Something?
Am I missing something about the outdoor mounting of the tx? Since the limit is on radiated field strength and not tx power there is no advantage to minimizing the coax/balun loss at these power levels and overall efficiency doesn’t matter. This is different that the situation on the BCB and LW where the power input is limited.
As mentioned earlier just adjust the power to get the field strength needed and keep the tx indoors.
Neil
this is your brain on AM BC band
Only the AM broadcast band and the longwave band rules call for power outpt limits and makes you want to mount the transmitter near the antenna ,all other part15 stuff is rated in field strength radiated irregardless of feedline length. This leaves us the old problem of not being able to measure it,so we have to calculate it including feedline loss and antenna gain which gets us close enough.
Antenna Predictions
These are some antenna simulations prepared by PhilB for the Big Talker SW Transmitter Project.
ANTENNA & FILTER TALK by PhilB
Submitted by PhilB on June 21, 2011 – 03:49.
Here are simulation results for some antennas from EZNEC at 13.56 MHz:
Half-wave dipole elevated 20 ft:
Len: 34.7 ft
Impedance: 88.9 – J 0.01388 ohms
2:1 SWR bandwidth: 1.2 MHz
Gain: 7.14 dBi at 65 degree elevation angle
(sky wave), bidirectional
Field strength at ground level at 30 meters with .0025W antenna power: 661.36 uV/m RMS
Half-wave dipole elevated 30 ft:
Len: 35.58 ft
Impedance: 89.31 + J 0.1196 ohms
2:1 SWR bandwidth: 1.25 MHz
Gain: 7.32 dBi at 37 degree elevation angle
(sky wave), bidirectional
Field strength at ground level at 30 meters with .0025W antenna power: 3,857.04 uV/m RMS
1 quarter wave vertical at ground level:
Len: 17.6 ft
Impedance: 36.07 + J 0.2016 ohms
2:1 SWR bandwidth: .95 MHz
Gain: 5.15 dBi at zero degree elevation
(ground wave), omnidirectional
Field strength at ground level at 30 meters with .0025W antenna power: 16,237 uV/m RMS
COMMENTS:
The quarter wave vertical appears to be the clear winner for maximum ground wave signal in all directions. It was modeled with a #12 wire. The wire could be attached to a 17.6 ft length of PVC pipe. It might be good to construct it with several tapering sections of pipe to reduce overall mass while maintaining strength at the bottom. A ground rod and at least 4 17 ft radials are required for lightning protection and RF ground. Use 50 ohm coax with a vertical.
Even though the dipoles perform worse for ground wave propagation, they can be brought up to the FCC max 15,848 uV/m level by increasing the transmitter power to compensate. Choose a dipole if you want bidirectionality. Use 75 ohm coax with a dipole.
The antenna power level of .0025W was used in all models. It gives close to the FCC field strength limit for the quarter wave vertical. Actual transmitter input power will probably be around .005W (5 mW) to account for an estimated 50% transistor + filter efficiency. Results may vary.
FIELD STRENGTH AT DISTANCE:
For the vertical with 16,237 uV/m at 30 meters, the range for perfect ground will be as follows:
30 m: 16,237 uV/m
.5 mi: 615.62 uV/m
1 mi: 307.82 uV/m
1.5 mi: 205.21 uV/m
2 mi: 153.91 uV/m
2.5 mi: 123.13 uV/m
3 mi: 102.61 uV/m
Beyond .5 to 1 mi, the local ground conductivity will reduce the ground wave below the values shown. The FCC has “inverse distance” graphs that can be used to show the effect of ground conductivity on the ground wave field strength. It ain’t easy. Bottom line: expect less range depending on your local ground conductivity.
FILTER REQUIREMENT:
All antennas show resonance below 3:1 SWR at ODD HARMONICS, so a low-pass filter is mandatory.
Simulations
Simulations only go so far in the real world. Useful for a starting point, but totally useless when its time to string up that antenna over that less than perfect real world ground next to all that real world RF absorbing objects like trees and nearby buildings and effects caused by constant weather and environment changes.
Finally, anyone running ANY TX on ANY frequency without a filter should NOT be running ANY TX at all!!
At least that is how I view it. It has always done me good and because of that, I do not veer from that practice.
RFB
Missing Nothing
Your not missing anything. It is merely a different way of doing the same thing.
Besides, its more of a challenge and more of a learning experience than to just merely crank up the power to compensate.
To each their own.
RFB
Problem Measurements
“This leaves us the old problem of not being able to measure it,so we have to calculate it including feedline loss and antenna gain which gets us close enough.”
Any good engineer will tell you, even the FCC field guys know this…that their incredibly sensitive meter used to conduct viable measurements wont be at the fringe range of the limit, but rather at the half way point instead simply because at the 15uV level (close enough for 16uV) is in the noise and very difficult to detect accurately with all the spectrum junk and noise generated by everything else.
Ever see one of those Potomac’s in use during a field strength test? With your TX shut off, that meter picks up a micro-burst of any kind of EMF and displays it. So instead of wasting all day trying to get an accurate reading in the noise, they move to the half point and calculate what your field strength should be there, then take a reading and get far more accurate results.
Anyway as to my idea of what “I” would do with a 22 meter TX and placing it at the antenna is just that..what “I” would do and why not..considering I have a run of power and audio lines going out there to the antenna farm anyway.
But I don’t disagree with the TX being indoors feeding a coax to a long wire or dipole or whatever. If the rules allow it, why not. But I tend to think beyond the easy and always consider that there may not be on hand a length of coax available, or won’t be for the time being..therefore if I wanted to get on the air that badly, then what is the next possible configuration to do so with that outdoor antenna?
Could balance the output and run some twin lead or even twisted pair telephone wire, if that material is available and the TX is geared for a balanced output. All nice and dandy if those things are all lined up and in place in advance. But not everything lines up so neatly unless prepared well in advance.
So for quick and dirty ways to get on the air, why not throw it to the antenna feed point? Is it such a bad thing to not even put it into the possibility category?
I think not. After all, isn’t this all about experimenting and enjoying a hobby, or is it one size fits all one method one way only?
RFB
Can’t Have What We Want
I love it when there’s a choice. Like with 22-meters, the transmitter can be indoors or outdoors.
I hate it when there’s no choice. The AM or LW transmitter must be at the antenna.
In fact, I’d like to have one transmitter room where all the transmitters could be together. Can’t do it. They would interact and all the other problems.
Like to have all the antennas on one tower. No way.
Some Exceptions
Well not all situations call for limited feed line. A good example of that is the TH or iAM units and their “extender” antenna, which runs on a 60 foot length of 75 ohm coax to an outdoor antenna and tuning unit equipped with a ground slug to connect a ground. All FCC certified.
If that can be allowed, then there is no reason why just such a unit built for the LW band couldn’t get a fancy FCC number either.
Just because it does not exist now does not mean it cannot later. What would be said if today was the era before the Talking House transmitters with that external coax fed antenna system?
I can only imagine how many sore feet there would be after all the stomping and yelling of “not possible, wont be allowed blah blah”
And there is nothing standing in the way of anyone coming up with a design to be certified where a coax is used to feed an outdoor antenna on bands that sport that length limit when right now there IS just such a system carrying that certification. It may not be the LW band, but who says one cannot get a certification? Only time one can say with assurance is when their submission for certification is turned down. Until then, never say never.
RFB
More Than One
“In fact, I’d like to have one transmitter room where all the transmitters could be together. Can’t do it. They would interact and all the other problems.”
Can’t do it? Why not? Why won’t multiple TX’s in the same room not work..especially if they use a coax to feed an outdoor antenna?
You may run into issues if all your antennas are indoors in the same location near audio gear etc. But that is a given and to be expected with just such an arrangement.
But if transmitters could not be located in the same building, or multiple antennas on the same tower, there would be a ton of transmitter sites right now that would prove that assumption wrong right off the bat!
Ever hear of a “community antenna”? How about walking into a transmitter site building and seeing more than one transmitter in the room?
I can go up to Casper Mountain Radio Hill and show you 6 towers right now all with different types of antennas hung on them, all operating on different frequencies, with their coax lines all running into the same building. I am sure that exists elsewhere too.
For our purposes the choices are limited, but only to the extent of what you have on hand to use. If all you have is a kit designed to work at the butt of a loading coil outside, then that is what it is meant to operate under, not indoors with wires strung across the room shoving RF into every other wire and cord in there.
Anyway I do not mess with 22 meter stuff simply because that is not where the audience is. Oh ya there is the die hard radio DX’er who will sit there for hours picking out faint signals in the cluster of noise, and if they are lucky they “might” pick up your 13.56 signal…and that is a BIG might at these power levels. In any case, to me anyway, it is not where the audience is nor is where my targeted audience will be. If I wanted to broadcast to only the die hard DX’ers , then ya I might play around with it and hope more than myself sends me a QSL card. Other than that, to me anyway, it would be nothing more than a side project for amusement rather than any serious broadcasting efforts to serve the public interest.
JMO..no need for ruffled feathers.
RFB
More Tinkering Fun…
Reference the END FED DIPOLE, I now have the RG-174 coax and torroid cores so I’m going to try it out.
I’m going to cut it for the 20 meter Ham band, 14 mHz, but if it works well there then cutting one for 13.566 mHz should work also.
I’ll be running my MFJ Cub at 1.2 watts output so of course my radiated signal would be much stronger but, I’m interested in comparing it to the center fed, loaded dipole I’m currently using. It is what’s left of an old Mosley TH-3 multi-band Yagi beam antenna.
Maybe this weekend…
MRAM & the END-FED ANTENNA
MRAM, did you ever try your End-Fed and compare it to center fed dipole?
Where Does The Time Go…
I did get it put together.
It’s been a bit hecktic here but perhaps this weekend I’ll give it a try.
I believe I have enough coax to get it out by the horizontal loaded dipole. That way I can switch between the two for comparison.
If you have a 20 meter receiver perhaps we could coordinate test reception on your end. The horizontal is aimed more or less East/West.
20 METER RECEIVABLE
Yes, I can check the 20-meter region. Just tell me what to look for.
Testing, Testing…
The XYL has a long list for me today but if I can hang the wire, I’ll let you know.
I’ll give you the frequency and send some ***- ***- ***- -** * -*- *- —** **-* ***- *– which translates to VVV DE KA8FVW.
Email me your phone number, I’ll call if I can get this going today.
BIG TALKER TIME
The Big Talker Shortwave Transmitter has been running several months now and yesterday I decided to tinker with it.
I removed power from the final RF stage and noticed that the carrier from the 2-stage front-end (oscillator, buffer) was still getting over to the Sangeon radio 13-feet away.
Checked the voltage to the oscillator-buffer and it was 9VDC, according to specs. So I wondered how low it could go.
At 4.5VDC the oscillator-buffer dropped out, so I set the voltage at 5VDC.
Next, reconnected the final stage and turned the DC as low as it would go, which was 2.9VDC. Measured the current in the final which was 9.9mA. Therefore the output power was 28.7mA.
Then I went back up in power and set the oscillator-buffer at 9VDC, the final way up at the top of iots range, which was 15VDC. Current on the final was 57mA, putting output power at 855mW. Almost 1-Watt.
Unable to think of any other variations to experiment with, I had dinner.
Idea of the Day
For most of the afternoon I studied the End-Fed Dipole Lite link presented earlier by MRAM
http://heartandhoof.com/radio/End-Fed-Dipole.pdf
And also I found the previous article mentioned in the paper and studied what it had to say.
I will be ordering the toroids and coax to build this for 13.560, but a whole new idea crept into the small space just underneath my hair-cut….
This question will be theoretical, since 15.219 does not leave enough length for a transmission line from an indoor transmitter to an outdoor 3-meter antenna, so what if……
What if this same end-fed design were used to drive an end-fed 3-meter vertical pole?
Since the transmission line on the transmitter side of this design does not radiate, it would meet the spirit of the rule and put all the radiance in the 3-meter vertical side of the circuit.
Comments?
Didn’t Work for KENC…
The thought being that by putting the torroid choke at the end just before the 3 meter radiator, the coax shield back to the transmitter would not become part of the antenna system?
Don’t forget, you’ll still need to put the loading coil just before the 3 meter radiator. And, you’d need some type of radial system to form the RF ground side of the antenna.
The end fed dipole uses 1/4 wavelength of the coax shield as the ground half of the dipole. The radiator (connected to the center conductor) is the other 1/4 wavelength. Together they form a 1/2 wavelength dipole.
In theory, I suppose your idea would be similar to Hamiltons idea of a choke on the ground lead.