Since the two AM transmitters and antennas just got a very complete tune up, with the new AMT5000 and all, it was time to check out Big Talker, the shortwave transmitter at 13.560mHz. It has been running everyday since being built but I checked it out and re-adjusted the power.
I backed off the modulation a bit, since the audio quality is so crystal clear it sounds like an FM station, and I don’t want those highs to splatter too much.
The power is set at 495mW, which is high, but since the antenna is still indoors I doubt that it matters very much.
Once the antenna is outdoors I’m backing down to PhilB’s recommended 45mW.
Hi Carl!
45 mW seems high to me for an outside
antenna. Am I wrong, my friend?
(Well – into a dipole – that’s what I
was thinking.)
Best Wishes,
Bruce, DOGRADIO STUDIO 2
Could Be
Hey MICRO Dog!
Back during the design of Big Talker PhilB ran some simulations and posted a beautiful antenna chart for achieving the FCC allowed power level at 13.560 using 3-different antenna types, including a dipole.
He said that in each case the average power to the input of the final would be 45 mW, taking into account the various inefficiencies and losses that would be normal.
The only version of Big Talker that goes down to 45mW is the PhilB version. The Radio8z circuit has a higher power range, for us indoor users and anyone with a poor antenna.
Proper Power
Guys, there is no way a guesstimate from a software program or just pulled out of a wabbit hat is going to be adequate in assuring that field strength limit is not exceeded.
Once again….man I need a parrot for this….real world conditions do not occur in virtual computer programs and assumptions based on one location or observation that is applicable to all does not fly either.
Your going to need to measure that signal off that external antenna as it is in the environment it is built for. Unless Phil lives next door to you, 45 mW may not be enough, or too much simply due to the variances from one location to another.
Maybe start out at 45mW and call a two way radio place and arrange for one of their techs with those fancy IFR’s to come measure your field strength. (hopefully they have a Motorola instead)
Added: Does this antenna chart include all the thousands of variables from location to location or just figures picked out of thin air created by a software program? Did the chart account for all the environment variables as well? If it does, that must be one HUGE chart!…is it?
I think we have had enough of the “out of thin air” via the financial system to be spreading that over into engineering.
JMO
RFB
Hi Carl abd RFB!
Nice to hear from you guys.
Thanks for the info and I hope all
is well.
Bruce, DOGRADIO STUDIO 2
The Antenna Simulation
Here is PhilB’s antenna simulation for 13.560mHz SW
http://www.kdxradio.com/am_files/bigtalk_antennas.txt
This simulation is the only document of attempted compliance available, as without it there’s no available way of verifying compliance, except the very costly step of hiring an engineering professional.
Updates
“This simulation is the only document of attempted compliance available”
Maybe adding more data with field results to the document would be beneficial. As to the expense of finding an engineer who could perform the measurements on site, that can be overcome by getting to know one and negotiate.
Bartering is still a viable option.
RFB
Hmmm
Interesting indeed.
As to the expense of finding
As to the expense of finding an engineer who could perform the measurements on site, that can be overcome by getting to know one and negotiate.
Bartering is still a viable option.
Buy him a beer
Shortwave Question
how do you set up a shortwave TX and antenna is it like AM or FM, or is it completely different? can anybody explain it to me, because honestly i have no idea?
thanks
Shortwave Part 15
Glad you asked that question, ABMedia1
This would be a good time to clarify the Part 15 rules for shortwave, which are different from either AM_MW or FM. It has been awhile since these details were posted.
The rule most often discussed pertains to broadcast at 13.560mHz, which allows higher power (as measured in the field at a distance) and any kind of antenna.
15.225 (a) Operation within the band 13.553 – 13.567 mHz
(13.560 is in the very center of that band)
I will let you look it up for yourself.
There are other rules for other shortwave frequencies which are in the same general section of the rules, but they have very low power levels.
You Are The Only One
Carl, you are the only person in our group that
is actually transmitting Part 15 AM on 13.560 MHz.
As far as we know.
There was that nice guy in Germany (?) that was
experimenting there. And one member of our
group had been on there at some point. But we
don’t know if either of them are still on.
I wish I could finish my unit. It will happen at some
point.
Meanwhile, I wish I lived next door to you, Carl. I would
park my old Hammarlund (SP?) HQ-140X on 13.560.
That would be fun!
Bruce, DOGRADIO STUDIO 2
Round Trip Radio
Bruce MICRO Dog 2, if you lived next door with your Hammerlund (is that right?) you could listen to me and I could listen to you and we could call it Round Trip Radio.
The guy in Germany is in France, Radio Bon Esprit, and I haven’t heard from Bertrand since he got his 13.870 transmitter on the air.
The other SW on the site is WILCOM LAB but I don’t know the status of his station.