Back when you (RFB) reported that I could safely run at low wattage, your estimate at that time was that it might start oscillating at about 5Watts, but I found that it goes into oscillation at 3Watts.
Back at that time I ran for awhile at 2Watts, but this second time I'm being more cautious and only doing 1Watt, which seems to have good coverage.
"Back when you (RFB) reported that I could safely run at low wattage, your estimate at that time was that it might start oscillating at about 5Watts, but I found that it goes into oscillation at 3Watts."
The reason why I could run up to 5 watts before self oscillation is because I tested on an AM-30 unit, which it's low pass filter contains higher voltage rated caps in the lpf. At 5.5 it began to go into self oscillations.
What I did not report was that same test was performed on an AM-5 unit. It went into self oscillation at 1.7 watts. Both the AM-5 and AM-30 units are rigged for the low band.
See the reason why?
It's the different voltage ratings of the caps in the low pass filter. The AM-5 has lower voltage rated caps compared to the 2-20, and the 2-20 has lower voltage rated caps than the AM-30.
The intent was to see if your CC configuration would do well at the frequency of 970Khz. Apparently it does and that is good. Believe it or not, a CC configuration is not always workable across the entire MW band. Fortunately your configuration will work with both the lower portion of the band and the mid portion without having to modify or drastically change your CC connection configuration. Saves a lot of headache and needless work.
RFB
It is impressive how many themes and variations you are able to recite regarding the carrier current experience.
Carrier current Radio 970 is doing very well everyday at 1-Watt, and I just checked on the capacitor order, for rebuilding the output filter, and so far one of nine items will be in by June 21.
Even though the order seems unusually slow, I'm not going to complain because I am grateful a company would even have such rarely ordered items.
I'll be posting a picture of the setup as soon as I get some audio processing in the rack.
All at once when least expected I got a friendly note from Mouser about shipping the capacitors so I can build the low pass filter for the LPB transmitter operation at 970kHz Carrier Current.
It is one day before the Summer Solstice.
This proves that synchronicity is a word that comes to mind.
I was fiddling with The Crow's Part 15 Map of America and found
The Cat - Sealy, Texas, 580 kHz CC
bigvoices.net
Opened the door to get the mail and found a box from Mouser, containing the long awaited low pass filter capacitors.
Next step, shut down the 970kHz transmitter;
Take all apart;
Remove low-band inductors & capacitors;
Install mid-band inductors & capacitors;
Slap it all back together;
Test;
Triumphantly return to the air.
The whole expedition will be outlined here.
I'm very interested.
Please keep us informed.
Best Wishes,
Bruce. DRS2
Brought the LPB up from the lower parking level, put it on the work-cart, oh by the way today I got some new LED indoor bulbs to replace the compact fluorescents and they are much better. The new light is a mood improver.
Unscrewed the giant heat sink and unsoldered the final stage circuit card.
Removed the low-band capacitors and toroids.
Shut her down for the night. Will resume in the morning.
KDX will sign on at 10 AM minus the 970 signal, and the people who anxiously search for it will begin to lose their hopes, but probably by the afternoon the transmitter will start back up and smiles will spread through the town.
All day today all I did was examine the dismantled LPB RF Amp, study my documentation, and eventually rewind the toroids to prepare them for the AM mid-band.
The solder points on the circuit got solder-wicked so they would be clean and ready.
Working from left to right, four capacitors and two toroids went into place.
The RF section got reconnected within the case, a matter of half-a-dozen wires and cables.
The giant heat sink got re-attached, and the whole thing underwent a final visual inspection.
Carried the LPB transmitter downstairs very carefully.
Re installed it on its roll-around rack, RF cable, audio wires, A.C.
Turned it on and the power level shot up to 6-Watts!
When it was last turned off the power level had been set at 1-Watt. There was a huge improvement in efficiency.
I dialed it down to 2-Watts and re-calibrated the coupler.
The SWR is at an amazing 1.25:1, just a tad above perfect.
This is the work of RFB who supplied all the data needed for this job.
Many, many thanks
This week is "Low Power Week" here at KDX.
The LPB transmitter, which ran at 1-Watt NI (Neutral Injection) before the filter upgrade, was set all weekend at 2-Watt with the new filter.
But this morning, Monday, I dialed down to 1/2 Watt to mark "Low Power Week"
What does it all mean?
We have reached the stage where we are ready to bring in a professional field strength service to help us determine the permanent power setting.
I figure that if we start at very low power, the field test engineer can call me on his cell phone and have me turn up the power until it hits the sweet spot. But I need to install a telephone down by the transmitter. I do not have a cell phone.
In the meantime, the half-Watt doesn't seem at all weak on house radios.
"I need to install a telephone down by the transmitter. I do not have a cell phone."
Perhaps a "cordless" phone might help?
RFB
Thank you again, RFB.
Did I so soon forget that only recently I asked about the state of the art of cordless phones?
Perfect!
I'm really enjoying your CC journal. I had a CC station back in the early 90's, but had not heard of neutral loading at that time. Being on a farm, well, maybe the horses could listen. Once the signal hot the transformer out back, the signal vanished.
Sounded great in the house, though.
I'm really curious as to whether or not the CC setup (vs the iAM system) would be of any advantage. I'm out of the city limits on family property, so no HOAs or any of that nonsense to deal with.
A 75 year old radio colleague of mine, who is retired, has a Rangemaster on the air now on 1610 but is wondering whether a CC would be better. I didn't have an answer to that one! He
lives on the coast around Lanark Village, FL.
"I'm really curious as to whether or not the CC setup (vs the iAM system) would be of any advantage. I'm out of the city limits on family property"
Although neutral loading bypasses the utility transformer and allows the signal to continue down line, you still have to make sure that signal is not exceeding 221 in band and 209 out of band emissions.
An example. The frequency of operation is 600Khz. The formula (in feet) is 157,000 divided by frequency (600Khz) equals 262 feet (261.666666). This means that at 261 feet or so, that signal MUST hit 15uV, or the noise floor. So even if that neutral line carries your signal 20 miles down the road, the signal cannot emit any further off that line than 261 feet.
Carrier Current is NOT a far field radio transmission system. It is a near field, or inductive field system and relies on just that, the inductive field, which anywhere within the specification called for in 221, the signal will be rock solid crystal clear, even 20 miles down line from the source point within the 261 feet from that line.
A CC system can compliment a 219 setup. The 219 setup puts signal beyond 261 feet and into vehicle radios and portables no where near any power line or neutral line. And the CC system can compliment the 219 by sending signal directly into homes and businesses via that neutral line. Since CC is primarily a localized controlled range broadcasting method, it will make sure people who cannot pick up your 219 system will still be able to tune into your station via the CC signal coming right into their homes and businesses via the power grid wires.
Since your out in mostly open space with some distance between your location and another, a CC system probably won't be of any real good use except for ensuring that at night when skywave wreaks havoc on a 219 signal, the CC signal will not have that problem and folks will still get a rock solid crystal clear signal, unless you end up transmitting on a frequency that becomes occupied during the night from skywave, so pick a frequency where that will not happen if a CC system is being considered.
RFB
You've provided clear information that makes a lot of sense. Thank you for the response.
Alan