So I would like to use the SStran AMT3000 in the longwave band, to achieve this C30 a 180 pF capacitor must be changed to a slightly higher value.
The pll with 180 pF cap installed will only allow the amt3000 to go as low as 350 KHz, anything lower and the pll won't lock on to say 170 khz.
So i did a search for a 190 pF capacitor, hmm wasn't many to choose from, so what gives?
Should i search again or is there a value slightly higher than 190 pF?
I am sure the part exists, maybe google isn't my friend anymore.
My idea is to transmit on 170 KHz LW using the SSTran even though the FCC rules allow for 1 watt, i would be happy with the 100mW -+ into a 50 foot vertical.
And I would have the Talking House 5 handle 1620 KHz duties.
I am wondering if it would be better to install a mica compression trimmer cap with a value range of 190 pF to 760 pF. The original cap is ceramic.
Hmm, i may not order anything at all. Looks like i have a 200 pF ceramic cap here.
Below is an analysis of a longwave AM setup using a ~50' base-loaded monopole, 75 mW of unmodulated r-f output power at the input to the loading coil, and an r-f ground system loss of 50 ohms (about typical for a ground rod).
Note that:
1) The internal loading coil of most commercial, Part 15 AM, MW transmitters is not able to provide the inductance value needed to resonate this LW antenna system, and
2) Even if it did, the very low groundwave field strength that system could produce even at 1 km (and beyond) would not provide very useful reception to receivers due to the high ambient r-f noise level in the LW band, and the narrow r-f/a-f bandwidth of that transmit system (which is much less than telephone quality).
That's actually fine with me, first few months of broadcasting on the LW band will be a simulcast of 1620 khz until i find a suitable keying circuit for the amt3000.
My idea is to use some kind of auto keying circuit much like the ham use on 10 meter beacons and in other bands. The narrow bandwidth would not matter much if the transmitter is only transmitting tones. In this case CW.
If you need the cap value to be accurate without varying with temperature changes don't use a ceramic, use one of the other types like polyester, silver mica, mylar, etc.
Mark
Deleted.
With C30 = 180 pF and R23 = 4.7k the datasheet for the 74HC4046 shows it should operate below 170 kHz without changing these values. In fact, I built a similar PLL which operates down to 20 kHz but it uses a different loop filter. It is a matter of setting the DIP switches for the frequency you want.
If you do want to change the cap remember that capacitors in parallel add so you can increase it by putting another in parallel but I don't see that this is necessary. You mentioned that yours doesn't lock below 350 kHz which might be a limitation due to R23 and C30 but it could also be that the loop filter needs to be changed.
Neil
Rich is confused perhaps?
The changing of the capacitor i mentioned in my original post has only one purpose, that is to open up the lower frequency limits of the pll circuit to allow for frequencies below 350 KHz, otherwise no matter what settings the dip switches are set at below 350 KHz , the pll will not lock. ( could try setting the tx for 170 all day and it will not lock )
Right now the AMT3000 is at the default settings as long as the 180 pF capacitor is inline with the pll, that frequency range starts at roughly 350 KHz and ends at 2560 KHz, IF the capacitor located and identified on the board as C30 were to be changed to a value higher than 180 pF the Frequencies below 350 KHz open up in that portion of the PLL but there is a trade off, you lose some of the upper frequencies.
That's fine with me, I have no business transmitting a signal no matter how weak it is , in the bands starting from 1705 KHz to 2560 KHz, some of which are ham,marine and tropical and if i am not mistaken, some areonautical.
Most hobbyist lump the frequencies 1800 to 2560 as being shortwave,
not true, it is actually medium wave.
Neil,
I think we were composing our posts at the same time and i failed to see yours until after i submitted my response.
Phil sent me a message after i inquired about the frequency range of this pll, he wrote:
I attached a PDF of showing the entire frequency range covered by all switch settings. The PLL won't lock below about 350 kHz unless cap C30 is changed from 180pF to a somewhat higher value. This would be at the expense of reducing the highest frequency lock range. C30 essentially determines a frequency range "window" which is smaller than the entire switch coverage range of 20 kHz to 2,560 kHz.
The output tuning should cover the entire range from ~350 kHz and up for a 3 meter long antenna. If you use a longer antenna, the LF frequency range will go lower, so if you can't tune a particular LF frequency, you can lengthen the antenna until it tunes, or increase the output tuning inductance. If the output tuning won't tune to the highest frequencies you may need to reduce the output tuning inductance. See the graph "Frequency Range Graph for 3 Meter Antenna" on page 34 of the manual.
I have not been able to tune below 340 Khz
Barry,
By all means try Phil's suggestion about increasing C30 but if it doesn't work then maybe the loop filter can be changed.
I recall years ago designing PLL circuits using the CMOS equivalent of the 74HC4046 and the free running frequency of the VCO would vary +/- 40% from chip to chip with the same R and C used to set the frequency. It could be that the chip I have favors the lower frequency whereas yours doesn't.
You could also lower the frequency by increasing R23. This might be easier than changing C30.
Neil
Can you tweak that chart to reflect what those numbers would be with 1 Watt input to final? i'm assuming with an efficient final section you would get about 700mW tpo to antenna.
Part 15 Engineer,
700 mW i assume is your ball park figure, correct?
I am wondering if it wouldn't be much less if we take into consideration the larger coil or coils we have to work with on LW. Still, even if it is say, 500 mW +- that is way more than we can ever hope to see come from a 100 mW MW system with a much smaller coil.
I have seen some rather large coils for matching a LW transmitter to a 15 meter (50 foot) vertical.
Imagine the losses.
Just out of curiosity as to what could be involved with a loading coil for this project, I used Rich's number for 5228 uH and ran it through a design program. The results are:
Wire: 18 ga. enameled magnet wire
Turns: 228
Coil diameter: 7 1/8 inch
Coil length: 10 13/16 inch
This is rather big but it is doable.
Neil
Quote:
Wire: 18 ga. enameled magnet wire
Turns: 228
Coil diameter: 7 1/8 inch
Coil length: 10 13/16 inch
This is rather big but it is doable.
I agree Neil, some where on this forum or the alpb forum i posted a ham operators LW set up and i am going to find it so i can re-share the link here. I hope.
His coil was a monster!
Be back in a bit.
two links but not the exact links i was looking for.
The old video on Youtube of JAM 187 LW Transmitter is a bit fuzzy and hard to follow and the webpage for WD2XFJ (ex-'PLI') 183.5 kHz Super-LowFER Beacon
(FCC Part-5 licensed; ~150 watts input - 1 to 2 watts ERP) shows a large coil for 183 khz which should give us all an idea how big this can get.
Also i have not changed the capacitor on the sstran for LW below 350 Khz just yet, it's been busy here and what free time i do have, my hands are too shaky to mess with a soldering iron. Eh, maybe tomorrow when things have calmed down around here i can try to have that changed out.
For now enjoy the links.