Well let's look at one popular item that uses a crystal and is mounted outdoors..the Rangemaster.
What keeps that thing from being affected by temperature swings? They do not have any oven, and are not inside vented cabinets.
Is the frequency drift a trivial matter since it is a low power unlicensed transmitter, or is the drift not that big of a concern due to the drift being miniscule?
I fail to see the significance of concern over outdoor temperature ranges when there are transmitters right now mounted outside in the ice cold snowy environment and little to no posts anywhere about these units having frequency drift issues.
And if they do drift, they must drift by only a few cycles, or have incredibly tight tolerance crystals built to military specifications. And military specifications call for temperature ranges between -50* to 150* F.
Unless you are living above the arctic circle or down below at the south pole, there is no way anywhere else that temperatures are going to swing that wildly in typical populated areas of the country.
Anyway..answering Carl's question...the best and cheapest way is to use a simple frequency counter being fed by a pick up loop near the antenna/transmitter setup. There will be enough signal present that a simple 5 or 10 turn coil would suffice to detect the signal and feed it to a frequency counter.
For those with the fortune of having a spectrum analyzer or communications service monitor, that of course is the preferred way. But a simple frequency counter and detector loop is good enough for either spot checking or continuous monitoring.
Neil, your idea of having the main oscillator indoors driving the signal down a line from a TTL or logic driver is a good approach, and similar to the idea I pitched here a few months ago about having the main oscillator indoors and the rest of the transmitter circuitry (final) outdoors at the antenna. But I think someone balked at that idea because of the feed line restriction for 209.
I see no reason why it could not be done and no reason why it would be considered outside of 209 when the actual final stage is at the antenna system...in essence and technically there is no feed line with final RF on it feeding the antenna outside. I believe the balking was because it is a viable and great approach that they wanted to keep people from actually trying it while they quietly in the background design such a system and market it as a kit.
RFB
Regarding the example of the Rangemaster not being affected by temperature, I don't know that it is or is not.
My interest in this is due to the co-channel stations I hear on my selected AM frequency, especially at night. Even during the day there is occasional fade in and out on channel. Keeping the frequency within 10 Hz of nominal just reduces another potential interference to an already weak signal. The interference will still be there but at least the growl or tone won't. I am not trying to give all of us another thing to fret about rather I am just sharing information.
For information, my pickup for checking the frequency is a shielded lead probe such as a 1X scope probe placed about 6 inches from the loading coil. The counter I use has enough sensitivity to lock onto the signal. Another note is modulation can cause error so this is best done with no audio.
Neil
You have just made my brain circuits compute the reason why I hear a growl at 1680 when I drive just to the edge of my signal. I means that either I, or other stations, are not perfectly locked on-frequency.
I will study the matter further.
Stations are not going to be precisely on frequency from one station to another..I guarantee it. The only way that can be done is to synchronize all the station's oscillators to a common reference pulse with delay compensation to feed the pulse at the proper time interval to every station in existence. Not practical!
Even if they all referenced to WWV, there is still propagation delay to compensate for. And they cannot use the 60 cycle frequency reference of the power grid either, as the frequency of the power grid also varies in phase from one grid array to another. This is why the power company does a synchronization prior to a switch over from one grid to another.
The only incredibly accurate frequency pulse reference will be an atomic clock, but only on to itself, again taking pulse propagation delay factors into account, even through a direct connection via a wire.
So the best we can hope for is being close and in the ball park as much as possible. There are simply too many variables to prevent everything from running precisely on frequency from one device to another over a distance.
This is why there is a specific frequency tolerance specification in the FCC rules. A +/- tolerance and stations
try to maintain within this tolerance. That is why instead of hearing a bunch of tone or growl, we hear a swooshing of the stations on the same channel which sometimes can even be counted by ear, and usually falls within just a few cycles.
Now if you want precise frequency control...you will need to purchase professional stuff, or buy very expensive precise crystals for your oscillators or PLL's or data buss clocks and those won't be cheap.
No matter how hard you try, you will never accomplish a 100 percent all the time accurate frequency that never drifts, it will always drift by at lease a few hz. And attempting to synchronize to a licensed station at some distance to prevent tone or growl..well good luck! The best you can hope for is the slight swooshing effect simply because your frequency will not be precisely in phase and rise/fall times as theirs. But your more than welcome to try! 😀
RFB
"My interest in this is due to the co-channel stations I hear on my selected AM frequency, especially at night."
I get this same effect on my 1670 frequency at night. Obviously it is not a problem within a several block area, but at the outer fringes of the CC coverage, it becomes a night time nightmare, especially during the winter.
This is why I switch over to the lower third of the MW band during the winter. A lot less skip activity down there and for some odd reason, the CC signal travels down the power line better on the lower frequencies in the winter than the summer. In the summer the station operates on 1670, in the winter, either 630 or 710, mostly 710 because KTWO 1030, a 50Kw clear channel station, floods 630 with one heck of a splattering ghost signal during their daytime pattern. At night when they switch patterns, that splatter mess goes away, but sometimes a station in Utah on 630 comes in pretty clearly so 630 is pretty much useless. 710 however, is clear all the time.
RFB
As you guys know, I love the local AM channels.
(1230, 1240, 1340, 1400, 1450, and 1490 kHz.)
A couple of years ago, I logged about 30 stations
on those channels. I was very proud of that.
My best DX was 399 miles away.
Then I lost the list. Now I have to do it all over
again because I don't remember all of the stations.
Some guys have been AM DXing those channels
for many decades. They have heard hundreds of stations.
It is very very hard to do, but it can be done.
Here, in Hartford, almost every night, I hear a hetrodyne
on 1400 kHz. I 'm not sure, but the offending station
is pretty far off, maybe 100 HZ or more. The het is usually
there. It just adds to the coolness of the whole DXing thing,
as far as I'm concerned. The funny thing is, the het sticks
out like a sore thumb in the gigantic jumble of stations.
But I don't see any way of telling where it is originates. It
would take A LOT of time and luck to figure it out.
Best Wishes,
Bruce, DOGRADIO STUDIO 2
"Here, in Hartford, almost every night, I hear a hetrodyne on 1400 kHz. I 'm not sure, but the offending station is pretty far off, maybe 100 HZ or more."
That is a lot. Will most certainly cause an annoying tone or growl.
Well whatever station is causing that will find out the hard way come the next inspection! Not sure what the fine is for operating beyond the frequency specs, but the station could be tagged for repeated violations if they do not correct it pretty darn quick.
RFB
Maybe that HET is a legacy station from the tube days still going strong with his Knight Kit!
Those Variable Oscillators seem fine on an old analog radio, which the guy probably has.
Maybe, maybe it's a ghost station from the 1950s that comes in only for Dog Radio!
With two days and nights worth of experience with the DNO frequency add on to my transmitter I am pleased to report that there is a notifiable improvement in my signal.
Here's the situation. My monitor radio is connected to my "big ear" dipole antenna which is in the woods behind my abode and it has been confirmed that the radio only hears signals from this antenna. So, essentially this radio is receiving my signal some 100 feet from my transmit antenna. For quite a while I have noticed hum on my signal and have tried the usual cures. The hum would come and go so it was difficult to get a fix on it or explain this. I even thought perhaps it was due to appliances cycling on and off but could not correlate the hum with anything.
Now I realize that the hum was possibly due to heterodyning with co-channel signals since my station was some 40 Hz or so off nominal. At present it is 7:47 AM and with my carrier off I hear a station on frequency though it is weak. But there is absolutely no hum with my dead carrier on and last evening my signal was hum free.
While this is not very scientific and may not apply to other stations I am very pleased that my frequency control effort appears to be worth the effort.
Neil
To hum or not to hum, that may be part of what was learned in your new experiment, radio8z.
Where you previously aware that hum might be a bi-product of hetrodyning with another station? You said you thought it was a power line-related problem, which it sometimes can be, but the hetrodyning cause is at least to me, a whole new possible reason for a hum in the carrier.
My signal at 13.560mHz has a strong hum that occurs in donut-shaped circles around my indoor antenna, but is not on the signal outdoors away from the house...... therefore it's being detected by the portable radio but is not actually on the carrier. I am assuming it is a reflection of the signal coming from house wiring. But maybe it's a hetrodyning with some other signal in the air.
"My signal at 13.560mHz has a strong hum that occurs in donut-shaped circles around my indoor antenna, but is not on the signal outdoors away from the house...... therefore it's being detected by the portable radio"
This is being caused by too much signal at the receiver due to having your transmitting antennas indoors and receivers in such close proximity to those transmitting antennas. And yes it's going to induce the EM fields produced by currents on the AC wiring in the house..and your gonna hear it on the receiver. Using that same receiver tuned to another frequency of a station not transmitting RF right into your head in the same room, you won't hear that hum.
And is why when you take the radio away from the room and house, the hum goes away.
Good thing your working with low power stuff eh. With all your transmitters and indoor antennas emitting EM fields, its bound to be a big EM mess in your house!
I bet a Geiger counter would go nut's in there! 😉
RFB
Where you previously aware that hum might be a bi-product of hetrodyning with another station?
No because I assumed that I was on frequency and therefore didn't think about this. My other AM txs. stay nearly on frequency once set and so did this one until I put the lid on the box. I can't claim for certain that this was the source of the hum, only that the signal is quiet now. I can still hear the other stations' audio at times with a very low frequency beat now and then.
I think RFB's explanation regarding AC line proximity may be a factor in your hum. A tuned ear can usually discriminate between 60 Hz hum and lower frequency heterodyne. It appears that what fooled me was the heterodyne was in the vicinity of 60 Hz. Again, this is only a theory.
Neil
"I think RFB's explanation regarding AC line proximity may be a factor in your hum. A tuned ear can usually discriminate between 60 Hz hum and lower frequency heterodyne. It appears that what fooled me was the heterodyne was in the vicinity of 60 Hz. Again, this is only a theory."
It's most likely that the 40hz difference, and whatever off frequency factor the distant station was at, is what caused you to hear a near 60 cycle like hum. Both your 40hz off frequency carrier and the other station's off frequency factor, which could have been just a few hz, combined to form the final result of what you were hearing as a 60 cycle hum that might make one think its from the AC power source.
I believe in Carl's situation, there is enough RF energy present from the indoor transmitting antenna that it is inductively sending the AC power hum to the radio when the transmitted signal passes through the house wiring, and the receiver is merely doing what it is supposed to do..pick up EM fields at a specific frequency it is tuned to, and since his transmitting antennas are indoors, and in close proximity to both the receiver and the house electrical wiring, is why his radio picks up the hum and does not when outside further away from the house wiring.
I once chased a similar problem for days, thinking it was a fault in the transmitter power supply or ground loop, and I had an indoor transmitting antenna on a mere 20mW signal. Then I thought let's see what happens if I run the antenna outside...and wala..hum went away.
It's the same effect you get in your audio chain if a strong enough EM field is nearby and inducing AC cycle current into the audio gear and wiring, saturating it with both the RF EM field and induced AC current EM field.
Gotta love EM physics!
RFB
hey neil what are the chances of getting schematics, board layout, etc so i can try and replicate this setup? i'm always interested in new transmitter designs. whether i build them or not i like to archive everyone i can get to study them.
Robert, are you asking about the crystal heater or the whole transmitter or both? I can try to accommodate.
Neil