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Post by jimhenry2000 on Apr 17, 2017 4:10:56 GMT
dk here is where I wonder what part of peaking my AMT-5000 is science and what is magic and black arts. As of yesterday, I felt I had a fairly well tuned xmtr with pretty good range but I still felt it could be improved upon. Here are the parts of the documentation which confuse me: C25 - the docs state the screw head should be aligned from front to back, which is fine,but you can probably rotate this cap at least half a dozen times and still align the screw slot front to back with any of them. Does that matter??? Seems like it should. Cap C2 - Well my xmtr is attempted to be tuned to 1610 so C2 should supposedly be set to minimum capacitance. I have looked and looked and looked at this cap as I rotated it and I can never notice the stators and rotors mesh., they just seem to rotate freely and keep the distance between the stator and rotor stay constant. Now my xmtr is set for 1610 khz so perhaps this is not that important, but I'd like my procedure to align with the manual. I can't seem to make any significant difference in performance by trying to adjust C2. It just seems to freewheel as I try to rotate the stator. Now for C1. I can adjust that for peak but the variability across the entire tuning range is tiny. Typically my peak might be 1.69mv or of course 0.0169v based on the charts in the manual.These of course are way below the values in the manual which start at 1.50v.
checking the last parameter, RF input current, the values still seem way too low. Turning up R1, the RF input power adjustment to max seems to get things closer to where they should be but still too low power. My concern here is something is wrong with the instructions for C25, and or for C2, or both. Now yesterday I had things working rather well but some minor adjustments that should have led to improvements shot it all to hell. Please help me if you can! Thanks. Jim
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Post by Druid Hills Radio on Apr 17, 2017 11:57:33 GMT
Carl: Your turn.
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Post by Deleted on Apr 17, 2017 13:48:07 GMT
There Goes MondayWhy is it always me. Is this not a worldwide hobby with thousands of transmitter teams constantly tuning theirs? I recall encountering some of the same issues described by Mr. Henry back when I tuned mine, and was eventually successful. Only last week I cleaned and returned to service the AMT5000 which is on the air now. What I will do during the day today is confirm its tuning and make detailed notes to compare with Mr. Henry's observations. I've got to order another one of these. You should order one too. It's the AMT5000 from SSTran_com.
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Post by Druid Hills Radio on Apr 17, 2017 15:04:08 GMT
There Goes MondayWhy is it always me. Is this not a worldwide hobby with thousands of transmitter teams constantly tuning theirs? I recall encountering some of the same issues described by Mr. Henry back when I tuned mine, and was eventually successful. Only last week I cleaned and returned to service the AMT5000 which is on the air now. What I will do during the day today is confirm its tuning and make detailed notes to compare with Mr. Henry's observations. I've got to order another one of these. You should order one too. It's the AMT5000 from SSTran_com. Have you compared the tuning procedure to the actual output power? In other words, when you are at maximum efficiency do you see more power on a signal strength meter?
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Post by Deleted on Apr 17, 2017 16:12:07 GMT
Question To Be Answered
DHR asks about the tuning results with an AMT5000 Transmitter: "Have you compared the tuning procedure to the actual output power? In other words, when you are at maximum efficiency do you see more power on a signal strength meter?"
I have not done this in the past but I will do it today using a spectrum analyzer.
At this moment, with the AMT5000 set on "old" settings, and with the spectrum analyzer being 35-feet away with its un-calibrated 13" vertical receiving antenna, the signal at 1680 kHz reads: 44 dBu, a relative reading, not true dBu.
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Post by Deleted on Apr 17, 2017 20:18:07 GMT
Preliminary Work
I had a 1-hour break at 1 PM CDT when I thought I might be able to re-tune the AMT5000, but the setup and lunch used up the hour and the next break will come at 4 PM CDT.
Meantime let's cover a few items:
Jim's question: "C25 - the docs state the screw head should be aligned from front to back, which is fine,but you can probably rotate this cap at least half a dozen times and still align the screw slot front to back with any of them. Does that matter??? Seems like it should."
C25 is a 1-rotation fine-tuning capacitor for the frequency oscillator which adjusts the crystal frequency by a few hundred Hz. Following the instruction as given is adequate to put the transmitter in a "same each time" state, and any actual fine-tuning with C25 is not done until after the RF output/antenna is completely tuned.
Jim's next question: "I have looked and looked and looked at this cap (C2) as I rotated it and I can never notice the stators and rotors mesh., they just seem to rotate freely and keep the distance between the stator and rotor stay constant."
I had exactly the same experience and have never been certain where C2 ended up being set, but everything else seems to work regardless, so I no longer do anything to C2.
In our next session I will go through all the jumper settings, including the toroid coil taps, RF power control, and C1 RF trimmer capacitor.
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Post by Deleted on Apr 17, 2017 20:28:12 GMT
Re-Visiting a Question From Earlier
In an earlier post this question was mentioned, and is repeating now:
DHR asks about the tuning results with an AMT5000 Transmitter: "Have you compared the tuning procedure to the actual output power? In other words, when you are at maximum efficiency do you see more power on a signal strength meter?"
I see that the question is answered in the manual under the tuning procedure section, which indicates that adding the "1 extra rotation of C1 to enter Class E Mode will cause a slight drop in RF current peak, BUT THIS IS THEN RECOVERED BY INCREASING THE RF POWER CONTROL.
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Post by Deleted on Apr 17, 2017 20:30:32 GMT
A Question For Jim
Jim, I'm guessing that the results you've had so far have been accomplished with the transmitter still indoors?
If so, that may be part of the problem, but I'll wait for your report on where the adjustments took place before I say any more.
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Post by jimhenry2000 on Apr 17, 2017 20:54:22 GMT
Unfortunately I don'tthink I have a signal strength meter. There Goes MondayWhy is it always me. Is this not a worldwide hobby with thousands of transmitter teams constantly tuning theirs? I recall encountering some of the same issues described by Mr. Henry back when I tuned mine, and was eventually successful. Only last week I cleaned and returned to service the AMT5000 which is on the air now. What I will do during the day today is confirm its tuning and make detailed notes to compare with Mr. Henry's observations. I've got to order another one of these. You should order one too. It's the AMT5000 from SSTran_com. Have you compared the tuning procedure to the actual output power? In other words, when you are at maximum efficiency do you see more power on a signal strength meter?
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Post by Deleted on Apr 17, 2017 22:07:25 GMT
Answers Straight Ahead
Most recent post from JH: "Unfortunately I don't think I have a signal strength meter."
At this time you won't need one, Jim, I think DHR might have been asking me about that, and I already have the answer thanks to my spectrum analyzer, which will be posted along with a full report.
Yes, during my window of opportunity between 4 and 4:30 PM CDT I was able to run a complete re-tuning of the AMT5000 and the results will be posted soon along with a batch of information about jumper settings and other tips.
JIM - Was your transmitter indoors when you last tuned it?
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Post by jimhenry2000 on Apr 18, 2017 4:20:48 GMT
Hi Carl, so far, ALL of my adjustments have been done indoors and on my workbench while the antenna, ground radials, have been laid out around the transmitter. Answers Straight AheadMost recent post from JH: " Unfortunately I don't think I have a signal strength meter." At this time you won't need one, Jim, I think DHR might have been asking me about that, and I already have the answer thanks to my spectrum analyzer, which will be posted along with a full report. Yes, during my window of opportunity between 4 and 4:30 PM CDT I was able to run a complete re-tuning of the AMT5000 and the results will be posted soon along with a batch of information about jumper settings and other tips. JIM - Was your transmitter indoors when you last tuned it?
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Post by Deleted on Apr 18, 2017 9:03:43 GMT
Secrets of the AMT5000 Part 1
Jim Reports: "ALL of my adjustments have been done indoors and on my workbench while the antenna, ground radials, have been laid out around the transmitter."
In the Manual p. 20 Section 8 RF Tuning / Set the RF Output Tuning Range, it reads:
Note: the Tuning Range charts were developed using a typical antenna capacitance of 30 pF. Your antenna will likely vary up to plus or minus 6 pF from the typical value.
As the earliest builder to publish results with the new AMT5000 at part15_us I was fortunate to have PhilB, the transmitter's designer, in constant contact. Phil was not pleased by the antenna I had available, what I call a "Wintenna", a metal window frame with verticle wires attached top and bottom to achieve 3-meters of total vertical length.
Using a capacitance meter between the Wintenna and ground I showed 4,000 uF which is way out of range of the transmitter's output as designed. The room I am in has stucco walls on 3-sides containing metal stucco mesh putting me in a virtual metal cage. I found a solution!
By adding a 20 pF capacitor between the RF output and the Wintenna I was able to tune up perfectly.
PhilB and another radio engineer both approved of this method of matching my odd-ball antenna.
At that time PhilB released details for building a Dummy Load to supply the transmitter with a simulated antenna at 30 pF. It consists of 2 parts: 1 - 30 ohm resistor and 1- 30 pF capacitor wired in series. The transmitter RF output goes to one end (let's say the capacitor) and the transmitter ground to the other end (the resistor) and a proper load is supplied for bench testing without a full-scale antenna.
What I suspect, Jim Henry, is that your basement walls, ceiling & contents contain enough metal work to shift the capacitance out of transmitter range. The above information might help you improve the indoor test results.
Coming up next - Yesterday's AMT5000 Re-Tuning.
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Post by Deleted on Apr 18, 2017 10:08:19 GMT
AMT5000 Re-Tuning Special
Only 12-hours ago here at KDX Worldround Radio we closed down the audio for half-an-hour so we'd have an un-modulated carrier while re-tuning our AMT5000 at 1680 kHz.
35-feet away the spectrum analyzer, as recently reported, was showing a carrier peak of 44 dBm (*non calibrated).
*The graticules on the analyzer are organized in "dBm" however are not true dBm measurements because we don't have the laboratory standard calibrated receiving antenna).
We noticed the RF Power Output control on the AMT5000 was set to Maximum, but the tune-up procedure calls for Mid RF Power Output, and after making the correction the spectrum analyzer reads 40 dBm, our reference level for today's re-tuning.
All 3 audio controls on the front of the AMT5000 set CCW;
Probes of our digital Voltmeter attached to RF Input Current test-points;
Volt reading prior to any changes: .4077 VDC;
Toroid Loading Coil Tap: S7 un-changed (note: this tap places our transmitter/antenna into correct tuning range so C1 finds the peak at center-turn);
Re-Peaked to: .4087 VDC;
Spectrum analyzer shows: 40 dBm;
One full additional turn CW of C1 per instruction: .2986 VDC;
Spectrum analyzer shows: 40 dBm.
Note: Here is the answer everyone has wondered about! That additional turn of C1 to achieve Class E tuning, while it reduces the RF current, DOES NOT REDUCE THE FIELD STRENGTH!!
We will stop this report for now, and when we return we'll have all the jumper settings for our AMT5000.
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Post by Deleted on Apr 18, 2017 10:26:54 GMT
Comment On Opening Post
Jim, in your opening post you said: "I can adjust that for peak but the variability across the entire tuning range is tiny. Typically my peak might be 1.69mv or of course 0.0169v based on the charts in the manual.These of course are way below the values in the manual which start at 1.50v."
The peak tuning is done according to RF Current Test Points.
According to the RF Input Voltage-Current Chart Page 39
RF Input Current Range is: 0.667 to 0.183;
RF Input Voltage Range is: 1.50 to 5.45.
Although the current number in your statement is lower than numbers on the chart, your mention of "1.50 V" would not be a current number but is a voltage number. I think you are mixing the two.
Again, in the peaking procedure we are only looking at current numbers.
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Post by Deleted on Apr 18, 2017 12:16:05 GMT
Jumpers
The Jumpers (S1 - S22) in the AMT5000 can be confusing and require careful attention to make sure each one is set right.
When some of the jumpers are ON they DISable a function by shorting across it.
When other jumpers are ON they ENable a function by making a connection to it.
Some of the jumpers must be in place for proper operation.
Other jumpers are optional and depend on your choice.
S1 should be OFF for transmitters operating in the HIGH BAND. By being OFF it DIS-CONNECTS C2. Read that again Jim Henry. You were concerned about meshing the stator and rotor of C2, but with J1 OFF, C2 isn't even in the circuit!
S2 should be OFF for antenna systems employing the built-in Toroid Loading Coil. By jumpering S2 the Internal Toroid Coil is bypassed in favor of an external loading coil;
S3 - S11 are Taps to the Toroid Loading Coil. In our KDX transmitter S7 is the tap that places C1 in its proper tuning range. For your transmitter a different tap may be needed;
S12 is ON for our transmitter bypassing L2. This is an optional jumper. See manual;
S13 is ON for our transmitter bypassing L3. This is an optional jumper. See manual;
S14 is OFF for our transmitter bypassing C8. This is an optional jumper. See manual;
S15 is ON for our transmitter enabling C7. This is an optional jumper. See manual;
S16 & S17 should be OFF except for transmitters on battery power. Important!
S18 & 19 is ON for our transmitter disabling L5 & L6. These are optional jumpers. See manual;
S20 does not exist.
S21 Not Used;
S22 is ON for our transmitter enabling NRSC PreEmphasis. This is optional.
Setting certain jumpers incorrectly can prevent the transmitter from operating correctly.
My next report titled Secrets of the AMT5000 Part 2 will provide a detailed description of parts and hookup for a professional audio line from indoors to outdoors.
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