You are saying that by mistuning the Rangemaster (peaking on the wrong peak), Liberty 1640 was able to increase its power. That makes a lot of sense because it explains why the field strength was so high from what was claimed to be a Rangemaster. I wonder if they had to modify the modulator to get enough modulation percentage.
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Willful vs. Unintentional Non-compliance with FCC §15.219
- Thread starter rfry
- Start date
You are saying that by mistuning the Rangemaster (peaking on the wrong peak), Liberty 1640 was able to increase its power. That makes a lot of sense because it explains why the field strength was so high from what was claimed to be a Rangemaster. I wonder if they had to modify the modulator to get enough modulation percentage.
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I made the statement "a few blocks" because it was the best I knew to describe.. however,in my post, some google maps were also provided of the area to indicate just how far a few blocks actually are in my instance... but reallymy range tends to vary (without a ground), some days the signal only reaches 2 blocks, other days it might go three...
Anyway, there are a couple of other factors to consider with my situation (or so I think), 1. the conductivity here is an 8, so that's a plus. 2. I contemplate, without any genuine knowledge, that perhaps the metal roof is acting as an advantage - as kindof a re-radiator, even though my xmtr ground is not actually touching it, but approximately an inch from it... but then again, I was achieving the same range when it was atop my own roof.. which by the way is only about six foot away from the metal roof.
3. Again, speculating without any genuine knowledge, this island is only 1/2 wide and surrounded by ocean, I suspect that the high ground conductivity combined with the fact that the ocean is only "few blocks" away in three directions from my transmitter.. I can't help but suspect that the close proximity of the ocean adds an extra boost to my range even though the transmitter is ungrounded.
My objective is cover the main strip (hwy 80) for about 2 miles+. Proper ground installs are practically unfeasible, so in a quest to legally succeed the objective, it seems that multiple elevated ungrounded installs down the main stretch is the most realistic possibility.. or at least, that's what I perceive to be the most likely route to pursue.
I more than welcome corrections or advice on this matter.
On another subject.. I have never experienced multiple peaks when tuning a Rangemaster, and the post here making references to it makes me say huhh??
I made the statement "a few blocks" because it was the best I knew to describe.. however,in my post, some google maps were also provided of the area to indicate just how far a few blocks actually are in my instance... but reallymy range tends to vary (without a ground), some days the signal only reaches 2 blocks, other days it might go three...
Anyway, there are a couple of other factors to consider with my situation (or so I think), 1. the conductivity here is an 8, so that's a plus. 2. I contemplate, without any genuine knowledge, that perhaps the metal roof is acting as an advantage - as kindof a re-radiator, even though my xmtr ground is not actually touching it, but approximately an inch from it... but then again, I was achieving the same range when it was atop my own roof.. which by the way is only about six foot away from the metal roof.
3. Again, speculating without any genuine knowledge, this island is only 1/2 wide and surrounded by ocean, I suspect that the high ground conductivity combined with the fact that the ocean is only "few blocks" away in three directions from my transmitter.. I can't help but suspect that the close proximity of the ocean adds an extra boost to my range even though the transmitter is ungrounded.
My objective is cover the main strip (hwy 80) for about 2 miles+. Proper ground installs are practically unfeasible, so in a quest to legally succeed the objective, it seems that multiple elevated ungrounded installs down the main stretch is the most realistic possibility.. or at least, that's what I perceive to be the most likely route to pursue.
I more than welcome corrections or advice on this matter.
On another subject.. I have never experienced multiple peaks when tuning a Rangemaster, and the post here making references to it makes me say huhh??
I don't know if pascoradio ("wdcx" at the website where you posted about "blocks"), who also operates a Rangemaster, has any further information about the tuning of the Rangemaster at Liberty 1640. He didn't post that he has first-hand knowledge of what was happening at Liberty 1640, but the mistuning was something that he had read. I don't think that just adjusting the input power above 100 mW would have done the trick for obtaining the high field strength that was recorded.
The Liberty 1640 transmitter was said to be a Rangemaster, but there must have been some "engineering" done on the unit that was used to get the input power up to some hundreds of milliwatts.
The Rangemaster output circuit has three MOSFETs in TO-92 plastic packages connected in parallel, and there should be enough power handling capacity to allow the input power to be increased to over a watt.
The Liberty 1640 transmitter was said to be a Rangemaster, but there must have been some "engineering" done on the unit that was used to get the input power up to some hundreds of milliwatts.
The Rangemaster output circuit has three MOSFETs in TO-92 plastic packages connected in parallel, and there should be enough power handling capacity to allow the input power to be increased to over a watt.
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A NEC analysis of a system perhaps similar to this case (below) shows that an output power of less than 1 watt could produce the field measured by the FCC with a 20-ft vertical conductor connected between the transmitter chassis and a single ground rod.
The mis-tuning comment came from Keith on this site but before the "improvements" so now I can't find it. The real beef was that the second and third harmonics were off the scale. This can be cause by tuning on the wrong peak. That peak on the fundamental will be lower but has an adverse effect on the harmonics @ 3280KHZ which is used by aircraft S&R as Bill pointed out on his site.
The high field at 30 meters measured on 1640 kHz by the FCC indicates that the antenna system probably was optimized for operation on 1640 kHz.
However NEC shows that the SWR at the input of the antenna system previously modeled would be on the order of 3800:1 on the 3280 kHz 2nd harmonic of 1640 kHz , and >8600:1 on the 4920 kHz third harmonic.
Such high SWR at the antenna system feedpoint would reflect virtually all of the energy applied to it on those harmonics back to the source (transmitter), and almost none of it would be radiated.
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I made a mistake which is rare for me. In fact it happens so infrequently that I am not afraid to admit it. I confused Liberty 1640 with this NOUO: http://transition.fcc.gov/eb/FieldNotices/2003/DOC-301931A1.html
However I was told this was a mis-tuned transmitter. Not the Liberty 1640. Sorry for the mistake.
However I was told this was a mis-tuned transmitter. Not the Liberty 1640. Sorry for the mistake.
FCC Certfied Part 15 Transmitter is Not a Free Pass
Whatever transmitter (FCC certified or not) that Liberty 1640 used at the time of the NOUO probably wasn't being operated in a configuration permitted by FCC §15.219, as indicated by:
1) the reported use of a 20 foot ground lead (in the NOUO).
2) the field intensity measured by the FCC 30 meters from the antenna system required substantially more output power from the transmitter than could be produced by the 100 mW transmitter input power permissible under §15.219(a).
Whatever transmitter (FCC certified or not) that Liberty 1640 used at the time of the NOUO probably wasn't being operated in a configuration permitted by FCC §15.219, as indicated by:
1) the reported use of a 20 foot ground lead (in the NOUO).
2) the field intensity measured by the FCC 30 meters from the antenna system required substantially more output power from the transmitter than could be produced by the 100 mW transmitter input power permissible under §15.219(a).
I can honestly say that I have experimented with the Rangemaster maxed out at around 0.6 watts. There was significant degradation of the audio meaning that it could not be modulated to 100%. That being said, I found an area of around 0.35 watts where 100% modulation could be achieved. With the Rangemester mounted on a rooftop and the ground tied into the conduit attached to the rooftop A/C units, I achieved a car radio range of about 1 mile before it faded into the noise. Also, driving it with a 222 processor and a Ultradyne audio processor. The experiment was to see if operating under 15.221 was feasible as the transmitter was located on a college campus.
One accurate measurement is worth a thousand expert opinions in my opinion.
But in the test case described wouldn't your observation (not measurement) be affected by the sensitivity of the receiver, the directivity of the receive antenna in/on that vehicle, the propagation path, ambient r-f noise and interference at the receive site and other factors -- none of which have been reported, and which may be unknown?
Yes.
pascoradio,
Thank you for your observations about the limits of adjusting the input power to the Rangemaster. By just increasing the AM modulator power, the field strength can be roughly doubled over what it is at 100 mW input, and there may have to be relatively small additional "engineering" changes to get up to the field strength observed at Liberty 1640.
Thank you for your observations about the limits of adjusting the input power to the Rangemaster. By just increasing the AM modulator power, the field strength can be roughly doubled over what it is at 100 mW input, and there may have to be relatively small additional "engineering" changes to get up to the field strength observed at Liberty 1640.
Increasing (or decreasing) the AM modulator power relative to the carrier power by itself does not significantly change the average field intensity of the carrier that the FCC would measure for that installation.
It is the average value of that carrier that might be used as a basis for an NOUO (FCC citation).
It is the average value of that carrier that might be used as a basis for an NOUO (FCC citation).
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My experiences with the Rangemaster echoed that of PascoRadio. With a measured input of 100mw, and a Symetrix 421 and an Inovonics 222 in the audio chain, and a ground mounted installation in soil with excellent conductivity (a river delta), I was able to achieve a range of approximately 1 mile to a sensitive car radio. Unfortunately, I have no instruments capable of measuring field strength.
However, even increasing the input up to a measured 1/2 watt, I was not able to significantly increase the range.
However, even increasing the input up to a measured 1/2 watt, I was not able to significantly increase the range.
It is posts like this one that betray Fry's fundamental lack of knowledge about technical matters, and such previous posts had caused me to look into his background on the Internet to find out what he has actually studied and learned. When the input power to the final power amplifier of an AM transmitter is increased, higher collector or drain modulator power is required to get 100% modulation. This is why pascoradio noticed that he was able to get full modulation in the Rangemaster with 350 mW of input power, but when the input power was increased to 600 mW, he could not get full modulation. This is because insufficient modulator power was available at 600 mW input power to get 100% modulation, and why a higher power modulator is needed when the input power is increased.
If the d-c input to r-f output efficiencies, and the amplitude modulation percentages/characteristics of the carrier at the final r-f stage of an AM transmitter are the same at 1/2 watt input power as at 1/10 watt input power, then for other conditions the same, the accurately measured groundwave field intensities produced by those two carriers at every distance would favor the use of the 1/2-watt condition by the square root of the difference in radiated power, which is about 2.24 X.
That amount of such an increase in radiated groundwave field for a given propagation path would lead to a significant improvement in useful range, other things equal.
If this was not the observed case, then probably some unrecognized factors were responsible for the reported results.
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Yes Ermi in the old days of plate modulated AM transmitters one needed at least 50% audio power related to the DC input RF power. For those who might be functionally challenged this means that a 100 watt AM transmitter needs a minimum of 50 watts audio power to fully modulate the 100 watt carrier to 100%. So as you correctly stated, when the Rangemaster was pushed beyond 0.35 watts the audio section of the transmitter fell well below what was necessary to fully modulate the transmitter. I applied a 1000hz tone to the audio section and while observing (yes Rich observing) I could see the modulation level drop as power was increased beyond 0.35 watts. So IMHO no real benefit is obtained by running a Rangemaster at max power with a modulation level falling below 70%.
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