"Calibrating" Tecsun radio based on FCC License-specified Monitor point fields?
I've been wondering if there was a way to figure out the approximate field strengths of various signals based on the indications of a DSP radio with a "dBµ" signal strength display. In my case, I'm using the Tecsun PL-606 (which according to a reviewer has the same internal antenna as the PL-310), and also have a PL-380 that isn't quite completely operational.
I had been using FCC groundwave charts and specified 1 km inverse field data for various stations to attempt to approximate a conversion factor for my PL-606. This would be done by calculating what the field intensity should be at a certain spot (based on ground conductivity, distance, and inverse field in that direction), converting from mV/m to dBµV/m, then reading the display on my PL-606 at the same spot. This was done for a few stations, but was getting to be tedious.
Several weeks / a couple months ago while browsing the FCC database info, I stumbled across links to the licenses on a few local licensed stations. (These were found by clicking "Application Info" on the query/detail page for a station, then clicking "View Authorization" and clicking the link on the next page. Unfortunately some stations do not have those publicly available, unless I was looking in the wrong place.)
Among other things, I found the monitor points information in there for a couple stations near me. These apparently specify field strengths at specified distances along several specified radials for daytime and nighttime operation (all for directional antennas - I don't see these for stations using non-directional antennas that have the information available).
In looking at the authorizations for 910 KECR El Cajon, CA and 1170 KCBQ San Diego, CA, I found several monitor points that I could go visit in order to attempt to "calibrate" my radio's display (read: come up with a conversion factor). I did not visit all of them due to the impracticality of getting to some of those sites (being on a bicycle, with their transmitter site [they diplex with each other] being a couple miles from the end of the nearest main bus route [although there is an extremely limited rural bus that goes fairly near there, as well as a casino shuttle that goes to within a couple miles of a couple monitor points I didn't visit]), but I did visit several of them. (They were visited on different days / evenings - not all were hit in one session.)
My observations at several monitor points are as follows:
KECR Day 102.0° 3.35 km 9.82 mV/m 79.842 dBµV/m
I had no difficulty finding this monitor point - a 2.5 mile marker on Wildcat Canyon Road. (Getting there enabled me to get plenty of exercise, as it was almost entirely uphill for about a couple miles.)
PL-606: 910 = "52/25"
80 - 52 = 28 dB difference, PL-606 being lower
KECR Day 141.0° 4.30 km 6.80 mV/m 76.650 dBµV/m
I'm not completely sure if I correctly found this one. The description in the license mentioned a gate on El Monte Rd at Hanson Way a specified direction from Lake Jennings Park Rd. I found a gate at approximately the specified distance from LJPR (also based on using the terminal coordinates program from the transmitter site), but there was no mention of Hanson Way.
PL-606: 910 = "54/25" - in front of the gate, as specified.
77 - 54 = 23 dB difference, PL-606 being lower
However, I noticed something quite interesting. The reading on KCBQ (1170) was 81/25 at that spot, but the peaks were on completely DIFFERENT azimuths in spite of both stations diplexing at the same transmitter site! (I also noticed this at a few other spots.) I went across the street to get out from under the overhead power lines, and there 1170 was reading 83/25 and...
PL-606: 910 = "63/25" - across the street (not under the power lines)
77 - 63 = 14 dB difference, PL-606 being lower
KECR Night 76.5° 3.01 km 18.00 mV/m 85.105 dBµV/m
This one describes a monitor point as at the end of a concrete curb across from a fire hydrant. However, somehow I incorrectly guessed the monitor point, as there was another one a little farther down the road. (There was another monitor point a bit farther down for another station, but I was unable to find it.) I did calculate the fields based on groundwave curves and inverse field specifications at the two sites, and there appears to be only about a 1 dB error or so.
PL-606: 910 = "58/25" or "59/25" (IIRC was cycling between the two)
85 - 58 = 27 dB difference, PL-606 being lower
KECR Night 114.5° 5.23 km 7.10 mV/m 77.025 dBµV/m
This one was easy enough to find, but when I took the readings of 910 and 1170 ("43/25"), I had to face different azimuths, even though like I said both stations diplex from the same antenna farm.)
PL-606: 910 = "48/25"
77 - 48 = 29 dB difference, PL-606 being lower
KCBQ Day 113.0° 4.73 km 23.03 mV/m 87.245 dBµV/m
I'm not totally sure if I accurately found this one, but I think I probably did based on the distances specified from other roads as well as the terminal coordinates. (Neither were exact, especially the terminal coordinates, so I'm wondering if I'm using the wrong type of coordinates (NAD27 vs NAD83).)
PL-606: 1170 = "65/25"
87 - 65 = 22 dB difference, PL-606 being lower
KCBQ Day 148.5° 4.52 km 189.50 mV/m 105.552 dBµV/m
PL-606: 1170 = "86/25"
105 - 86 = 19 dB difference, PL-606 being lower
I should note that at this level the PL-606 is beginning to desense significantly. For example, at a few spots much closer to the site, I saw the PL-606 say "95/25" when I first tuned to 1170, then a second later it said "89/25". A few seconds later it said "86/25" or thereabouts. At another spot within a few km of KCBQ's site while checking 1130 KSDO (several km to the southwest), I saw something like "72/25", then a second later "54/25" with a noisy signal. Also, I noticed the display would not stay above "89/25" until I was about 0.45 km SSW of the array, at which point it stayed at "90/25". At my house about 9.3 miles S of the transmitter, it typically indicates "80/25" in the daytime. Also I typically don't notice the diplay-one-number-then-a-second-later-a-lower-number phenomenon when the strongest signal is below about "80/25", and even then it has to get well up into the mid 80s "dBµ" before it really begins to do that.
BTW, While this post is mostly about calibrating based on weaker signals, I wonder if it might be even remotely possible to "calibrate" very strong signals based on how far off frequency I see "50/00" or "49/00" readings on blank channels, and/or the strength of shortwave harmonics. For example, here are two videos of my PL-606 near KCBQ's site, during which I inductively couple to a Select-A-Tenna (tuned to 1170) and a utility pole grounding wire (about 95 meters from the nearest tower in the 4-tower daytime array, almost directly in line with the main ~200 kW ERP lobe), as well as another video shot 14.9 km @ 187.43° from the site. I would be interested in figuring out what are the approximate field strengths necessary to duplicate what happens at the signal peaks in those first two videos... A - using only the radio's built-in ferrite loopstick, B - disconnecting the loopstick (so the pin on the Si4734 chip is the only antenna), and C - using a crystal diode and earphone without any antenna (save for the length of the lead on the diode and/or the length of the earphone cord). (Oh and I may as well add "D" - how close would R. Fry. need to get to a station near him of his choice to get the same effect on his PL-310, using only its built-in ferrite loopstick, as in the videos I shot near KCBQ's site.
) {I don't know that I would quite take it to the level of figuring out the field necessarily to spontaneously fry the DSP chip or a germanium diode over-the-air without a direct physical connection to the transmitter/antenna, though. } Also what is likely electrically happening when the radio is overloading like that? IIRC front-end overload is manifest by the desensing (reduction in sensitivity on nearby channels with, interestingly, an increased signal strength displayed), but what about when the audio begins distorting on-channel, then sounds like an unmodulated carrier (then once it gets strong enough is actually audible, though heavily distorted, even when changing controls/settings on the radio during which it would normally be muted)? Would that be the audio stage rectifying the signal by itself without the RF stages, for example, or what's likely happening?
KCBQ Night 102.5° 5.68 km 0.63 mV/m 55.986 dBµV/m
At this point, I noticed possible skywave/groundwave fading, as well as co-channel interference and a ~70 Hz heterodyne due to KCBQ being slightly off frequency at night. Also, 1170 and 910 "peaked" at different azimuths. (910 at peak was reading "53/25".)
PL-606: 1170 = "30/19" to "37/25", rotated to the opposite of 910's peak, observed possible skywave fading. Also saw a brief flash of "39/25" but was unable to duplicate it.
PL-606: 1170 = "31/18" to "36/25", rotated to the same as 910's peak, observed weak co-channel QRM underneath.
56 - 30 = 26 dB difference, PL-606 being lower
56 - 36 = 20
56 - 39 = 17
KCBQ Night 131.0° 4.63 km 13.80 mV/m 82.797 dBµV/m
PL-606: 1170 = "63/25"
83 - 63 = 20 dB difference, PL-606 being lower
As you can tell, there was absolutely no consistency in the readings vs. the specified field strengths. Could it be the fact that I was using the radio's directional loopstick antenna (as opposed to an omnidirectional whip I guess the pros would use when taking those monitor readings), or was I doing something wrong, or is the Tecsun radio really that erratic on its readings? Or is there some way to come up with an approximate conversion factor, as well as a way to figure out when that conversion factor would not work (for example attempting to calculate the field of a weak-sounding station indicating "50/00" when there's a "89/25" just up the dial that's badly desensing the radio)?
I've been wondering if there was a way to figure out the approximate field strengths of various signals based on the indications of a DSP radio with a "dBµ" signal strength display. In my case, I'm using the Tecsun PL-606 (which according to a reviewer has the same internal antenna as the PL-310), and also have a PL-380 that isn't quite completely operational.
I had been using FCC groundwave charts and specified 1 km inverse field data for various stations to attempt to approximate a conversion factor for my PL-606. This would be done by calculating what the field intensity should be at a certain spot (based on ground conductivity, distance, and inverse field in that direction), converting from mV/m to dBµV/m, then reading the display on my PL-606 at the same spot. This was done for a few stations, but was getting to be tedious.
Several weeks / a couple months ago while browsing the FCC database info, I stumbled across links to the licenses on a few local licensed stations. (These were found by clicking "Application Info" on the query/detail page for a station, then clicking "View Authorization" and clicking the link on the next page. Unfortunately some stations do not have those publicly available, unless I was looking in the wrong place.)
Among other things, I found the monitor points information in there for a couple stations near me. These apparently specify field strengths at specified distances along several specified radials for daytime and nighttime operation (all for directional antennas - I don't see these for stations using non-directional antennas that have the information available).
In looking at the authorizations for 910 KECR El Cajon, CA and 1170 KCBQ San Diego, CA, I found several monitor points that I could go visit in order to attempt to "calibrate" my radio's display (read: come up with a conversion factor). I did not visit all of them due to the impracticality of getting to some of those sites (being on a bicycle, with their transmitter site [they diplex with each other] being a couple miles from the end of the nearest main bus route [although there is an extremely limited rural bus that goes fairly near there, as well as a casino shuttle that goes to within a couple miles of a couple monitor points I didn't visit]), but I did visit several of them. (They were visited on different days / evenings - not all were hit in one session.)
My observations at several monitor points are as follows:
KECR Day 102.0° 3.35 km 9.82 mV/m 79.842 dBµV/m
I had no difficulty finding this monitor point - a 2.5 mile marker on Wildcat Canyon Road. (Getting there enabled me to get plenty of exercise, as it was almost entirely uphill for about a couple miles.)
PL-606: 910 = "52/25"
80 - 52 = 28 dB difference, PL-606 being lower
KECR Day 141.0° 4.30 km 6.80 mV/m 76.650 dBµV/m
I'm not completely sure if I correctly found this one. The description in the license mentioned a gate on El Monte Rd at Hanson Way a specified direction from Lake Jennings Park Rd. I found a gate at approximately the specified distance from LJPR (also based on using the terminal coordinates program from the transmitter site), but there was no mention of Hanson Way.
PL-606: 910 = "54/25" - in front of the gate, as specified.
77 - 54 = 23 dB difference, PL-606 being lower
However, I noticed something quite interesting. The reading on KCBQ (1170) was 81/25 at that spot, but the peaks were on completely DIFFERENT azimuths in spite of both stations diplexing at the same transmitter site! (I also noticed this at a few other spots.) I went across the street to get out from under the overhead power lines, and there 1170 was reading 83/25 and...
PL-606: 910 = "63/25" - across the street (not under the power lines)
77 - 63 = 14 dB difference, PL-606 being lower
KECR Night 76.5° 3.01 km 18.00 mV/m 85.105 dBµV/m
This one describes a monitor point as at the end of a concrete curb across from a fire hydrant. However, somehow I incorrectly guessed the monitor point, as there was another one a little farther down the road. (There was another monitor point a bit farther down for another station, but I was unable to find it.) I did calculate the fields based on groundwave curves and inverse field specifications at the two sites, and there appears to be only about a 1 dB error or so.
PL-606: 910 = "58/25" or "59/25" (IIRC was cycling between the two)
85 - 58 = 27 dB difference, PL-606 being lower
KECR Night 114.5° 5.23 km 7.10 mV/m 77.025 dBµV/m
This one was easy enough to find, but when I took the readings of 910 and 1170 ("43/25"), I had to face different azimuths, even though like I said both stations diplex from the same antenna farm.)
PL-606: 910 = "48/25"
77 - 48 = 29 dB difference, PL-606 being lower
KCBQ Day 113.0° 4.73 km 23.03 mV/m 87.245 dBµV/m
I'm not totally sure if I accurately found this one, but I think I probably did based on the distances specified from other roads as well as the terminal coordinates. (Neither were exact, especially the terminal coordinates, so I'm wondering if I'm using the wrong type of coordinates (NAD27 vs NAD83).)
PL-606: 1170 = "65/25"
87 - 65 = 22 dB difference, PL-606 being lower
KCBQ Day 148.5° 4.52 km 189.50 mV/m 105.552 dBµV/m
PL-606: 1170 = "86/25"
105 - 86 = 19 dB difference, PL-606 being lower
I should note that at this level the PL-606 is beginning to desense significantly. For example, at a few spots much closer to the site, I saw the PL-606 say "95/25" when I first tuned to 1170, then a second later it said "89/25". A few seconds later it said "86/25" or thereabouts. At another spot within a few km of KCBQ's site while checking 1130 KSDO (several km to the southwest), I saw something like "72/25", then a second later "54/25" with a noisy signal. Also, I noticed the display would not stay above "89/25" until I was about 0.45 km SSW of the array, at which point it stayed at "90/25". At my house about 9.3 miles S of the transmitter, it typically indicates "80/25" in the daytime. Also I typically don't notice the diplay-one-number-then-a-second-later-a-lower-number phenomenon when the strongest signal is below about "80/25", and even then it has to get well up into the mid 80s "dBµ" before it really begins to do that.
BTW, While this post is mostly about calibrating based on weaker signals, I wonder if it might be even remotely possible to "calibrate" very strong signals based on how far off frequency I see "50/00" or "49/00" readings on blank channels, and/or the strength of shortwave harmonics. For example, here are two videos of my PL-606 near KCBQ's site, during which I inductively couple to a Select-A-Tenna (tuned to 1170) and a utility pole grounding wire (about 95 meters from the nearest tower in the 4-tower daytime array, almost directly in line with the main ~200 kW ERP lobe), as well as another video shot 14.9 km @ 187.43° from the site. I would be interested in figuring out what are the approximate field strengths necessary to duplicate what happens at the signal peaks in those first two videos... A - using only the radio's built-in ferrite loopstick, B - disconnecting the loopstick (so the pin on the Si4734 chip is the only antenna), and C - using a crystal diode and earphone without any antenna (save for the length of the lead on the diode and/or the length of the earphone cord). (Oh and I may as well add "D" - how close would R. Fry. need to get to a station near him of his choice to get the same effect on his PL-310, using only its built-in ferrite loopstick, as in the videos I shot near KCBQ's site.
) {I don't know that I would quite take it to the level of figuring out the field necessarily to spontaneously fry the DSP chip or a germanium diode over-the-air without a direct physical connection to the transmitter/antenna, though. } Also what is likely electrically happening when the radio is overloading like that? IIRC front-end overload is manifest by the desensing (reduction in sensitivity on nearby channels with, interestingly, an increased signal strength displayed), but what about when the audio begins distorting on-channel, then sounds like an unmodulated carrier (then once it gets strong enough is actually audible, though heavily distorted, even when changing controls/settings on the radio during which it would normally be muted)? Would that be the audio stage rectifying the signal by itself without the RF stages, for example, or what's likely happening?KCBQ Night 102.5° 5.68 km 0.63 mV/m 55.986 dBµV/m
At this point, I noticed possible skywave/groundwave fading, as well as co-channel interference and a ~70 Hz heterodyne due to KCBQ being slightly off frequency at night. Also, 1170 and 910 "peaked" at different azimuths. (910 at peak was reading "53/25".)
PL-606: 1170 = "30/19" to "37/25", rotated to the opposite of 910's peak, observed possible skywave fading. Also saw a brief flash of "39/25" but was unable to duplicate it.
PL-606: 1170 = "31/18" to "36/25", rotated to the same as 910's peak, observed weak co-channel QRM underneath.
56 - 30 = 26 dB difference, PL-606 being lower
56 - 36 = 20
56 - 39 = 17
KCBQ Night 131.0° 4.63 km 13.80 mV/m 82.797 dBµV/m
PL-606: 1170 = "63/25"
83 - 63 = 20 dB difference, PL-606 being lower
As you can tell, there was absolutely no consistency in the readings vs. the specified field strengths. Could it be the fact that I was using the radio's directional loopstick antenna (as opposed to an omnidirectional whip I guess the pros would use when taking those monitor readings), or was I doing something wrong, or is the Tecsun radio really that erratic on its readings? Or is there some way to come up with an approximate conversion factor, as well as a way to figure out when that conversion factor would not work (for example attempting to calculate the field of a weak-sounding station indicating "50/00" when there's a "89/25" just up the dial that's badly desensing the radio)?