I know that for most people selectivity is a problem sometimes, but I live about 30 miles north of Dallas and cannot receive staions on either side of several local stations in this area. For example because 1080 is a Dallas station I cannot receive anything on 1070 or 1090. This is especially true during the daytime. This situation repeats itself about six or seven places across the AM band. I have a pretty good receiver (Icom R75) , but even on the narrow filter is not tight enough. I have thought about getting a preselector. Has anyone else had any luck with taking care of selectivity issues? Thanks
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In Search of better Selectivity
- Thread starter RoyTex
- Start date
My experience is that preselectors are better at improving image and intermodulation problems, and blanketing from signals 50 or more kHz away. You might be able to get a slight improvement in selectivity, but not dramatically. A narrower IF is what you need for better selectivity. And if the signal actually has sidebands in another channel, like IBOC, it won't help.
Have you tried the Tecsun radios? They have that DSP chip and the sensitivity and selectivity are excellent on AM and FM. For example, I live two miles from a 10,000 watt AM statiion's transmitter on 1070 in Sunbury, Pa. WBAL in Baltimore at 1090 is 140 miles away and is easily audible during the day. Great radio. I have three of them, the 380, 390 and the 606. All excellent.
Another approach for this might be to use a receiver with synchronous AM detection of either the upper or lower sideband (selectable). This technique also reduces the effects of selective fading of the transmitted AM carrier. My Sony® ICF-SW7600GR is one example of such a receiver, at a fairly reasonable price.
I also have a DSP-based Tecsun® PL-310 not using synchronous detection, but having four steps of r-f bandwidth ranging from 12 kHz down to 2 kHz -- the detected a-f bandwidth being half of that. Excellent MF, HF, and VHF performance (AM or analog FM mono/stereo in appropriate bands), from a ~$50 consumer receiver. It also has an LCD display of "signal strength" (not the arriving field intensity), and the audio S/N ratio of the received signal.
I also have a DSP-based Tecsun® PL-310 not using synchronous detection, but having four steps of r-f bandwidth ranging from 12 kHz down to 2 kHz -- the detected a-f bandwidth being half of that. Excellent MF, HF, and VHF performance (AM or analog FM mono/stereo in appropriate bands), from a ~$50 consumer receiver. It also has an LCD display of "signal strength" (not the arriving field intensity), and the audio S/N ratio of the received signal.
There are also antenna tricks, if you're attached to a particular receiver. Loops are nice for nulling out strong signals, as are phased antenna setups http://www.dxtools.com/Phaser.htm
And if anyone is looking for selecticity on FM, the Grundig G8 is great.
I haven't owned many of the radios often mentioned here but I was amazed at the FM selectivity and sensitivity of the g8 and I got it only for shortwave.
The speaker is mono but you can hear FM stereo if you use earphones.
I haven't owned many of the radios often mentioned here but I was amazed at the FM selectivity and sensitivity of the g8 and I got it only for shortwave.
The speaker is mono but you can hear FM stereo if you use earphones.
The G8 also has pretty decent selectivity on AM. I have 3 very storn locals at 580, 1200, and 1310. There are 2 moderatetly strong AM's on 1350 and 1670. 1310 sends a LOT of signal right at me, esepcially at night, and I can still hear stations at 1300 and 1320 with very little, if any splatter from 1310. During the day, I do experience a bit of sensitivity lot if the radio is facing southwest (where the 3 strongest stations transmitters are). It still manages to pull in a very weak 1340 out from to a listenable level, with no splatter from local 1350 at all.
R. Fry, I've also noticed that vertically tilting a radio with an internal loopstick can enhance the nulls, besides just holding it horizontal. Different stations require different amounts of tilt for the deepest null. I have been able, though, with precise positioning, to practically completely wipe out reception of 50 kW blowtorches less than 10 miles away.
A couple videos demonstrating this are at:
https://www.youtube.com/watch?v=MDgIvpB7LHI - 760 KFMB night, 50 kW 7.3 miles from me. (I suspect reception was enhanced being near some house wiring - normally 760's strength is only about 80 or 81 dBµ or so.)
https://www.youtube.com/watch?v=f7fU5hIIuOY - 1170 KCBQ day, 50 kW 9.3 miles from me
I think that deeper nulls are definitely possible with a loopstick, but would require even much more precise positioning than demonstrated in the videos.
For anyone (not just R Fry) in keeping with the thread, I also would like to find better selectivity in an inexpensive portable radio, but from steep filter slopes, and excellent stop-band attenuation, without desensitizing the radio to weak signals in the presence of strong ones like my DSP radios tend to do.
Below are a few examples of using another radio's IF oscillator output (by tuning 450 kHz lower, +/- a few Hz due to the radio being set for 9 kHz spacing) to produce a beat-note with a target station's carrier. The target station is totally undetectable without this method using the equipment I used.
Links to youtube videos are for an entire bandscan for the radios involved, which may take several minutes. Times are included in the links so it will automatically seek to the desired time. In some cases there will be multiple links to the same video with different timestamps. Receive coordinates are approximately 32.760656, -116.945883. The videos were recorded on the dates and times indicated in the video titles.
Using a Sony SRF-M37W, modified with a narrower filter (I bought it used with the filter installed):
http://youtu.be/ouf7tw6aalE?t=4m58s - 1140 kHz station (presumably KNWQ Palm Springs) is detected via the 3 kHz heterodyne. (There's another slightly lower pitch tone, the source of which is undetermined.) The pest station, local 1130 KSDO playing Spanish religious music, is heard at 4:48. At 4:52 I tune to 1140 (without the oscillator / other radio on) and you can really hear the splash.
According to Radio-Locator, I'm just about right on the edge of KNWQ's 0.15 mV/m fringe contour.
http://youtu.be/ouf7tw6aalE?t=5m41s - 1160 kHz station (presumably XEQIN San Quintin) detected with 1 kHz heterodyne. When I turn off the Panasonic RQ-SW20 (which is generating the heterodyne tone, tuned to 711 kHz (711+450=1161, 1161-1160=1 kHz)), you can prominently hear splash from 1170 KCBQ, which is tuned to at 6:00. (Splash is still clearly audible even with the het enabled.)
According to the Radio-Locator coverage map, and overlaying on Google Maps (via a photo editor), I suspect I'm about 2-3x past XEQIN's 0.15 mV/m fringe contour. (I also think R-L may underestimate Baja California's ground conductivity. For example, 560 KBLU Yuma, AZ, should be omnidirectional, but take a gander at their pattern...)
http://youtu.be/ouf7tw6aalE?t=6m38s - 1180 kHz station (presumably KERN Wasco-Greenacres) faintly detected with 1 kHz heterodyne. With this one I had to wait a bit to hear the heterodyne - while the talk show on 1170 KCBQ was playing lead-out music to go into a break, the splatter completely masked the het. Even at the time indicated in the link, the 1 kHz het is very faint. At 6:51, the het is still on for a couple seconds, then I turn the radio off and the het goes away. (I used this method to double-check whether I was hearing a het at all, or just imagining things.)
According to Radio-Locator, I'm approximately 2-2.5x past KERN's 0.15 mV/m fringe contour.
Using the Sony SRF-59:
http://youtu.be/SUS17HH4V8E?t=5m57s - 1140 KNWQ detected via 3 kHz heterodyne from RQ-SW20's offset-tuned oscillator. At 6:09 the osc is briefly turned off, making the het vanish & revealing more splatter from 1130 KSDO.
http://youtu.be/SUS17HH4V8E?t=6m56s - 1160 XEQIN detected via 1 kHz heterodyne. At 7:02 the osc is turned off, eliminating the het & revealing strong splatter from 1170 KCBQ.
http://youtu.be/SUS17HH4V8E?t=7m19s - 1180 KERN detected via 1 kHz heterodyne. At 7:33 the RQ-SW20 is switched off, eliminating the faint het & revealing more KCBQ splatter.
(continued in next post)
A couple videos demonstrating this are at:
https://www.youtube.com/watch?v=MDgIvpB7LHI - 760 KFMB night, 50 kW 7.3 miles from me. (I suspect reception was enhanced being near some house wiring - normally 760's strength is only about 80 or 81 dBµ or so.)
https://www.youtube.com/watch?v=f7fU5hIIuOY - 1170 KCBQ day, 50 kW 9.3 miles from me
I think that deeper nulls are definitely possible with a loopstick, but would require even much more precise positioning than demonstrated in the videos.
For anyone (not just R Fry) in keeping with the thread, I also would like to find better selectivity in an inexpensive portable radio, but from steep filter slopes, and excellent stop-band attenuation, without desensitizing the radio to weak signals in the presence of strong ones like my DSP radios tend to do.
Below are a few examples of using another radio's IF oscillator output (by tuning 450 kHz lower, +/- a few Hz due to the radio being set for 9 kHz spacing) to produce a beat-note with a target station's carrier. The target station is totally undetectable without this method using the equipment I used.
Links to youtube videos are for an entire bandscan for the radios involved, which may take several minutes. Times are included in the links so it will automatically seek to the desired time. In some cases there will be multiple links to the same video with different timestamps. Receive coordinates are approximately 32.760656, -116.945883. The videos were recorded on the dates and times indicated in the video titles.
Using a Sony SRF-M37W, modified with a narrower filter (I bought it used with the filter installed):
http://youtu.be/ouf7tw6aalE?t=4m58s - 1140 kHz station (presumably KNWQ Palm Springs) is detected via the 3 kHz heterodyne. (There's another slightly lower pitch tone, the source of which is undetermined.) The pest station, local 1130 KSDO playing Spanish religious music, is heard at 4:48. At 4:52 I tune to 1140 (without the oscillator / other radio on) and you can really hear the splash.
According to Radio-Locator, I'm just about right on the edge of KNWQ's 0.15 mV/m fringe contour.
http://youtu.be/ouf7tw6aalE?t=5m41s - 1160 kHz station (presumably XEQIN San Quintin) detected with 1 kHz heterodyne. When I turn off the Panasonic RQ-SW20 (which is generating the heterodyne tone, tuned to 711 kHz (711+450=1161, 1161-1160=1 kHz)), you can prominently hear splash from 1170 KCBQ, which is tuned to at 6:00. (Splash is still clearly audible even with the het enabled.)
According to the Radio-Locator coverage map, and overlaying on Google Maps (via a photo editor), I suspect I'm about 2-3x past XEQIN's 0.15 mV/m fringe contour. (I also think R-L may underestimate Baja California's ground conductivity. For example, 560 KBLU Yuma, AZ, should be omnidirectional, but take a gander at their pattern...)
http://youtu.be/ouf7tw6aalE?t=6m38s - 1180 kHz station (presumably KERN Wasco-Greenacres) faintly detected with 1 kHz heterodyne. With this one I had to wait a bit to hear the heterodyne - while the talk show on 1170 KCBQ was playing lead-out music to go into a break, the splatter completely masked the het. Even at the time indicated in the link, the 1 kHz het is very faint. At 6:51, the het is still on for a couple seconds, then I turn the radio off and the het goes away. (I used this method to double-check whether I was hearing a het at all, or just imagining things.)
According to Radio-Locator, I'm approximately 2-2.5x past KERN's 0.15 mV/m fringe contour.
Using the Sony SRF-59:
http://youtu.be/SUS17HH4V8E?t=5m57s - 1140 KNWQ detected via 3 kHz heterodyne from RQ-SW20's offset-tuned oscillator. At 6:09 the osc is briefly turned off, making the het vanish & revealing more splatter from 1130 KSDO.
http://youtu.be/SUS17HH4V8E?t=6m56s - 1160 XEQIN detected via 1 kHz heterodyne. At 7:02 the osc is turned off, eliminating the het & revealing strong splatter from 1170 KCBQ.
http://youtu.be/SUS17HH4V8E?t=7m19s - 1180 KERN detected via 1 kHz heterodyne. At 7:33 the RQ-SW20 is switched off, eliminating the faint het & revealing more KCBQ splatter.
(continued in next post)
(continued from previous)
Using the GE Superradio III:
http://youtu.be/KrCdjEa4OR4?t=9m11s - 1140 KNWQ detected via 3 kHz het.
http://youtu.be/KrCdjEa4OR4?t=10m36s - 1160 XEQIN detected via 1 kHz het. At 10:44 the RQ-SW20 is switched off, eliminating the het. This reveals strong splatter from 1170 KCBQ, along with a Spanish-speaking female in the background. (I'm not sure, though, if this is XEQIN on 1160, or residual splash from 1130 KSDO, which also carries Spanish-language programming.)
http://youtu.be/KrCdjEa4OR4?t=11m23s - 1180 KERN detected via 1 kHz het. The het is a little more easily audible at around 11:31. At 11:34 the RQ-SW20 (generating the het) is switched off, revealing more 1170 splatter. At 11:40 it's again briefly switched on for a few seconds, revealing the het, then switched off.
Using the Tecsun PL-398mp:
Note that first I enabled a feature I discovered in this radio to modify how the radio behaves with weak signal near strong signals. This is demonstrated in the beginning of the video.
http://youtu.be/BJl5lebq4jY?t=3s - powered on radio, signal weakly received on 1110 kHz showing a signal strength of 45 / 00, dropping a couple seconds later to 43 / 00. I've noticed that these DSP radios will show a high RSSI strength when a weak or no signal is present when in the presence of a strong signal. In some cases I've seen 50/00 and heard no signal when tuned several hundred kHz away from a mega-strong pest.
http://youtu.be/BJl5lebq4jY?t=3s - I begin the sequence to enable the feature. The steps are:
1. Switch radio to SW (press either the "v" or "^" button)
2. Hold the VF button until the radio starts scanning.
3. Quickly & briefly rotate the tuning knob down. If this is done correctly and you're not tuned in the vicinity of a strong station, you will notice the audio get much louder, and the signal display should show 00 / 00 or something like that. (Normally the minimum in LW, MW (AM) and SW modes is 15 / 00.) (I find it interesting that the audio gets louder on blank channels when the signal strength display gets lower. This is even noticeable in "normal" mode.)
When enabling this, the radio defaults to 2 kHz bandwidth setting (which for you traditional radio users is a 4 kHz IF bandwidth), regardless of what it was set at previously. To turn this mode off, turn the radio off and back on, or switch to FM then back to one of the AM-mode bands.
http://youtu.be/BJl5lebq4jY?t=16s - after switching bandwidth to 1 khz (audio, 2 kHz IF), I switch back to AM, revealing a much more easily heard 1110 KDIS. Then, at 0:26 I punch up 1130, revealing local KSDO with a 75 / 25 strength, then at 0:33 up comes 1170, revealing my strongest daytime local, 1170 KCBQ, at 80 / 25 strength.
http://youtu.be/BJl5lebq4jY?t=2m20s - While tuned to 590 kHz, a faint signal from presumed KTIE San Bernardino is trying to break through, but not having much if any success. (Note that a few seconds before, when the radio is oriented differently, strong IBOC hiss is heard. This is from 600 KOGO, which shows a signal strength of 68 / 25.
http://youtu.be/BJl5lebq4jY?t=2m57s - Tuning to 610 kHz reveals a faint station, presumably KAVL Lancaster, trying to break through KOGO's IBOC hash.
BTW I currently lack a stable enough battery-operated oscillator to generate heterodynes at the low end of the AM band, or in longwave. My dad does have an AC-powered vacuum-tube grid-dip meter with an oscillator that can tune from about 400 kHz to about 250 MHz, but it drifts terribly, often by several kHz or a few 10s of kHz just by breathing on it.
Any idea where I can get or make an inexpensive one ($10-15 hopefully) that's stable and has continuous tuning from about 150 kHz to 22 MHz and 64 MHz to 108 MHz or so? I'd also like variable strength on the output, ranging from no detectable signal with it placed right next to my radio, to overloading my radio as badly as in this video taken near 1170 KCBQ's transmitter site (using the SAT and utility ground wire to give what I'd guess, based on this to be a 50-60 dB or more signal boost) from a meter or so away. Bonus points for being able to hook up an audio source via 3.5mm jack, and transmit in AM mode (and hopefully be able to vary its audio bandwidth over a wide range) or in FM mode.
http://youtu.be/BJl5lebq4jY?t=15m57s - a 3 kHz het is audible on 1140 kHz (presumed KNWQ), after switching BW to 6 kHz IF / 3 kHz audio. (In 1 kHz (audio) BW it was too narrow to pass the oscillator on 1143 kHz.)
At around 15:40 when tuning to 1140 kHz, strong splatter from 1130 KSDO is there, in spite of using the narrowest bandwidth setting (1 kHz audio, 2 kHz IF) the radio has. This seems to indicate to me that the skirt selectivity and/or stopband rejection may not nearly be deep enough on the Tecsun.
At 16:12 the RQ-SW20 (used to generate the het by setting it to 9 kHz tuning steps) is switched off briefly, eliminating the het and revealing strong 1130 splatter, then at 16:15 the het returns, proving (to me) that it's not a figment of my imagination.
http://youtu.be/BJl5lebq4jY?t=17m8s - 1 kHz het audible on 1160 (presumed XEQIN). At 17:12 the RQ-SW20 (off camera at this point) is switched off eliminating the het & allowing more 1170 splatter, then at ~ 17:15 the RQ-SW20 is turned back on, returning the 1 kHz het. At around 17:24 the SW20 is in the frame and positioned to try to still hear the het (and not overload the signal I'm trying to beat-note). I then switch it on and off a couple times to verify I'm hearing the het.
http://youtu.be/BJl5lebq4jY?t=18m3s - 1 kHz het faintly audible on 1180 (presumed KERN). At 18:10 the SW20 is switched off, then at 18:14 switched back on, to verify the presence of the het. While the het is off there's fairly strong splatter from 1170 KCBQ.
(next post is last one in series)
Using the GE Superradio III:
http://youtu.be/KrCdjEa4OR4?t=9m11s - 1140 KNWQ detected via 3 kHz het.
http://youtu.be/KrCdjEa4OR4?t=10m36s - 1160 XEQIN detected via 1 kHz het. At 10:44 the RQ-SW20 is switched off, eliminating the het. This reveals strong splatter from 1170 KCBQ, along with a Spanish-speaking female in the background. (I'm not sure, though, if this is XEQIN on 1160, or residual splash from 1130 KSDO, which also carries Spanish-language programming.)
http://youtu.be/KrCdjEa4OR4?t=11m23s - 1180 KERN detected via 1 kHz het. The het is a little more easily audible at around 11:31. At 11:34 the RQ-SW20 (generating the het) is switched off, revealing more 1170 splatter. At 11:40 it's again briefly switched on for a few seconds, revealing the het, then switched off.
Using the Tecsun PL-398mp:
Note that first I enabled a feature I discovered in this radio to modify how the radio behaves with weak signal near strong signals. This is demonstrated in the beginning of the video.
http://youtu.be/BJl5lebq4jY?t=3s - powered on radio, signal weakly received on 1110 kHz showing a signal strength of 45 / 00, dropping a couple seconds later to 43 / 00. I've noticed that these DSP radios will show a high RSSI strength when a weak or no signal is present when in the presence of a strong signal. In some cases I've seen 50/00 and heard no signal when tuned several hundred kHz away from a mega-strong pest.
http://youtu.be/BJl5lebq4jY?t=3s - I begin the sequence to enable the feature. The steps are:
1. Switch radio to SW (press either the "v" or "^" button)
2. Hold the VF button until the radio starts scanning.
3. Quickly & briefly rotate the tuning knob down. If this is done correctly and you're not tuned in the vicinity of a strong station, you will notice the audio get much louder, and the signal display should show 00 / 00 or something like that. (Normally the minimum in LW, MW (AM) and SW modes is 15 / 00.) (I find it interesting that the audio gets louder on blank channels when the signal strength display gets lower. This is even noticeable in "normal" mode.)
When enabling this, the radio defaults to 2 kHz bandwidth setting (which for you traditional radio users is a 4 kHz IF bandwidth), regardless of what it was set at previously. To turn this mode off, turn the radio off and back on, or switch to FM then back to one of the AM-mode bands.
http://youtu.be/BJl5lebq4jY?t=16s - after switching bandwidth to 1 khz (audio, 2 kHz IF), I switch back to AM, revealing a much more easily heard 1110 KDIS. Then, at 0:26 I punch up 1130, revealing local KSDO with a 75 / 25 strength, then at 0:33 up comes 1170, revealing my strongest daytime local, 1170 KCBQ, at 80 / 25 strength.
http://youtu.be/BJl5lebq4jY?t=2m20s - While tuned to 590 kHz, a faint signal from presumed KTIE San Bernardino is trying to break through, but not having much if any success. (Note that a few seconds before, when the radio is oriented differently, strong IBOC hiss is heard. This is from 600 KOGO, which shows a signal strength of 68 / 25.
http://youtu.be/BJl5lebq4jY?t=2m57s - Tuning to 610 kHz reveals a faint station, presumably KAVL Lancaster, trying to break through KOGO's IBOC hash.
BTW I currently lack a stable enough battery-operated oscillator to generate heterodynes at the low end of the AM band, or in longwave. My dad does have an AC-powered vacuum-tube grid-dip meter with an oscillator that can tune from about 400 kHz to about 250 MHz, but it drifts terribly, often by several kHz or a few 10s of kHz just by breathing on it.
Any idea where I can get or make an inexpensive one ($10-15 hopefully) that's stable and has continuous tuning from about 150 kHz to 22 MHz and 64 MHz to 108 MHz or so? I'd also like variable strength on the output, ranging from no detectable signal with it placed right next to my radio, to overloading my radio as badly as in this video taken near 1170 KCBQ's transmitter site (using the SAT and utility ground wire to give what I'd guess, based on this to be a 50-60 dB or more signal boost) from a meter or so away. Bonus points for being able to hook up an audio source via 3.5mm jack, and transmit in AM mode (and hopefully be able to vary its audio bandwidth over a wide range) or in FM mode.
http://youtu.be/BJl5lebq4jY?t=15m57s - a 3 kHz het is audible on 1140 kHz (presumed KNWQ), after switching BW to 6 kHz IF / 3 kHz audio. (In 1 kHz (audio) BW it was too narrow to pass the oscillator on 1143 kHz.)
At around 15:40 when tuning to 1140 kHz, strong splatter from 1130 KSDO is there, in spite of using the narrowest bandwidth setting (1 kHz audio, 2 kHz IF) the radio has. This seems to indicate to me that the skirt selectivity and/or stopband rejection may not nearly be deep enough on the Tecsun.
At 16:12 the RQ-SW20 (used to generate the het by setting it to 9 kHz tuning steps) is switched off briefly, eliminating the het and revealing strong 1130 splatter, then at 16:15 the het returns, proving (to me) that it's not a figment of my imagination.
http://youtu.be/BJl5lebq4jY?t=17m8s - 1 kHz het audible on 1160 (presumed XEQIN). At 17:12 the RQ-SW20 (off camera at this point) is switched off eliminating the het & allowing more 1170 splatter, then at ~ 17:15 the RQ-SW20 is turned back on, returning the 1 kHz het. At around 17:24 the SW20 is in the frame and positioned to try to still hear the het (and not overload the signal I'm trying to beat-note). I then switch it on and off a couple times to verify I'm hearing the het.
http://youtu.be/BJl5lebq4jY?t=18m3s - 1 kHz het faintly audible on 1180 (presumed KERN). At 18:10 the SW20 is switched off, then at 18:14 switched back on, to verify the presence of the het. While the het is off there's fairly strong splatter from 1170 KCBQ.
(next post is last one in series)
(final, continued from previous. I broke these up cause it looked too long for a single post when I used preview.)
Also, my grandma lives 1/3 mile SW of a 23 kW on 1300 (KAZN Pasadena) and a 50 kW on 1430 (KMRB San Gabriel). When I visit her, if I have time to listen to the radio in the middle of the day, I'd like to be able to hear 1290 KKDD San Bernardino (barely inside 0.15 mV/m) or KZSB Santa Barbara (~30% past 0.15 mV/m), and 1440 KUHL Santa Maria (~ 2.5x past 0.15 mV/m) or KFNY Riverside (between 0.15 and 5 mV/m R-L contours). Also making things possibly difficult for 1290 is the presence of KFRN Long Beach on 1280, for which she's likely just inside their 2.5 mV/m contour. At her house, though, 1300 makes even 1280 a tough catch, even with the DSP radios. (I haven't been to her house since I got the PL-398mp, though.) With ordinary radios the splatter from 1300 makes 1280 virtually unreceivable.
Another friend lives about 0.6 mile W/NW of 50kW 1110 KDIS, which spews IBOC. A desired station (if/when I visit them next & have time to listen) would be 1100 KFNX Cave Creek, AZ, for which they are about 2.25x past the R-L 0.15 mV/m contour.
If I ever go to Columbia Park in Torrance, CA, desired daytime reception targets, especially from the SW part of the park (where 1070 KNX's tower is) would include:
1060 KDUS Tempe, AZ (~ 3x past 0.15 mV/m)
1060 KKVV Las Vegas, NV (~ 2.5x past 0.15 mV/m)
1060 KTNS Oakhurst, CA (~ 3x past 0.15 mV/m)
1080 KSCO Santa Cruz, CA (~ 2.5x past 0.15 mV/m)
1080 KSLL Price, UT (~ 4-5x past 0.15 mV/m)
Even with my DSP radio Tecsun PL-398mp set to its narrowest bandwidth, the splatter from local stations completely covers any programming from the desired adjacents in the example videos linked above. What would it take to have much steeper and deeper filters than in the Tecsuns?
I'd like to be able to get full 10 khz stereo audio (on a receiver that has C-Quam capability) on almost all the above targets with NO splatter from the pests, even if I'm facing their transmitter. "Almost all" - as for the stations next to IBOC pests, I still want to be able to receive them, but full 10 khz audio isn't required. For 590 KTIE next to 600 KOGO and its IBOC, for example, I'd be satisfied with getting 4.8 kHz of stereo audio by using a passband from 590.1 to 594.9 kHz, sandwiching between KOGO (595 to 600+) and its IBOC (585 to 590). Same principle goes for 1100 KFNX vs 1110 KDIS at my friend's house.
For 1290 KKDD and KZSB at my grandma's house, though, since neither 1280 KFRN or 1300 KAZN run IBOC, I'd want full 10 kHz audio on the 1290s.
So you may be wondering why I'm looking for daytime reception of stations 2x and 3x past their Radio-Locator 0.15 mV/m contours? A couple links below should show you that it IS possible on my DSP radios in the absence of strong signals.
One day in June 2011 I went to Cameron Corners, CA around midday with my PL-606. (Reception location was ~ 32°37'48"N 116°28'23"W.)
A couple barefoot audio recordings are below:
1090 XEPRS - R-L says XEPRS is DA-N, but DavidEduardo says they're DA-1. Looking at their night pattern (used in the daytime) I was about 3x past their 0.5mV/m contour. (the 0.15mV/m doesn't show on R-L's night patterns.)
1160 XEQIN - I was about 2.5x past their 0.15 mV/m contour.
Also, my grandma lives 1/3 mile SW of a 23 kW on 1300 (KAZN Pasadena) and a 50 kW on 1430 (KMRB San Gabriel). When I visit her, if I have time to listen to the radio in the middle of the day, I'd like to be able to hear 1290 KKDD San Bernardino (barely inside 0.15 mV/m) or KZSB Santa Barbara (~30% past 0.15 mV/m), and 1440 KUHL Santa Maria (~ 2.5x past 0.15 mV/m) or KFNY Riverside (between 0.15 and 5 mV/m R-L contours). Also making things possibly difficult for 1290 is the presence of KFRN Long Beach on 1280, for which she's likely just inside their 2.5 mV/m contour. At her house, though, 1300 makes even 1280 a tough catch, even with the DSP radios. (I haven't been to her house since I got the PL-398mp, though.) With ordinary radios the splatter from 1300 makes 1280 virtually unreceivable.
Another friend lives about 0.6 mile W/NW of 50kW 1110 KDIS, which spews IBOC. A desired station (if/when I visit them next & have time to listen) would be 1100 KFNX Cave Creek, AZ, for which they are about 2.25x past the R-L 0.15 mV/m contour.
If I ever go to Columbia Park in Torrance, CA, desired daytime reception targets, especially from the SW part of the park (where 1070 KNX's tower is) would include:
1060 KDUS Tempe, AZ (~ 3x past 0.15 mV/m)
1060 KKVV Las Vegas, NV (~ 2.5x past 0.15 mV/m)
1060 KTNS Oakhurst, CA (~ 3x past 0.15 mV/m)
1080 KSCO Santa Cruz, CA (~ 2.5x past 0.15 mV/m)
1080 KSLL Price, UT (~ 4-5x past 0.15 mV/m)
Even with my DSP radio Tecsun PL-398mp set to its narrowest bandwidth, the splatter from local stations completely covers any programming from the desired adjacents in the example videos linked above. What would it take to have much steeper and deeper filters than in the Tecsuns?
I'd like to be able to get full 10 khz stereo audio (on a receiver that has C-Quam capability) on almost all the above targets with NO splatter from the pests, even if I'm facing their transmitter. "Almost all" - as for the stations next to IBOC pests, I still want to be able to receive them, but full 10 khz audio isn't required. For 590 KTIE next to 600 KOGO and its IBOC, for example, I'd be satisfied with getting 4.8 kHz of stereo audio by using a passband from 590.1 to 594.9 kHz, sandwiching between KOGO (595 to 600+) and its IBOC (585 to 590). Same principle goes for 1100 KFNX vs 1110 KDIS at my friend's house.
For 1290 KKDD and KZSB at my grandma's house, though, since neither 1280 KFRN or 1300 KAZN run IBOC, I'd want full 10 kHz audio on the 1290s.
So you may be wondering why I'm looking for daytime reception of stations 2x and 3x past their Radio-Locator 0.15 mV/m contours? A couple links below should show you that it IS possible on my DSP radios in the absence of strong signals.
One day in June 2011 I went to Cameron Corners, CA around midday with my PL-606. (Reception location was ~ 32°37'48"N 116°28'23"W.)
A couple barefoot audio recordings are below:
1090 XEPRS - R-L says XEPRS is DA-N, but DavidEduardo says they're DA-1. Looking at their night pattern (used in the daytime) I was about 3x past their 0.5mV/m contour. (the 0.15mV/m doesn't show on R-L's night patterns.)
1160 XEQIN - I was about 2.5x past their 0.15 mV/m contour.
R
rbrucecarter5
Guest
Besides the nulling techniques described in great detail above - I find the CCrane radio EP, with its narrow +/- 2 kHz IF setting, can help selectivity. It is not quite up to transatlantic split channels in the middle of the country, but perhaps on the coasts.
The SRF-59 and M-37 use 50 kHz IF frequencies, which allow quite a bit more selectivity than the standard 455 kHz IF - something akin to the old Delcos of the 60's and 70's which used 262.5 kHz. The lower the IF frequency, the higher the selectivity. In general - there are exceptions but this is a fairly dependable route. Sony is the only one that can use their 50 kHz IF chip - and that chip has been reported in some other Sony models, including a larger portable.
There is a mod you can do on your own to any AM radio. Most cheap wireless keyboards and mice use a circuit that has a three element, stagger tuned 455 kHz ceramic filter. It is available from a couple of manufacturers, but all will have the number "455" on the top. They are usually five lead, which makes it hard to unsolder from a double sided board. Usually, all the grounds are along one edge, with input and output along the other edge. It will take some little jumper wires and dexterity, but you can usually use it to replace the single, cheap and wide ceramic filter in most modern radios. It helps quite a lot in most radios, although the ceramic filter has a +/- 6 kHz response. First adjacents aren't helped that much.
If you are specifically trying to get stations either side of KRLD, they have been reported to use IBOC, so more selectivity will not help you. Prior to IBOC, I had no trouble getting KNX in the early morning hours.
The SRF-59 and M-37 use 50 kHz IF frequencies, which allow quite a bit more selectivity than the standard 455 kHz IF - something akin to the old Delcos of the 60's and 70's which used 262.5 kHz. The lower the IF frequency, the higher the selectivity. In general - there are exceptions but this is a fairly dependable route. Sony is the only one that can use their 50 kHz IF chip - and that chip has been reported in some other Sony models, including a larger portable.
There is a mod you can do on your own to any AM radio. Most cheap wireless keyboards and mice use a circuit that has a three element, stagger tuned 455 kHz ceramic filter. It is available from a couple of manufacturers, but all will have the number "455" on the top. They are usually five lead, which makes it hard to unsolder from a double sided board. Usually, all the grounds are along one edge, with input and output along the other edge. It will take some little jumper wires and dexterity, but you can usually use it to replace the single, cheap and wide ceramic filter in most modern radios. It helps quite a lot in most radios, although the ceramic filter has a +/- 6 kHz response. First adjacents aren't helped that much.
If you are specifically trying to get stations either side of KRLD, they have been reported to use IBOC, so more selectivity will not help you. Prior to IBOC, I had no trouble getting KNX in the early morning hours.
RoyTex said:
It's possible to use the R75's twin PBT controls to narrow the IF further to get the adjacents next to strong locals that don't use IBOC, or if the 1080 isn't using the IBOC, then you may want to try to flip the mode to LSB to get anything on 1070, and turn both PBTs toward counterclockwise, or use USB and the PBTs toward the other way to get anyting on 1090.
RoyTex said:
I used to have the same problem when using my DX-160 through a longwire. Some channels just were nothing but splatter, and there was nothing I could do about it. Then when I got my boombox in the 1980's I learned -- almost by accident -- that you can eliminate most splatter by rotating the radio.
So -- like one of the other posters here has said -- try running that R75 through a loop antenna. Then rotate the loop, it will 'null' out the splatter from the offending station most times. If that doesn't help enough, after rotating the antenna, put the radio on its narrow filter and tune to the side of the target channel away from the offending channel.
An example: I tune my radio to 720 Khz. Local splatter master KIRO-710 generally covers it on all my radios, whether boombox, Superadio, TRF, or a digital portable like the DX-398.
After tuning to 720, I turn the radio to KIRO's "null" (actually, the spot where the splatter weakens). Usually, this means one of the ends of the radio's loopstick is aiming at the offending station's transmitter. If propagation is in I will be able to just make out KFIR in Oregon, or KDWN in Las Vegas. If I tune my radios just a hair towards the high side of 720, the splatter will be reduced even further.
You don't even need a radio with terrific selectivity to do this. If I can do it with a boombox or a TRF, you could probably do it with a better radio.
And like Pianoplayer88key says, if you've got a portable, you can also tilt the radio at an upwards or downwards angle, and it often will weaken the offending signal even further. Some guys who have big wire loops also tilt them at an angle to deepen a 'null'.
I was able to hear KXEL Waterloo, Iowa in local station KXPA-1540's weak spot by rotating my TRF to KXPA's weakest spot, and then tilting the radio, which weakened KXPA even further. I could still hear KXPA, but KXEL was audible behind it. It helped that KXPA's weak spot had the TRF facing E-W (towards Iowa).
I've never used an R75 (or even seen one, aside from a photograph), but
I'm guessing that with a loop antenna your R75 would be able to do the job adequately. Or you might try one of the portables mentioned here. From what I've heard, some of them have terrific selectivity.
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