[AMRadio] I'm not an antenna expert
I don't even play one on TeeVee... So, in advance of a lot of EZNec work (and I don't have the experience with that program to derive much 'good' out of it right now) - I'd like to ask what may seem to be a rather obvious HF antenna question. Due to the usual reasons - my HF antenna is a loop suspended from my backyard fence - approx 430' total, closed loop, 5' off the ground, fed by 450 ohm ladder line back into the shack, using an Ameritron ATR-15 tuner to match the system to my Valiant. The tuner and transmitter are bonded to a very heavy ground system via an 8' stake less than 3' from the gear. There is no ground system under the antenna, other than that which Nature provided - and with the current winter conditions, the ground is rather wet and conductive. This antenna system exhibits the following SWR: 160M - 1.3:1 80M - 1.1:1 40M - +3:1 20M - 2:1 15M - +3:1 10M - +3:1 The tuner capacitors end up being all-the-way-meshed on the 'misbehaving' bands - not so on 160, 80, and 20. So I'll see Y'all on 3880 and just fergit the rest. ;} No but seriously folks: obviously the feedpoint resistance is outside the tuner's ability to cope with it at various frequencies. I'm thinking the first unscientific experiment might be to go to the opposite side of the loop from the feedpoint and cut it into a big horizontal bent dipole - mainly because that will take about 45 seconds to accomplish - one of the benefits of having one's entire antenna at ahoulder-height. But I'd like to get some other opinions - I know there's an electrical Pattern here from the info - and I have some other ideas based on that. And no, I can't put up a real antenna so I'm pretty much comiited to making this one work as well as I can. Until I move the QTH to somewhere with a few acres and room for Lots of Wire. Cheers John KB6SCO
[AMRadio] RE: Homebrew PW Modulator
The homebrew modulator has been sold. On 11 Jan 2006 at 9:26, Brian Carling wrote: FOR SALE: Neat little homebrew 15-25W modulator with pair of push-pull 6AQ5s. Has gain control and RCA input. No power supply. Excellent job - I did not build it, but whoever did was an expert. Has 12AX7 preamp etc. All in nice shape. Available for $35.00 plus shipping
Re: [AMRadio] I'm not an antenna expert
John Lawson wrote: On Wed, 11 Jan 2006, Brian Carling wrote: Should work great for close in work, out to about 200-500 miles. Well, except for the bands where the system SWR is over 3:1 - then it don't work at all ;} and I'm afraid of what I'm doing to the tuner/transmitter at that amount of reflected power. There's no law that says you have to run full power output, to tune SWR on an impedance matching device... I'd just as soon use a solid state rig, that has SWR protection in it... slowly adjust the impedance matching device, until you get full output of the ricebox, and minimum standing wave ratio. Then, DON'T TOUCH IT! Just switch rigs, and tune the transmitter to that setting. it's resonant. otherwise, you might be loading up on some harmonic -- 73 = Best Regards, -Geoff/W5OMR
Re: [AMRadio] Negative Loading circuits - good, bad, or ?
In a message dated 1/11/06 5:26:15 AM, [EMAIL PROTECTED] writes: The 3 diode circuit is supposed to prevent the plate voltage from going to zero. I use variacs on the power supply so I can set the point at which the circuit starts working, and no matter if I set it to 95, 90, or 85% I get splatter if the audio would exceed 100% negative, so the circuit seems to do no good. Brett, What circuit are you using? The ones I referenced don't call for variacs or auxiliary power supplies. Dennis D. W7QHO Glendale, CA
Re: [AMRadio] I'm not an antenna expert
In a message dated 1/11/06 9:18:50 AM, [EMAIL PROTECTED] writes: I'm afraid of what I'm doing to the tuner/transmitter at that amount of reflected power. John, What kind of a tuner are you using and where are you measuring the SWR? Dennis D. W7QHO Glendale, CA
[AMRadio] ARRL bandwidth petition draws anti-AM'ers out of the woodwork.
Proceeding: RM-11306 Type Code: CO Date Received/Adopted: 01/10/06Date Released/Denied: Document Type: COMMENTTotal Pages: 1 File Number/Community:DA/FCC Number: Filed on Behalf of: Richard L. Tannehill Filed By: Attorney/Author Name:Document Date: Complete Mailing Address: 5410 W. diana Ave. Glendale, AZ 85302 -4870 Brief Comment I agree with the ARRL petition for regulation by bandwidth, and support it, with one major exception. The League claims that their plan does not favor one mode over another. Not true. It favors AM-DSB operators. It would allow for 9 KHz AM modulation, in bands which otherwise are limited to 3.5 KHz. These include the lower HF bands, which are quite crowded at times. The solution is simply to restrict AM-DSB to above 28.5 MHz. (10 meters above) Amateurs and the league have been upset in the past over wide-SSB modulation, meant to improve audio quality. AM is no different from this. It is an old modulation that adds nothing to advancing the technological art, and should be confined to bands where there is ample spectrum available. Richard L. Tannehill P.E. - W7RT ARRL Life Member (45-years amateur licensed) ___ This message was typed using the DVORAK keyboard layout. Try it - you'll like it. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/
RE: [AMRadio] I'm not an antenna expert
I would be curious as to what the fundamental resonance frequency is and what the high impedance and low impedance actually is at the feed point of the antenna without balanced line. If the feed point at the transmitter end of the line is too low, add or subtract some feed line. You can also add and subtract line from the opposite side of the antenna. You mentioned earlier about opening up the opposite end. This could be a good experiment. And also consider capacitance or inductance added where you make the cut or adding transmission line at that point with and open or closed end going nowhere except to a stick to hold it up off of the ground. It doesn't take a mathematical antenna expert to experiment You only need some extra wire. Fun Stuff John, WA5BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Lawson Sent: Wednesday, January 11, 2006 10:44 AM To: amradio@mailman.qth.net Cc: [EMAIL PROTECTED] Subject: [AMRadio] I'm not an antenna expert I don't even play one on TeeVee... So, in advance of a lot of EZNec work (and I don't have the experience with that program to derive much 'good' out of it right now) - I'd like to ask what may seem to be a rather obvious HF antenna question. Due to the usual reasons - my HF antenna is a loop suspended from my backyard fence - approx 430' total, closed loop, 5' off the ground, fed by 450 ohm ladder line back into the shack, using an Ameritron ATR-15 tuner to match the system to my Valiant. The tuner and transmitter are bonded to a very heavy ground system via an 8' stake less than 3' from the gear. There is no ground system under the antenna, other than that which Nature provided - and with the current winter conditions, the ground is rather wet and conductive. This antenna system exhibits the following SWR: 160M - 1.3:1 80M - 1.1:1 40M - +3:1 20M - 2:1 15M - +3:1 10M - +3:1 The tuner capacitors end up being all-the-way-meshed on the 'misbehaving' bands - not so on 160, 80, and 20. So I'll see Y'all on 3880 and just fergit the rest. ;} No but seriously folks: obviously the feedpoint resistance is outside the tuner's ability to cope with it at various frequencies. I'm thinking the first unscientific experiment might be to go to the opposite side of the loop from the feedpoint and cut it into a big horizontal bent dipole - mainly because that will take about 45 seconds to accomplish - one of the benefits of having one's entire antenna at ahoulder-height. But I'd like to get some other opinions - I know there's an electrical Pattern here from the info - and I have some other ideas based on that. And no, I can't put up a real antenna so I'm pretty much comiited to making this one work as well as I can. Until I move the QTH to somewhere with a few acres and room for Lots of Wire. Cheers John KB6SCO __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
Re: [AMRadio] Negative Loading circuits - good, bad, or ?
Thanks, Larry, I'll be interested in that. I understand that one large AM network - Clear Channel, I believe - is cutting their AM audio bandwidth to 5 KHz to make distant AM reception better (less splash from adjacent channels). I remember back in the late 60s, a little 250 watt daytime station on 540 KHz in Islip, Long Island ran some sort of clipping to sound louder. I don't know about splatter, but it really didn't sound good that way. It was pretty loud, though. But in amateur operation, some gentle curvature can curb the peaks that would get sharply snipped off by overmodulation, without a lot of splatter. Overall, it would probably reduce the general splatter level somewhat. Also it would be useful to have some kind of diode and resistor to catch peaks that do overmodulate, and keep them from making a voltage spike that could blow the modulation transformer. But if the circuit is being used to achieve high audio levels, then a low pass filter ought to follow the diodes. And the transient performance of the filter must be such that overshoot is minimized, because overshoot would overmodulate and splatter too. Generally a non-overshoot filter gives a soft cutoff rather than a sharp cutoff, unless it is complex and high order. I use low level asymmetrical clipping, and I can filter that with a 3.5 KHz low-pass filter in crowded conditions when I push the clipper hard. I accidentally found that a side chain servo loop could have its time constant aligned with the modulator, and produce very good clipping control, so that's how I do it. The clipper is really a limited amount of extremely fast peak limiting compression, with a time constant around a millisecond or so, riding on the slower 0.2 second time constant of the peak limiter, with a slower time constant coupled on a resistive divider for some slow average compression action as well. using a moderately complex RC network as a gain control loop filter. Because of this time constant, sibilents are treated with a more peak limiting action so there is less intermodulation, and lower frequency stuff is softly clipped. I shorten the time constant and increase the audio drive to push this harder, accepting some distortion for punch. When I push it like that, I use the low-pass filter, which is just a second-order Sallen-Key. I got a comment on how narrow the signal was, and yet it sounded clear because of upper midrange boost. The millisecond range time constant of the servo-clipper avoids a lot of high frequency harmonic generation before the audio hits the filter. Bacon, WA3WDR - Original Message - From: Larry Will [EMAIL PROTECTED] To: Discussion of AM Radio amradio@mailman.qth.net Sent: Wednesday, January 11, 2006 7:07 PM Subject: Re: [AMRadio] Negative Loading circuits - good, bad, or ? Bacon, I'll pull out a copy of the NRSC spec on the AM B'CST audio shelving filter when I get a chance and pass along some details. Larry At 11:16 AM 1/11/2006, you wrote: Any distortion of the modulating waveform causes harmonic distortion and therefore splatter. The sharper a waveform discontinuity is, the more high-level harmonic energy it contains, and that harmonic energy becomes splatter on the air. This is why a low-pass filter is used in speech clipping systems. But the sharp clipping caused by overmodulation can not be filtered at the audio level. The extreme sharpness of clipping resulting from overmodulation is the reason that overmodulation causes so much splatter. The idea of the diode loading system is to produce a softer clipping that produces much less splatter than raw overmodulation. Additional diodes and resistors are often added to provide protective loading for the modulator on negative peaks that would have been unloaded in simple diode systems or with no diodes at all. This protective loading reduces voltage spikes that can destroy the modulation transformer. Some distortion is still produced with the diode loading system, and therefore some splatter will result. But unless there is some other problem, the splatter is much less severe than raw overmodulation, and the high frequency products caused by this action can be filtered at the audio level. You can add a high level splatter filter, although that will limit your high frequency response. You can have a few filters or a few filter settings, like 10 KHz for clear conditions, 6 KHz for intermediate conditions, and 3.5 KHz for crowded conditions. Some technical problems can cause extra splatter. If the modulator is marginally stable, it is possible that the dynamic change in loading resulting from the diode action can cause triggered parasitics at specific points on the audio waveform. This can result significant splatter, and it might have a distinctive resonant sound, which you would hear as resonances or concentrated spectral points in the splatter on a sideband receiver tuned some
Re: [AMRadio] Negative Loading circuits - good, bad, or ?
Hi Gary, Yes, a smooth one-sided curvature produces an even-order nonlinearity that generally produces even harmonic distortion with low intermodulation. Sharper asymmetrical clipping with sharp slope transitions causes intermodulation and higher order even harmonics, and symmetrical clipping produces odd harmonic distortion and intermodulation. My asymmetrical clipper clips positive and negative peaks, with moderately sharp slope discontinuity, although at different voltages positive and negative, so odd and even harmonics are produced. A square-law characteristic would produce some even-order harmonic distortion and some soft clipping of peaks in one direction. The closer the operating point is to zero on this curve, and the higher the signal amplitude, the more the one side gets squeezed. Most of the distortion would be second harmonic, which will cause sibilents and upper midrange sounds to cause some splatter, but sounds below 1.5 KHz will not cause splatter beyond 3 KHz from the carrier unless they go below zero on the square law curve (which is impossible, so they get cut off), or they reach overmodulation proportions. Maybe a variable-bias square law processor at low level, with a low level variable cutoff low-pass filter, would help. The diodes can remain at the modulator output to catch occasional errant peaks. I just thought about how capacitance after the diodes can cause diagonal clipping, a slew-rate limitation due to the changing impedance presented to the capacitance and the modulated stage. This would add to the distortion and splatter, because the diode action would not be what was expected, and it would be worse at higher frequecies. The capacitance itself would filter the higher frequency distortion products somewhat, but I think that the diagonal clipping would increase close-in splatter. - Original Message - From: Gary Schafer [EMAIL PROTECTED] To: 'Discussion of AM Radio' amradio@mailman.qth.net Sent: Wednesday, January 11, 2006 10:16 PM Subject: RE: [AMRadio] Negative Loading circuits - good, bad, or ? Did you know that clipping an asymmetrical audio signal produces even order harmonics where clipping symmetrical signals produces only odd order products. 73 Gary K4FMX -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Bob Bruhns Sent: Wednesday, January 11, 2006 9:43 PM To: Discussion of AM Radio Subject: Re: [AMRadio] Negative Loading circuits - good, bad, or ? Thanks, Larry, I'll be interested in that. I understand that one large AM network - Clear Channel, I believe - is cutting their AM audio bandwidth to 5 KHz to make distant AM reception better (less splash from adjacent channels). I remember back in the late 60s, a little 250 watt daytime station on 540 KHz in Islip, Long Island ran some sort of clipping to sound louder. I don't know about splatter, but it really didn't sound good that way. It was pretty loud, though. But in amateur operation, some gentle curvature can curb the peaks that would get sharply snipped off by overmodulation, without a lot of splatter. Overall, it would probably reduce the general splatter level somewhat. Also it would be useful to have some kind of diode and resistor to catch peaks that do overmodulate, and keep them from making a voltage spike that could blow the modulation transformer. But if the circuit is being used to achieve high audio levels, then a low pass filter ought to follow the diodes. And the transient performance of the filter must be such that overshoot is minimized, because overshoot would overmodulate and splatter too. Generally a non-overshoot filter gives a soft cutoff rather than a sharp cutoff, unless it is complex and high order. I use low level asymmetrical clipping, and I can filter that with a 3.5 KHz low-pass filter in crowded conditions when I push the clipper hard. I accidentally found that a side chain servo loop could have its time constant aligned with the modulator, and produce very good clipping control, so that's how I do it. The clipper is really a limited amount of extremely fast peak limiting compression, with a time constant around a millisecond or so, riding on the slower 0.2 second time constant of the peak limiter, with a slower time constant coupled on a resistive divider for some slow average compression action as well. using a moderately complex RC network as a gain control loop filter. Because of this time constant, sibilents are treated with a more peak limiting action so there is less intermodulation, and lower frequency stuff is softly clipped. I shorten the time constant and increase the audio drive to push this harder, accepting some distortion for punch. When I push it like that, I use the low-pass filter, which is just a second-order Sallen-Key. I got a comment on how narrow the signal was, and yet it sounded clear because of upper midrange boost.
Re: [AMRadio] Negative Loading circuits - good, bad, or ?
Sharper asymmetrical clipping with sharp slope transitions causes intermodulation and higher order even harmonics Oops... not just even, but odd too, if positive and negative peaks are clipped. Bacon, WA3WDR
Re: [AMRadio] ARRL bandwidth petition draws anti-AM'ers out of the woodwork.
have to agree W7RT need to check into a rest home for the warped. as for the ARRL what i do not understand is WHY we keep putting these fools back in office ? i keep my membership just so i can vote for the new guy each time. and stay in the dxcc program. other then that the ARRL is about useless anymore. 73 Tony wa4jqs since 1962
