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New member Username: Norm_mccombPost Number: 1 Registered: Nov-18 | I've recently acquired an early 1970's Sherwood S-7100A receiver with analog tuning. I've attached a 60 foot long-wire antenna to a nearby tree for AM reception and enjoy searching for distant AM stations late at night (my record is Nashville, TN from western MA). The only experience I've had with digital tuning is on my car radio where tuning is in 10 kHz increments set by the radio itself; there is no ability to fine tune a weaker station as with an analog tuner. I realize that AM stations broadcast at 10 kHz intervals, but because of atmospheric conditions, the best reception can sometimes be received slightly off the broadcast frequency. This is where fine tuning becomes important (at least for faint stations). I'd be interested in upgrading to a nice digital tuner but am concerned about the ability to fine tune a faint station. It seems with a digital tuner, if you don't 'get it' at the 10 kHz interval, you won't receive it at all. Am I correct that there is no way to 'scroll' between the 10 kHz intervals with a digital tuner as one can with an analog tuner, or is the reception of faint stations with a digital tuner more dependent on the quality of the external antenna than the tuner? Thanks for any reply. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18587 Registered: May-04 | . De-tuning with an analog tuner is most often a matter of the vagaries of an analog tuner. You should notice a "log scale" on your tuner's face. It is used to mark more precise points for tuning that are not related to the more conventional "570", "1080" or "820" marks on the tuner glass. If you are unfamiliar with the operation of an analog tuner, open the top of your receiver and look at the mechanism that moves the tuning dial. Not exactly a precision piece of equipment nor is it a highly reliable component over time. As you have noted, atmospheric conditions play into long distance reception. AM radio waves however are quite long and tend to wrap around the curvature of the Earth. Cloud cover however can cause spurious reflections that will overcome the ability of an analog tuner to discriminate between the actual signal and the reflected signal, somewhat similar to what is called "multipath" in an FM tuner. Detuning can (sometimes) select between the two incoming signals and allow the user to select the stronger of the two, though background noise levels will tend to increase in such a situation. Changes in the location and position of your wire antenna might make a difference. The problem with that approach is, you tend to play a game of whack-a-mole with stations where this location is best for this bandwidth on your tuner and that location for that bandwidth on your tuner. I haven't dealt with roof top antennas in over two decades but there were a few which offered better-than-a-wire AM reception. Since the greatest majority of AM stations with sufficient broadcast wattage available to make dx'ing possible have long ago switched to 24/7/365 talk and religious broadcasting, which nicely accommodates the truckers, AM has lost any value to a typical high end tuner designer. It was quite common in the 1970's to have far better long distance reception from your car's AM radio than from your home's receiver. Similar to any other digital audio device, the selected frequency of a digital tuner is locked to an oscillator that ensures exact frequency tuning. There is no way to de-tune a digital tuner, only the ability to buy a tuner with greater discrimination between lock points. * IMO Sherwood's tuners were never among the best as a line of products. By the mid-70's Sherwood was a lesser line and they were more likely to recycle older designs rather than go for new performance levels. Add to that, after the '70's, tuners were judged on their FM performance. AM tuning was a lesser concern for designers after FM began to gain in popularity and the number of stations grew rapidly in the late 1970's and early 1980's. By the mid-60's FM radio had moved far beyond its college station roots. It was no longer only the very large, and mostly East Coast, cities which boasted well regarded FM stations. Very few of my customers even asked about the performance of the tuner in any receiver they were considering. If you really wanted improved tuner performance, you sought out a separate tuner rather than the thrown in component found in most receivers. Receivers began more and more to consider tuners a throw away inclusion which only had to provide the bare necessities of radio performance. Other devices crowded out tuners as desirable music sources. Of the mid-priced separate tuners available, my choice would be either a top'o'the line Sansui or a Kenwood. Pioneer had a few very good separate tuners, but not enough to recommend them as a line IMO. Kenwood was known as Trio in the rest of the world and they were a well known name in the ham radio market. The real dx-ers preferred ham radio which gave Kenwood/Trio a real leg up in tuner design. If you can swing the cost, a McIntosh or a Marantz separate tuner would be your best choice for reception and quality. McIntosh included very good to near excellent tuners on their early receivers but soon were producing FM only tuners. Marantz, as it existed under Saul Marantz, never built a receiver. . |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18589 Registered: May-04 | . I imagine you might have already found this information but for completeness I will say there are numerous portable radios which are said to have excellent long distance reception. Quite different from experimenting with a vintage receiver but vintage receivers do have the typical issues of vintage receivers. If your interest is more in seeing just what's out there on the radio, give a thought to a few of the better portables. https://www.google.com/search?q=ge+superradio&rlz=1CAACAY_enUS754US756&oq=ge+sup erradio&aqs=chrome..69i57.7764j0j1&sourceid=chrome&ie=UTF-8 https://www.google.com/search?q=best+AM+radios+for+long+distance+reception&rlz=1 CAACAY_enUS754US756&oq=best+AM+radios+for+long+distance+reception&aqs=chrome..69 i57.14413j0j1&sourceid=chrome&ie=UTF-8 Of course, with any radio your reception quality will be determined by the quality and location of your antenna; https://www.ccrane.com/expert-advice/all/1/article/18 . |
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New member Username: Norm_mccombPost Number: 2 Registered: Nov-18 | Jan, thank you for the great information, it was far more than I'd expected. I've recently retired and spend more time 'puttering around' in my basement than I used to (I'm actually asking my wife if there are any chores she'd like me to do). I was at a neighbor's tag sale and saw the Sherwood with a pair of box speakers for $35.00 and felt it would be a nice addition to my work area. Unfortunately, being below ground in the basement wasn't great for reception. A T-antenna from Walmart helped with FM but did nothing for AM. Having time on my hands, I began researching external AM antennas online and came across the long wire. This helped immensely and I was suddenly 'hooked' on DXing. Your statement: "Similar to any other digital audio device, the selected frequency of a digital tuner is locked to an oscillator that ensures exact frequency tuning. There is no way to de-tune a digital tuner, only the ability to buy a tuner with greater discrimination between lock points." was the exact answer I was looking for. One more question about digital tuning: If, for example, there are two stations (A and B) broadcasting at the same frequency in roughly a straight line to my receiver ( C), won't I only always pick up the stronger station and never the weaker?, Is this a situation where a directional antenna and/or a tuner with better discrimination becomes critical? 5000 watts 1000 watts A---------------B---------------C Forgive my ignorance, this is new to me, but I find it interesting. In analog tuning if I find a weaker station next to a stronger station, I can 'shade' the turner away from the stronger toward the weaker for better reception. From your explanation my understanding is that there is no way to do this with a digital tuner because it is locked to a specific frequency. That the only way to increase my chances of receiving that weaker station is to use a radio with better sensitivity ("better discrimination between lock points"). That there is no human intervention in deciding on the station, that the stronger station will always be locked onto electronically......unless I use a radio with better discrimination. The links you've provided are a great help and nice place to start. They show me that there are much better radios than what I have for what I want to do, and at reasonable prices, too. Thanks. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18594 Registered: May-04 | . First, realize that while I sold high end audio for over 30 years and was involved in pro audio for many of those years, it's been 20 years since I left sales. And separate tuners were never a big seller so my recollection of tuner specs may be a bit weak. As I said, I seldom discussed the tuner built into a receiver. Second, don't take my comments about the Sherwood as a knock on the receiver. It's only to say that if you are interested in DX'ing, there are better tuners available which are more specifically designed for RF performance. And, finally, the one truism of tuners is, they are only as good as their antenna. I'm going to assume you are asking primarily about AM performance. Allow me to take the time to warn you about vintage audio equipment. All audio components are designed around parts that will age. Caps are the most sensitive to aging, a condition which can exhibit drying out or leakage of the internals in most vintage equipment. The most serious of the failing caps in a receiver will be the power supply filter caps and the coupling caps which exist between stages of the circuits. When a receiver has been allowed to sit in storage, it is quite common for the caps to begin to fail. While it is not uncommon for the receiver (or other component) to power up at first when removed from storage, the caps cannot typically withstand continually being hit by 120VAC with each power up. A vintage component may continue to work indefinitely or it may fail with the second or third (or more) week of use. There's not much the new owner can do to prevent this situation and the only repair would be to have someone willing to work on vintage equipment do a complete overhaul of the component. This often exceeds the monetary value of the vintage component. Just a warning. There's virtually nothing to do which will prevent the failure unless you have a test full of equipment. If the component continues to operate, go with it. If it fails to power up, or there is a low 60Hz hum which begins to accompany the sound, the caps are on their way out. If the noise occurs first, I would no longer use the component as complete failure in likely. Better to repair minor problems that continue on until the unit totally fails. Should the caps fail, there is always the chance DC Voltage may pass through the component's circuitry. AC Voltage is rectified within the component and most of the receiver actually operates on DC. Even a tiny amount of DC reaching the speakers will destroy them. Other problems with vintage gear can be associated with specific parts such as caps and resistors drifting off their specified value. This can allow excessive/insufficient Voltage to enter a low Voltage circuit. Excessive distortion and noise are the first signals of such an event though there typically is not much warning, the unit simply does not function well. Good luck. . |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 18595 Registered: May-04 | . "A T-antenna from Walmart helped with FM but did nothing for AM." Correct, they are two discrete circuits within the tuner and should have discrete antenna connections on the back of the receiver. A "whip" antenna was typically supplied with the receiver and it allowed decent AM reception in most urban settings. Some tuners simply supplied one connector for the AM antenna while others might give the user the option of two connectors which would give the user the option to use an AM loop type antenna. https://www.google.com/search?q=AM+loop+antenna&rlz=1CAACAY_enUS754US756&oq=AM+l oop+antenna&aqs=chrome..69i57.6768j0j1&sourceid=chrome&ie=UTF-8 "If, for example, there are two stations (A and B) broadcasting at the same frequency in roughly a straight line to my receiver ( C), won't I only always pick up the stronger station and never the weaker?" Depends on the tuner and the strength of the signals. Sensitivity is simply the measure of how little signal Voltage is required to get the tuner to respond to the frequency. Most tuners have long had the ability to lock onto a frequency and it is this locking capacity that is important. Sensitvity alone doesn't fully describe the ability of a tuner to avoid signal drift. https://www.google.com/search?q=rf+tuner+signal+drift&rlz=1CAACAY_enUS754US756&o q=rf+tuner+signal+drift&aqs=chrome..69i57.10773j0j1&sourceid=chrome&ie=UTF-8 Typically the FCC has spaced channels far enough apart within the typical broadcast range of each channel to make two channels arriving on the same frequency less likely. However, depending on the tuner and the antenna and the atmospheric conditions, there is the chance for AM stations to overlap since they have the greatest range for distance reception. FM seldom has this problem because FM radio waves are far shorter than are AM waves and FM's maximum distance for decent reception is about 75 to 100 miles on the high end. This allows the FFC to keep overlapping FM channels rather well spaced out within geographical regions. FM is far more sensitive to "multipath" reflections which overwhelm its ability to discriminate between two signals on the same frequency but arriving at the tuner's front end due to reflections of the direct signal off nearby buildings and structures. https://www.google.com/search?rlz=1CAACAY_enUS754US756&ei=pH3rW4SVEsO5gged4r7IAg &q=rf+tuner+multipath&oq=rf+tuner+multipath&gs_l=psy-ab.3...295385.300318..30197 6...0.0..0.126.1072.3j7......0....1..gws-wiz.......0j0i71j0i67j0i22i30j33i160.DL 3eGcnSPmg There are various circuits built into an AM receiver which will discriminate between two signals and tend to select the stronger of the two. This spec is termed "selectivity". While most people interested in tuner performance look first at sensitivity, selectivity is actually the more critical spec in most cases. https://en.wikipedia.org/wiki/Selectivity_(electronic) One problem more associated with AM reception is the cheater channel. FCC regulations require any AM station to reduce its broadcast wattage after a certain time each evening. This is intended to prevent congestion on the AM bandwidth at a time of day where DX'ing is a natural occurrence due to the absence of the sun and the effect that has on the atmosphere. However, if you remember Wolf Man Jack, he was broadcasting on a rogue channel which did not reduce power and that allowed his signal to be heard well over 1,000 miles away. The channel also had sufficient wattage to overwhelm most local channels abiding by the law. Today, there are numerous "clear channel" AM stations which, while following the regulations, are powerful enough to still swallow up many lower powered local channels. Related closely to the selectivity spec is "alternate/adjacent channel rejection" which is intended to inform a potential buyer of the tuner's ability to only select one channel when two signals, alternate or adjacent, reach the front end of the tuner. https://www.google.com/search?rlz=1CAACAY_enUS754US756&ei=037rW_3IK8WOggeLga6QCg &q=rf+tuner+alternate+channel+rejection&oq=rf+tuner+alternate+channel+rejection& gs_l=psy-ab.3...229527.241672..243663...0.0..1.223.3669.20j15j1......0....1..gws -wiz.......0j0i71j33i160j0i22i30j0i67j0i22i10i30j33i22i29i30j33i299.Jkkiifk3mV0 So those are the two most important specs to look at when buying a tuner. However, ... there's always a "however" in consumer audio. Specs are seldom taken in real world conditions. Tuner specs are often the result of a bench set up where the entire test in confined to a space no larger than a compact automobile. Secondly, specs can be weighted. Weighting is a system of allowances given to any test which would be preferential to the component under test conditions only. There are numerous weighting systems/allowances and most are not required to be designated as being included in the final test bench specification. All that means tests are often rather worthless and unless you know you are comparing two components which were tested identically and weighted similarly, they can be totally meaningless. Personal experience reviews are helpful but with a tuner dependent on an antenna and the location and directionality of the antenna, they too can be tricky. "Is this a situation where a directional antenna and/or a tuner with better discrimination becomes critical?" Use the specs provided to select a tuner then hope for the best. The most critical component of any tuner is, as I have said, the antenna. Read the article I linked to on antenna location and directionality. In the past, serious dx'ers would put up a rotating antenna with a controller inside their house. Not only will the rotator allow you to point the antenna towards the strongest signal, it also allows you to point the antenna away from the weaker signals. A good many antennas today have the ability to select a direction for the antenna without a physical rotator. One note on antenna amplifiers, they are non-discriminatory and broadband. Meaning they amplify all signals equally. With the switch to HD television and HD radio, the FCC has opened up a great deal of the frequencies which had been allotted to conventional radio/TV broadcasts. That means there are now a tremendous number of RF generators that were not in existence in the last century. A modern home is chock full of RF frequencies and taking into account an urban area, the number of interference devices for AM radio boggles the mind. Hold your TV's remote control near your tuner and when you press a command on the remote, you'll probably hear the RF interference it creates within the AM bandwidth. An antenna amplifier does not select what signals to amplify. If you are amplifying a weak signal, you will be amplifying the noise created by that weak signal. At that point, it's up to the tuner to do its best. "From your explanation my understanding is that there is no way to do this with a digital tuner because it is locked to a specific frequency. That the only way to increase my chances of receiving that weaker station is to use a radio with better sensitivity ("better discrimination between lock points"). That there is no human intervention in deciding on the station, that the stronger station will always be locked onto electronically......unless I use a radio with better discrimination." Pretty much that's it. Digital does not have the ability to de-tune the reception. The alternative is to select a tuner with better specs for selectivity and alternate channel rejection. Though, the downside to that is the tuner may skip over signals which are marginal. The answer to that is again a better and more directional antenna with the ability to reject unwanted signals from ever reaching the tuner's front end. . |
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New member Username: OptratucsonPost Number: 4 Registered: May-19 | Hi everyone. I want to know what are the methods or equipment to use, to sent or transmit strong radio frequency wirelessly to interfere a PA speaker system. I came across the product called hackRF one, but I am not sure if it works. Thanks. |