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Michael Black wrote:
You've made a classic mistake, that because shortwave receivers carry relatively high price tags, that they then offer superior FM broadcast reception. In the first place, a higher price tag may reflect the limited interest in shortwave. If you have to design something out of the ordinary, it will cost more than an average design. And if fewer people are interested, then you have to recoup the cost by a higher price. But more important, any design concerns will be put into what the radio is intended for, ie shortwave. And for anyone who understands radio design, there is virtually no overlap between what's good for an FM broadcast receiver in the 88 to 108MHz range, and a shortwave receiver. One is for FM reception, the other is for AM reception. One is for wideband signals relative far apart in a part of the spectrum that is at least three times the upper frequency of the other, while the other is for narrow signals with narrow spacing between channels and still at a relatively low frequency. Shortwave and the FM broadcast band are not close together. All of this means that there is very little where the designs overlap. What you are buying is a shortwave radio (and maybe/likely that circuitry is used to tune the AM broadcast band since the frequencies are adjacent and the mode and signal bandwidth would be the same) and an FM broadcast radio in the same box. Traditionally, shortwave radios did not include an FM band, with a few exceptions; it changed as small shortwave receivers from Asian companies became the norm. In other words, the FM BCB section is thrown in as a marketing matter. Since that FM section does nothing for the main selling point of the radio, that shortwave reception, then any money put into that section will take away from the design of the shortwave section. So realistically, one might as well put in as cheap an FM section as possible, since it's just added circuitry, and one can so very easily pick the same sort of circuit that is in any average FM radio. Buying a shortwave radio will not automatically give better FM reception, and depending on specific design, it may be inferior to what you could find elsewhere. Car radios are often good, because they require sensitivity yet also the ability to withstand strong signals. FM reception is a key part of the design, so it gets the attention. I have various digitally tuned Delco car radios around the house, and they are the best FM radios I've ever had. I have no idea of the absolute performance, just that in my passing contact with relatively low end receivers the FM section is great. On FM, the PLL is well designed so I don't get spurious responses. The sensitivity seems good, yet it doesn't overload. It is rare to find a station where it doesn't belong. Selectivity is pretty good. The other day, conditions were great and a non-local station was booming in. It's adjacent to another non-local station but which comes in regular (though it's strength varies). There was no problem that day from adjacent channel interference. FM broadcast receivers intended for good performance will also be good contenders. Note that you have to go for something with a beyond average design. Just as in those shortwave radios, FM (and AM even moreso) are considered not so important in a "hifi" situation, so they put little money into the tuner section. You would have lousy FM radios in consumer equipment twenty and thirty years ago, and you have it today, whether they are digitally tuned or not. Such receivers are intended for local reception (who would be interested in that noisy signal from a bit further out, especially since the ads and traffic reports aren't local?) so weak signal reception is not a concern in the design. And as with a lot of FM receivers, they tend to be too sensitive, but that never becomes useful for weak signal reception because that sensitivity also means a tendency to overload on the local and strong signals. Michael Points: I think some of the the points you raise are probably applicable to any radio that is not FM only. I do not think I can buy a PLL FM only RX, and besides I'd want AM broadcast band at least, in addition. One would imagine a portable that was just FM and broadcast band (no shortwave) the money would be spent on better FM performance. But, I suspect that in many cases that might not be the case. Not sure whether poor FM perfornance is related to PLL. Maybe not, but generally to use of IC's. Maybe biggest reason that the the ICFM33RDS FM performance at FM might not be that good is because it's an inexpensive set. Maybe. Maybe no modern worldband RX will be that good on FM. Then again maybe some are at least as good as (say) an old Grundig. Perhaps the likely candidates would be FM/Broadcast band ony RX. Or the more expensive worldband. As usual, you get what you pay for. Bottom line for me I guess is that I'd like to feel that if I went ahead an spent say £80 to £100 on a PLL radio, that FM performance would be as good as an old Grundig. Worldband RX or no. Or is it the case that I could spend much more than this and still not get the old Grundig performance. If that was the case, surely that would say something about modern FM design? I could end up with two radios, a FM/Broadcast band RX. Plus a worldband set. That article really does scathe rec.radio,shortwave"!! Ha!! That was just unfortunate, I was not concentrating on that part of the article. Just came with the bit I was interested in.:c) |
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