Home |
Search |
Today's Posts |
#1
|
|||
|
|||
What does a Q Multiplier do?
I never could quite figure out exactly what a "Q Multiplier" does. There is a Heathkit model QF-1 Q Multiplier on ebay and that got me to wondering. I know what "Q" is regarding inductors and capacitors ("Quality factor", reactance divided by resistance) but I don't know exactly what a Q Multiplier does or how it connects (I assume it connects to a receiver but am not even sure about that). Obviously it "multiplies the Q" but of what component(s) or stage(s)? Any of you boat anchor enthusiasts know about this? |
#2
|
|||
|
|||
What does a Q Multiplier do?
Rick ) writes:
I never could quite figure out exactly what a "Q Multiplier" does. There is a Heathkit model QF-1 Q Multiplier on ebay and that got me to wondering. I know what "Q" is regarding inductors and capacitors ("Quality factor", reactance divided by resistance) but I don't know exactly what a Q Multiplier does or how it connects (I assume it connects to a receiver but am not even sure about that). Obviously it "multiplies the Q" but of what component(s) or stage(s)? Any of you boat anchor enthusiasts know about this? Well this isn't the boatanchor newsgroup, though you'd often be confused by the recent equipment that gets posted about over there. A Q-multiplier is a regenerative stage. You might be familiar with the regenerative receiver, where positive feed back is introduced to a stage so the same signal is amplified, fed back to the input, and amplified again. This re-amplification allows for far more gain than if the stage only amplified the signal once, and it increases the selectivity of the tuned circuit involved. There is a means of controlling regneration, so you can limit the amplification, or kick it up so the receiver goes into oscillation, providing a beat note for reception of CW signals. A Q-multiplier is the same thing, though it doesn't bother to demodulate the signal. Generally, the point is to increase selectivity in the IF section of the receiver. It connects to the plate of the mixer with a single connection, in parallel with that stage. INcrease the regeneration of the Q-Multiplier, and it increases the selectivity. It gives a nice peak, though does little to improve the skirt selectivity. It's prime was in the days of the 455KHz IF, where the improved selectivity would actually make a difference. At a higher frequency, it would still increase the selectivity of the tuned circuit, but not enough to narrow the passband for voice or CW. It was often an add-on for low end receivers, because for the cost of a single stage, you'd boost selectivity. Sometimes it was included in the receiver (and sometimes the effect was done by adding some positive feedback to the IF stage, so it could go into regeneration). It was sometimes seen in more expensive receivers, where a variant was often the reason. A rearrangement of the circuit, and it could be used as a notch filter, to knock out a nearby signal, which was often more useful in receivers with good IF selectivity where the peaking was less of an improvement. One early use for the Q-Multiplier, which never saw that much use, was for boosting the received carrier in reference to the sidebands of an AM signal. This peaking of the carrier made sure it was strong relative to the sidebands, and made for better AM demodulation. The Q-multiplier was good for this, since it peaked up the carrier but the bad skirt selectivity didn't attenuate the sidebands too much. The same basic notion that is the point of synchronous detectors for better AM reception today. For a brief while in the sixties, there'd be construction articles with Q-Multipliers at the front-end of receivers. Someone described an early single conversion receiver with a 9MHz IF, and put a front end Q-Multiplier in to improve the selectivity of the single tuned circuit at the front end, to improve image rejection. (Though, it never fully made sense, since image rejection was much easier with the high frequency IF.) The scheme was continued in a few other receivers, basically because it had been done. And that was the end of that. Q-Multipliers faded as IF frequencies increased, and good filters such as mechanical and crystal came along to replace a string of IF transformers. MIchael VE2BVW |
#3
|
|||
|
|||
What does a Q Multiplier do?
Good afternoon, Michael. Thank you very much for the very interesting and informative article on Q multipliers. I learned a lot today. :-) |
#4
|
|||
|
|||
What does a Q Multiplier do?
|
#5
|
|||
|
|||
What does a Q Multiplier do?
"pltrgyst" wrote in message news On 9 Apr 2007 18:53:01 GMT, (Michael Black) wrote: A Q-multiplier is a regenerative stage. It's prime was in the days of the 455KHz IF, where the improved selectivity would actually make a difference. At a higher frequency, it would still increase the selectivity of the tuned circuit, but not enough to narrow the passband for voice or CW. So what about audio Q-multipliers? Do they function on the same principle? -- Larry AUDIO Q-MULTIPLIER http://cs.okanagan.bc.ca/ve7ouc/eng/...ultiplier.html Lamont |
#6
|
|||
|
|||
What does a Q Multiplier do?
"pltrgyst" wrote in message news On 9 Apr 2007 18:53:01 GMT, (Michael Black) wrote: A Q-multiplier is a regenerative stage. It's prime was in the days of the 455KHz IF, where the improved selectivity would actually make a difference. At a higher frequency, it would still increase the selectivity of the tuned circuit, but not enough to narrow the passband for voice or CW. So what about audio Q-multipliers? Do they function on the same principle? -- Larry Yes. The idea of a Q-Multiplier is to increase selectivity. They use regeneration (positive feedback) to decrease the bandwidth of a tuned circuit. The frequency can be whatever is desired. Q-Multipliers were popular at a time when most receivers had inadequate selectivity. They are relatively cheap and, with some limitations, work pretty well. As receivers with more sophisticated filters (like mechanical filters or multi-pole crystal filters) became available the Q-multiplier fell out of use. BTW, the old regenerative receiver works on the same principle. In fact, one can see a Q-Multiplier as a sort of regenerative receiver working at the IF or audio frequencies. -- --- Richard Knoppow Los Angeles, CA, USA -- Posted via a free Usenet account from http://www.teranews.com |
#7
|
|||
|
|||
What does a Q Multiplier do?
pltrgyst ) writes:
On 9 Apr 2007 18:53:01 GMT, (Michael Black) wrote: A Q-multiplier is a regenerative stage. It's prime was in the days of the 455KHz IF, where the improved selectivity would actually make a difference. At a higher frequency, it would still increase the selectivity of the tuned circuit, but not enough to narrow the passband for voice or CW. So what about audio Q-multipliers? Do they function on the same principle? -- Larry Originally yes, though I've seen "audio Q-multipliers" described in construction articles that are more strictly average audio filters. They may even come out of the same place. The selectoject was described in QST in the late forties, by O. G. Villard, and it uses the principle of regneration to get better selectivity at audio. And O. G. Villard is the name I'd associate with the use of the Q-Multiplier for better reception of AM (there are references to a QST article by him on that topic in an early ARRL SSB manual). But I've never seen a specific link between the selectoject and the Q-Multiplier at the IF of a receiver, so I don't know if he came up with the IF Q-multiplier as we know it, or someone else did. Certainly O. G. Villard, who died only three years ago, came up with quite a few things important to amateur radio, including a lot of work in SSB in the early days. Michael VE2BVW |
#9
|
|||
|
|||
What does a Q Multiplier do?
Among us kids who were licensed as teens in the mid 50's, the Q
multiplier was a hot item. Most of us could not afford the latest and greatest receivers so the Heathkit Q-Multiplier was a desired accessory . I believe is could also do a notching function. I never had the Heath version myself, but many friends did. I had a Hammarlund HQ-100 immediately upon its introduction and as far as I can recall that was the first commercial radio to have a Q-Multiplier built in as opposed to an add-on accessory. More expensive radios had crystal filters and the Cadillac of the era, the Collins 75A4 had mechanical filters. The $500 price tag of the 75A4 put it in the "dream-on" category to those of us who only had part-time jobs or in my case (I was 13 when licensed) too young to even work at anything legally. It actually was pretty effective once you got to learn how to use it. As I remember it was far more effective on CW than phone (which was still heavily standard full carrier AM phone.) The Hammarlund version only had a "peak" function. I believe the Heathkit version's notch function could be used for reducing heterodyne squeals although I have very liitle experience with that. I believe the Heath also had a third function, but I don't remember what it was. Jon W3JT On Tue, 10 Apr 2007 08:32:51 -0700, Dick wrote: On 10 Apr 2007 04:11:25 GMT, (Michael Black) wrote: pltrgyst ) writes: On 9 Apr 2007 18:53:01 GMT, (Michael Black) wrote: A Q-multiplier is a regenerative stage. It's prime was in the days of the 455KHz IF, where the improved selectivity would actually make a difference. At a higher frequency, it would still increase the selectivity of the tuned circuit, but not enough to narrow the passband for voice or CW. So what about audio Q-multipliers? Do they function on the same principle? -- Larry Originally yes, though I've seen "audio Q-multipliers" described in construction articles that are more strictly average audio filters. They may even come out of the same place. The selectoject was described in QST in the late forties, by O. G. Villard, and it uses the principle of regneration to get better selectivity at audio. And O. G. Villard is the name I'd associate with the use of the Q-Multiplier for better reception of AM (there are references to a QST article by him on that topic in an early ARRL SSB manual). But I've never seen a specific link between the selectoject and the Q-Multiplier at the IF of a receiver, so I don't know if he came up with the IF Q-multiplier as we know it, or someone else did. Certainly O. G. Villard, who died only three years ago, came up with quite a few things important to amateur radio, including a lot of work in SSB in the early days. Michael VE2BVW Interestingly, this month's QST in the 50 Years Ago column lists a variable band width Q-Multiplier by Ronald Ives (April 1957.) The article references the original Villard article in the April 1952 issue of "Electronics" magazine. Dick - W6CCD |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Q-multiplier for Mosley CM-1 | Boatanchors | |||
Q multiplier for SX-28 | Boatanchors | |||
FA>> Heathkit QF-1 Q Multiplier | Swap | |||
FA>> Heathkit QF-1 Q Multiplier | Swap | |||
Q-Multiplier at RF stage? | Homebrew |