JR radios and Horizon Hobbies.
07-09-2002, 11:25 AM
#1
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JR radios and Horizon Hobbies.
It is alarming to read on this forum and RC ducted fans that Horizon is despatching JR Radios that are not in perfect RF tune and that some are way out .
I have used JR radios (including some on 72 mHz purchased in the US) for over 20 years without a single failure and I carefully carry out range checks, but these suggestions, from knowledgeable individuals, of mistuned receivers and transmitters are very worrying.
Perhaps JR reps. can check with Horizon to see if there is any truth in these suggestions and if so what corrective action is being taken.
Bottom line is that EVERY unit sold should be tuned perfectly before despatch. Anyone disagree?
BRG,
David Gladwin
I have used JR radios (including some on 72 mHz purchased in the US) for over 20 years without a single failure and I carefully carry out range checks, but these suggestions, from knowledgeable individuals, of mistuned receivers and transmitters are very worrying.
Perhaps JR reps. can check with Horizon to see if there is any truth in these suggestions and if so what corrective action is being taken.
Bottom line is that EVERY unit sold should be tuned perfectly before despatch. Anyone disagree?
BRG,
David Gladwin
07-09-2002, 12:07 PM
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I can personally verify at least one case where the TX and RX were not tuned. I bought them form a local hobby shop who ordered them for me from Horizon. The RX was the 649 8CH and the module was supposed to be matched to the receiver. I asked the hobby shop to verify with Horizon if the RX and TX were tuned to each other and the response was yes! However, as I installed the RX in my roo I was only about to get about 10 feet away before signal loss!! And this was with the RX antenna outside the fuse and the TX antenna collapsed but installed!
I took the module and receiver to D@M electronics to have Dave tune it and he told me that it was horribly out of tune and that there is no way Horizon could have had this tuned before they shipped it. He said that at first when he hooked everything up to his scopes and equipment that it looked like the TX was not transmitting at all. Needless to day I did not use that combination in my Roo...
On a side note, and this is hearsay only, I was at a swap meet this past winter and was looking at buying a used 950 receiver when I commented to the owner, a local guy who always and only flies JR, that it was too bad that the receiver was not on my channel and I would have to buy another Xtal and have it sent back to get tuned. This guy responded that JR radios and receivers are never supposed to be tuned and that they are all made to be in the center of the band for all channels. He claimed that by having them tuned, even by a professional AMA sticker station, would mess up the output and cause a crash.
I just laughed politely and walked away
Randy
I took the module and receiver to D@M electronics to have Dave tune it and he told me that it was horribly out of tune and that there is no way Horizon could have had this tuned before they shipped it. He said that at first when he hooked everything up to his scopes and equipment that it looked like the TX was not transmitting at all. Needless to day I did not use that combination in my Roo...
On a side note, and this is hearsay only, I was at a swap meet this past winter and was looking at buying a used 950 receiver when I commented to the owner, a local guy who always and only flies JR, that it was too bad that the receiver was not on my channel and I would have to buy another Xtal and have it sent back to get tuned. This guy responded that JR radios and receivers are never supposed to be tuned and that they are all made to be in the center of the band for all channels. He claimed that by having them tuned, even by a professional AMA sticker station, would mess up the output and cause a crash.
I just laughed politely and walked away
Randy
07-09-2002, 07:53 PM
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JR radios and Horizon Hobbies.
Have any of you guys ever looked at your JR Xtals?
They have a little black dot on them, Right , centered or on the left.
Ideally Your Rx Xtal and your TX Xtal are supposed to match. That is both should have the dot in the same location. Right, centered or left.
If you have a centered dot on your Tx xtal, you can use any rx dot location. BUT, the best is to have them match.( You should NEVER run one left and one right.
All of mine are centered dots, and I have range up the ying yang.
They have a little black dot on them, Right , centered or on the left.
Ideally Your Rx Xtal and your TX Xtal are supposed to match. That is both should have the dot in the same location. Right, centered or left.
If you have a centered dot on your Tx xtal, you can use any rx dot location. BUT, the best is to have them match.( You should NEVER run one left and one right.
All of mine are centered dots, and I have range up the ying yang.
07-09-2002, 10:20 PM
#4
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JR radios and Horizon Hobbies.
My ranges are great too BUT where does JR explain the crystal dot system , certainly not in my manuals.
I am not for one second knocking JR or Horizon, I trust all of my models to that brand of radio but I sincerely hope that the increased and deserved success in terms of sales volume does not result in JR and Horizon allowing quality control standards to fall. Even the cheapest 700 receiver ( and I have one of those too, works great in my sport aerobatic model) as well as the more sophisticated receivers and Tx modules should be peak tuned.
Anyway, over to the JR reps !
BRG,
David Gladwin
I am not for one second knocking JR or Horizon, I trust all of my models to that brand of radio but I sincerely hope that the increased and deserved success in terms of sales volume does not result in JR and Horizon allowing quality control standards to fall. Even the cheapest 700 receiver ( and I have one of those too, works great in my sport aerobatic model) as well as the more sophisticated receivers and Tx modules should be peak tuned.
Anyway, over to the JR reps !
BRG,
David Gladwin
07-10-2002, 01:18 AM
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JR radios and Horizon Hobbies.
Back in the early eighties I had one of the first JR sets imported into the US. I think it was that 7 or 8 channel system that a lot of us used for pattern. It was horribly out of tune from Circus or that may have been before Circus even got into it. They fixed it, but not before it almost trashed my #1 pattern plane.
07-10-2002, 02:12 AM
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I have trusted all of my airplanes to JR radios for many years now, everything from cheapo prop jobs to giant scale and now my jets. I have always had great range, and total trust in my JR equipment. Supposedly the dot system is the tolerance on the crystals. I always insure that I have a transmitter with the dot in the center, and the reciever crystals in the most expensive planes on the center dot as well. I have flown prop planes with the dots on opposite sides and never noticed any difference.
David Reid
David Reid
07-10-2002, 02:23 AM
#9
JR radios and Horizon Hobbies.
Here is a reply I was sent to post here.
Straight from the JR technicians mouth---all JR equipment is center tuned unless the receiver and module are sold as a matched set. So, if you buy a receiver or module new off of the shelf without the crystal it is center tuned. You can send in your receiver and module and have it custom tuned. I asked about the dots on the crystals and was told that it denoted a receiver or module that was tuned to the left, right, or center of that particular channel,but not to worry----they don't use or pay attention to the dots anymore. The dots were for an older way of tuning.
I have flown JR equipment for years and have never had a radio related crash and have always had tons of range. A JR rep was at the Mississippi Afterburner Jet Rally and showed several of us the proper way to range check the radio. The radio should be held straight out from the side of your body at arms length--chest high. Walk straight back in an open area (NO OBSTRUCTIONS!!!) You should get at least 300 feet (antenna off) before going into failsafe. I easily got 350 feet on the BobCat with the JetCat 4.0 ecu on. While performing the range check---do not allow the transmitter to vary in height or block the signal with your body. You would be surprised at how much range is affected by allowing the transmitter to drop from chest high or by shielding it with your body. Do this EVERY time to develope a standard and if range is degraded severely----DO NOT FLY!!!
Kevin
Straight from the JR technicians mouth---all JR equipment is center tuned unless the receiver and module are sold as a matched set. So, if you buy a receiver or module new off of the shelf without the crystal it is center tuned. You can send in your receiver and module and have it custom tuned. I asked about the dots on the crystals and was told that it denoted a receiver or module that was tuned to the left, right, or center of that particular channel,but not to worry----they don't use or pay attention to the dots anymore. The dots were for an older way of tuning.
I have flown JR equipment for years and have never had a radio related crash and have always had tons of range. A JR rep was at the Mississippi Afterburner Jet Rally and showed several of us the proper way to range check the radio. The radio should be held straight out from the side of your body at arms length--chest high. Walk straight back in an open area (NO OBSTRUCTIONS!!!) You should get at least 300 feet (antenna off) before going into failsafe. I easily got 350 feet on the BobCat with the JetCat 4.0 ecu on. While performing the range check---do not allow the transmitter to vary in height or block the signal with your body. You would be surprised at how much range is affected by allowing the transmitter to drop from chest high or by shielding it with your body. Do this EVERY time to develope a standard and if range is degraded severely----DO NOT FLY!!!
Kevin
07-10-2002, 05:52 PM
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JR
After reading all of the comments, I am wandering about the single versus dual conversion receivers.
I have used JR single conversion ABC&W receivers for about 10 years and have never had a problem. From .20 size glow to 4.2 gas. Little sport planes, helis and large scale warbirds with the antennas running along the fuse inside. I am new to the jets, so I guess my questions is what is the difference in using single conversion in the jets?
I have used JR single conversion ABC&W receivers for about 10 years and have never had a problem. From .20 size glow to 4.2 gas. Little sport planes, helis and large scale warbirds with the antennas running along the fuse inside. I am new to the jets, so I guess my questions is what is the difference in using single conversion in the jets?
07-10-2002, 07:35 PM
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Single vs dual conversion
I think you will find dual conversion receivers a little bit better at rejecting interferring signals and/or noise. I think that is the main advantage of dual conversion. I would guess this is the reason most of the "jet" people use dual conversion receivers. They may have a little bit better sensitivity resulting in a little more range.
Dual conversion uses two IF frequencies - 10.7 mhz on the first conversion and then 455 khz on the second. Single conversion receivers use only one IF frequency - 455 khz. So the complete conversion must take place in the only conversion stage of the receiver. With dual conversion radios this narrows the bandwidth thus rejecting a little more of any interfering signal or noise. In my opinion the higher your operating frequency is the more important the dual conversion becomes.
I fly on 53.3 Mhz and always use dual conversion receivers. I think dual conversion would be even more important on 72 Mhz with other frequencies only 10 khz away on each side of your operating frequency.
IMHO dual conversion is usually superior to single conversion. In JR it only costs $10 more for dual conversion and it is just a little bit better. I think it is worth it.
Dual conversion uses two IF frequencies - 10.7 mhz on the first conversion and then 455 khz on the second. Single conversion receivers use only one IF frequency - 455 khz. So the complete conversion must take place in the only conversion stage of the receiver. With dual conversion radios this narrows the bandwidth thus rejecting a little more of any interfering signal or noise. In my opinion the higher your operating frequency is the more important the dual conversion becomes.
I fly on 53.3 Mhz and always use dual conversion receivers. I think dual conversion would be even more important on 72 Mhz with other frequencies only 10 khz away on each side of your operating frequency.
IMHO dual conversion is usually superior to single conversion. In JR it only costs $10 more for dual conversion and it is just a little bit better. I think it is worth it.
07-10-2002, 07:59 PM
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JR radios and Horizon Hobbies.
I think it improves the I2M adjacent channel rejection.
Someone standing close to you on a nearby channel can have their signal mix with yours and form a new signal that gets braodcast from your trans. This signal can get through the 455khz filters in a single channel reciever.
JR's ABC&W filters are supposed to be good enough to remove this I2M signal.
I've flown their ABC&W recievers for years and never had a problem.
I do use the 940 receiver on my jet, just in case.
I think I'm remembering this correctly, if not some of you radio dudes correct me.
Someone standing close to you on a nearby channel can have their signal mix with yours and form a new signal that gets braodcast from your trans. This signal can get through the 455khz filters in a single channel reciever.
JR's ABC&W filters are supposed to be good enough to remove this I2M signal.
I've flown their ABC&W recievers for years and never had a problem.
I do use the 940 receiver on my jet, just in case.
I think I'm remembering this correctly, if not some of you radio dudes correct me.
07-10-2002, 08:49 PM
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JR radios and Horizon Hobbies.
I think if you did a poll at any jet rally you would find the majority of JR jet fliers are using the 950 or 955 rx, which are JR's "single conversion" ABC&W rx. And I have seen very few problems with those rx's, none in any of my jets. I have heard that in some areas of the country, and in some installations, the 940 or the 945 dual conversion rx's are giving better operation. I have tried both types and I have had zero problems with either.
It's important to realize that if you are having an RF interference problem, the source of the interference may dictate what is the "best" receiver type to use. What bothers a single conversion may not bother a dual, and vice versa. That is why JR offers both types.
The best insurance against any radio problem is still a proper, thorough range check prior to that first flight. And after that, paying close attention to the equipments performance flight after flight. Any loss of control however short in duration should be treated as a symptom of a potential problem. That's one of the reasons I like the JetCat V4.0 ECU, it can tell you if it ever sees a fail-safe during the flight. If I ever see a count, I will start a systematic checkout of the equipment.
BTW, just in case some aren't aware, the 945 and the 955 are the current rx's offered by JR. The 940 and the 950 have been replaced with these models.
It's important to realize that if you are having an RF interference problem, the source of the interference may dictate what is the "best" receiver type to use. What bothers a single conversion may not bother a dual, and vice versa. That is why JR offers both types.
The best insurance against any radio problem is still a proper, thorough range check prior to that first flight. And after that, paying close attention to the equipments performance flight after flight. Any loss of control however short in duration should be treated as a symptom of a potential problem. That's one of the reasons I like the JetCat V4.0 ECU, it can tell you if it ever sees a fail-safe during the flight. If I ever see a count, I will start a systematic checkout of the equipment.
BTW, just in case some aren't aware, the 945 and the 955 are the current rx's offered by JR. The 940 and the 950 have been replaced with these models.
07-10-2002, 08:56 PM
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Single vs dual conversion
Why do they continue to make single conversion receivers? Good question!
Another question might be "Why do people buy single conversion receivers when dual conversion only costs $10 more?" About the only answer to that I can think of is people don't realize the value of the dual conversion receivers. If you are putting this receiver in a $5000 jet what does $10 matter?
As for continuing to make single conversion receivers the answer is even harder to come up with. These type of receivers come with the upper end radio sets - in JR the 8103 and 10X. Most of the rest (lower end) use FM receivers. IMHO these are far inferior to the single or dual conversion PCM receivers. I can see the dollar difference beween FM and the PCM receivers. Even then you are looking at only $100 to $150 difference. Neither the FM or the single conversion receivers make much sense when you are talking about many thousands of dollars for the complete
package.
I guess the answer to continuing to produce single conversion receivers is most people do not know the difference and why spend $10 more than you think you have to. Someone needs to enlighten people as to the value of the additional cost of $10 for the dual conversion! If everyone knew this they would sell a lot fewer single conversion receivers.
Another question might be "Why do people buy single conversion receivers when dual conversion only costs $10 more?" About the only answer to that I can think of is people don't realize the value of the dual conversion receivers. If you are putting this receiver in a $5000 jet what does $10 matter?
As for continuing to make single conversion receivers the answer is even harder to come up with. These type of receivers come with the upper end radio sets - in JR the 8103 and 10X. Most of the rest (lower end) use FM receivers. IMHO these are far inferior to the single or dual conversion PCM receivers. I can see the dollar difference beween FM and the PCM receivers. Even then you are looking at only $100 to $150 difference. Neither the FM or the single conversion receivers make much sense when you are talking about many thousands of dollars for the complete
package.
I guess the answer to continuing to produce single conversion receivers is most people do not know the difference and why spend $10 more than you think you have to. Someone needs to enlighten people as to the value of the additional cost of $10 for the dual conversion! If everyone knew this they would sell a lot fewer single conversion receivers.
07-10-2002, 09:28 PM
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JR radios and Horizon Hobbies.
TO get back on track, my question was nor related to dual or single conversion, the question was : are transmitter modules and receivers being sold which are NOT in perfect tune. and if so are steps being taken to ensure that all equipment is perfectly tuned before sale ?
I fly with all of my jets equipped with an MAS volt logger which also records any radio glitches or lockouts, however brief. So far with my JR 1000 (and 945 in the US) receivers not a single hit has been recorded, but since the mis-tuning issue has been raised by others perhaps we can, should, hear a definitive answer to that issue from Horizon via the JR reps. and the matter settled once and for all !
BRG,
David Gladwin
I fly with all of my jets equipped with an MAS volt logger which also records any radio glitches or lockouts, however brief. So far with my JR 1000 (and 945 in the US) receivers not a single hit has been recorded, but since the mis-tuning issue has been raised by others perhaps we can, should, hear a definitive answer to that issue from Horizon via the JR reps. and the matter settled once and for all !
BRG,
David Gladwin
07-10-2002, 09:53 PM
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David,
Your question is really impossible to answer. It's in the class of "Have you quit beating your wife?" The best way I can try to answer you is to tell you that I know that every effort is made by JR and Horizon, and I'm sure by every other brand, to ensure that all equipment sold or serviced is operating properly. But anybody who might tell you that everything that they ever produce and ship out will always be 100% perfect is either stupid or lying. Mistakes will always occur. That is why we as owner/operators should always do a proper and thorough check of any new equipment you install in your model. To not do so would be less then responsible.
Hope I've helped.
Your question is really impossible to answer. It's in the class of "Have you quit beating your wife?" The best way I can try to answer you is to tell you that I know that every effort is made by JR and Horizon, and I'm sure by every other brand, to ensure that all equipment sold or serviced is operating properly. But anybody who might tell you that everything that they ever produce and ship out will always be 100% perfect is either stupid or lying. Mistakes will always occur. That is why we as owner/operators should always do a proper and thorough check of any new equipment you install in your model. To not do so would be less then responsible.
Hope I've helped.
07-10-2002, 10:32 PM
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I'll second
Originally posted by TonyF
David,
Your question is really impossible to answer. It's in the class of "Have you quit beating your wife?" The best way I can try to answer you is to tell you that I know that every effort is made by JR and Horizon, and I'm sure by every other brand, to ensure that all equipment sold or serviced is operating properly. But anybody who might tell you that everything that they ever produce and ship out will always be 100% perfect is either stupid or lying. Mistakes will always occur. That is why we as owner/operators should always do a proper and thorough check of any new equipment you install in your model. To not do so would be less then responsible.
Hope I've helped.
David,
Your question is really impossible to answer. It's in the class of "Have you quit beating your wife?" The best way I can try to answer you is to tell you that I know that every effort is made by JR and Horizon, and I'm sure by every other brand, to ensure that all equipment sold or serviced is operating properly. But anybody who might tell you that everything that they ever produce and ship out will always be 100% perfect is either stupid or lying. Mistakes will always occur. That is why we as owner/operators should always do a proper and thorough check of any new equipment you install in your model. To not do so would be less then responsible.
Hope I've helped.
I must mention here Tony is a little more diplomatic than I have been in some of my other posts. I have been describing my experiences with my radio purchases over the years. And what I have learned is don't assume it's up to snuff till you see for yourself, and then find a way to keep checking on the status. The Jet Cat's fail-safe count system is great for doing just that, as Tony has mentioned, also Jet Cat did it double right by allowing us to time delay any turbine shutdown during a fail-safe condition. The best of both worlds ------
Lee ----
07-10-2002, 11:42 PM
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JR radios and Horizon Hobbies.
[QUOTE]Originally posted by TonyF .
It's important to realize that if you are having an RF interference problem, the source of the interference may dictate what is the "best" receiver type to use. What bothers a single conversion may not bother a dual, and vice versa. That is why JR offers both types.[QUOTE]
This is interesting. For my 50 years in amateur radio I always thought radios with the most stages of conversion were the best-especially at higher frequecies. Looks like I am going to get an education on this.
What type of RF interference or type of noise would bother a dual conversion receiver but not a single conversion receiver? Maybe better said "Under what conditions would a single conversion receiver be preferable to a dual conversion receiver?".
I have been under the impression that dual conversion receivers would always be the better receiver under any conditon. Maybe I should not spend my money foolishly buying dual conversion receivers any more.
It's important to realize that if you are having an RF interference problem, the source of the interference may dictate what is the "best" receiver type to use. What bothers a single conversion may not bother a dual, and vice versa. That is why JR offers both types.[QUOTE]
This is interesting. For my 50 years in amateur radio I always thought radios with the most stages of conversion were the best-especially at higher frequecies. Looks like I am going to get an education on this.
What type of RF interference or type of noise would bother a dual conversion receiver but not a single conversion receiver? Maybe better said "Under what conditions would a single conversion receiver be preferable to a dual conversion receiver?".
I have been under the impression that dual conversion receivers would always be the better receiver under any conditon. Maybe I should not spend my money foolishly buying dual conversion receivers any more.
07-11-2002, 12:24 AM
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FM / FM-PCM
Gordon,
Sorry about that. I sure did not make myself very clear did I? I am aware both radios use an FM carrier - it is the type of modulation that differs.
Actually it was the "dollar difference" I was referring to - not the type of modulation.
It is rather difficult to put a post here which someone cannot find fault with.
Have a nice day.
Sorry about that. I sure did not make myself very clear did I? I am aware both radios use an FM carrier - it is the type of modulation that differs.
Actually it was the "dollar difference" I was referring to - not the type of modulation.
It is rather difficult to put a post here which someone cannot find fault with.
Have a nice day.
07-11-2002, 12:35 AM
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single vs dual
I can attest to at least one place where a sigle conversion rx is better than a dual. The Las Vegas field where the T.O.C. is held, as a member of Steve Strickers team from 84 to 99 we always had range problems at that field that we didn't have in the desert practing, ask any of the guys who were flying Futaba radios back then, the only way we had to fix the problem was to go to a whip antenna and fly on ham band. Not one of the Jr guys who were flying on single conversion rx's that I know of had a problem. It was just not us I remember Bill Cunningham goming into land and lose a plane right at the end of the field, also Dave Von Linsowe lost his very first Toc plane on the first flight at the field. After all of the problems we had it was a running joke to the new guys who had dual conversion Rx's " have you flown at the Field yet" some guys over the years waited as we did until the contest to fly there as the risk of loss of the model was huge and at least the guys from Futaba and Jr were there to help us then. I am not saying that a single is better than a dual but you will have a hard time getting me to change the 950 rx that i have in my jet to something else other than another single conversion Rx from JR.
Not a member of any factory team as of now.
Not a member of any factory team as of now.
07-11-2002, 12:48 AM
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Well all I know is I sent in 5 radio's with nothing wrong with them and four came back out of tuned. I will not send them back to them. 4 were PCM 10'S and 1 10SXII. I am more than pissed. :boxing:
Dave R
Dave R
07-11-2002, 12:52 AM
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Single vs dual conversion
Ron,
If it ain't broke don't fix it!
If I were you and I was having good luck then I would do just as you are doing - stay with what is working.
I have always flown on 6 meters and rarely had a problem. But at the Nationals in Dayton YEARS AGO, that field was death to a 6 meter plane. The best that could be figured out was a close by TV station on a particular channel was causing the problem. That was with single conversion equipment. I don't think dual conversion would have made any difference.
Your experiences at Las Vegas TOC is why I have been on the Amateur Bands for almost my entire time in RC - which started in 1948.
If it ain't broke don't fix it!
If I were you and I was having good luck then I would do just as you are doing - stay with what is working.
I have always flown on 6 meters and rarely had a problem. But at the Nationals in Dayton YEARS AGO, that field was death to a 6 meter plane. The best that could be figured out was a close by TV station on a particular channel was causing the problem. That was with single conversion equipment. I don't think dual conversion would have made any difference.
Your experiences at Las Vegas TOC is why I have been on the Amateur Bands for almost my entire time in RC - which started in 1948.
07-11-2002, 12:55 AM
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Dual ver Single
What type of RF interference or type of noise would bother a dual conversion receiver but not a single conversion receiver? Maybe better said "Under what conditions would a single conversion receiver be preferable to a dual conversion receiver?".
I have been under the impression that dual conversion receivers would always be the better receiver under any conditon. Maybe I should not spend my money foolishly buying dual conversion receivers any more.
quote from:
Jack Mathias W9FMW
AMA 7654 since 1937
This is getting a little out of my league, but it's my understanding that the high and low image frequencies for a given (channel) / frequency are totally different for a single conversion receiver than a dual conversion receiver. Example channel 52 (72.830) single conversion receiver high image frequency is: 73.285 and the low image freq is: 72.375. And a Dual conversion receiver crystal controlled & aligned to channel 52 (72.850) high image frequency is: 83.530 and the low image freq is: 62.130.
Given this data if we had a source of RFI that happened to be fairly strong within 1 mile of a flying site or was being generated by on-board equipment and was modulating at a frequency of 62.130, the dual conversion receiver would be getting hammered, not on it's primary frequency but on it's lower image frequency. Whereas under the same exact circumstances the Single conversion receiver would not "see" the RFI on 62.130 and not be affected by the RFI that the dual conversion receiver was getting hammered with.
Someone with a little more knowledge please step in here if I am off base with this analogy and correct my mis-understandings. I maybe wrong here but I think the reason the dual conversion receiver has been considered to be better at rejecting outside interference is because that interference was presumed to be 3IM generated by other transmitters at the same field. Notice the spread from the primary frequency of the image frequency's between the dual and single conversion receivers. Given that larger spread the dual conversion receiver would not be as affected by 3IM being generated on a crowded flight line.
I am really getting out of my knowledge base here but the ABC&W receiver design that JR uses has a more complicated blocking system than just to call it a Single conversion receiver. I think Mike Byrd once told me it was more like a triple stage conversion than a single stag. Someone with more expertise please here again step in and correct any inaccuracies so we all can learn a little more here than we really wanted to know -------
And naturally it gets more complicated in that as we know not only are we subjecting these receivers to 3IM but also with weird computer clock RFI from our ECU's, EMI from fuel pump motors etc. etc.
I think in-conclusion weather the receiver is a dual, single, ABC&W or pink with black spots the best one to use is the one that only "hears" your transmitter and nothing else !!
Lee -----------
I have been under the impression that dual conversion receivers would always be the better receiver under any conditon. Maybe I should not spend my money foolishly buying dual conversion receivers any more.
quote from:
Jack Mathias W9FMW
AMA 7654 since 1937
This is getting a little out of my league, but it's my understanding that the high and low image frequencies for a given (channel) / frequency are totally different for a single conversion receiver than a dual conversion receiver. Example channel 52 (72.830) single conversion receiver high image frequency is: 73.285 and the low image freq is: 72.375. And a Dual conversion receiver crystal controlled & aligned to channel 52 (72.850) high image frequency is: 83.530 and the low image freq is: 62.130.
Given this data if we had a source of RFI that happened to be fairly strong within 1 mile of a flying site or was being generated by on-board equipment and was modulating at a frequency of 62.130, the dual conversion receiver would be getting hammered, not on it's primary frequency but on it's lower image frequency. Whereas under the same exact circumstances the Single conversion receiver would not "see" the RFI on 62.130 and not be affected by the RFI that the dual conversion receiver was getting hammered with.
Someone with a little more knowledge please step in here if I am off base with this analogy and correct my mis-understandings. I maybe wrong here but I think the reason the dual conversion receiver has been considered to be better at rejecting outside interference is because that interference was presumed to be 3IM generated by other transmitters at the same field. Notice the spread from the primary frequency of the image frequency's between the dual and single conversion receivers. Given that larger spread the dual conversion receiver would not be as affected by 3IM being generated on a crowded flight line.
I am really getting out of my knowledge base here but the ABC&W receiver design that JR uses has a more complicated blocking system than just to call it a Single conversion receiver. I think Mike Byrd once told me it was more like a triple stage conversion than a single stag. Someone with more expertise please here again step in and correct any inaccuracies so we all can learn a little more here than we really wanted to know -------
And naturally it gets more complicated in that as we know not only are we subjecting these receivers to 3IM but also with weird computer clock RFI from our ECU's, EMI from fuel pump motors etc. etc.
I think in-conclusion weather the receiver is a dual, single, ABC&W or pink with black spots the best one to use is the one that only "hears" your transmitter and nothing else !!
Lee -----------