Receiver hi-low explanation

I am contemplating buying a 9CAF Futaba radio. I have an older Futaba
FP-T7UAF transmitter which in on ch. 34. If I buy a new radio lets
say it is on ch 38 which is called the high because it is above 36 can
I still use my ch 34 module? I suppose this only applies to the
receivers and not the transmitters.
Has this Hi-Low thing on receivers always been around? I have never
paid any attention until lately, when I started thinking about getting
a new radio. I need some clarification.
Thanks
Reply to
JRO
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You SHOULD be able to use it since it is close to the lower limit. If in doubt, have it checked before use.
Reply to
Paul McIntosh
Sorta new, anyway.
The deal is, receivers were shipped tuned to the crystal specified by the customer which meant they were a bit 'off' if a different crystal was installed.
That worked ok for the old wide-band systems, but left something to be desired when the 1991 specs came along.
Futaba changed to the high-low scheme wherein the receiver is tuned either to the middle of the "high" half of the frequency band, or tuned to the middle of the "low" half of the frequency band.
The result means that if you stay within the half of the band where the receiver was originally tuned, you can swap crystals all you want without having to get the thing re-tweaked.
The down side is that if you move a high-end receiver to the low end, you could have a receiver with marginal performance unless you have it tweaked.
6 of one, half-dozen of the other.
For best performance, have the receiver tuned to the specific crystal and get another receiver if you need a different channel - you'll have two receivers with optimum performance instead of two receivers with mediocre performance. Cheers, Fred McClellan The House Of Balsa Dust
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Reply to
Fred McClellan
No one has answered your question yet. THEORETICALLY you can switch from any frequency to another, within the same operating band. PRACTICALLY, it's wise to not go farther than 3-4 channels fomr the original frequency, unless you change the whole module or have the radio re-tuned. The "high/low" refers to when the frequencies were alloted. In olden days, our legal operating band stopped at ch. 36, then the FCC allocated us the "low band", 12-34. Dr.1 Driver "There's a Hun in the sun!"
Reply to
Dr1Driver
What does this have to do with Futaba sending out receivers tuned to either high or low channels? This is a relatively new thing, not dating back to the original channel allocations.
Reply to
Paul McIntosh
This has been discussed many times. In fact, the decision for Futaba to sell high band and low band receivers was suggested in this very forum. Until recently, Futaba sold its receivers with a crystal for a specific channel. If you wished to change the channel, they offered a service for retuning them. They still offer that service. Frequency changes are performed at a cost of $15.00.
However, the factory actually made 72 MHz. receivers in batches which were center tuned to either a high (36 up) or low (35 down) band. This allowed satisfactory performance without having to peak each receiver to the exact crystal used. Some competing receivers are sold without a crystal, so Futaba decided to do the same. They just continued the practice already being used.
Channel 34 is right at the boundary of high and low band. It is likely that a channel 34 crystal will provide satisfactory performance in either a high band or low band receiver. The problem is knowing which you have. Many used receivers were peaked to a specific channel. So, they aren't either high or low band. If the receiver has a channel sticker on it, it's probably factory tuned. If not, all bets are off.
Your best bet is to range check, and if you don't like the result, have the receiver retuned.
Jim - AMA 501383
JRO wrote:
Reply to
James D Jones
Not a lot basically. Theoretically as well as practically a reciever that is tuned exactly to a cyrstal will outperform one that isn't.
Since we like to swap crystals, the receivers are tuned to somewhere in the middle - either of the whole band, or in some case to the middle of the upper part, or lower part.
Reply to
The Natural Philosopher
TNP,
You missed the point on this one. The reason Futaba sells high or low channel receivers has nothing to do with some ancient channel allocation.
Reply to
Paul McIntosh
Then explain to me why for about 10 years Hitec/RCD has been able to sell receivers that accepted the full range of crystals without a problem. I have about 7 Hitec receivers and not one has given me a problem. Does Hitec put together a more forgiving Receiver, or do they use better technology than Futaba to minimize this tuning issue. Don
Reply to
Twinster2
I would guess the latter. And, I would guess that if Futaba center-tuned their receivers, they would act the same.
Reply to
Paul McIntosh
The only bit that needs retuning on a receiver with a crystal change is the front end tuned circuit(s) before the mixer.
Its perfectly possible to make those a pass band circuit covering teh whole band, or a single stage unit covering just a section well, and teh rest poorly
What Futaba or hitrec do at 72Mhz I dunno. We r8n at 35MHz and its a bit didfferent here.
Reply to
The Natural Philosopher
Bandwidth and channel spacing is essentially the same so no reason it couldn't be done by all manufacturers.
Reply to
Paul McIntosh
Hitec receivers don't have tuned filters before the mixer. That's why they don't need tuning. Futaba chose to pass a narrow RF band at the input. Theoretically, this should make them less susceptable to high power, nearby, off channel interference. Why they chose to make it so narrow as to not pass the entire 72 MHz band without tuning is beyond me. But, they don't have this problem on other bands. In my experience, the Hitec FM receivers work very well without the extra circuit.
I now buy Futaba receivers for PCM only. Hitec's quality and superior service make their FM receivers a clear choice. But, Futaba's PCM 1024 system is my choice for any expensive model.
Jim - AMA 501383
Paul Mc> I would guess the latter. And, I would guess that if Futaba
Reply to
James D Jones
It is acrualy only realted by design, and has no bearing on what I was saying. Look up the principles of superhets and come back later.
Yawn.
Reply to
The Natural Philosopher
Then they are total; crap and have absoultelty zero al;ternate channel rejectoon. I have never seen any rdaio thathas no tuning before the mixer, that was anythimg other than either a piece oof total kiddiy toy garbage, or a hobbyisist construction kit.
Because to elmintate the alternate channel - which is why it needs to be narrow, and still cover the whole band on a S/C set is physically impossible, and on a a DC set it is hard and expensive.
Reply to
The Natural Philosopher
What I should have said was a tunable filter. The filter is fixed. I'm sure that you know that they aren't crap if you know about them at all.
OK, why then do Hitec receivers perform so well over the entire band? It can't be physically impossible, since it has obviously been done. They are also less expensive, have reasonably priced crystals, and a warranty policy far superior to Futaba.
Reply to
James D Jones

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