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72mhz AM tx with 75mhz crystal

Old 09-13-2004, 08:24 PM
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jboy381-RCU
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Default 72mhz AM tx with 75mhz crystal

i've been trying to figure this one out...i have an AM radio system...the tx says 72mhz but it has a 75mhz crystal in it...the rx is a 2 channel,it also has a 75mhz crystal...will someone explain to me how it works??? i want to get another rx for another plane but i don't what to get...BTW the radio system is futaba...

thanks john
Old 09-14-2004, 12:11 AM
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JohnBuckner
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Default RE: 72mhz AM tx with 75mhz crystal

This is a no, no. By FCC regulation Aircraft are to use the fifty channels on the 72 mhz band, surface vehicles (boats, cars) are only to use the thirty channels on the 75 mhz band. The only exception to this is on the 27 mhz band where the six channels are shared by surface and aircraft. Usually the only aircraft to venture onto this band are just small park flyers, to fly anything beyond that would be unwise on 27 and illegal on 75.

Someone has substituded a set of surface crystals in your radio.

John
Old 09-14-2004, 01:22 PM
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Default RE: 72mhz AM tx with 75mhz crystal

The 6 meter "Amateur" frequencies also have no restrictions on the type of model.
Old 09-14-2004, 01:44 PM
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Default RE: 72mhz AM tx with 75mhz crystal

Yup agreed that is correct but I left this out to avoid confussion as it clearly does not apply in this case as the tx is a 72 mhz unit.

John
Old 09-14-2004, 01:52 PM
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Default RE: 72mhz AM tx with 75mhz crystal

Yup agreed that is correct but I left this out to avoid confusion as it clearly does not apply in this case as the tx is a 72 mhz unit . Thank you and perhaps I should have also mentioned the two ham bands and their lack of model type restriction also.

John



Hmm I somehow double posted. In the edit mode I cannot find the delete button for my incomplete post above. Anyone know if this ability has changed? It seems that this was avaliable in the past.
Old 09-14-2004, 05:41 PM
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Default RE: 72mhz AM tx with 75mhz crystal

john,
i know it's not right...what i want to know is how does this set up work???i'm using it for small 1\8 & 1\2A two channel models...i have another radio for my big planes...if i buy a AM 72mhz rx and put a AM 75 mhz crystal in it will it work with the tx???
i bought it at a swap meet,not knowing it was set up like this...the rx was in a plane at the time and i had no way to check it...i crashed the plane due to battery failure...thats when i found this set up...i still want to use it with the small planes i build...i have two planes built but only one rx...

john


the rx looks like this...it didn't have a case with it in the plane...from what i can tell,the servo plugs and the place where the crystal goes are the same...
Old 09-14-2004, 06:03 PM
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Default RE: 72mhz AM tx with 75mhz crystal

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Old 09-14-2004, 06:33 PM
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Default RE: 72mhz AM tx with 75mhz crystal

ORIGINAL: jboy381-RCU

john,
i know it's not right...what i want to know is how does this set up work???i'm using it for small 1\8 & 1\2A two channel models...i have another radio for my big planes...if i buy a AM 72mhz rx and put a AM 75 mhz crystal in it will it work with the tx???
john

John I realize your frustration and understand you want to do it right. Unfortunately there is no easy answer and the answer to your question of how does it work has to be a guarded maybe, maybe not. First off there are a lot of wide band Futaba AM radios floating around out there that are not even legal anymore. Yes I realize AM's are still produced by all the majors that are narrow band but the problem is identifying what you got. I would go to the Faq on the Futaba website which does list the legal narrow band Futaba AM tx's model numbers. If your model # is not listed don,t waste any money on this radio it is time for retirement. OK another indicator but not neccessarily accurate way to tell if this is a wideband Tx,Rx is to look on the Rx and if it says it is Dual Conversion then the likelyhood is that at least the Rx is narrowband Yes I know that there are modern single conversion Rx's that are narrowband but in the case of older Futaba it is an indicator. Another indicator is if the Tx has a gold sticker on it somewhere, If so then your are probably OK.

OK all of the above is just the wide/narrow band problem but a far more devious one is the fact you do not know which Channel on 72 the tx was tuned to originally. By the way its likely that this is the reason that you lost that airplane in a crash more so than battery failure. Putting crystals of an entirely different band in, is most certainly going to result in a detuned Tx with an unknown loss of performance. Now if you know what channel the Tx was orginally on then you could install that crystal and you may be OK However if you put just any crystal in that is in the 72 band I would not fly that radio untill it was tuned for the channel that you changed to.

Only just my opinion. Swap meet Radios especially AM are frequently a bad investment if you don,t know exactly what you are looking at.

John
Old 09-15-2004, 06:28 PM
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Default RE: 72mhz AM tx with 75mhz crystal

thanks john,

it is a gold stickered tx... the 72mhz channel is a mystery as you have stated...i'll send it to futaba for a make over...thanks agian john

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