|Emma Yates 1||14/07/2018 20:52:06|
|2 forum posts||Hi,|
My husband is driving me crazy by constantly looking for macgregor digimac transmitter receiver crystals 3. Please help me find some or point me in the right direction.
Many thanks Emma
|Michael Gilligan||15/07/2018 08:50:25|
14270 forum posts
Sorry, not my field, Emma ... 'though I'm sure my obsessions cause my wife similar suffering
This **LINK** may serve as a reminder to those better able to help.
|Jon Lawes||15/07/2018 09:03:20|
329 forum posts
It would probably work out more cost effective to buy modern 2.4ghz radio gear, I realise for some people using the older kit is half the appeal though. The newer stuff has hugely superior battery life, range, resistance to shared channels and is a fraction of the price.
|1272 forum posts|
Hi Emma, the 3 quoted doesn't indicate frequency of crystal required.
The early sets were using 27 Mhz and later models used 35 Mhz so you need to state which frequency your set is designed to operate on.
Ask on the FB BMFA page for the crystals when your have confirmed the frequency required.
|4863 forum posts|
Try googling for 'Radio Control Crystals'.
Crystals of this type aren't as readily available as they used to be because technology has moved on. ebay may be your best bet. I found this RC seller disposing of unwanted stock. RS Components sell crystals
Also Farnell and others. You can have them made to order, but that's expensive for one-offs. This chap in the USA specialises in older crystals.
The important thing is the frequencies of the crystals, for which you need to read the manual. The transmit crystal and receive crystal are off-set from each other by a gap that suits the receiver. I don't know if radio control offsets are standard or peculiar to each model. Perhaps another forum member knows?
The other issue with crystals is the package. They come in various sizes with pins spaced to fit various types of socket. I'd guess an old transistor unit would be HC6/U or HC48. Some are soldered in. If a crystal doesn't fit the socket the connection can be bodged to make it work, but this isn't for everybody.
Obviously hubby has a good reason for wanting to revive an antique radio control unit. But, if he just wants to use it for bog standard radio control, tell him it's far less stressful to buy a new one. Disheartening when you have gone to a lot of time, trouble, and expense sourcing crystals to switch on and find that the transmitter, receiver, or both are faulty.
347 forum posts
If the crystals sets you require are the 27mhz AM type, the pin spacings may be a standard spacing have a look Here
|Neil Wyatt||15/07/2018 11:14:18|
16754 forum posts
Don't listen to the nay sayers. A pair of crystals will cost less than a fiver, so have a try before throwing the gear out.
You need a transmitter and receiver pair, and they must be 27Mhz or 35MHz band to suit the transmitter.
The key point is they don't need to be Macgregor crystals, any brand will do as long as they are intended for remote control. The internet seems to be awash with cheap Futaba pairs, they will work fine - you may need to unclip the transmitter crystal from a plastic carrier to fit it in the Macgregor unit..
|Emma Yates 1||15/07/2018 11:28:16|
|2 forum posts||Thank you to everyone who has responded.|
I will look into the links and ideas you have given me.
Hopefully it will save some money and stop my house looking like cardboard warehouse!
Many thanks again!
|Martin W||15/07/2018 11:32:28|
|795 forum posts|
There is a copy of the manual for the Digimac system here. This gives data on the crystal numbers re their frequency and for No. 3 crystals this is Tx 27.020 MHz and Rx 26.550 MHz. As Neil says you probably don't need branded Macgregor crystals its just the frequency you need to verify. The difference in frequency between the crystals is defined by the receiver IF strip frequency, in this case 470 KHz which should be standard across most manufacture's systems at that time. Unless he desperately needs to operate on channel 3 then any pair of crystals desinged to work within the 27 MHz band should be fine.
Hope this helps
A modern list of Tx frequencies is given here and from this it looks like Channels 6 and 7 are the closest modern equivalent at 27.015 MHz and 27.025 MHz respectively. However looking on Ebay it would appear that this has not been universally accepted and that the crystals on offer refer to an intermediate channel numbering system, the nearest offered units would appear to be T8/R8 at 27.025 MHz as listed here.
Edited By Martin W on 15/07/2018 12:00:13
|John Paton 1||15/07/2018 22:59:51|
|182 forum posts|
I am pretty sure I have some (used) 27 Mhz crystals (pairs) that will suit - let me know what your husband needs and I can let you know if I have them - say £3.50 a pair including UK postage.
Later 27mhz sets were closer tolerance than early ones but all will work, its just interference rejection from transmitters on adjacent frequencies that causes problems with the wider tolerance crystals and early radio sets.
|Trevor Drabble||16/07/2018 01:13:33|
205 forum posts
Ripmax sell 27Mhz crystals , which are available from many model shops . Their web page lists local suppliers .
|Dodgy Geezer 1||12/11/2019 06:44:33|
|3 forum posts|
The key point is they don't need to be Macgregor crystals, any brand will do as long as they are intended for remote control....
The above is not quite an accurate statement.
Crystal-controlled receivers are usually 'super-hetrodyne' designs. This radio technique converts the received frequency to a lower 'intermediate' frequency signal which is easier to manipulate. As part of this process, the receiving set uses a crystal which has a slightly different frequency from the transmitting crystal.
The transmitting crystal can be any frequency in the 27MHz band, though you will find that 27MHz crystals are invariably on one of the 'spot' frequencies (google for precise data). Later sets were capable of using frequencies in between these 'spots' (called 'split' frequencies). It is true that any specific spot crystal will do for the transmitter.
BUT the receiver will need a crystal which precisely matches the frequency offset that that receiver is designed to operate at. The radio control community developed a common standard for this - it was 455KHz less than the transmitting frequency. So a transmitter on the RED spot frequency (27.045MHz) would have a corresponding matched receiver crystal at 26.590MHz.
So far, so good. Now we come to the problem. The early Macgregor sets did not comply with this standard, and used an offset of 470KHz. IF your set is an early Macgregor, then you will need a receiver crystal of 26.575 MHz if your transmitter is on RED, as an example. The set will probably not work with a 26.590 receiver crystal, which would be the common RED Futaba receiver crystal. Certain other manufacturers also had different offsets, but your problem is finding out whether this set is an early Macgregor, and, if it is, finding a pair of matching Macgregor crystals of that vintage...
Edited By Dodgy Geezer 1 on 12/11/2019 06:49:17
|1272 forum posts|
No doubt very informed information but I think it may be a bit too late, this is an old thread.
|Dodgy Geezer 1||19/11/2019 06:37:39|
|3 forum posts|
It is old - but people who look for vintage parts are often searching for years, and I thought that it was also worth putting this data up on the web for any others who might be wondering why apparently matching crystals that work in one radio set will sometimes not work in another...
|Michael Gilligan||19/11/2019 07:33:46|
14270 forum posts
Excellent logic, Sir
P.S. I just looked back at your first post [in 2014] and note that the link appears to be dead
In the spirit of what you have done on this thread ... is the resource still available ?
Edited By Michael Gilligan on 19/11/2019 07:38:05
|Simon Lumsdon||20/11/2019 20:55:47|
|1 forum posts|
Dear Dodgy Geezer
The power of the internet
i have just received an old 27am macgregor radio set from ebay and its missing an RX crystal! Having investigated it looks like 470khz if crystals are unobtainium. Do yku have any suggestions on what i could do to get this to work please?
TX has a blue crystal and i have a red 27.045 tx spare. Is there a combination using splits that might be close enough to work?
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