Radio Control Crystal Frequency!!!! - UK Vintage Radio Repair and Restoration Discussion Forum

John100 · 5th Oct 2014, 4:37 pm

Hi
I'm a bit at a loss with this one!
I have a vintage radio controlled robot, the transmitter frequency is 75.670Mhz, the crystal in the receiver is 37.609Mhz. All works fine and the technical manual refers to the fact quote 'regenerative feedback through the receiver crystal causes the autodyne converter to oscillate at the crystal's second harmonic frequency.
Now the problem!
I acquired a second remote control robot (identical to the first in circuit design)), the transmitter frequency is 75.870Mhz,it did not have a receiver, I was lucky to find one but the crystal value is the same as the first robot i.e. 37.609Mhz and no surprise it does not work with the transmitter!
What frequency does the crystal have to be in the receiver circuit and where am I likely to find a supplier of the 'new' crystal.
Any help would be appreciated.

John

John100 · 5th Oct 2014, 5:09 pm

The 'quote' was stated in the technical manual which accompanied the robot!

5th Oct 2014, 5:27 pm

I am quite sure that 75MHz is not a legal RC frequency in the UK, see here http://www.ofcom.org.uk/static/archi..._info/ra60.htm You may get away with it for a ground based robot, but for a flying model the right frequencies are essential so you don't get interfered with and hit someone.

Free to use frequencies (in the UK, controlled by OFCOM) are quite numerous, some are more defined on to what they should be used for e.g. surface and air radio control have different bands.

John100 · 5th Oct 2014, 5:36 pm

The robot did originate from the US (Heathkit) and it was manufactured in the 1980's.

Biggles · 5th Oct 2014, 5:52 pm

Hi John, if you double the xtal frequency of the working receiver then subtract that frequency from the transmitter frequency you get 452 KHz. This would appear to be about correct for the IF frequency of a superhet type receiver. From this assumption it would be possible to work back and find the xtal frequency required for the second receiver you have to enable it to work with your other transmitter. Three problems though; one off crystals are expensive, the frequency is probably not allowed in the UK, and finally, the receiver may not be a superhet. If you could find some info on the receiver type that may be helpful.
Alan.

5th Oct 2014, 6:10 pm

Quote:

The robot did originate from the US

And they do have a 75MHz RC band http://rcvehicles.about.com/od/frequ...requencies.htm I was given an RC helicopter with a 72MHz radio, soon swapped out for a 2.4GHz jobbie.

Worth doing if your robot has a separate reciever as it is legal, crystal free (it works its self out, very clever) and remarkably cheap.

John100 · 5th Oct 2014, 6:12 pm

This is not an area that I am conversant with, the documentation does not state it is a superhet receiver, however your reply is very helpful in determining the crystal frequency.

mole42uk · 5th Oct 2014, 6:29 pm

Just to be clear, 75MHz is NOT a legal frequency for model control in the UK.

John100 · 5th Oct 2014, 6:31 pm

Noted and thanks for your reply.

trickie_dickie · 5th Oct 2014, 6:49 pm

In my younger days, it was 35mHz for aircraft. Crystals are available on Ebay.

mole42uk · 5th Oct 2014, 7:19 pm

AFAIK:

27MHz is still legal for all model control
35MHz is legal for aircraft only
459MHz is legal for all model control
2.4 GHz is legal for all model control

richrussell · 6th Oct 2014, 11:31 am

From OFCOM's website: http://www.ofcom.org.uk/static/archi..._info/ra60.htm

26.96 to 27.28MHz General use
34.945 to 35.305MHz Aircraft only
40.66 to 41.00MHz Surface only
458.5 to 459.5MHz General use
433.050 to 434.790MHz Telemetry from model to base

Plus the 2.4GHz unregulated band which is gradually replacing use the HF bands, for digitally encoded (and bidirectional) control systems.

5th Oct 2014, 4:37 pm	#1
John100 Triode Join Date: Nov 2008 Location: Solihull, West Midlands, UK. Posts: 14	Radio Control Crystal Frequency!!!! Hi I'm a bit at a loss with this one! I have a vintage radio controlled robot, the transmitter frequency is 75.670Mhz, the crystal in the receiver is 37.609Mhz. All works fine and the technical manual refers to the fact quote 'regenerative feedback through the receiver crystal causes the autodyne converter to oscillate at the crystal's second harmonic frequency. Now the problem! I acquired a second remote control robot (identical to the first in circuit design)), the transmitter frequency is 75.870Mhz,it did not have a receiver, I was lucky to find one but the crystal value is the same as the first robot i.e. 37.609Mhz and no surprise it does not work with the transmitter! What frequency does the crystal have to be in the receiver circuit and where am I likely to find a supplier of the 'new' crystal. Any help would be appreciated. John

5th Oct 2014, 5:09 pm	#2
John100 Triode Join Date: Nov 2008 Location: Solihull, West Midlands, UK. Posts: 14	Re: Radio Control Crystal Frequency!!!! The 'quote' was stated in the technical manual which accompanied the robot!

5th Oct 2014, 5:27 pm	#3
Guest Guest Posts: n/a	Re: Radio Control Crystal Frequency!!!! I am quite sure that 75MHz is not a legal RC frequency in the UK, see here http://www.ofcom.org.uk/static/archi..._info/ra60.htm You may get away with it for a ground based robot, but for a flying model the right frequencies are essential so you don't get interfered with and hit someone. Free to use frequencies (in the UK, controlled by OFCOM) are quite numerous, some are more defined on to what they should be used for e.g. surface and air radio control have different bands.

5th Oct 2014, 5:36 pm	#4
John100 Triode Join Date: Nov 2008 Location: Solihull, West Midlands, UK. Posts: 14	Re: Radio Control Crystal Frequency!!!! The robot did originate from the US (Heathkit) and it was manufactured in the 1980's.

5th Oct 2014, 5:52 pm	#5
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: Radio Control Crystal Frequency!!!! Hi John, if you double the xtal frequency of the working receiver then subtract that frequency from the transmitter frequency you get 452 KHz. This would appear to be about correct for the IF frequency of a superhet type receiver. From this assumption it would be possible to work back and find the xtal frequency required for the second receiver you have to enable it to work with your other transmitter. Three problems though; one off crystals are expensive, the frequency is probably not allowed in the UK, and finally, the receiver may not be a superhet. If you could find some info on the receiver type that may be helpful. Alan.

5th Oct 2014, 6:12 pm	#7
John100 Triode Join Date: Nov 2008 Location: Solihull, West Midlands, UK. Posts: 14	Re: Radio Control Crystal Frequency!!!! This is not an area that I am conversant with, the documentation does not state it is a superhet receiver, however your reply is very helpful in determining the crystal frequency.

5th Oct 2014, 6:29 pm	#8
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,614	Re: Radio Control Crystal Frequency!!!! Just to be clear, 75MHz is NOT a legal frequency for model control in the UK. __________________ Richard Index: recursive loop: see recursive loop

5th Oct 2014, 6:31 pm	#9
John100 Triode Join Date: Nov 2008 Location: Solihull, West Midlands, UK. Posts: 14	Re: Radio Control Crystal Frequency!!!! Noted and thanks for your reply.

5th Oct 2014, 6:49 pm	#10
trickie_dickie Hexode Join Date: Jan 2011 Location: Aberdare, South Wales, UK Posts: 403	Re: Radio Control Crystal Frequency!!!! In my younger days, it was 35mHz for aircraft. Crystals are available on Ebay. __________________ Richard

5th Oct 2014, 7:19 pm	#11
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,614	Re: Radio Control Crystal Frequency!!!! AFAIK: 27MHz is still legal for all model control 35MHz is legal for aircraft only 459MHz is legal for all model control 2.4 GHz is legal for all model control __________________ Richard Index: recursive loop: see recursive loop

6th Oct 2014, 11:31 am	#12
richrussell Heptode Join Date: Jul 2008 Location: Selby, North Yorkshire, UK. Posts: 979	Re: Radio Control Crystal Frequency!!!! From OFCOM's website: http://www.ofcom.org.uk/static/archi..._info/ra60.htm 26.96 to 27.28MHz General use 34.945 to 35.305MHz Aircraft only 40.66 to 41.00MHz Surface only 458.5 to 459.5MHz General use 433.050 to 434.790MHz Telemetry from model to base Plus the 2.4GHz unregulated band which is gradually replacing use the HF bands, for digitally encoded (and bidirectional) control systems.