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17th Jul 2019, 11:37 pm | #1 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,934
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Use of a Ceramic Resonator in a BFO
A search of the net reveals one or two projects where people have used a 455kHz ceramic resonator (usually encountered in the form of a 3-pin filter), in place of a quartz crystal or tuned circuit, as the basis for a stable BFO. The rationale is that it offers better stability than may be easily obtained from a tuned circuit but is more easily pulled than might be the case with a crystal.
There's also been some use of ceramic resonators in VFO's. I wonder if anyone has been down this route or can see any pitfalls? B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. Last edited by Bazz4CQJ; 17th Jul 2019 at 11:42 pm. |
17th Jul 2019, 11:59 pm | #2 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
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Re: Use of a Ceramic Resonator in a BFO
Can’t see why not do it. Has to be more stable than the BFO kit I had when I was a kid. That was basically an IFT and a transistor and some biasing components.
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18th Jul 2019, 5:27 am | #3 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,339
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Re: Use of a Ceramic Resonator in a BFO
Using ceramic resonators in BFO's and VFO's has been around for years (not so much these days with all the you beaut DDS/Clock chips around).
One gotcha, be wary of any DC across them, they start to get noisy and can fail. |
19th Jul 2019, 11:09 am | #4 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,996
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Re: Use of a Ceramic Resonator in a BFO
The big problem I can see here is that the ceramic resonator will work on a fixed frequency, whereas a BFO/CIO really needs to be tunable so you can put it on the appropriate side of the signal.
Will the stability degrade if you try 'pulling' it VXO-style? Depending on the style of resonator you may be able to buy 100 of them cheap off Alibaba, check their resonant frequencies, and then use the two most-widely-differing ones for your sideband-select switch. |
19th Jul 2019, 12:50 pm | #5 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: Use of a Ceramic Resonator in a BFO
I think you can pull them in a VXO further than a crystal.
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20th Jul 2019, 12:38 pm | #6 |
Hexode
Join Date: Oct 2007
Location: Bristol, UK.
Posts: 444
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Re: Use of a Ceramic Resonator in a BFO
http://www.pan-tex.net/usr/r/receivers/sbfo.htm
I recently built this two terminal resonator circuit on stripboard and it works fine. So far withiout adding the transformer. Don m5aky |
20th Jul 2019, 3:44 pm | #7 |
Guest
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Re: Use of a Ceramic Resonator in a BFO
455kHz resonators are used in lots of remote controls BTW.
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21st Jul 2019, 5:13 am | #8 | |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,934
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Re: Use of a Ceramic Resonator in a BFO
Quote:
If I do replace the existing BFO (with its LC circuit), I must check the level of drive the BFO feeds in to the product detector so that I can replicate that. The oldest BFO circuit using a ceramic resonator that I found was a 1988 circuit from Rad Com, again, using a FET. B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
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21st Jul 2019, 8:45 am | #9 |
Nonode
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 2,102
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Re: Use of a Ceramic Resonator in a BFO
Lowe used them (2-pin) in their receivers, starting with the HF-123. They are tuned ±1.25kHz for USB and LSB. More stable than most L-C types
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21st Jul 2019, 2:55 pm | #10 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,934
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Re: Use of a Ceramic Resonator in a BFO
I think that most of the resonators I have in stock are three-pin devices, so the circuit below is interesting.
B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
21st Jul 2019, 3:36 pm | #11 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 963
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Re: Use of a Ceramic Resonator in a BFO
Hi used one of 456khz pulled by .5khz for upper sideband carrier ins osc . Does not drift at all Mick
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21st Jul 2019, 3:42 pm | #12 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
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Re: Use of a Ceramic Resonator in a BFO
Mmm... sounds like this is a good way to go for a BFO!
B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
22nd Jul 2019, 8:30 am | #13 |
Nonode
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 2,037
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Re: Use of a Ceramic Resonator in a BFO
I struggled with this when I built my homebrew 160m transceiver. The design is a straightforward single superhet with an IF of 455 kHz, so obviously it needs carrier oscillators for generating the AM and SSB signals. The one on 455 kHz for AM was fine, just a cheap Murata 455 ceramic filter in a Colpitts osc, but the one for SSB had to be pulled down to 453.5 kHz. I went through many ceramic filters before I found one that would pull far enough in the right direction and start reliably. A lot of 'optimising' of the feedback capacitors was called for.
However, it all worked fine in the end and the rig is still in use.
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Andy G1HBE. |
22nd Jul 2019, 9:19 am | #14 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,934
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Re: Use of a Ceramic Resonator in a BFO
I wonder (suspect) if it is the case that the resonators have greater temperature sensitivity than a crystal, so the tempco of the capacitors in the circuit may need to reflect that? I must checkout which resonators I have in stock; I think I have about 4 different types, all bought some time ago for project which (as yet) never proceeded.
Additionally, I'm interested in making the BFO tune with a varicap diode. B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |