Hi, I'm trying to replicate the following circuit diagram, but I can't seem to find any sites/stores that are still selling the ceramic filter that they use (SFZ455F), so I was just wondering if its possible to replace it with some other ceramic filters.


http://www.qsl.net/pa3fdc/tech/hrx80/hrx80r1b.gif


And just another question, what does SFZ actually mean? I've tried googling for the datasheet and I just can't seem to find any revelent stuff.

Thanks in advance.

 

This appears to be an older Murata part number. I looked in their most recent Ceramic filter catalog for North America and don't see it there, probably because they have changed over to marketing mostly SMT packages. I found an alternative at Oscilent.com in their series number 739, see part no. 739-455-HL-C, which seems to be a close alternative.

http://www.oscilent.com/spec_pages/Filters/F-739.html

Be sure to check if the package of this part still fits into the circuit board layout, as I did not do that.

Otherwise here is a link of a potential supplier of the Murata part:

http://www.xs4all.nl/~barendh/Cateng...g_x-filter.htm

__________________
RadioRon

 

Hi Forever99482,

These are simple old style filters, in/out impedance 3k.
The "F" stands for 12 kHz bandwidth. (+/- 6 kHz.)
They usually come in pairs or triples but sometimes also single.
The orange one's are two three pin filters glued together.
A possible substitute could be a SFD455F from Murata, that's
the red one. It actually has five pins, only one ground pin.
It contains two SFZ455F's in one package.
No matter what you do stick to the 3k in/out impedance.
The 455 kHz center frequency is not critical in this design,
you can replace them with 450 or 460 kHz filters.

on1aag.

Attached Images

	ceramic filters.JPG (9.7 KB, 23 views)
	TCA440.GIF (16.7 KB, 25 views)

 

Thanks for the given information, it was very useful.

About the 739-455-HL-C, what does the selectivity actually mean? As stated by on1aag, shouldn't the selectivity be +/- 6 kHz?

Can anyone find a datasheet on the SFZxxxF series?

 

murata has CMF455f see the datasheet attached on page 13
possible that you get this item locally

__________________
Regards,
Sarma.

 

Did you meant CFWS455F? But the input/output impedance is not the same as SFZ455F. If the input/output impedance differs from 3k, what effect will it actually have on the circuit diagram(pin 12 and 15).

circuit diagram:
http://www.qsl.net/pa3fdc/tech/hrx80/hrx80r1b.gif

Thanks.

 

Imagine you replace those resistors with 2k2. secondly these are not meant for handling DC voltage and they recommend coupling caps . thus you can always terminate with a lower impedence like 2k2 after the coupling caps.

How ever it is many years since we stoped dreaming for TCA440 as it was not available in our country. After so long time you have shown a schematic. but I fear that this item will be in short supply or unduely priced.

__________________
Regards,
Sarma.

 

The selectivity of the filters is chosen to suit the bandwidth of the signal that you are receiving. This receiver project appears to be designed for radio direction finding, being an SSB receiver set up to receive LSB on 80 meters. For SSB, it is typical to choose filters for a cascaded response providing about 2.4 to 3 KHz overall bandwidth. When researching alternate filters, I found that the AM filters available are often quite wide, so I chose the narrowest model, the 739-455-HL-C. This part has a spec BW of 4 KHz at -3dB, so when two of these are cascaded, the net response is likely to be close to 3 KHz. Of course, you can choose any bandwidth you want from the Murata lineup, but I recommend going with something around 3.5 to 4.5 Khz per filter, or even a bit narrower is OK.

The impedance of the filter will affect the efficiency of the match to the 440 IC, but this is not a highly critical match. Note that there is a 3.3 Kohm resistor right beside each filter. If you change this value to be the same as the filter impedance, that is about all you need to do.

__________________
RadioRon

 

Hi Forever99482,

These filters are really cheap stuff. It is also difficult to tell what
the bandwidth is because I don't know if a single or a multiple unit
is used. Say you have a 15 kHz (-6dB) wide filter and you add
another one, the bandwidth of the combined filter will be reduced
to let's say 12 kHz (-6dB) and the flanks of the filter will become
steeper too.
You could lower the resistance values at pins 7 and 15 to match
the new filters but the gain of these stages will also be reduced
with the same amount. However pin 15 is a whole new ball game,
it's an input with an internal 3 k resistor.
Of course it can be matched too but you could use a battery charger
as a receiver as well.
So stick to the single resonator filters with their 3k in/out impedance
and don't worry too much about the bandwith of the filters. You
can always add some more if you like.

http://www.toko.co.jp/products/en/fi...ndex_am_e.html

http://www.alldatasheet.com/datashee...NS/TCA440.html

http://www.xs4all.nl/~barendh/Indexeng.htm

on1aag.

 

So do you mean that I could probably ignore the selectivity at Fo+/-9kHz, and perhaps go ahead with a CFM3 or CFA type of filter?

 

Yes you can, because there are two of them in series. So the bandwidth
will probably be about right. And if you find that the IF bandwidth is a bit
wide, you can always add an extra filter because their in/out impedance
is 3 k. But I wouldn't make the IF bandwidth too narrow because the
design has a manual tuning.

on1aag.

 

hmm...... I seem to have trouble finding a company (like farnell, or rswww) that provides this sort of filter, could you please direct me to some site that sells it?

Thanks.

 

you are likely to get them in shops at Malaysia itself
RS Components has a branch at Malaysia

Ps: heregoes malaysia link

RS Web Helpline: 603 5032 7633 or onlinehelp.MY@rs-components.com

__________________
Regards,
Sarma.

 

Could someone please tell me why there is a capacitor in between the ceramic filters, SFZ455F (both 47pF)? If I change the SFZ series to a CFA series from toko, do I need to change the value of the capacitor?

Thanks.

 

F1 and F2 are sets of filters coupled by a capacitor. F3 is individual single , but used for oscillation at 455KHz.
You could imagine 2 numbers each of SFZ455F at locations of F1 and F2. Earlier, there used to be single filter with 6 pins with a provision for external coupling capacitor . Perhaps they may be available now too.

Toko Ceramic filters you have selected are too broad like 13+/-3 KHz while sfz455F series are narrow. Whether it would serve your needs ? This replacement amounts that the second part of the filter is not there and thus no need for 47pF.

__________________
Regards,
Sarma.