Benefits of the Yaesu XF-130CN 300 Hz Crystal Roofing Filter

Do You Need That Filter?


The Yaesu FT-DX10 comes standard with a 500 Hz crystal (xtal) roofing filter, but offers an optional 300 Hz roofing filter.  Should you purchase the optional filter?

The 300 Hz roofing filter is twice the size of the 500 Hz filter so it must be twice as good right?  

If you casually switch back and forth between the two filters on a noisy band, it sounds like the 300 Hz filter markedly improves selectivity and quiets the noise.  But try this: Select the 500 Hz filter and narrow the bandwidth (using the bandwidth control) to 300 Hz, then switch to the 300 Hz filter. 

When you digitally narrow the bandwidth of the 500 Hz filter to 300 Hz you will "hear" the same reduction in noise as you have cut out 200 Hz of higher frequency sound.  Engaging the 300 Hz filter lowers the volume a bit (3-6 dB) due to insertion loss.  

So what you are actually "hearing" when you switch back and forth between the filters without changing the digital bandwidth is the reduction of the higher frequency noise that can be accomplished using the bandwidth control alone with the 500 Hz filter.

So, from a selectivity standpointthe 300Hz filter doesn't gain you anything over using the digital filtering with the 500 Hz filter.  The real benefit should come in the form of adjacent signal rejection.  So let's look at that.

In the video below I demonstrate the signal rejection of a 40 dB over S9 adjacent signal to a weaker S3 - S5 signal.


From the video you can hear that there is a very small demonstrable difference in strong signal rejection when using the 300 Hz optional filter, but the difference is so small that I doubt many of us would find practical benefit over simply narrowing the DSP bandwidth while using the 500 Hz filter. Even when contesting.  The digital filtering built into the FT-DX10 is really, really good when using the included 500 Hz roofing filter alone.

Yes, I spent the $200 for the optional filter thinking it would help, but I wished I had known what I do now.  I would have $200 for some other nifty radio gadget to spend instead. 


That's all for now.

Lower your power and raise your expectations

Richard AA4OO

https://www.hamradioqrp.com

Richard Carpenter, AA4OO, is a regular contributor to AmateurRadio.com and writes from North Carolina, USA. Contact him at [email protected].

4 Responses to “Benefits of the Yaesu XF-130CN 300 Hz Crystal Roofing Filter”

  • Howard AC4FS:

    So, perhaps sell the 300Hz filter to someone that doesn’t read your blog? 🙂

    73, Howard
    AC4FS

  • Chris Hart, CT7AMT:

    Good heads-up Richard.
    I’m sure Howard’s comment is tongue-in-cheek. You wouldn’t do that. Would you?
    I wonder if that filter would be good in another radio model? Then you could flog it.
    In any case, you have saved somebody else 200 bucks. Good man.
    Chris

  • Clint KA7OEI:

    I’ve been looking with interest at that same radio, having glanced at its circuit topology – which is both “retro” and “modern” at the same time: Retro in the sense that – unlike many modern radios with “direct sampling” A/D converters it is first converted to an (analog) IF before being demodulated – digitally, in this case.

    It’s informative to note that some of the best-performing radios in terms of surviving “close-in” strong signals are those that apply the techniques used here – consider the Elecraft K4 with its “HD” version which is intended for those situations where very strong signals may be present that would overwhelm the A/D converter: This variant of the K4 has pretty much the same architecture of the FT-DX10.

    The “short version” of what this means is that the FT-DX10 (and the K4-HD) is quite likely to be able to operate – given appropriate care – in a situation like a DXpedition or Field Day where there is another transmitter on the *same* band – something that most all direct-sampling rigs simply *cannot* do without serious effort in isolation and/or very tight filtering.

    * * *

    The 300Hz versus 500Hz filter?

    If one reads the history at the Sherwood Engineering site you’ll see the back-story when it comes to the roofing filter on the Drake twins: The narrower filter allowed very strong, very nearby signals to be filtered to avoid overloading the receiver’s later (IF) stages – and it’s likely that the same can be said for this as well.

    Unless you plan to run under conditions of extreme pile-ups where a signal that is >40+ dB stronger than the one of interest is causing interference due to limitations of the dynamics of the receiver itself, then the answer is that you probably *don’t* need the 300Hz filter.

    Considering the architecture of the FT-DX10, if the gain distributions are properly applied, I’d have trouble thinking of a more-than-rare situation where having this narrower filter would make a difference: Most likely, the limitation in such crowded conditions will be the cleanliness of the other stations’ transmitters involved in the melee rather than the ability of the receiver itself.

  • Bart AA7VA:

    Now try it using IF shift, Contour, Notch. That can make all the difference in the world

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