[minima] Re: Does the size of the Crystal Oscillators matter?
- From: "Joe Rocci" <joe@xxxxxxxxxx>
- To: <minima@xxxxxxxxxxxxx>
- Date: Tue, 11 Mar 2014 13:01:12 -0400
I think that's good. I bought 50 pcs of these from EBay shipper ocean-beach for
$4.11 with free shipping. Haven't tested them yet.
----- Original Message -----
From: hcker2000
To: minima@xxxxxxxxxxxxx
Sent: Tuesday, March 11, 2014 12:48 PM
Subject: [minima] Re: Does the size of the Crystal Oscillators matter?
Thanks I was just planing on buying a bunch from china in one go to avoid
paying $8 for shipping on $8 worth of parts. Do you think 20 would be enough to
get 8 that match?
On Tue, Mar 11, 2014 at 10:57 AM, Joe Rocci <joe@xxxxxxxxxx> wrote:
I believe what I wrote in my previous is substantially true for any crystal
ladder filter; ie, the single most important factor is frequency matching. In
general, you should try to match frequencies to be within a range of no more
than about 5% of the filter bandwidth. The less variation, the better the
shape. Since this filter is a bit wider than BITX, the allowable range of
crystal frequency variation is also bigger. All of this gets more stringent
when you're trying to build a narrow band filter for CW, which by the way, will
be difficult to implement at 20 MHz without incurring large insertion loss.
Joe
W3JDR
----- Original Message -----
From: gurudatta panda
To: minima@xxxxxxxxxxxxx
Sent: Tuesday, March 11, 2014 10:44 AM
Subject: [minima] Re: Does the size of the Crystal Oscillators matter?
@Joe: That means, there will be lot of relaxation from Crystal Matching
in comparison to BITX?
On Tue, Mar 11, 2014 at 7:37 PM, Joe Rocci <joe@xxxxxxxxxx> wrote:
The filter bandwidth in this radio is so wide that typical crystal
variations shouldn't have a significant effect.
If you want the nicest shape, then:
1) Buy a batch of 10-15 crystals from the same manufacturer, supplier &
model. Here in the US, these crystals are available from Digikey and Mouser for
about $.40/ea., as are higher frequency fundamental mode crystals all the way
to 50 MHz.
2) Build a test oscillator and select the 8 crystals that are closest
together in frequency. Try to get a set that are within about 150 Hz of each
other. Absolute frequency isn't so important as frequency match.
3) If you want to get the last few percent of performance possible, you
can Google ways to match crystals for their Q and loss resistance.
The filter in this radio is so wide that only #1 & #2 above are really
critical. Random crystals will probably function, but the passband shape won't
be optimum. Low profile crystals should work as long as their series loss
resistance isn't too high. Even if it is higher, it will mostly affect filter
loss. In the ones I've looked at, it seems OK.
Joe
W3JDR
----- Original Message -----
From: hcker2000
To: minima@xxxxxxxxxxxxx
Sent: Tuesday, March 11, 2014 9:45 AM
Subject: [minima] Does the size of the Crystal Oscillators matter?
Is it ok to use low profile ones?
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Mike "hcker2000" Ashcraft
http://bigironinteractive.com
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Gurudatta Panda
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Mike "hcker2000" Ashcraft
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