EMRFD Message Archive 7847

Message Date From Subject
7847 2012-10-10 23:55:59 Tamás Fábián Series resonant color burst crystals
Hello everyone,

I'm trying to rebuild the Warbler PSK transciever for 80 meters
formerly sold by Small Wonder Labs.

I'm finished with the receiver part and the T/R circuitry, and tested
it in the past few days.

The Warbler is a direct conversion receiver that uses a ladder filter
made of 3.579 MHz crystals right in front of the product detector, so
it achieves SSB reception while being direct conversion.

The ladder filter is a three element min-loss type with 33pf
capacitors, and terminated in 1.5 KOhm.

My problem is that the passband is about 3,579.3 - 3,580.5 KHz which
is slightly lower than the passband spec. in the original manual
(3,580 - 3.581 KHz). Also I'm not entirely satisfied with the overall
gain of the receiver, but It's just a feeling, I'm yet to do
measurements. I tried to select and match crystals with higher
frequencies using the circuit on fig. 3.35 (G3UUR measurement circuit)
with not much luck.

I read the manual more carefully and I found that the original rig
used series resonant color burst crystals, and I probably using
parallel resonant ones. Can this be the root of the problem?

If this is the case, can anyone name a source of series resonant
crystals of this frequency?

Alternatively, can I somehow shift the passband downwards, or I have
to completely redesign the filter to be wider and also to have steeper
skirt (for good carrier / image rejection)?

Thank you,

Tamas HA5FTL
7848 2012-10-11 02:48:41 Ashhar Farhan Re: Series resonant color burst crystals
Tamas,

The passband doesn't seem to be too much away from what the manual
specified. That said ...

1. Every crystal has a parallel resonance and a series resonance. It
is highly unlikely that the crystals you have are not colour burst.
Made to order crystals are almost ten times costlier. Oth, the colour
burst crystals are made to wide variation in specs. I would say that
what you got was within the tolerance limit.

2. In psk rigs, lower gain is better. It has to drive the mic input.
Overdriving can lead to distortion and loss of intelligence. Nor
should you bother so much with the passband shape. Fidelity is of
lesser value in psk than in the case of ssb.

The proof is really in hooking it up to your compand 'reading' the waterfall.

- Farhan

On 10/11/12, Tamás Fábián <giganetom@gmail.com> wrote:
> Hello everyone,
>
> I'm trying to rebuild the Warbler PSK transciever for 80 meters
> formerly sold by Small Wonder Labs.
>
> I'm finished with the receiver part and the T/R circuitry, and tested
> it in the past few days.
>
> The Warbler is a direct conversion receiver that uses a ladder filter
> made of 3.579 MHz crystals right in front of the product detector, so
> it achieves SSB reception while being direct conversion.
>
> The ladder filter is a three element min-loss type with 33pf
> capacitors, and terminated in 1.5 KOhm.
>
> My problem is that the passband is about 3,579.3 - 3,580.5 KHz which
> is slightly lower than the passband spec. in the original manual
> (3,580 - 3.581 KHz). Also I'm not entirely satisfied with the overall
> gain of the receiver, but It's just a feeling, I'm yet to do
> measurements. I tried to select and match crystals with higher
> frequencies using the circuit on fig. 3.35 (G3UUR measurement circuit)
> with not much luck.
>
> I read the manual more carefully and I found that the original rig
> used series resonant color burst crystals, and I probably using
> parallel resonant ones. Can this be the root of the problem?
>
> If this is the case, can anyone name a source of series resonant
> crystals of this frequency?
>
> Alternatively, can I somehow shift the passband downwards, or I have
> to completely redesign the filter to be wider and also to have steeper
> skirt (for good carrier / image rejection)?
>
> Thank you,
>
> Tamas HA5FTL
>

--
Sent from my mobile device
7849 2012-10-11 03:44:51 Fábián Tamás L... Re: Series resonant color burst crystals
Hi Farhan,

thanks for the answer. Yes, the passband is annoyingly close. You might
be right, and if I would have a bigger pile of stones to pick from, I
could easily choose the ones with higher frequencies.

After a bit of digging, I found some sources that specified their color
burst crystals to be serial, and I confirmed that mine are indeed
designed for parallel resonance operation i.e. the number on them is the
parallel resonance frequency, so the passband is a bit down if used as
filters.

I decided not to hunt for the seemingly rare serial resonance color
burst xtals, and simply replaced the 33pf capacitors to 22pf. The
passband widened to just include 3,581.0 :) Now I have a receiver with
double the passband, with slightly improved insertion loss, slightly
degraded shape (I don't really care), and still awsome sideband
rejection (I could not notice the screaming K2 on my desk tuned to the
opposite sideband, however it would overdrive the hell out of the
circuit when I tuned it into the passband).

I still have to modify and carefully test the other filter at the
transmitter side, but for now, I'm satisfied.

Cheers,

Tamas HA5FTL

2012-10-11 11:48 keltezéssel, Ashhar Farhan írta:
> Tamas,
>
> The passband doesn't seem to be too much away from what the manual
> specified. That said ...
>
> 1. Every crystal has a parallel resonance and a series resonance. It
> is highly unlikely that the crystals you have are not colour burst.
> Made to order crystals are almost ten times costlier. Oth, the colour
> burst crystals are made to wide variation in specs. I would say that
> what you got was within the tolerance limit.
>
> 2. In psk rigs, lower gain is better. It has to drive the mic input.
> Overdriving can lead to distortion and loss of intelligence. Nor
> should you bother so much with the passband shape. Fidelity is of
> lesser value in psk than in the case of ssb.
>
> The proof is really in hooking it up to your compand 'reading' the
> waterfall.
>
> - Farhan
>
> On 10/11/12, Tamás Fábián <giganetom@gmail.com
> > wrote:
> > Hello everyone,
> >
> > I'm trying to rebuild the Warbler PSK transciever for 80 meters
> > formerly sold by Small Wonder Labs.
> >
> > I'm finished with the receiver part and the T/R circuitry, and tested
> > it in the past few days.
> >
> > The Warbler is a direct conversion receiver that uses a ladder filter
> > made of 3.579 MHz crystals right in front of the product detector, so
> > it achieves SSB reception while being direct conversion.
> >
> > The ladder filter is a three element min-loss type with 33pf
> > capacitors, and terminated in 1.5 KOhm.
> >
> > My problem is that the passband is about 3,579.3 - 3,580.5 KHz which
> > is slightly lower than the passband spec. in the original manual
> > (3,580 - 3.581 KHz). Also I'm not entirely satisfied with the overall
> > gain of the receiver, but It's just a feeling, I'm yet to do
> > measurements. I tried to select and match crystals with higher
> > frequencies using the circuit on fig. 3.35 (G3UUR measurement circuit)
> > with not much luck.
> >
> > I read the manual more carefully and I found that the original rig
> > used series resonant color burst crystals, and I probably using
> > parallel resonant ones. Can this be the root of the problem?
> >
> > If this is the case, can anyone name a source of series resonant
> > crystals of this frequency?
> >
> > Alternatively, can I somehow shift the passband downwards, or I have
> > to completely redesign the filter to be wider and also to have steeper
> > skirt (for good carrier / image rejection)?
> >
> > Thank you,
> >
> > Tamas HA5FTL
> >
>
> --
> Sent from my mobile device
>
>
7850 2012-10-11 08:40:11 William Carver Re: Series resonant color burst crystals
"ECS", available from Mouser, makes a 3.579545 MHz xtal at series
resonance: ECS-35-S-1X, ten for $4.10. These are specified to be within
30 ppm which is about 110 Hz.

But the rig should work in all other respects, and its passband overlaps
the design passband, so you should be able to work other Warblers. You
might want to satisfy yourself with its performance first, and if you
were satisfied then you could replace the filter crystals to move it up
slightly.

W7AAZ
7851 2012-10-11 09:20:13 Fábián Tamás L... Re: Series resonant color burst crystals
William,

thank you very much. I already feel comfortable with the
double-bandwidth version I've managed to achieve with the parallel
resonant crystals. Unless I run into trouble with the transmitter
section, I think I'll just stay with what I've got so far.

Thanks again for the part number, it's likely I'll need those series
resonant rocks anyway. :)

Cheers,

Tamas HA5FTL

2012-10-11 17:40 keltezéssel, William Carver írta:
>
>
> "ECS", available from Mouser, makes a 3.579545 MHz xtal at series
> resonance: ECS-35-S-1X, ten for $4.10. These are specified to be within
> 30 ppm which is about 110 Hz.
>
> But the rig should work in all other respects, and its passband overlaps
> the design passband, so you should be able to work other Warblers. You
> might want to satisfy yourself with its performance first, and if you
> were satisfied then you could replace the filter crystals to move it up
> slightly.
>
> W7AAZ
>
>
7852 2012-10-11 09:25:38 Ashhar Farhan Re: Series resonant color burst crystals
Why can't we have a simple direct conversion transciever for psk31?
The bpsk modulation is just a dsb modulator and the direct conversion
receover can easily receive psk. Suren you maybe barking up the wrong
sideband. But keeping the badnwidth open to something like 15khz will
ensure that image sideband is away from psk slice of the edge.
- farhan

On 10/11/12, William Carver <bcarver@safelink.net> wrote:
>
>
> "ECS", available from Mouser, makes a 3.579545 MHz xtal at series
> resonance: ECS-35-S-1X, ten for $4.10. These are specified to be within
> 30 ppm which is about 110 Hz.
>
> But the rig should work in all other respects, and its passband overlaps
> the design passband, so you should be able to work other Warblers. You
> might want to satisfy yourself with its performance first, and if you
> were satisfied then you could replace the filter crystals to move it up
> slightly.
>
> W7AAZ
>
>
>

--
Sent from my mobile device
7853 2012-10-11 10:13:07 William Carver Re: Series resonant color burst crystals
Consider this Tamas: when you reduce the coupling capacitors and widen
the filter, this moves the HIGH EDGE UP. The low edge doesn't move very
much. This is exactly what you want!

So if the additional bandwidth is OK, and your other transmitted
sideband isn't too strong, your "correction" for the lower crystal
frequency is OK.

W7AAZ
7854 2012-10-11 10:19:48 William Carver Re: Series resonant color burst crystals
On Thu, 2012-10-11 at 21:55 +0530, Ashhar Farhan wrote:
>
> Why can't we have a simple direct conversion transciever for psk31?
> The bpsk modulation is just a dsb modulator and the direct conversion
> receover can easily receive psk. Suren you maybe barking up the wrong
> sideband. But keeping the badnwidth open to something like 15khz will
> ensure that image sideband is away from psk slice of the edge.
> - farhan
>

You're right farhan, it could be done as a direct conversion setup if
you had a very stable VFO for tuning and a built-in phase-to-digital
demodulator. BPSK would be VERY simple in that case! One could implement
AFC to "lock" the VFO to the received signal.

But the Warbler, and all of the BPSK, has been implemented as BPSK
modulation of a tone, and applying that tone to an SSB transceiver (the
Warbler is a simple SSB transceiver). "Tuning" is done by choosing the
audio tone you want to demodulate and its frequency for transmitting,
making the "VFO" a fixed frequency xtal oscillator.

W7AAZ






> On 10/11/12, William Carver <bcarver@safelink.net> wrote:
> >
> >
> > "ECS", available from Mouser, makes a 3.579545 MHz xtal at series
> > resonance: ECS-35-S-1X, ten for $4.10. These are specified to be
> within
> > 30 ppm which is about 110 Hz.
> >
> > But the rig should work in all other respects, and its passband
> overlaps
> > the design passband, so you should be able to work other Warblers.
> You
> > might want to satisfy yourself with its performance first, and if
> you
> > were satisfied then you could replace the filter crystals to move it
> up
> > slightly.
> >
> > W7AAZ
> >
> >
> >
>
> --
> Sent from my mobile device
>
>
>
>
7855 2012-10-12 01:56:08 Fábián Tamás L... Re: Series resonant color burst crystals
This is exactly what I have noticed, and it's Ok.

During the last night's 80m opening I could SWL quite a few stations. I
saw that much of the traffic is around 3.5781, extending up to 3.5782.
I'll try to include 3.5782 somehow, possibly by adding one more crystal.
I'm yet to see if this is possible at all.

Otherwise I'm satisfied with the results.


2012-10-11 19:13 keltezéssel, William Carver írta:
>
>
> Consider this Tamas: when you reduce the coupling capacitors and widen
> the filter, this moves the HIGH EDGE UP. The low edge doesn't move very
> much. This is exactly what you want!
>
> So if the additional bandwidth is OK, and your other transmitted
> sideband isn't too strong, your "correction" for the lower crystal
> frequency is OK.
>
> W7AAZ
>
>