Hi Dave, my experience of mixer-vcos with two crystals in a similar
frequency range is that they at OK up to QRSS10. The are ok on QRSS30 and 60
provided you are not trying to fit into a 0.3Hz slot amongst other stable
transmissions. In other words they will stay on an ARGO screen for several
hours, but you could end up using a fair bit of the bandwidth. The proviso
here is that you use "proper" crystal oscillator circuits (such as a
Colpitts) not "logic oscillators". I think Dave G0MRF found logic
oscillators ok for hand-keyed CW speeds.
The pair of crystals can be "shrouded together" and maybe insulated with
poly foam to guard against draughts. As they tend to drift together the
difference is not too temperature sensitive. It is probable that a lot of
the remaining drift comes from the tuning components which should probably
be inside the "shroud".
A "mixer VCXO" can be made by putting the two crystals in parallel in the
same osc circuit (TT some time back), I believe though I have not tried it.
You lose the chance to tweak them apart though.
Pulled ceramics are Ok for CW and probably not too bad for QRSS3, but I have
not measured them seriously.
Cheers de Alan G3NYK
----- Original Message -----
From: Dave Brown <[email protected]>
To: <[email protected]>
Sent: 25 April 2007 14:42
Subject: Re: LF: [ 500] EASY START - ceramic resonators et al
> So just how stable are the resulting outputs using these things?
> Anyone looked at that yet? Its a given that you will need very good to
> excellent frequency stability once things go beyond the aural CW
> stage.(And I'm not saying that's good or bad-just that it's bound to
> happen!)
>
> A reminder that some rigs will likely work 'as is' on 500 kHz- I have
> only tested the Yaesu FT757GX II but Yaesu rigs with similar pa
> design are likely to also work OK. Only proviso is to keep the output
> down to 50 watts or so-try for any more out and it shuts
> down-presumably in self protetction mode. From memory rx sensitivity
> is in spec or very close to-would have to check again to verify.
> 73
> Dave, ZL3FJ (a 500 kHz waiter!)
>
> ----- Original Message -----
> From: <[email protected]>
> To: <[email protected]>
> Sent: Thursday, April 26, 2007 12:34 AM
> Subject: Re: LF: [ 500] EASY START - ceramic resonators et al
>
>
> > Dave,
> >
> > Thanks for saving me the effort of doing the testing on ceramic
> > resonators! I see Rapid also stock these, and the 11.0592 xtals too.
> >
> > I've got my NoV application ready to post tonight and I retire on
> > Monday, so hopefully I can turn all this blathering into results
> > within a couple of weeks!
> >
> > 73,
> >
> > Alan
> >
> > [email protected] wrote:
> >> Hi Alan, Alan and LF.
> >>
> >> I've done a few tests with trying to "pull" crystals and resonators
> >> up into
> >> the 501-504 kHz band. I used a single NPN transistor in a Colpits
> >> configuration with a 3 - 30pf trimmer capacitor in series with the
> >> crystal.
> >>
> >> Firstly, I tried a few 1.000 and 2.000 MHz HC6u crystals, available
> >> from RS
> >> Components. These would only move a few tens of Hz maximum, before
> >> they
> >> stopped.
> >>
> >> Secondly, I tried ten 500kHz resonators, type Murata 500 CSB. These
> >> are
> >> little yellow plastic cuboids approx 10 x 8 x 4 mm with two legs at
> >> the
> >> bottom. These all came out low, typically in the 498-499 kHz range,
> >> and
> >> couldn't be pulled much higher before they died.
> >>
> >> Thirdly, I tried some 1 MHz resonators, type Murata 1000J. These
> >> are even
> >> smaller blue plastic cuboids approx 7 x 5 x 2mm also with two legs
> >> on the
> >> bottom. These were much more amenable to "pulling", and would tune
> >> from 989
> >> to 1011 kHz quite happily (494.5 to 505.5 kHz) The frequency
> >> stability seems
> >> quite good, and a hot soldering iron on one of the legs moved the
> >> frequency
> >> about 200 Hz, coming back on frequency as it cooled down. You would
> >> need to
> >> be careful using one of these, however, as you could easily slip
> >> out of band
> >> if you moved the trimmer too far.
> >>
> >> So one of these 1MHz resonators would seem to be a good source,
> >> once divided
> >> by two. You could leave the oscillator running continously for
> >> maximum
> >> stability, and key the divider. I might even have a circuit of a
> >> divider
> >> using a double triode if anyone wanted to stay with the retro
> >> "Valve theme"!
> >> Otherwise a 74LS74 or a CD 4013 will do the trick nicely.
> >>
> >> BTW, RS Components and Farnell sell a 11.0592 MHz crystal, costing
> >> the
> >> princely sum of 19 pence, which when divided by 22 will give 502.69
> >> MHz.
> >> (74LS161 followed by 74LS74...no problemo...)
> >>
> >> 73, Dave G3WCB IO91RM
> >>
> >> -----Original Message-----
> >> From: [email protected]
> >> [mailto:[email protected]]On Behalf Of Alan Melia
> >> Sent: 23 April 2007 23:36
> >> To: [email protected]
> >> Subject: Re: LF: 500 EASY START
> >>
> >>
> >> Hi Alan, there is not a lot of "accumulated wisdom" on 500kHz yet
> >> but most
> >> of the 136khz experience seems to work. The best tutorial for
> >> aerials at LF
> >> is the pages by Rik Srobbe ON7YD. You will find a lot else there as
> >> well.
> >> http://www.qsl.net/on7yd/ and click on "The 136kHz Amateur Band"
> >> in the
> >> left-hand bar.
> >>
> >> Low frequency crystals are almost unknown these days. It is so easy
> >> to
> >> divide down. Two techniques have been used straight division like
> >> Mal
> >> suggests or mixing crystals in the 5 to 6 meg range...pulling one
> >> up and the
> >> other down with a 2 gang variable cap. as Dave Sargent recently
> >> described.
> >>
> >> Have you though of trying at 50p ceramic resonator !! 500kHz is a
> >> stadard
> >> frequency for these and they are fairly "bendable" so may come up
> >> into the
> >> band. I think GW3EUP uses one.
> >>
> >> You will find a spreadsheet on my web site (beside a lot of other
> >> junk)
> >> which attemmpts to simplify the ERP calculation.
> >> http://www.btinternet.com/~alan.melia/programs.htm
> >> It is an EXCEL sheet and should download OK.
> >>
> >> I hope that helps ...welcome to LF and remember LF=Lotsa Fun !!
> >>
> >> Cheers de Alan G3NYK
> >>
> >>
> >> ----- Original Message -----
> >> From: Alan Ibbetson <[email protected]>
> >> To: <[email protected]>
> >> Sent: 23 April 2007 23:03
> >> Subject: Re: LF: 500 EASY START
> >>
> >>
> >> > Hello everyone, Alan G3XAQ here. I just joined this mailing list.
> >> > I'm
> >> > preparing my application for a 501KHz NoV, so Mal's note on an
> >> > easy
> >> > start is very timely.
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >
> >
>
|
