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.
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