Checking correct nyquist filter values for 70cm...?

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Codeine
Posts: 10
Joined: Thu Dec 01, 2011 1:59 pm

Checking correct nyquist filter values for 70cm...?

Post by Codeine » Thu Dec 01, 2011 2:07 pm

Hi All

I know I need to make changes for 70cm to the Nyquist filter values
and change L1,2,3,4 and C13/14/15/16/17/18. I have all ready
changed to a AD8345 for but need to check I am puting the components
in the right order before I solder them....!

I this order correct...! L1 and L3=33uh C13 and C16=1.2nF
L2 and L4=27uH C15 and C18=3.9uF and should I leave
or do I need to change C14 and C17 currently both 1.2nF..?

Any help or advice greatly received.Finally a Digital Tx I can
just about afford and a great project keep up the good work.

73 Paul

M0PDA Suffolk

g0uhy
Posts: 81
Joined: Fri Aug 05, 2011 3:09 pm

Re: Checking correct nyquist filter values for 70cm...?

Post by g0uhy » Thu Dec 01, 2011 3:46 pm

Hi Paul,

the values we were using with the" poor mans DATV" were designed for 1Ms but worked ok at 2Ms. However, Rob, M0DTS, has come up with some better values for use with the DigiLite on 70cm. The values go from left to right on the serialiser o/p towards the modulator ( hope that makes sense,lol? Here's a copy of his posting, hope it helps.

73

Malc

Re: Nyquist filter coils L1,L3,L2,L4

Postby M0DTS » Sat Nov 26, 2011 9:36 pm
We may have an issue with values being used for 2Ms on 70cm configuration...

If i remember correctly:
2Ms we should be using 560pf/12uH/2n2/15uH/560pf
1Ms it should be 1n2/27uH/3n9/33uH/1n2

Rob
M0DTS

Codeine
Posts: 10
Joined: Thu Dec 01, 2011 1:59 pm

Still Checking my Nyquist filter values for 70cm...?

Post by Codeine » Fri Dec 02, 2011 12:46 pm

Hi Malc

Thanks for your reply.I think I understand your
comment about looking at it from left to right from
the "serialiser o/p towards the modulator" whilst
looking at the Digilite circuit diagram...?

If I have understood you correctly for 1Ms I need
C13=1n2 L1=27uH C14=3n9 L2=33uH C15=1n2
and then repeat this for the remaining for L3 & L4
C16=1n2 L3=27uH C17=3n9 L4=33uH C18=1n2


I don't have the values for 2Ms without ordering
yet more components so will have to give the
above values a try and see how it goes. Still waiting
for back order inductors from Farnell so may be the
new year before it's finshed.

73 Paul

g0uhy
Posts: 81
Joined: Fri Aug 05, 2011 3:09 pm

Re: Checking correct nyquist filter values for 70cm...?

Post by g0uhy » Fri Dec 02, 2011 2:29 pm

Hi Paul,

yes that's the way it works. If you are using the v5.7 PCB Dave has some pads for SMD inductors which are available from Farnell. You will have to remove the solder mask but I have used SMD inductors in some of my modulators and although the 'Q' is not as good they do work.

Good luck with the build.

73

Malc

G4EWJ
Posts: 1358
Joined: Wed Feb 17, 2010 10:11 am

Re: Checking correct nyquist filter values for 70cm...?

Post by G4EWJ » Fri Dec 02, 2011 8:49 pm

If you have the components for the 4MS filter then you can just double up each inductor and capacitor to give the same impedance at 2MS. Inductors in series and capacitors in parallel.

Brian

G1LWX
Posts: 75
Joined: Sun Mar 27, 2011 11:10 pm

Re: Checking correct nyquist filter values for 70cm...?

Post by G1LWX » Mon Mar 05, 2012 11:26 pm

Hi
Can anyone supply me with wire ended inductors values 12uh and 15uh two of each
for my 70cms nyquist filter.
I could put two 5.6 and two 6.8 in series but if I could get the correct ones the board would
look better
I have a quantity of 5.6uh and 6.8uh which I could exchange and will cover all postage costs.

73's Mike G1LWX

M0ATV
Posts: 81
Joined: Fri Aug 13, 2010 6:00 pm

Re: Checking correct nyquist filter values for 70cm...?

Post by M0ATV » Tue Mar 06, 2012 10:31 am

I have a couple left over here Mike, send me your delivery address & I'll drop them in the post, I dont need any of yours as I have too many of the other ones as it is. Tony

on4bhm
Posts: 79
Joined: Mon Oct 24, 2011 5:52 pm

Re: Checking correct nyquist filter values for 70cm...?

Post by on4bhm » Tue Mar 06, 2012 12:08 pm

I'm also looking for the components that are different between the 23cm version and the 70cm one.

I ordered a second print to start building a 70cm version.
But i don't have the items for the filter.

Can someone supply them to me?
i can play with paypal.

please PM me:
on4bhm (at) telenet.be

thanks

G0KTD
Posts: 45
Joined: Wed Jun 08, 2011 7:39 am

Re: Checking correct nyquist filter values for 70cm...?

Post by G0KTD » Tue Mar 06, 2012 5:38 pm

I have managed to construct a version of the Digilite for use on the 70cm band. I'm using the same serialiser and the same basic modulator circuit. Although some people have managed to get the modulator to work on 70cm using the AD8346 chip, it is not really intended to run at that frequency. I have therefore replaced the AD8346 with an AD8345 which is identical physically but is intended to run at lower frequencies. The Nyquist filter also needs to be modified to allow the transmitter to operate at 2Ms/s and keep the required bandwidth down. For 1Ms/s use Nyquist filter values 1.2nF/33uH/3.9nF/27uH/1.2nF.
For 2Ms/s use 560pf/12uH/2n2/15uH/560pf.
The above extract is from the Digilite Web Page on http://www.g8ajn.tv/ page 2/5
Hope this Helps
all other parts are the same.
Keith

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