To: rsgb_lf_group@blacksheep.org
References: <923db48e-ca8e-67d5-e70d-3c9695277b97@n1bug.com>
 <CAA8k23TgQWG5ocKDjHV3AA5ZnhX8mWhMwGGwkL6-PGc7CuLqsg@mail.gmail.com>
 <2e4b6c93-746c-f933-93cd-69973f902ae4@n1bug.com>
 <cb09c941-4091-0b07-d1c3-67d4a64581a6@dctower.co.uk>
 <57ff16de-67c2-d7d9-ab41-cb63aba83fb9@n1bug.com>
 <0aceecaa-9b43-d255-316e-5fa994e01f11@yahoo.co.uk>
From: Nick <M0HGU@dctower.co.uk>
Organization: Organised - you must be joking!
Message-ID: <13e8f700-f8d3-1141-6a41-e45d31589821@dctower.co.uk>
Date: Wed, 10 Jan 2018 16:22:39 +0000
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.5.0
MIME-Version: 1.0
In-Reply-To: <0aceecaa-9b43-d255-316e-5fa994e01f11@yahoo.co.uk>
Subject: Re: LF: Progress? with the PA
Content-Type: multipart/signed; micalg=pgp-sha256;
 protocol="application/pgp-signature";
 boundary="O1rZZnoPbOtZXrahm4ozXebelraCkIkoT"
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

This is an OpenPGP/MIME signed message (RFC 4880 and 3156)
--O1rZZnoPbOtZXrahm4ozXebelraCkIkoT
Content-Type: multipart/mixed; boundary="BZ8Cqy8WWx6CwQNkgIoXTRkxfLjLkEFZw";
 protected-headers="v1"
From: Nick <M0HGU@dctower.co.uk>
Reply-To: M0HGU@dctower.co.uk
To: rsgb_lf_group@blacksheep.org
Message-ID: <13e8f700-f8d3-1141-6a41-e45d31589821@dctower.co.uk>
Subject: Re: LF: Progress? with the PA
References: <923db48e-ca8e-67d5-e70d-3c9695277b97@n1bug.com>
 <CAA8k23TgQWG5ocKDjHV3AA5ZnhX8mWhMwGGwkL6-PGc7CuLqsg@mail.gmail.com>
 <2e4b6c93-746c-f933-93cd-69973f902ae4@n1bug.com>
 <cb09c941-4091-0b07-d1c3-67d4a64581a6@dctower.co.uk>
 <57ff16de-67c2-d7d9-ab41-cb63aba83fb9@n1bug.com>
 <0aceecaa-9b43-d255-316e-5fa994e01f11@yahoo.co.uk>
In-Reply-To: <0aceecaa-9b43-d255-316e-5fa994e01f11@yahoo.co.uk>

--BZ8Cqy8WWx6CwQNkgIoXTRkxfLjLkEFZw
Content-Type: text/plain; charset=utf-8
Content-Language: en-GB
Content-Transfer-Encoding: quoted-printable

On 09/01/18 20:33, Alan de G1FXB wrote:
> Hi Paul , Nick and any others using that PA design,

Just as a reply to another message - yes a dummy load in perfect up to
silly voltage

I had not really thought that the reactance 'off frequency' might be an
issue but I can see it could be a possibility

> (I 've being subscribed to the RSGB LF feed for 4-5 years ? and of
> course seen reference to the blacksheep feed but interpreted that as
> being a legacy rather than where I recently I subscribed and found to b=
e
> where the activity is.
> I make it brief=C2=A0 in-case I'm so wide off topic I'll fall of the ed=
ge of
> the planet, and NOT to sound like I know what I'm talking about....

Well, you may know more than me ...but I am trying to learn :-)

> What MAY explain that circuits instability WRT to antenna loads as
> opposed to a 50 Ohm load)
>=20
> Tony's design
> =C2=A0http://qrp-labs.com/ultimate3/u3mods/lfamp.html
> was made around the era of the QRP Labs U3 using the AD9850 module with=

> a sine wave + associated DDS spectra through the BS170 PA
> IF you are using the current U3S design that uses the Si5351 synthesise=
r
> it is driving through the untuned PA a square wave with a very differen=
t
> spectra.
> I think Hans has described HIS PA as just being untuned=C2=A0 broadband=
 in
> the sine wave fed U3
> and 'Class D in the biased adjusted U3S design, not class E as there ar=
e
> no frequency dependant components.

Ah!, yes I have the OCXO

> To further blur the situation on the referring page,
> http://qrp-labs.com/ultimate3/u3mods.html#lf
> Tony details coupling capacitor value changes, which are now used in th=
e
> U3S design?? But also a change to what will be your driver stage ferrit=
e.
> So his PA would probably be driven by this modified U3?

OK the U3s is stock, other than 3 x BS170s and the ability to use 5V or
13.8V for the PA stage.

> (Everybody has their own goals, favourite topology and most importantly=

> junk box....
> If it were a clean sheet of paper and you wanted a class E PA using a
> common switcher FET device, rather than an RF device.)
> Work with the fact the Si5351 outputs square waves, use that to drive
> the final stage rather than through an (RF) driver stage.
> If you need a pulse shaper or just like the idea of a buffer stage, the=
n
> do it at logic switching levels in the PA Gate rather than RF.

Ah, a small glimmer may be about - I do have the LPF in the U3s so I
'should' be driving it with a sine wave.

However the fact that an increase in drive level means less tendency to
oscillate and lowering the drain voltage improves things - looks like it
is drive related, at least in part - but of course FET gates are not a
static impedance thing.

I accept that the output ferrite may need to be adjusted - I need to
look at G4JNT's article from 02/2013 where, whilst he is talking about a
push-pull arrangement, there is some maths around impedance matching to
input & output of the FET(s)

> Hopefully not being interpreted arrogant interloper. :-[
> regards Alan
>=20

Not all, I am happy to pick the brains of anyone, the more the merrier
as far as I am concerned.

All the best

Nick
M0HGU

--=20
Mrs Evadne Cake was a medium, verging on small.
(Reaper Man)
16:10:01 up 1 day, 7:48, 5 users, load average: 0.20, 0.25, 0.30


--BZ8Cqy8WWx6CwQNkgIoXTRkxfLjLkEFZw--

--O1rZZnoPbOtZXrahm4ozXebelraCkIkoT
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename="signature.asc"

-----BEGIN PGP SIGNATURE-----
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/
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=mc+N
-----END PGP SIGNATURE-----

--O1rZZnoPbOtZXrahm4ozXebelraCkIkoT--