Topics

Nokia pa on 13cms? - Doherty


Neil Smith G4DBN
 

Any indication of two-tone IMD performance vs power, Robin? I have a few of those PAs to convert.  I was expecting to have to de-rate them significantly for SSB, although my main use would be for CW and digimodes.

Neil G4DBN

... I am seeing a nice solid 15A total now, about 11A on the carrier side, 4A on the peaking side, I think this is about flat out for this amp. ...  I found a resistor fault on the biasing of the drive amp and corrected that, it is now stable where as it was all over the place before. 

The SMA lead connecting the amp to the dummy load (a 250W slab load out of an old band IV transmitter) gets quite warm after 30 seconds of carrier so something is coming out :) 


militaryoperator
 

... I am seeing a nice solid 15A total now, about 11A on the carrier side, 4A on the peaking side, I think this is about flat out for this amp. ...  I found a resistor fault on the biasing of the drive amp and corrected that, it is now stable where as it was all over the place before. 

The SMA lead connecting the amp to the dummy load (a 250W slab load out of an old band IV transmitter) gets quite warm after 30 seconds of carrier so something is coming out :) 
--------------------------------------------------

What drive power you using Robin?


Ben


Robin Szemeti - G1YFG
 

Yep, noted, I understnad the basic principle with the 90 degree phase shift and carrier/peaking etc

... I am seeing a nice solid 15A total now, about 11A on the carrier side, 4A on the peaking side, I think this is about flat out for this amp. ...  I found a resistor fault on the biasing of the drive amp and corrected that, it is now stable where as it was all over the place before.

The SMA lead connecting the amp to the dummy load (a 250W slab load out of an old band IV transmitter) gets quite warm after 30 seconds of carrier so something is coming out :)

Going to go and have a listen on 13cm for beacons later.


On Mon, 14 Sep 2020 at 18:46, David GM6BIG <gm6big@...> wrote:
Hi Robin,

Doherty amps work in a less obvious way.
The Carrier device could easily be running 10 times the current of the
Peaking side.
The two sides may be biased differently.

The are moderately narrowband, there is much 1/4 wave phasing in there.

The method has been around a long time, so lots on the web to read up on
them.
Essentially, instead of increasing the PA volts (Carrier device) to get
more power, decrease the Carrier load impedance (Using the Peaking
device)...

This will get you started...
https://www.electronics-notes.com/articles/radio/doherty-amplifier/design.php

https://mengtianyu.wordpress.com/2010/02/09/the-doherty-amplifier-new-after-70-years/

https://www.radioworld.com/columns-and-views/reinventing-bill-doherty-and-his-highefficiency-amplifier

An early use of the method was in big AM transmitters, an efficient way
to make AM RF without a big oily and expensive audio rated modulation
transformer.
Not so easy to move in freqy, but ideal for, say, an AM broadcast
transmitter...

Now applied to microwave stuff...!

Cheers, DAvid

On 12/09/2020 22:52, Robin Szemeti - G1YFG wrote:
> In theory, it is supposed to run in Doherty mode .. the transistor on
> the right biased into Class A/B and pulling about 1.8A quiescent ... the
> one on the left turned hard off and only coming on with peaks.
>
> I'm finding I can pull about 10A through the right hand device, but
> barely anything through the left hand device, no matter how hard I hit
> the input. I've increased the drive by 6dB and its not really pushing it
> any harder ... something isn't quite right.
>
> On Sat, 12 Sep 2020 at 20:53, militaryoperator via groups.io
> <http://groups.io> <Military1944=aol.com@groups.io
> <mailto:aol.com@groups.io>> wrote:
>
>     https://morepicture.webs.com/hamradio.htm
>
>
>     The Nokia pa for 13cm. I know about the circulator, removing etc,
>     but what about the bias. Has anyone sorted out better biasing for
>     this unit?
>
>     Ben
>
>
>
>
>     --------------------------------------
>     Curator, Owner and Display coordinator
>     Military Wireless Museum
>     Kidderminster, UK.
>     Museum Web Site <http://www.militarywirelessmuseum.co.uk/>
>
>     This message was meant for the recipient
>     Any likeness to persons living or dead is odd
>     ---------------------------------------
>
>
> --
> Robin Szemeti - G1YFG
>

--
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--
Robin Szemeti - G1YFG


David GM6BIG
 

Hi Robin,

Doherty amps work in a less obvious way.
The Carrier device could easily be running 10 times the current of the Peaking side.
The two sides may be biased differently.

The are moderately narrowband, there is much 1/4 wave phasing in there.

The method has been around a long time, so lots on the web to read up on them.
Essentially, instead of increasing the PA volts (Carrier device) to get more power, decrease the Carrier load impedance (Using the Peaking device)...

This will get you started...
https://www.electronics-notes.com/articles/radio/doherty-amplifier/design.php

https://mengtianyu.wordpress.com/2010/02/09/the-doherty-amplifier-new-after-70-years/

https://www.radioworld.com/columns-and-views/reinventing-bill-doherty-and-his-highefficiency-amplifier

An early use of the method was in big AM transmitters, an efficient way to make AM RF without a big oily and expensive audio rated modulation transformer.
Not so easy to move in freqy, but ideal for, say, an AM broadcast transmitter...

Now applied to microwave stuff...!

Cheers, DAvid

On 12/09/2020 22:52, Robin Szemeti - G1YFG wrote:
In theory, it is supposed to run in Doherty mode .. the transistor on the right biased into Class A/B and pulling about 1.8A quiescent ... the one on the left turned hard off and only coming on with peaks.
I'm finding I can pull about 10A through the right hand device, but barely anything through the left hand device, no matter how hard I hit the input. I've increased the drive by 6dB and its not really pushing it any harder ... something isn't quite right.
On Sat, 12 Sep 2020 at 20:53, militaryoperator via groups.io <http://groups.io> <Military1944=aol.com@groups.io <mailto:aol.com@groups.io>> wrote:
https://morepicture.webs.com/hamradio.htm
The Nokia pa for 13cm. I know about the circulator, removing etc,
but what about the bias. Has anyone sorted out better biasing for
this unit?
Ben
--------------------------------------
Curator, Owner and Display coordinator
Military Wireless Museum
Kidderminster, UK.
Museum Web Site <http://www.militarywirelessmuseum.co.uk/>
This message was meant for the recipient
Any likeness to persons living or dead is odd
---------------------------------------
--
Robin Szemeti - G1YFG
--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus