[hpsdr] Munin revisited.

[n3evl]

Hi Kjell,

That's good to hear that there are so many Munin implementations out 
there - mine has been in pretty much constant use for the last few years 
- although it's all packaged up now along with the rest of my kit for 
eventual unpacking somewhere in Scotland!  Good also to hear about the 
excellent results of your experimentation.  You mentioned that you can 
get 100W with less than 1W of drive - have you tried using Penelope as 
the source of the drive - and if so what input/output power levels did 
you see?

73, Pete, N3EVL/Future MM0???


On 8/3/2017 9:41 AM, Kjell Karlsen wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi all.
>
> Some years ago I did a layout for a 100W PA using a pair of RD100HHF1 
> MOSFET transistors and called it Munin and an updated version, Munin 
> II. As far as I know more than 250 of them were built around the world.
>
> Munin was more or less a copy of the 100W PA´s used by ICOM, Kenwood 
> and Yaesu. Apache Labs also have used a variant of this PA in all the 
> 100W units sold until now. It is extremely robust and I have only 
> managed to destroy 1 pair of them when I forgot to install the heat 
> sink and used them for a long time at 100W out.
>
> In the ANAN-7000, Apache Labs has removed the Push Pull Driver stage 
> that uses 2 pcs. RD16HHF1 and drive the RD100HHF1 directly from the 
> Orion MKII board that can deliver maximum 3W out.
>
> I was very surprised when I saw this so I decided to test with one of 
> my Munin boards. Using the same values as in the -7000 for the input 
> circuit and a 1:1 transformer, I got 100W OUT with <3W IN on all bands 
> except 6 meter. I measured the input Return Loss and found that by 
> removing a 200 pF capacitor across the secondary of the transformer, 
> the output on 6 meter could be reach with 2,5W IN.
>
> Then I tried to reduce the feedback in the PA. The feedback resistors 
> were 2 pc. 22 Ohm in parallel on each transistor and by increasing 
> them to 39 OHM each, I can get 100W out with <1W drive on all bands! 
> That means that the gain is >20 dB! And the linearity is not worse 
> using less feedback.
>
> According to the data from Mitsubishi, the gain on 30 MHz is 11,5 dB 
> for one devise so for 2 in Push Pull the gain is 3 dB higher, 14,5 dB. 
> So were does all this extra gain come from?
>
> The gates are purely capacitive (Ciss=260 pF for each gate) so no 
> power is lost in the input. So by just using a 1:1 transformer and 
> load it with 50 Ohm on the secondary, the driving voltage is 20V P-P. 
> There is a mismatch on the highest frequencies so one should expect 
> that the gain should drop a lot of dB but still the gain is above 20 
> dB. It might be possible to optimize the input RL but I see no point 
> in that as we have the Gain By Band adjustments in PSDR and PiHPSDR.
>
> Another positive observation I did was that the efficiency is better 
> when using this solution.
>
> When using the original Munin, the current draw at 100W OUT was 
> between 18 and 20A on all bands up to 10 meter and 22A on 6 meter. But 
> now the current is <15A up to 10 meter and just a bit higher on 6 
> meter. I have no explanation for this!
>
> May be it is time to do a new layout for a MUNIN III? It can be really 
> small.
>
> 73, Kjell
>

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