[hpsdr] MUNIN III boards

[Chris Smith]

Hi Jim

Attached below is Kjell Karlsen’s original message to this reflector. In it he explains the design philosophy.

Cheers & 73

Chris G4NUX

> Begin forwarded message:
> 
> From: Kjell Karlsen <la2ni at online.no>
> Subject: [hpsdr] Munin revisited.
> Date: 3 August 2017 at 14:41:14 BST
> To: "hpsdr at lists.openhpsdr.org" <hpsdr at lists.openhpsdr.org>
> Resent-From: <chris at vspl.co.uk>
> 
> ***** 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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