DB6NT 23cm filter PCB MKU 13 LPF

I bought an MKU 13 LPF PCB from Alan G3NYK, and built it into one of his excellent tinplate boxes.  Loss at 23cm is about 0.45dB. Best rejection is 46dB at 1.977 GHz and above 3GHz where it is over -50dB.  I did not measure the response at the third harmonic.


That mirrors the spec on the DB6NT site fairly closely.

Equipment used: HP E4421B signal generator, HP 436A power meter, 3dB pad before and after the filter.

Next, I tested the output voltage using my 23cm transverter as source and a 30dB 20W 4GHz attenuator to measure the power out of the filter versus voltage on the detector.  It is pretty much log-law up to about +33dBm.


I used an 0805 51R, face-down, as the terminating load, a 470 ohm 1/16th watt in series with the feedthrough and the recommended 1nF 0805 for the diode bypass.  I couldn’t find a BAT62-03W, so I have used a  SMS7630-079LF from Farnell. Measurements were made using a 10M input resistance DVM. and the 30dB 20W attenuator on the output, followed by the HP436A using 8481A and 8481D sensors.



DF9IC 23cm PA progress

My first DF9IC 23cm 250W PA board has been running for a month and it is working well, although I think the output capacitor positions still need a little optimisation. I am using the 9160s from utsource.net and the professional PCBs direct from Henning.

At about 8W drive, my Bird 4410A with a 1GHz slug reports 230W out for 7W in.   I think the 4410A 1kW slug reads 9% low at 1296MHz, so that is about 250W in reality.  That is using 30V and about 22A.

The 2p2 caps on the output lines are 12,76mm and 11,55mm from the FET body.  I will build two more PAs and try to tune those more carefully, but for now, this one is working fine.


I soldered the PCBs to the heatspreader using the same 138C low-temperature solder as I used to fix the FETs.


I am using a water-cooling plate for the PAs.  The heatspreader is a copper block 100mm x 71mm x 12.7mm.  After 3 minutes of full power, the heat spreader temperature close to the FETs is 23.5C.  I think that is cool enough!  It works really well on JT modes and CW at full power.

I find that running 1.5A standing current for each FET gives best IMD performance on SSB.

Looking at the two-tone spectrum, with 165W actual output, taking 12.4A at 30V, the output spectrum from a pair of pure tones 1.2kHz apart looks like this:


At higher power, the IMDs start to rise, with the 3rd order -20dB at about 220W actual power, and the 9th and higher start to come up much above that.  With speech it looks nice and clean, very straight sides to the spectrum at 150W and still OK at 200.

Next stage is to combine two PAs.

Henning’s website is at www.df9ic.de

GB3MCB 1296MHz beacon recording 458km

Recording of audio from GB3MCB this evening 18 Sept 2016 18:45, 100Hz bandwidth CW, G4DDK preamp, Kuhne TR1296H, Elad FDM-DUO with SW2. Beacon was audible up to 20dB over noise for 40 minutes, very deep QSB with a period of around 50 seconds

CWID keying sidebands in SpecLab.  Couple of bit of AS, but this was solid tropo.



Cluster spot:
2016-09-18 17:37 GB3MCB 1296.8597 IO70OJ<TR>IO93NR RST 529  458km

GB3BSS 13cm beacon recording 11th Sept

GB3BSS in IO81SR is 248km from here. It has been audible most of the day, with a few aircraft scatter peaks.  This morning it was a solid 549 but now it is fading and it only about 12dB above noise in 11.7Hz SDR bins.  Recording is with 100Hz CW filter and two notches alongside to reduce ringing.  The rapid fading is fast and deep enough to remove whole characters from the CW.

Screengrab shows the FSK CWID with characteristic keying sideband fuzz, and a bit of weak aircraft scatter at 22:09:10