Wednesday, November 14, 2018

DATV Predriver Amplifiers

Having built the BATC Portsdown DATV transmitter I realised I needed amplifiers between it and my final amplifiers. The neatest solution would be to use Mitsubishi Power Modules. I managed to obtain some

I used RA070608 on 4m, RA081317 on 2m, RA07H4047 on 70cm. Each could produce around 7W. I managed to source some G4DDK PA/LPF PCB onto which these modules would fit.

Each amplifier was mounted in a diecast box, with an SMA input connector (to match the Portsdown output connector) and BNC output connector to match the following amplifier. A BTS4140 high side switch IC driving a 78L05 regulator was used to provide switched 5V to bias the module. Switching was achieved with an earth on transmit signal from Portsdown. The amplifier also provides an earth on transmit output to switch the following amplifier.

Each module produces 7W output with all harmonics over 55dB down on the fundamental


The Fourth amplifier, the one on the right, is a Chinese broadband 2 to 900 MHz 2.5W amplifier from Ebay, that may come in useful one day!

Thursday, October 25, 2018

A weekend at Dorstone on 71MHz and 50MHz

Having got my 71MHz NOV and built a 71/437 MHz Transverter,  I decided I needed an outing to exercise them.  I noted the 50MHz AFS was happening shortly so I decided to combine the two events in a weekend in Dorstone IO82LB. G8GTZ would be out at IO91GI (136km) over the weekend so I would have someone to work

I set out from Malvern on Saturday morning. Got to site and erected the new 2" mast system with the 5 ele 70MHz Powabeam.

I transmitted to G8GTZ who could see my signal a few db above the noise floor but could get no video.  However I did receive Noel's 15W signal and decode it easily at 125kB.

Noel retired to fault find his receiver while I retired to the Pandy arms for the night

The following morning I returned to the site and assembled the old 5 ele Tonna antenna along with the K3S and KPA500 for AFS.


After a very slow start I managed to work 96 stations, best DX being PA4VHF at 640km. During AFS Noel informed me he had fixed his receiver by disabling his laptop PSU to lower his noise floor 10dB, so we could try again.
When AFS finished at 1400 I took down the 6m 5 ele yagi and put up the 4m 5 ele yagi again. This time Noel received my signal:-

I also received Noel, this time with much better MER, up to 24dB which shows the system had some performance left for a longer path

I returned to Malvern Sunday evening after a great weekend, including my first DATV QSO on any band

Sunday, August 5, 2018


While testing before the IOTA contest at G8X the K3S came up with the error "HI SIG" warning

From the manual:-

"An extremely strong, sustained signal (e.g., a broadcast station’s carrier) may be causing
excessive post-mixer amplifier current when operating on the present band. The K3 will automatically turn the preamp OFF, and in extreme cases will also turn the attenuator ON"

After disconnecting the antennas and turning the rig back on again the same error was displayed, and all controls were sluggish. At this point the K3 was used as a replacement and survived the whole contest without issue.

An Internet search suggested that the IF amplifier following the mixer consisting of Q8 and Q9 had now got shorted devices. Elecraft support were contacted and quickly responded confirming this theory. The devices used for Q8 qnd Q9 were discontinued, but some were found on EBAY. These took 24 hours to arrive and when fitted resolved the issue. The IF amplifier in the sub receiver had escaped unscathed. As a note Q8 and Q9 were easy to replace as you just have to remove the front half cover underneath the K3S, they are soldered to the underside of the motherboard

Elecraft support also mentioned that for a time the K3S was shipped  with R66 in the IF amplifier as 10 ohm

"On K3S, make sure R66 is 15 ohm  E500610 not 10ohm. We briefly shipped with it 10 and reverted back, **AND at the same time changed R60 & 75 so if R66 is 10 ohm, change it to 15 E500610 and R60 to 150 ohm E500251 and R75 6.2 ohm E500265"

My K3S was one of these radios so having replaced Q8 and Q9 and checked it worked, I changed the values of R60, 66 and 75.

Monday, June 11, 2018

RIP Meg. Died 11 June 2018

 Meg Robinson 1947-2018 (G7FRE), M0FRE, (KB2NCP) N2NQI, 9H3MW

W2SZ/1 50MHz 1993

Thursday, June 7, 2018

HF NFD 2018

Unable to go out portable for this years contest i decided to have a go in the fixed station with the remote MW2I station

The interesting part of the fixed section is that if the station worked is not a portable or is not a multiplier then it is valueless. Hence no point in calling cq and working streams of no point qsos

The K3 was used at 70W with the Cushcraft A3S 2.5 element tribander on 10/15/20 and the 80m dipole on 40/80/160m

The remotehams software was used to remote the k3 front panel and send the audio to the client computer. Remote desktop was used to run the N1MM logging software on the server computer. Keying was achieved witha K1EL winkey at the server end

 It was only possible to operate 11.5 hours during the contest but the goal of 100000 points was achieved:-

 Band     QSOs     Pts  DXC  Pt/Q
   1.8      32           248    7   7.8
   3.5      63           220   17   3.5
     7       52           182   18   3.5
    14      60           200   27   3.3
    21      50           136   26   2.7
    28      20             52   13   2.6
 Total     277         1038 108   3.7
Score: 112,104

The 80m dipole worked surprisingly well on 160m and 40m.
The result was better than expected 6th in the fixed section (4th UK station), not bad for 11.5 hours!

Wednesday, February 7, 2018

432MHz AFS 2018

The final leg of the RSGB as usual is held in February starting at 0900, meaning waking up at 0500! This would be the first opportunity to try the newly built G4DDK Iceni 432MHz Transverter, along with the K3S, solidstate amplifier, HA8ET masthead Preamp and a 20 element yagi at 20'

As the first 2 hours overlapped a French Cumulative contest there was some interesting DX to be worked, which made up for the lack of ANY DL/ON/PA stations! There were a few snow flakes before and after the contest but during the contest freezing feet were the main hazard

The only equipment issue was the audio from the K3S. At times there would be buzz on the monitor audio on transmit. The monitor was set at level 2 and the buzz was equally as loud Eventually it was correlated with the fans running on the K3S.  The fan was running more often than previously as the Iceni was placed on top of the K3S, as shown above.

Searching the Elecraft website after the contest revealed there was a mod for this issue, although they were slightly confused as to whether the hum was on transmit or receive. The fix was a 470uF capacitor mounted on the KPAIO3. The modification was done and the issue resolved

The equipment seemed to have done the trick, again we won the open section:

Resulting in a winners certificate and , in conjunction with other Bristol contest group operators won the G0ODQ Trophy. Perhaps it was worth getting up at such an unearthly hour!

Thursday, February 1, 2018

10MHz Distribution Amplifier

I have had a need for a distribution amplifier for a while now. Searching around I found the design by G4JNT in Radcom, which filled my needs. I redrew the circuit for 4 outputs and had PCBs made. (if you want one conteact me!)  I now have the units in my M1DST 10MHz Thunderbolt monitoring project and in my LPRO101 10MHz Rubidium source. The project is written up at