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 RA07H0608 on 4m, RA08H1317M 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

K3S "HI SIG" WARNING

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 http://g4fre.com/10MHz_distribution.htm

Tuesday, January 30, 2018

BARTG 2018 RTTY Sprint




This is a fun contest. It starts and finishes at a reasonable hour (noon) and as a sprint only serial numbers are exchanged; no reports. The hardest part was that neither the confirmed dates, rules or the experts list were available on the BARTG web site or any hint where they were located before the contest

Radio conditions were poor. 15m only opened for 30 minutes on Sunday morning. 20m didnt have the usual quantity of far eastern DX. 40m was subdued. 80m was good overnight into the USA, the only failure was AD5XD in Texas, despite many attempts. The highlight was being called by YC4BGN on 40m Saturday night giving me the 6th continental multiplier (OC).

The dual vfo FSK configuration using a pair of TinyFSK worked very well using the method by K0SM , Although N1MM v1.0.7013 was supposed to support TinyFSK natively, when tried it showed highly corrupted text in the transmit window meaning it could not be used effectively to see what was being sent! Hence I resorted to the K0SM setup configuration

There were no equipment issues. I used my newly made accesory cable to replace the elecraft made one that caused trouble the previous weekend on the RSGB Data AFS which worked fine switching the KAT500

Results:-
        Band     QSOs     Pts  DXC  Are  Con  
         3.5      90      90    4    0    0   
           7     224     224    9    0    1   
          14     256     256   39   19    5   
          21       7       7    0    0    0   
       Total     577     577   52   19    6   


  SOAB100W section Score : 245,802


Tuesday, January 23, 2018

RSGB Data AFS 2018

The original plan was to operate with G4BVY from GW0FRE. However he was detained elsewhere so I would have to do it single operator, I decided to use MW2I

As it is a dual band (80/40m) dual mode contest (RTTY/PSK63) I could not just use MMTTY. At his talk on data modes at the Malvern club G4BVY suggested using MMVARI, which I hade never used before. Using it on AFSK you could have one window for RTTY QSOs and one for PSK31 QSOs. With Rogers remote guidance (including a Skype call 10 minutes before the contest!) I managed to get it going

Originally I had intended to use the KPA500/KAT500 at 400/100W output. However during pre-contest testing there were many issues with the switching. Most often with the correct antenna and band selected on recieve, when i went to transmit the amp would change band (sometimes with "Invald" on the KPA500 display) the atu would switch antenna and try to tune it and the KPA500 would fault out.  With time running out a decision had to be made, so i used the K3s barefoot at 100w with its internal ATU and the 2 antenna ports switching between bands

Conditions were poor on 40m, just 6 RTTY (no PSK) qsos into central europe. 80m had a reasonable rate
              PSK        RTTY      Total
80m       52           90           142
40m       0             6              6


Grand Total 148 QSOs

After the contest I investigated the issue further. It was narrowed down to the 15pin to 15pin aux cables supplied by elecraft with the KAT500 and KPA500. One worked fine but the other appeared to have an intermittent short between the band1 pin and the ptt (hence why it changed band when going to transmit).  During the following week I cut apart the molding on the faulty cable and saw how unreliably it was assembled. Although their was a clamp that held the screen, which was doing a reasonable job on the screen, it did absolutely nothing to stop the cables in the bundle moving and rotating. This had happened and the band data lead was wandering around the plug, touching the PTT pin.



I looked at the cost of a replacement cable, but at nearly 50 pounds and the photos not assuring me the cable grip method was any better I decided to make my own

A search of the Farnell website revealed a 15 pin HD metal shroud that had a selection of cable clamps that would grip any cable firmly. They were not cheap (6.52) but I needed reliability.

As the Elecraft aux cable used only 10 cores I found some 10 core+screen cable and made a pair of 1 metre long 15 pin male to female cables; enough for the KAT500 and KPA500. I also made a shorter cable that could be used to connect the KAT500 to the KPA500 when the ATU is sitting on top of the PA,

 I also found my 3 metre 15pin to 15pin all pins connected cable (with moulded plugs), As it had 2 female connectors, i chopped it in half and with two of my newly purchased connectors made a pair of 1.5m male to female leads. These cables are useful when connecting to my K3 switching box which has a possible need for all pins