Saturday, 20 February 2021

SEC1223 Power Supply Repair

 While using my SEC1223 Power supply to resurrect my Drake TR7 PA It suddenly started producing less output and tripping Amplifier alarms. To check the PSU wasnt current limiting I swapped to mydel 30A PSU and it behaved normally. I then reverted back to the SEC1223 and again the amp misbehaved maxing out at 20W. I then noticed that at this power the amplifier volts display was down to 7.2V when the current was 7A. Obviously the SEC1223 was ill

Searching the internet it appeared the most common cause of demise was the output capacitors failing, so I took the cover off



Indeed two of the three output capacitors had black goop on the top and were bulging. The capacitors are 16mm diameter and 29mm tall. I searched for replacements at the usual suppliers but did not find anything. Then I did an ebay search and found identical capacitors Teapo 2200uF 25V at £4 for 10 units so I got them. When they arrived they did look the same so I started swapping them:-

1. Remove the Mains connector and wires
2. Remove the 4 screws under the chassis holding the fan in place
3. Remove the 2 black screws under the chassis holding the internal heat spreader in place. This saves risking damaging the 3 active devices taking them off the heatsink
4. Remove the 4 screws holding the PCB in place.

It was then possible to manouver the PCB to get under the old capacitors off the board. Two of them had put black goop on the PCB that was cleaned off, but all three were replaced

After reassembly the psu produced 13.8V and using the K3S producing 100w output, the PSU only showed a drop of 0.3V at 20A output. Repair finished  

I will be taking a look at my other two SEC1223 to see if they have capacitors about to fail


Thursday, 26 November 2020

Locking the Adalm Pluto to an external reference (Part 3; Software challenges)

 Having got the hardware finished it was time to convince th Pluto that it had a 50MHz NOT 40 MHz reference. This was easier said than done! 

It took 6 hours of internet research and trials before a working solution was finally found at https://tbspace.de/plutosdrclockinput.html  AND which would survive a pluto power down. 

The final solution was to execute the following on the pluto. No idea why it works or what it does, but it solved my problem

fw_setenvadi_loadvals fdt addr fit_load_address } && fdt get value fdt_choosen

/ fit_config }/ fdt && fdt get addr fdtaddr / fdt_choosen } data && fdt addr

fdtaddr }; if test ! n ${ad936x_skip_ext_refclk}; then if test n ${ad936x_custom_refclk}; then

fdt set /clocks/clock@0 clock frequency ${ad936x_custom_refclk}; elif test n

${ad936x_ext_refclk}; then fdt set /clocks/clock@0 clock frequency ${ad936x_ext_refclk}; fi; fi; if

test n ${model}; then fdt set / model ${model}; fi; if test n ${ attr_name } && test n ${ attr_val };

then fdt set /amba/spi@e0006000/ad9361 phy@0 ${ attr_name } attr_val };

fw_setenvad936x_custom_refclk "<50000000>"

To check if the changes were successful, we can read the device-tree:

cat /proc/device-tree/clocks/clock@0/clock-frequency | xxd

the response was

# 00000000: 02FA F080 .}x@

02faf080 is 50000000 in hex, Success

Having got the Pluto to work with the external reference I spent some time adjusting levels. It was suggested  on the internet that the pluto needed 0 to 10dbm to achieve lock but I found it needed much less than that, it would lock down to -22dbm input. I adjusted the output attenuator in the DFS50 to produce -10dBm output on mine

Sunday, 22 November 2020

Locking the Adalm Pluto to an external reference (Part 2)

 Having worked out how to inject the external reference the next question was what frequency to inject. Should I use 40MHz like the original?  Looking in my junk box I found a G4HUP DFC30 unit which takes a 10MHz reference and provides a 30MHz output. I tried retuning the output filter to 40MHz but the multiplier was very ineficent at times 4. So i tried retuning the output filter to 50MHz which worked fine. The reference was to be 50MHz

In my parts collection I found a 10MHz oscillator which could be used to drive the multiplier when no external reference was available. It also had a relay to switch between internal and external reference.

The 10MHz oscillator and DFS30 as deployed in the Langstone:-



That is the hardware done, next to get the 50MHz reference in the software!

Friday, 20 November 2020

Locking the Adalm Pluto to an external reference (Part 1)

 Having finished boxing up the Langstone Transceiver  which is based on an Adalm Pluto SDR, the next step was to improve frequency stability.

Some have tried changing the reference 40 MHz oscillator to a more stable device. The preferred device is very small and i can imagine the damage caused by taking out the old oscillator.

Others have tried feeding in an external 40MHz GPS locked signal. One discovery from here was that the existing oscillator has an enable/disable pin so it can be left in place when an external signal is injected. This is thr chosen route


Note that C123 and C124 form a potential divider to reduce the output level of the oscillator. However C124 is not fitted but it does provide solder pads to mount another 180pf 0603 capacitor (I am not brave enough to try an 0402 size!) through which to inject the external reference

This is how mine ended up:-



Note that the braid of the coax cable through which the reference is injected is soldered to the groundplane in two positions. This is to prevent the 0603 capacitor being ripped off the board if the cable moves.

Thursday, 15 October 2020

47 and 76GHz DATV Expedition to IO91GI


Having previously proved out the 47 and 76GHz equipment on narrowband modes it was time to try them on DATV. Advance planning with G8GTZ and G4LDR came up with some paths to try in and around IO91GI on October 14 so an expedition was planned

I left Malvern at 0815 aiming for Combe Gibbet IO91GI25 to meet Noel. G4LDR was going to the Stockbridge site IO91GC68.  My journey took longer than expected due to road works and I arrived at 1030. 47 GHz narrowband signals were very loud on NBFM both ways and a two way DATV QSO was easily had. Moving to 76GHz. I eventually had a two way qso with Neil (after finding a field solution to the transverter sticking on transmit with no IF radio attached) and Noel received G4LDR/P but could not be received by Neil. As time was flying by and the road would have tractors on it at 1400 (the local land manager told us) we decided to go to the next site


Combe Gibbet 47 and 76 GHz


Combe Gibbet 76GHz 


G4LDR 47GHz received at Combe Gibbet


47 and 76GHz at Combe mast alongside G8GTZ 76GHz

G4LDR 76 GHz received at Combe Gibbet


Neil went to the Butser site IO90MX13 while we moved across the ridge to the Radio mast site IO91GI61. Narrowband signals were loud both ways on 47 GHz and a two way DATV qso was had thereby extending the UK 47 GHz DATV record to 51.8km.  76 GHz narrowband signals were good both ways on both systems, but at this point the damp weather arrived, not good news for 76 GHz propagation. The optical path to G4LDR/P disappeared in the mist along with any hope of any DATV qsos.. It then started to rain so the attempt was abandoned at 1650. Due to rain and roadworks I got back to malvern at 1900.


G4LDR 47GHz received at the Combe Mast





Tuesday, 22 September 2020

BATC 2020 50/70MHz Contest

beaming at G4CPE, Malvern hills on horizon


Having participated in the BATC 144/432 MHz contest (and won it) It was time to think of the upcoming 50/70 MHz contest. Originally slated  for September 19 and 20, after I pointed that the sunday clashed with the RSGB 70 MHz AFS contest it was changed by BATC to a saturday 1300 to 1900 contest. As the IO82lB site, used for the 144/432 contest has interference on 70MHz somewhere else was needed. The previously used IO82QL Titterstone clee site was chosen

The thought of putting up a 5 ele on  6m and a 5 ele on 4m was discounted  quickly. I remembered that back in 2014 I bought an Innovantennas  dualband 4 ele on 6m and 4 ele on 4m antenna so that was unpacked (for the 1st time) The assembly manual wasnt very helpful, but a few emails to Justin got the answers. The boom and 4m elements fitted in my car, but one end of the 6m elements had to removed so it would fit.

Arriving on the site around 1000 it was found to be very very windy. The HF dipoles of the IOTA contestants were blowing all over the place. The possibilty of not being able to put up the antennas (one for the 50/70MHz yagi one for the 144/432 talkback colinear) was considered. As a test the 4/6m antenna was assembled on the mast and eventually raised to the skies. The swr was 1.8:1 on 6m and 2:1 on 4m but this was not a day to adjust antennas. It ws decided another mast was too risky so 2m talkback ideas were abandoned!

Had a 2 way on 4m with G8GTZ (MER15) Tried on 6m, Noel copied my signal easily but due to loud interference coming from the radio station at the bottom of the band I struggled to receive him, but eventually I copied him at 66ks near the top of the band (for my only 2 way QSO). Worked G0MJW on 4m (MER6). Due to the fine work of Noel acting as a Zello to 2m transponder, hooked up with G8VPG and had a 2 way with him on 4m (MER 16) When he turned his beam on noel he was still MER8 with me! Tried 4m and 6m with M0DTS with no luck, but my 4m signal was detected!. Worked Arthur G4CPE (for the 1st time!) on 4m (MER peaked at 7.5) at 156km for my best DX. He could not copy my 6m, probably due to cross polarised antennas. Copied Noel at MER6 when he transmitted 4m at Arthur! Managed to get my 6m received by G0MJW in the final act of the day

On 4m used Portsdown 2019 +modified G4DDK nacton 437/71MHz transverter + MITSUBISHI brick (20W) +minituner. On 6m Portsdown 2019 +modified G4DDK nacton 437/51MHz transverter + 7w MITSUBISHI brick+LDMOS amp (150W; the bigger amp is locked down in wales)+ minituner


G8VPG/P 120km on 4m showing intended loc.

G4CPE 156km on 4m

G8GTZ/P 141km on 4m

G4MJW 127km on 4m


The results  were subsequently published and came as a bit of a surprise with a win and a trophy!

Low Band 2020.gif





Thursday, 17 September 2020

My first 47GHz UK QSO

Having put the 47GHz system in a box it was time to try it out. An opportunity arose with the upcoming 47/76GHz contest so a visit to Cleeve common IO81XW was organised

As GW3TKH was going portable on the Blorenge IO81LS I Initially set up on the west side of the summit. We first tried on 24 GHz and signals were huge both ways on NBFM with both GW3TKH/P and GW4HQX/P. Moving to 47GHz signals were equally loud on NBFM  both ways with GW3TKH/P but I had to resort to SSB to work the GW4HQX/P QRP

47 GHz transverter on top of 24GHz Transverter

47GHz takeoff towards The Blorenge



 As there were no others on 47GHz I packed away that band and went manportable on 24GHz from the trig point and worked another 5 stations including the best DX of G8GTZ/P at Walbury at 74km to achieve 3rd overall place



Sunday, 13 September 2020

Housing the DB6NT 76GHz Transverter

Having also bought a DB6NT 76GHz transverter recently I decided it was time to be put in a box and join it's 47GHz cousin in the field.

It was found that the same size box as used to mount the 47GHz transverter would be suitable. However,  how to get RF signals in and out would be a challenge. After a long search a pair of 90 degree WR15 H plane bends were found on Ebay. They were similar but not identical in dimensions. These would allow the transverter to be mounted on the base of the box with the waveguide bends poking through holes in the sidewall.

The box was fitted with a an N type socket for the IF and a TNC socket for the 10MHz reference. A 3 pin XLR was used for the 12V power. A power LED,  lock LED and transmit LED were fitted

The local oscillator was mounted directly on the base of the box alongside the transvreter. As the 76GHz portion of the band used in the UK is 75976 MHz and the transverter has a 144MHz IF the local oscillator was programmed for 9479 MHz. Note that this is not an available standard frequency available in the MKU oscillator. I chose to reprogram the unit and replace the existing 9486 MHz 76 GHz LO with the 9479 MHz one.

The transverter has an RF output power Indication  which was connected up to my usual LM3914 and 10 LED bargraph indicator. Initially this was mounted inside the box on the local oscillator but it was found after its first outing to be more useful if visible from the outside ao a hole was filed and the unit mounted.



Wednesday, 9 September 2020

Housing the DB6NT 47GHz Transverter

 Having bought a DB6NT 47GHz transverter last year I decided it was time to use it, especially as I had a pair of W1GHZ horns that would avoid the need for a T/R relay.

Finding a big enough waterproof box for the xverter module was an issue but one was eventually found that was a close fit. It mounted fine in the box but the SMA plugs on the ends made it too long. Using a dremmel some of the inside walls of the box  were removed and it just fitted, even if the SMA plugs could not be unscrewed in situ!

The transverter was mounted "labels down" on flat base of the box with holes made to line up with the TX and RX waveguide ports

The local oscillator was mounted directly on the base of the box alongside the transverter. As the 47GHz portion of the band used in the UK is 47088 MHz and the transverter has a 144MHz IF the local oscillator was programmed for 11736 MHz. which is one of the available pre-programmed frquencies

The box was fitted with a an N type socket for the IF and a TNC socket for the 10MHz reference. A 3 pin XLR was used for the 12V power. A power LED,  lock LED and transmit LED were fitted.

The transverter has an RF output power Indication  which was connected up to my usual LM3914 and 10 LED bargraph indicator. Initially this was mounted inside the box on the local oscillator but it was found after its first outing to be more useful if visible from the outside ao a hole was filed and the unit mounted



Thursday, 13 August 2020

BATC 2020 146/437MHz Contest


 BATC announced a dual band 146/437 Dualband DATV contest on August 8/9 . Dorstone IO82LB was the obvious choice but due to other commitments only operation on Sunday 9th was possible. As G3UKV would be out portable on 5GHz FMTV equipment for that band was also taken

G8GKQ/P was easily worked on both 2m and 70cm IO81UC 118km. I could see his 5GHz FMTV signal but he could not copy my 8W signal.


My signals were successfully received by G3VKV (IO81XV) at 71km

M0YDH/P (IO82QL) was worked on both bands  along with G3UKV/P at the same site on 5GHz FMTV at 54km


G4CBW/P (IO93AD) was worked easily on 432MHz but it took 25 minutes to complete the QSO on 2m due to QSB at 141km


Finally my signals on both bands were received by G4NZV (IO82WA) at 63km. An interesting outing

The equipment on 144MHz was a Portsdown 2019+ 30W Mitsubishi brick to a 9 element portable tonna at 4m. On 437 MHz a Portsdown 2019 + Mitsubishi 7W brick + 400W LDMOS amp into a 21 element Tonna at 5m

The results  were subsequently published and came as a bit of a surprise with a win and a trophy!