Sunday, 8 August 2021

Plisch 432MHz amplifier module

 When I visited Frederichshavn in 2018 I purchased some small Plisch dual BLF861 device 28V 432 MHz amplifier modules  which had been used in TV trasnsmitters. I also got a larger two stage module with a single device driving  the same dual BLF861 devices.

When I returned I tried using the dual stage device but it saturated at 100W, even after doing the published modifications to the output stages at http://pa0ehg.com/70cmpa.htm and help from G4ERO. So the project was put to one side

I recently rediscoverd the modules and decided to try again, firstly with the dual device modules., With the same modifications I again got 100W output with 4W of drive. with each dual device set to 1A standing current.  I then reread the modifications and realised a PAIR of 5.6pf ATC capacitors were added across output capacitor, not a single one like I had been doing. Adding the capacitors and retweaking the input variable capacitor resulted in 190W output with 5W of drive, which is generally considered to be normal

A summary of my mods :-

Remove C62 and C63 (3pf)

Remove C7 and C27 (5.1pf)

Add TWO 5.6pf ATC capacitors across C9 AND C29

Add 22pf trimmer across C2 and C22

Add a 2N7000 FET at to turn the bias OFF on receive by earthing C19 V7 base junction (needs 5V on gate on receive)


The module after modification

Next task was to put it in a box. I did find the chassis from the defunct 6m 300W amp with coax relays and PIC controller so decided to repurpose it. 

The completed amplifier (with lid off module)


Saturday, 31 July 2021

PortsLang 4 Hardware Updates

 Having used the PortsLang 4 for a while I decided it needed 3 main improvements:-

1. The mouse for tuning works ok but is a bit clumsy and occasionally misses pulses

Fitting am Arduino Pro micro board emulating a USB mouse s described  at   https://wiki.microwavers.org.uk/Langstone_Project  with an Optically coupled encoder fixed this issue in my Langstone so the technique would be used again, There is not enough room for a turning knob on the Front panel. An external solution would have to be used.. The mouse simulator was built with 3 switches an an optical encoder in a small diecast box, allowing it to be plugged into the back panel of the PortsLang




2. The Adalm Pluto Oscillator drifts and has a frequency offset

This is not an issue in my Langstone as it has enough room to put a good oscillator and multiplier in the box.  There isnt enough room in the PortsLang to do that. Measuring the output frequency of the PortsLang showed the oscillator settled down 33kHz high at 437 MHz which was unacceptable. I had previously bought a couple of  the recommended replacement 49 MHz oscillators from Mouser, so decided to swap it out. The existing oscillator was carefully removed from the PCB with two soldering irons and the new oscillator soldered in place . Unfortunately when removing the original oscillator solder flicked onto the oscillator coutput capacitor and whilst removing this solder the capacitor vanished. A new 18pF 0402 capacitor , While I had the board out I also added the PTT output relay described at https://wiki.batc.org.uk/Custom_DATV_Firmware_for_the_Pluto#PTT_output

Measurements now showed the oscillator was now within 200 Hz at 437MHz without tweaking the Pluto calibration.

3. It has no speaker so a headset HAS to be used to listen

I had built a speaker into my Langstone so I could hear the signals when peaking a dish without tripping up on the headset lead. There was not enough room for a speaker in the PortsLang so an external box  was needed. Looking in my Junkbox I found a 12V 18W audio amp module, volume control,  a 2" speaker and a suitable plastic box, I built the amplified speaker with a DC connector to allow it to be powered from a 12V output from the PortsLang 


Sunday, 25 July 2021

Upgrading my Portsdown 4 to become a PortsLang 4



Inspired by a post by G8GKQ about new features available in the latest Portdown software release I decided it was time to upgrade my Portsdown 4 to enable it to be used as a Langstone on Narrowband modes, saving an extra box when man portable. The main change is the SDR is changed from the LimeSDR to an Adalm Pluto SDR. Looking at the benefits of the change revealed the only feature I would lose would be the Lime spectrum view which is not available on the pluto

I did have a spare Adalm Pluto obtained secondhand from HRD. but it was still in its plastic case. First task was to house it in a metal box which was much easier the second time around. Fitting it inside the Portsdown necessitated moving the antennuator board 1cm towards the front panel, which took much longer. 

The Langstone mode requires a "USB mouse" tuning knob and a USB sound card which would require additional USB ports (the RPI4 only has 4). I dug out the old USB3 powered hub and refitted it. I also found a dual port USB extension cable that allowed two of the ports on the hub to be accessed on the Portsdown rear panel.

The USB soundcard required fitting two 3.5mm stereo sockets for mic and phones to the rear panel to allow external access for a boom headset/microphone. A phono soocket was also added for a footswitch input to put the Langstone on transmit. The audio connector for the RPI audio output was kept.  All these additions made the portsdown rear panel crowded!

One great feature is that the band data pins on the RPI GPIO can be accessed from both the Portsdown and Langstone software so the band decoder can drive the 8 port RF switch and external transverter interface from both


Internal View

Rear panel is now very crowded

The powered USB and the Langstone USB soundcard

Sunday, 27 June 2021

47 & 76 GHz outing to Notgrove IO91BV

 Originally I had booked the afternoon of Friday 25th June off work to go and watch a worcester T20 cricket game, but my ticket was cancelled due to covid restrictions. The question was what to do with the spare time? The answer was to persuade Noel G8GTZ to go out portable so we could try the Notgrove to Combe Gibbet path on 47 / 76 GHz, something we didnt really have time to try in the IARU 2021 contest

Noel managed to receive my pictures on both 47 and 76 GHz but I could not receive his DATV signals in the reverse direction. We did however manage an SSB QSO on 47GHz over the 67km path

The path towards IO91GI from IO91BV



My 47GHz signal as received by Noel



My 76GHz signal as received by Noel


Saturday, 12 June 2021

IARU TV CONTEST 2021

Originally I ws not going to bother with this years contest, but after Noel said he was going to Dunkerry beacon there was a chance to set a few distance records if I went to Cleeve common, so i decided to venture out. 9 bands were packed (23cm, 13cm, 9 cm, 6cm,3cm 24GHz, 47GHz and 76GHz  and 2m FM). This number of bands would be quite challenging for the Portsdown software as it only has four transverter bands!

To get the best parking spot for the Dunkerry beacon path I went to Cleeve common early. Perhaps a bit too early considering the 1300 start time, but I used the time to go on an 8 mile discovery walk around the common

Two way TV QSOs were had with Noel on 23cm, 13cm, 9 cm, 6cm, 3cm and 24GHz. I briefly detected his signal on 47GHz but the river mist I saw on the path meant no two way qso. The only other station I heard on 2m talkback was G8GKQ but he was busy so I went home. Noel journeyed back to IO91GI overnight

5GHz and 10GHz point at IO81FD

The 23cm setup

On sunday morning I went early to cleeve common to try the path to IO91GI. I went man portable to the trig point and worked Noel on 24GHz at 0700z) but there were no signals either way on 47 GHz. I then retreated back to the car park and worked Noel on  13cm, 9 cm, 6cm, 3cm, By this time Cleeve Common was getting busy so I left and went to IO91BV.

Man Portable Sunday morning (note the shadow length!)

While at Notgrove my 7" display packed up (but not it;s touch screen!). With considerable effort (and Noels patience) we did manage qsos on 23cm, 13cm, 9 cm, 6cm,3cm and 24GHz

I was going to a third location to try it out, but with the failed display I didnt bother and went home. 

So I ended up with 16 QSOS, all working the same callsign! Activity was lower this year and being so far west denied me working the stations i worked when operating from walbury last year.



Sunday, 6 June 2021

Another 47 and 76GHz DATV Expedition to IO91GI


 Noel, G8GTZ had let me know that on June 3rd he was going portable on 47 and 76GHz to Combe Gibbet, to allow G1EHF to try out his 47GHz QRP system to work G4LDR/P and G8ACE/P (who I hadnt worked ) on narrowband so I decided to tag along

Two way qsos were had with G4LDR/P SSB (at Stockbridge IO91GC68, 26km) and G8ACE/P on both 47 and 76GHz. My signals on 47GHz were so loud with Neil that even a conductive plastic bag over my dish couldnt eliminate signals at his end! I used my Langstone as the IF, the spectrum view was very useful for finding signals. G1EHF had his first qso, all before lunch, so we retired to the pub for a drink

Noel and I decided to try 47GHz DATV, to convince him his system was working. Although I had brought the portsdown, i didnt think we would be doing any datv so I hadnt brought the USB lead for the minituner. Fortunately G1EHF had a spare which I could borrow. 

Noel went off to Stockbridge IO91 while I returned to Combe gibbet. The langstone spectrum view helped find Noels drifting signal and a two way qso was had 

Noels 76GHz signal over 26km

Noels signal on 47GHZ on DVB-T


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.