Saturday, 15 February 2020

The Langstone Narrowband Transceiver with Pluto and RPI 4

At the RAL TV meeting last year G4EML demonstrated a narrowband transceiver ("Hayling") using a raspberry Pi 4 a 7" LCD screen USB soundcard and an Adalm Pluto. Talking to G8GTZ at the recent Didcot Rally I found that the code has been uploaded to github ("Langstone")so on my return from the rally I decided to try it out.

The first attempt at building the code resulted in a no frequency display on the screen. The log seemed to be objecting to my USB sound card, so I changed it for another one I had and I was getting  the frequency readout but no audio

I then noticed that the display seemed to think I was on transmit. I consulted with G4EML and found that there should have been a pullup resistor on the GPIO PTT input pin. With this modification the display indicated RX and i got receive audio and could hear signals

I took a listen to my transmit signal. The dots sounded fine but i discovered the centre button on a 3 button mouse was needed to send CW, which I didnt have. I got no audio on transmit until I discovered the USB sound card mic input needed a computer headset (electret) microphone rather than my (dynamic) heil headset 

To try it out on the air I hooked up a 3W 1296MHz module and had a nice 2 way qso with a local on the band

I mentioned my findings to G4EML who updated the code to have a key input and a PTT output to drive an amplifier. He also added band output pins to auto switch external amplifiers and preamplifiers

I was then interested  to see how the system would work as a microwave IF. I connected it the radio on 144MHz to my 5760 to 144MHz Transverter and could hear the GB3OHM beacon on 5760.9MHz on a horn antenna. I then realised the pluto works directly on 6cm so I connected it directly to the horn antenna and could hear nothing. I then used the KX3 and the transverter to calibrate the Pluto and found there was a 65kHz offset, on which frequency I could just detect GB3OHM. I dug out a DEMI ATF36077 preamp and put that infront of the Pluto and the beacon became quite readable

All that is needed now to make the rig suitable for portable operation is a panoramic display!

Wednesday, 29 January 2020

CQ160 contest 2020

Having had so much fun in the ARRL 160 contest I returned do the CQ 160 in January from DEMI. To avoid the previous issues with connecting in Charlotte I flew on an American Airlines codeshare flight which was on a BA plane direct from Gatwick to Orlando, arriving early at 1430, Steve and Sandy met me at Orlando and after a fish supper we drove the 3 hours to Live Oak.

The rules for this contest are not quite the same as the classic CQWW rules. Multipliers are US states+VE provinces+countries. Although DX stations (and only DX stations)  send their zone, they dont add to the  multipliers!

The contest started at 1700 local on Friday under the call K0DI. Unfortunately the starting operator was stuck on a plane at the gate in Washington, so I was volunteered to start. Calling CQ for 10 minutes, nothing much happened, then the pileup started, which was a new "run" experience, which I continued for 2.5 hours before switching to mult duties retiring at 2300 I returned at 0600 and operated till the band closed at 0830 working some JA but no VK/ZL

Having not experienced the overnight shift I returned at 2300 to teamup with Steve. I ran , he searched. I ended up running for 8 hours. The band closed around 0800 sunday morning again . We resumed at 1600 that afternoon  after a visit to the club shack and surprisingly had 17 qsos in the last hour

For light entertainment on the monday after the contest we replaced the power supply in a quadra VL1000 amplifier which had been hit by lightening.

Saturday, 14 December 2019

ARRL 160m contest

While attending Microwave update I managed to get an invite to operate the ARRL 160m contest from the Downeastmicrowave site in Florida

I flew from Heathrow on Dec 3 to Orlando via Charlotte, NC. It was to be my first flight on an AA Airbus made plane. Unfortunately it broke so we spent two hours getting it fixed at Heathrow. This resulted in missing the Charlotte connection and being put on the standby list for the next flight. Luckily I was 1st on the standby list and was the only one (of 36 standby) to board. Steve and Sandy met me at Orlando and after supper we drove the 3 hours to Live Oak

The station and antennas were all ready to go, so all i needed was a training session which was easy as we were to use a pair of K3, The available multipliers were ARRL sections (83) and countries. The contest started at 1700 local time I shared the shift to 0300 doing most of the "running", then had a sleep.  The band closes at 1000 and we resumed at 1500. Again I operated till 0200 then sleep. During this period we managed to work the final two sections (NL and ND) needed for a clean sweep of all 83 sections. The contest ended at 1000 local time. The final score was as follows:-

 Band     QSOs     Pts    Sec
   1.8    1314        3201  136                     Score: 435,336

The Transmit Antenna
after the contest i hooked up the 1000' NE beverage to my RSP2PRO to take a listen on 474kHz WSPR. I was surprised to see so much of G0MRF:-

191210 0006   1 -30 -0.19   0.4757844  G0MRF IO91 37           0  5279km
191210 0138   2 -25 -0.23   0.4757845  G0MRF IO91 37       
191210 0208   2 -26 -0.23   0.4757845  G0MRF IO91 37
191210 0216   2 -23 -0.36   0.4757843  G0MRF IO91 37
191210 0232   2 -25 -0.27   0.4757845  G0MRF IO91 37 
191210 0238   1 -28 -0.27   0.4757845  G0MRF IO91 37
191210 0304   3 -23 -0.27   0.4757845  G0MRF IO91 37   
191210 0548   1 -28 -0.53   0.4757846  G0MRF IO91 37
191210 0602   2 -27 -0.53   0.4757845  G0MRF IO91 37   

Thursday, 21 November 2019

9cm Outing to Cleeve Common

Having finished the 9cm  power amplifier integration I decided it was time to try it out on DATV. Noel G8GTZ pointed out that there was to be a UKUWG contest on November 17 for which he would be going out for, so I could combine the two activities. I chose to visit the usual Cleeve Common IO81XW site. Noel did suggest that the site he was going to would be workable from the Radio Mast car park, avoiding the need to cart the gear across the common to the trig point area.

Arriving at the car park at 0930 there was so much fog I could not see across the field but I set up the narrowband system to check out the receive system.

The fog on arrival

GB3ZME and GB3OHM were loud so all seemed to be working. I then worked M0HNA/P, G8CUL, G4LDR and G3VKV. Noel then arrived on site and we worked easily on 9cm narrowband. I then switched to DATV. He saw my 9cm signals easily, however due to issues at his end it took me a long time for me to receive his signal, but I eventually succeeded.

The mobile DATV station
Noel's 9cm DATV signal

After finishing working Noel I eventually managed to attract the attention of G4ODA on ON4KST to try working him. The path didnt look too promising as shown in the following picture:-

With patience e did work on cw at 160km, being my best DX. As I could find noone new to work I left the site and came home. 

I even found time to put in an entry to the contest and was most surprised with the result:-



Thursday, 15 August 2019

A dedicated portable Narrowband/ DATV system for 6cm

Having previously used  parts of my 6cm eme system for portable DATV operation from Titterstone CleeBrown Clee and Cleeve common it was very apparent that the large numbers of interconnecting cables and its lack of waterproofness was a handicap. A dedicated, waterproof system was needed , in the style of the 24 GHz system.

Having not used the Fujitsu amp in the 6cm FMTV system I had an amplifier. I also had a DB6NT preamplifier, however I needed a compact Transverter. The DB6NT mk4 had good performance but cost a lot. I looked around for a second hand one to no avail. In a conversation with G4DDK at Heathrow airport on our way to Frederichshaven we were discussing what we were looking for. He was toying with the idea of a 6cm DB6NT mk4 xverter to upgrade the mk2 in his eme system. I offered to buy his mk2 and this convinced him to go ahead with the plan. Problem solved

Sam shipped the transverter which produced over 200mW (too much for the Fujitsu amp) and could hear the GB3OHM beacon on a patch antenna, time for encapsulation.

I found another waterproof box like the one used on 24 GHz in which the Fujitsu amp just fitted. The Transverter was mounted on a plate on the sidewall of the box, the amplifier was mounted in the base of the box.

To offer some protection and to allow monitoring when masthead mounted a PIC controller was deployed. It monitors  positive and negative volts, current and temperature. It also sequences the antenna change over relay and bias control

Tuesday, 13 August 2019

More 6cm FMTV upgrades

When operating on 6cm FMTV from cleeve common having multiple boxes in the system was a handicap. It meant a lot of cabling had to be changed when swapping bands. What I really needed was to have a display built into the control box, removing the need for an external monitor. Looking on ebayusa I found an unboxed cheap 7" LCD display with the usual selection of HDMI/VGA/Composite inputs that would run off 12V. The quoted dimensions convinced me it would fit in the control box.

When it arrived it worked fine and fitted easily in the control box, as shown below. The controls were mounted on the side of the box. There was still room left in the box; perhaps I can squeeze in the microphone amplifier and audio amplifier so it can have WBFM voice qsos?

Monday, 10 June 2019

24GHz DATV World Record extended

As it was IARU contest weekend and G8GTZ was going to be portable at Dunkerry Beacon IO81FD it seemed an ideal opportunity to extend the 24GHz DATV record from Cleeve Common IO81XW81. It would also nice to try out the upgraded 6GHz FMTV system. so a trip to Cleeve common was setup for the Sunday morning

Friday night I checked out the 24Ghz system and was getting low transmit output on both DATV and SSB. Many hours were spent investigating with no success

Saturday morning I got out the spare 2W W2PED amplifier module. Over coffee I spotted that the replacement amp had 6 bias pots, the installed amp had 5 bias pots. Analysis showed that one of the Bias pots had come off the installed board. The multiturn pot is very small so I had to resort to raiding a 2Ghz amp board to harvest one. It was installed and the bias set to match the voltage on the replacement module. After many lost hours we were good to go

Sunday morning, Arriving on site at 1030 first the FMTV was setup

Noels picture was quickly seen:-

After the 2 way QSO the FMTV gear was then removed and the 24GHz equipment Installed.

 To align the antennas we had a 24GHz narrowband FM QSO, Noels signal pinning the s-meter on the FT817, looked promising. I then transmitted DATV and Noel instantly saw the picture:-

Noel then transmitted and I instantly saw TV data being received but no picture. After Noel trying lots of datarates and parameter permutations a picture was finally seen:- 

Wednesday, 5 June 2019

Upgrading the 6GHz FMTV system

Having got the 6GHz system going for the trip to Brown Clee, it soon became apparent that, although the system worked well on sunny days, it would be unuseable on rainy days. Time for a rebuild!

The system consisted of two boxes, one containing the FPV receive and transmit modules, the other containing the large Fujitsu power amplifier

Not very waterproof!

Looking in the junk box I rediscovered an  8W power amplifier module obtained from G3OHM. I also found the connection details and with the help of G4JNT constructed a power supply.  It worked fine and i discovered it worked with just +-10.5V on the opamp supply, good news when running off a car  battery. The only issue was that it was quite a chunky unit, hard to mount at masthead.  I found a suitable waterproof diecast box and worked out that by dismantling the amplifier modules and PSU board it would fit

I also discovered a smaller FPV transmit module with adjustable power output to avoid overdriving the amplifier. 20mW through a 10dB attenuator proved to be sufficient. The following is how it ended up

It is powered by a 6 pin Bulgin power connector (the same as used on my rotators) allowing the use of thicker/more cables to reduce the voltage drop on Transmit (it takes around 4A when it produces 7W of DATV) Video out of the receiver is via an N-type connector, video in to the transmit module is via a TNC connector (more waterproof than BNC) There is room for a receive preamp and filter if needed. Now to try it out

Saturday, 25 May 2019

Custom drive on mast base finally finished!

For many years I have been using a drive on base to foot the antenna mast when out portable. It was made by GW5NF using two pieces of wood and a gate hinge, allowing a KR400 rotator to be mounted. It has survived many outings but recently the hinge had been showing signs of stress. Time for a new one, a possibility thought about a few years ago but never executed.

I had previously bought a drive on mast from Moonraker, made from welded steel angle with a piece of 2" tube mounted vertically at one end. This had no tilt mechanism and with an 18" long base it was also a bit short for the width of landrover tyres, 20" was optimum.

The other design consideration was that the new base should allow the mast to be raised parallel or perpendicular to the car, allowing antenna erection on narrow tracks.

The new hinge assembly consisted of two 178 x 178 x 12mm aluminium plates and a 4" ball bearing grade 13 steel hinge. The plates were drilled and tapped to assure vertical alignment by using G4BVY's pillar drill. Care was taken when positioning the holes for the rotator that the terminal block was in a suitable position, especially the edge nearest the tyre.

Next a welded base was needed to mount the hinge on. Having no welding facilities I searched for a local welder/fabricator. Driving back from Worcester one day I saw a sign for Melvs welding at Powick. I took along my moonraker base, the hinge and a dimension sketch, he was very helpful  and between us we came up with an executeable design. By using M8 tapped holes in the base on a square pattern, the hinge could be rotated easily to drop the antenna in any direction. Two units were ordered.

One week later the units were collected and he had done a great job, including spraying them with cold galv paint to preserve them. £96 for the pair was a good price.  The hinge and rotator were added quickly and all worked fine. The only slight issue was that due to the sloping gap between the top and bottom plate the mast, when near vertical stressed the hinge. This was cured by adding nuts to the two rear bolts securing the plate to the frame which meant the top plate and bottom plate were parallel at the resting position.

Note the two levelling nuts at the right of the plate.

Monday, 13 May 2019

24GHz DATV World Record

The day after the Wirral mini tv convention, 12 May 2019, it was planned to try to extend the 24GHz DATV distance record with a path from Brown Clee IO82QL and Winter hill IO83SO. M0MHO, G7ACD, G4FRE, G8AQA, Dave G8VZT. and G8GTZ were at Brown clee and the Wirral club G3NWR with G4CBW were at Horrockswood IO83SO.

I had recently upgraded my DB6NT 24048/432 Transverter to use a DB6NT local oscillator. Checking out the system it was seen to produce 2W of DATV when measured on an HP432C power meter. Searching in the loft I found my Practical wireless 18" dish with its penny feed which was pressed into service

After setting up, G4CBW signal was easily seen on 24GHz with a MER of 17dB and both myself and G8GTZ exchanged 2 way signals for a new world record.

The Wirral could be seen to the left of the Wrekin which houses the GB3ZME 24GHz beacon

The PW 18" dish on its tripod

The signal received from G4CBW

The signal G4CBW received from G4FRE/P