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:-

Pos   
Callsign
Loc
QSOS
Score
Norm
ODX
Kms
Power

1
G4FRE/P
IO81XW
6
486
1,000
G4ODA
160
5
2
M0HNA/P
IO91GI
7
474
975
G4ODA
182
15
3
G8CUL
IO91JO
4
315
648
G4ODA
150
10
4
G4LDR
IO91EC
3
306
630
G4ODA
212
15










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.

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



Thursday, 11 April 2019

6m RBTV Outing to Titterstone Clee

Having failed to make a 2 way QSO with G8GTZ/P on 50 MHz RBTV from the Tump due to his PA issues we decided to try again over a longer path from Walbury IO91GI to Titterstone Clee, IO82QJ. It would also be an opportunity to try the 5665 MHz FMTV system. Path profiles looked good for 6m , but a bit iffy on 6cm

Approaching the site I was surprised to see snow on the ground! The 6m gear was assembled and Noel was a good signal on NBFM, although there was deep QSB. Transmitting 50 W of DVBS to Noel he could not quite get a picture decode. As I was using my Portsdown 2019 system, which is Limesdr mini based, I had the option of running DVBS-2 transmissions, which supposedly gives the system an extra 2 dB capability. Switching to that mode allowed Noel to get a decode.


Noel then transmitted around 10 W of DVBS-2 back to me. The minitune receiver could not quite get a picture , but I left it running while on a long meander around the site trying to find cellular coverage, and when I came back had captured his  test card. Two way QSO of 140 km completed for a new UK record.

I then assembled the 5665 MHz equipment, with its 2' dish and FPV modules with an 8W Fujitsu amp. The FPV Transmit module needed a 20 dB attenuator to avoid overdriving the Amplifier. Talkback was on 6m FM. Noel couldnt see my signal, and I couldnt see his 3 W, with the exception of a 15 second period, assumed to be aircraft scatter where his signal was identified. Partial success at least, perhaps confirming the predictions were correct.
G8GTZ/P

G4FRE/P




Wednesday, 20 March 2019

SPE-1.3KFA Amplifier Efficiency

As the BARTG HF RTTY contest does not have different power sections I thought it would be a good time to try the new SPE 1.3KFA Amplifier on RTTY.

Originally I used the 4 band data lines from the K3 to steer the amplifier to the correct band, but experience showed it was better to use the CAT data giving the exact frequency to steer the internal ATU quicker. This was easy with the K3 but the K3S was a little harder to engineer as described at K3S to SPE.

Due to band conditions there was a lot of  CQing. From cold, after 8-10 CQ with the amp switch set to "max" at 750W  output a "PA overtemp" error would be shown and the amp switch to "mid". with the switch set to "max" again and backing off the amp to 500W output the error would reappear after 12-15 CQ

I continued running with the amp on "mid" for a while,  then, after a series of CQ the amp switched to "low" and complained of overdrive. I backed off the drive to give 400W and continued running and had no more issues for  the rest of the contest.

Explaining my findings to G4BVY after the contest he said that G4CLA had similar issues at P44K  when running an SPE amp on FT8. He found the efficiency of the SPE amps on "low" is much higher than on "mid" or "max" hence less overheating so less alarms.

Previously we had used the Elecraft KPA500 on rtty contests. This had no issues running 500W output for a 48 hour contest, apart from the noise of the cooling fans.

From the results the amp seems to have worked fine, 1st in EU, beaten only by a Californian!