Monday, June 10, 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, June 5, 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, May 25, 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, May 13, 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, April 11, 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, March 20, 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!


Wednesday, February 27, 2019

GB3MHz 13cm on PI4 mode again

With good conditions forecast over the 22nd February weekend I decided to have another look for GB3MHZ on 13cm from home. I have an indoor Tonna Yagi feeding my old EME 13cm multiband xverter which has a noise figure of around 0.5dB.

The beacon was very loud and after careful tuning to get the required tones input into the software, decodes happened this time.

I left the software running overnight, into Saturday morning and the beacon did not fade out until 0745 on feb

Saturday, January 26, 2019

GB3MHZ 13cm on PI4 mode

While on a visit to the South Birmingham club G3OHM to do some K3 upgrades I took the opportunity to see how the PI4 mode works, having never used it before. Looking through the UK beacon list there are only a few beacons running the mode, but one was GB3MHZ on 2320.830MHz, which was audible on cw from IO92AJ at 220km. Software was installed on the I7 laptop, audio was extracted from the K3S via its USB lead and the system left to run for 45 minutes



As can be seen, no decodes were received, despite the cw being audible. The 4 tones of PI4 can be seen between the cw / carrier sequence

Wednesday, January 16, 2019

6m RBTV outing to The Birtsmorton Tump

Having seen 6m and 4m RBTV pictures over the 230km path from Malvern to Kent over Christmas it was time to try for a 2 way QSO on 6m. I went to the Birtsmorton Tump at IO82UA and Noel G8GTZ went to Sparsholt IO91FN, a path of 73km. I used the Portsdown driving a retuned Nacton 6m/437MHz with the same transverter driving the Minituner on receive.

Despite high winds, making getting the 5 ele yagi into the air a challenge, the day started  well with Noel seeing my 30W signals at a 14dB MER. I went to receive and saw Noels signals, but before the receiver had time to lock the signal went away. Investigations at Noels end revealed a short circuit in his transverter, meaning the end of 6m testing



The wind having dropped , I replaced the 6m Yagi with a  9 element 144MHz yagi.  Noel saw my 333kS video at a 26dB MER and I saw a similar level from him


I also had a two way 146MHz exchange with G0MJW at 83km






Thursday, December 13, 2018

RBTV Expedition to Titterstone Clee

To coincide with the BATC activity weekend on 9th December I decided to go and see what could be worked from Titterstone Clee, IO82QJ. especially as G8GTZ said he was going to Win  Hill IO80XH which would allow an attempt on the 71MHz RBTV UK Record. I also packed a 2m system

4m Antenna system 5 ele Powabeam at 5m
DVBS Signals from Noel were successfully received on 4m using the 71MHz/435MHz Nacton Transverter and Noel had little trouble seeing my transmission using the Portsdown to drive the Transverter, extending the UK distance record to 160km. I then took the 4m antenna down and put up the 2m antenna. I used the contest MHP with the HA8ET preamp that supplied some pre-selection for the minituner. Unfortunately the Portsdown Transmitter couldnt produce any 2m output, so I switched to the Adalm Pluto. This enabled me to generate a signal so Noel could see me and give me my 1st 2m DATV QSO

2m antenna system 9 ele Tonna @ 5m
The G8GTZ 2m signal from 160km