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.




Wednesday, March 20, 2019

SPE-1.3KFA Amplifier Efficiency

As the BARTG 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

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




Wednesday, November 14, 2018

DATV Predriver Amplifiers

Having built the BATC Portsdown DATV transmitter I realised I needed amplifiers between it and my final amplifiers. The neatest solution would be to use Mitsubishi Power Modules. I managed to obtain some

I used RA07H0608 on 4m, RA08H1317M on 2m, RA07H4047 on 70cm. Each could produce around 7W. I managed to source some G4DDK PA/LPF PCB onto which these modules would fit.

Each amplifier was mounted in a diecast box, with an SMA input connector (to match the Portsdown output connector) and BNC output connector to match the following amplifier. A BTS4140 high side switch IC driving a 78L05 regulator was used to provide switched 5V to bias the module. Switching was achieved with an earth on transmit signal from Portsdown. The amplifier also provides an earth on transmit output to switch the following amplifier.

Each module produces 7W output with all harmonics over 55dB down on the fundamental

  

The Fourth amplifier, the one on the right, is a Chinese broadband 2 to 900 MHz 2.5W amplifier from Ebay, that may come in useful one day!

Thursday, October 25, 2018

An RBTV weekend at Dorstone on 71MHz and 50MHz

Having got my 71MHz NOV and built a 71/437 MHz Transverter,  I decided I needed an outing to exercise them.  I noted the 50MHz AFS was happening shortly so I decided to combine the two events in a weekend in Dorstone IO82LB. G8GTZ/P would be out at IO91GI (136km) over the weekend so I would have someone to work

I set out from Malvern on Saturday morning. Got to site and erected the new 2" mast system with the 5 ele 70MHz Powabeam.



I transmitted to G8GTZ who could see my signal a few dB above the noise floor but could get no video.  However I did receive Noel's 15W signal and decode it easily at 125kS.

Noel retired to fault find his receiver while I retired to the Pandy arms Inn for the night

The following morning I returned to the site and assembled the old 5 ele Tonna antenna along with the K3S and KPA500 for AFS.

 

After a very slow start I managed to work 96 stations, best DX being PA4VHF at 640km. During the AFS Noel informed me he had fixed his receiver by disabling his laptop PSU to lower his noise floor 10dB, so we could try again.
When AFS finished at 1400 I took down the 6m 5 ele yagi and put up the 4m 5 ele yagi again. This time Noel received my signal:-

I also received Noel, this time with much better MER, up to 24dB which shows the system had some performance left for a longer path

I returned to Malvern Sunday evening after a great weekend, including my first DATV QSO on any band!


Sunday, August 5, 2018

K3S "HI SIG" WARNING

While testing before the IOTA contest at G8X the K3S came up with the error "HI SIG" warning

From the manual:-

"An extremely strong, sustained signal (e.g., a broadcast station’s carrier) may be causing
excessive post-mixer amplifier current when operating on the present band. The K3 will automatically turn the preamp OFF, and in extreme cases will also turn the attenuator ON"

After disconnecting the antennas and turning the rig back on again the same error was displayed, and all controls were sluggish. At this point the K3 was used as a replacement and survived the whole contest without issue.

An Internet search suggested that the IF amplifier following the mixer consisting of Q8 and Q9 had now got shorted devices. Elecraft support were contacted and quickly responded confirming this theory. The devices used for Q8 qnd Q9 were discontinued, but some were found on EBAY. These took 24 hours to arrive and when fitted resolved the issue. The IF amplifier in the sub receiver had escaped unscathed. As a note Q8 and Q9 were easy to replace as you just have to remove the front half cover underneath the K3S, they are soldered to the underside of the motherboard

Elecraft support also mentioned that for a time the K3S was shipped  with R66 in the IF amplifier as 10 ohm

"On K3S, make sure R66 is 15 ohm  E500610 not 10ohm. We briefly shipped with it 10 and reverted back, **AND at the same time changed R60 & 75 so if R66 is 10 ohm, change it to 15 E500610 and R60 to 150 ohm E500251 and R75 6.2 ohm E500265"

My K3S was one of these radios so having replaced Q8 and Q9 and checked it worked, I changed the values of R60, 66 and 75.

Monday, June 11, 2018

RIP Meg. Died 11 June 2018

 Meg Robinson 1947-2018 (G7FRE), M0FRE, (KB2NCP) N2NQI, 9H3MW


W2SZ/1 50MHz 1993