New FM satellite AO-91 now live

A new FM repeater AMSAT satellite AO-91 has just been opened up for general use. Other than it being very popular and thus very busy in the early days, it sounds like it will be particularly easy to work, including from a handheld with a whip.

Downlink: 145.960

Uplink: 435.250 +/- Doppler

Tone: 67.0 Hz

John KG4AKV has put a great post up here with all the info.

Programming chart courtesy AMSAT UK:

Memory 1 (AOS) – Transmit 435.240 MHz (67.0 Hz Tone), Receive 145.960 MHz

Memory 2 (Approaching) – Transmit 435.245 MHz (67.0 Hz Tone), Receive 145.960 MHz

Memory 3 (TCA) – Transmit 435.250 MHz (67.0 Hz Tone), Receive 145.960 MHz

Memory 4 (Departing) – Transmit 435.255 MHz (67.0 Hz Tone), Receive 145.960 MHz

Memory 5 (LOS) – Transmit 435.260 MHz (67.0 Hz Tone), Receive 145.960 MHz

The Great Construction Contest – 9th Nov, Woodford Park

The great construction contest is on again. It doesn’t matter that you haven’t painted it yet, or haven’t powered up the PA, or that you made it years ago and never entered it. It can still win if the members think it’s the best entry.

Big software projects using commercial rigs and USB gadgets are popular, pure metalwork and craftsmanship projects and ambitious or novel hardware ideas have all won in recent years and the selection depends on the judgement of ALL the members with the voting system designed to support the idea behind every entry.

A really good entry might get 4 points from loads of people, but your subtly cleverer idea may well get many more 3s and you’d win. Loads of people have only entered after persuasion and then won.

In any case, it’s great to show off what you do and to show the whole membership that we are a great club with loads of dynamic people ready to show our expertise.

Robin G4IWS

Another ISS SSTV event this weekend

Another series of SSTV transmissions from the International Space Station is under way, running throughout this weekend.

Listen out on 145.800 FM. A handheld up to a smartphone’s mic will yield fairly good results.

Passes below – though it’s not expected to be on for every orbit, just select orbits that favour Moscow.

Sharp Resonance: A Low cost Audio filter from Screwfix; mag loop update

Tony Canning G2NF has an intriguing evening lined up for us next meeting:

Thursday 12th October, Woodford Park Leisure Centre, Woodley, 8pm

Some of you will remember his superb talk on ‘Tricks with Coax’.

He states:

“Given my interest in coax related stuff and various tricks, I have been
playing with an audio filter that can give the user with no IF 200Hz
filter a similar tool in a pile up, and like wise for the SSB operator
an audio notch filter. There is no eltrickery, smoke mirrors or power
supply involved. I think its a great resonance demo, as the relationship to coax filters and tuned circuits is uncanny.

Can be made from house hold items or from Wickes / Screwfix or BnQ etc.

This is not about Audio DSP but my simple efforts do appear to offer
comparable performance to some at a fraction of the price but much more fun building and learning.”

Continuing the theme of sharp resonance, I’m trying to twist G2DD’s arm (Loz) into bring along the coax based magnetic loop antenna he’s been working on as I know a few people would be interested in having a go at making something. Or indeed – if you have been working on one feel free to bring it along and tell us what you’ve been up to!

Refreshments to be served as usual with an increasingly wide selection of biscuits of variable age.

73

John
G4RDC

HF Digital Voice (HF-DV) communications by Dr. Alison Johnston, G8ROG

Dr. Alison Johnston G8ROG will be with us on Thursday 28th September to tell us all about the “high quality” voice communications now possible on HF.

Venue: Woodford Park Sports Centre, Woodley, 8pm, as usual.

Modern digital modulation techniques allow more information to be
exchanged in the few kilohertz of bandwidth we typically use on SSB, for example. This enables near-FM quality.

We will cover a bit of theory, the practicalities of interfacing the
necessary computing equipment (maybe even mobile phones???) with (HF) radios and there will be a demonstration using a couple of HF sets.

For me, HF DV is in the true spirit of amateur radio and is an exciting
development as the technology is open to all. If you wish to experiment with the software, you can. As far as I am aware it is not covered by any patents.

Refreshments to be served as usual.

A huge thankyou to Alison for supporting us. Her knowledge of radio is, shall we say, expansive to say the least, as you may be aware. So if you have related queries I’m sure she would be interested to hear them over a cup of tea.

Looking forward to seeing you there.

73

John
G4RDC

The events leading up to and including the Battle of Britain by Chris Wren MBE

Next meeting is on Thursday 14th September entitled “The events leading up to and including the Battle of Britain by Chris Wren MBE”.

Venue: Woodford Park, Woodley, 8pm.
Refreshments to be served as usual.

Chris is the curator of the WW2 underground bunker and museum at RAF Uxbridge built in 1939 some 60 feet below ground. He will introduce personalities of the time including Douglas Bader who had a flying accident not far from the our very own Woodford Park on the Woodley airfield and the most successful fighter squadron at the time.

Churchill visited the bunker during one confrontation and enquired what reserves we had – the answer was “none”.

I look forward to seeing you there to look back on those perilous times and be inspired by those incredibly brave men and women to who we owe so much.

X8.2 Solar flare

I was on 20m working EU and DX stations using FT8 this afternoon. Just after 16:00, I noticed all signals faded quite markedly and within a minute or two. It was sufficiciently ominous for me to check on http://dx.qsl.net/propagation/index.html and http://www.swpc.noaa.gov/products/goes-x-ray-flux. A couple of minutes later, I saw an X class flare reported. That explained the HF fadeout. About 5 minutes later I saw it was rated as X8.2, only a little weaker than the X9 flare we had on the 6th September. It will be interesting to see if the CME was Earth directed, and if so, how much aurora we’ll get for VHF propogation fun.

David M0DHO

Overdriven audio on FT8, or other data modes

This evening I came across a terrible signal on 15m FT8. The audio from a Cuban station sounded distorted. I won’t name and shame the station. The audio fundamental was about 600Hz, and the waterfall showed strong signals at 1200Hz and 1800Hz matching the 2nd and 3rd harmonic of the audio signal. This caused significant QRM across a significant part of the FT8 segment. Almost certainly the station was overdriving the audio, either causing distortion from their soundcard, and/or distortion in the rig’s modulation chain.

There are several things you can and should do to avoid this, especially when using significant power and/or gain antennas:

  1. Don’t use full output from your soundcard. Set at no more than 50% volume level. Play a pure tone at that level and listen to it on the soundcard output as you adjust the level.
  2. Some rigs, such as the Elecraft K3, have a dedicated data audio input and data mode that removes audio processing like compression or other ALC artifacts. Use this if possible.
  3. For rigs without dedicated data modes, disable all audio compression and set the RF power to a desired amount, say 25W, and start with a low audio signal so the RF power is much lower than that. Then increase the audio level using the soundcard volume and rig audio level  until just below the desired RF output while keeping the sound card level in the range 10% to 50%.
  4. Use an audio fundamental of at least 1400Hz. If necessary, tune the rig to adjust the dial frequency. For example, say you are using FT8 on 20m where the band segment starts at 14.074Mhz. You see a free frequency on the waterfall of 400Hz, and you want to start calling there. If you transmitted a 400Hz tone, then the 2nd, 3rd and 4th harmomics at 800Hz, 1200Hz, and 1600Hz will all be in the audio passband of the rig. Hence the rig will transmit the desired signal at 14.074400, as well as undesired signals at 14.074800, 14.075200, and 14.075600. To avoid this, retune the rig 1kHz lower, to 14.073Mhz and use an audio frequency of 1400Hz. This will generate the same RF for the audio fundamental, but the 2nd and higher audio harmonics will be mostly outside of the rigs audio passband and will be suppressed from the RF output.

Best regards,
David M0DHO

New FT8 data mode versus JT65 and JT9

I’ve been trying JT65 andf JT9 for about 5 weeks now. I thought I’d give FT8 a try. This is a new data mode designed by Joe Taylor, K1JT, and Steven Franke, K9AN. You can find more information at http://www.arrl.org/news/ft8-mode-is-latest-bright-shiny-object-in-amateur-radio-digital-world.

One of the strengths of JT65 and JT9 is that they are very sensitive, JT9 being slightly more so than JT65. However, each transmit or receive period is a minute. So it takes at least 4 minutes to complete a QSO. In many cases, the signal to noise ratio of stations is well above the minimum for a successful decode. So FT8 was designed for that, using 15 second periods rather than 1 minute. So one big advantage is that in many cases you can complete a QSO 4x faster with FT8 than JT65 or JT9.

Unfortunately, there’s a downside. Some JT65 and JT9 decoders, such as those in JTDX, are very good at decoding multiple replies to your CQ, even those on the same frequency (to the nearest Hz). It does this through multiple decoding passes where decoded stong signals are then deducted from the recorded data to expose weaker signals beneath. However, the same does not currently appear to be the case with the FT8 decoder in WSJT-X 1.8.0-rc1. So while you can see a reply on the waterfall, you often get no decode. This is particularly the case if your signal is strong at long distance and attracts multiple replies. Even with single replies, often decode fails despite a visible trace on the waterfall.

For working DX on 80m, I’ve found JT65 and JT9 is much better than FT8, being able to decode signals only just faintly visible on the waterfall. So which data mode you should use depends on what you are trying to achieve. For faster QSOs with decent strength signals where multiple repies are not the norm, then FT8 is a better choice. But for working DX with marginal signals, where your patience might be better rewarded, JT65 and JT9 might be better.

David M0DHO

Website for the Reading And District Amateur Radio Club