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Focus on VHF and Above 15 July 2018
Audio version here
In the tutorials that we have broadcast over the last couple of weeks, we have discussed just about everything there is to know to get started on digital modes.
We have set everything up, and we are ready to go live with digital modes. Now the question is, who transmits on the first period and who transmits on the second period and which mode to use.
There may be differing views when looking at the standard for timing, but old habits never die.
If you stay in an area where there are many active stations you don’t want to transmit when your neighbors are on receive, so when bands do open, prevent issues by deciding what period is going to be used in your crowded area and stick to it.
On HF, it is easy because you just click on the waterfall and the software will do the period changes automatically if you answer stations. If you have an omni-directional area you need to listen for local stations before you start transmitting in their receive period.
On VHF and Above this does become a problem because firstly the signals are not as visible and audible as on HF. If you just want to call to see who answers, then follow the following rule:
If your antenna is pointing North or West then use the first period or as we also know it as the odd period.
If you point South or East then use the second period or even period as some of us might call it.
Following this rule will also help you when arranging a sked.
If we are operating on CW or SSB then no software is involved and you transmit according to the period rule mentioned above. For CW then you transmit for a period of two and a half minutes and again listen for a period of two and a half minutes. For SSB or voice as some of us might may call it you transmit for one minute and listen for one minute.
Now we know when to transmit and when to listen. So now in which direction do I transmit?
There are in some modes Hot A and Hot B highlighted and you don’t understand why it changes some times.
We must now look at our position and the direction in which we want to operate and whether it is in the morning or the afternoon. Normally the Hot A or Hot B changes around midday when using Scatter modes and direct if using Tropo modes. So we realize the sun must have a role to play in Scatter communication. So, if we want to use Meteor Scatter then in the mornings you always want to work a direction pointing southwards away from the sun so that there is less sun noise, or in the afternoon the northerly direction as the sun is then moving behind or far away from the scatter point.
Why Hot A or Hot B?
Looking at an antenna radiation pattern and the fact that doing Meteor Scatter is based on a reflection of a signal from an ionized portion of the atmosphere that scatters in many directions both stations want to actually point to the same area where a scatter signal might be produced.
In the Southern Hemisphere, with the sun rising you would rather point to a common point away from any possible noise from the sun which means that you point more south of the station you want to work, thus creating a common reflection area.
In the afternoon the sun will be more to the West and then you can utilize a Northern common point between the stations.
When you want to do Lightning Scatter then of course you would look at the live weather maps on the Internet and look for a lighting storm showing not directly between you and the other station but at an angle to be able to utilize the ionization reflector created by the lightning storm. Lightning striking upwards will give longer distance coverage of the reflected signal.
Backscatter is also very interesting. Looking at rain storms very far to the North or South from you, you can use that as a reflector too. When operating on 6m and pointing North and you are staying in the Western part of Southern Africa you will hear backscatter signals from ZS6 call area coming back to you. On 2m the same is possible and at times we have a phenomenon on the West Coast where backscatter signals are received at much stronger levels than direct signals.
Now, when we want to use the Tropo modes then we point straight to the station we want to work.
How do I know what propagation is to be used?
Meteor Scatter bursts will be a burst that varies between a few milliseconds to a second or two. Backscatter will be audible but because you are pointing away from the station you will hear the call sign and there might be flutter on the signal at times. Tropo signals tend to have heavy QSB which is deep fading cycles on the audio as well as some distortion on the audio as well.
The software used for digital modes does cater for these variations already and you must just select the correct mode to work your DX call or that far station.
Thank you, Pieter V51PJ for the information provided for this weeks tutorial.
Let us now look at some news about VHF and Above bands...
Pieter, V51PJ reports that he is still trying to get feedback from St Helena Island as to what the location of the beacon be and what power will be available. Pieter is also still busy building and antenna for the St Helena Beacon. It is going to be a Lambda antenna with 50 Ohm impedance, omni-directional and horizontally polarised.
The conditions in the Northern Hemisphere is still outstanding for Sporadic E and there are daily openings on 2m and 6m. On Thursday morning there were openings between the US and Canada and D4C on Cape Verde was heard by EA8 stations on the Canary Islands.
There are also reports that a Canadian broadcaster transmitting on 88.5 MHz was heard across the North Atlantic Ocean. When the 6m activity started picking up, the Maximum Usable Frequency reached 109 MHz at times.
Pieter reports that there were even Sporadic E openings in South America and asks “Why have we not experienced any opening locally? Are we not active enough?”
The seasons are busy changing and the Sporadic E season for the Southern Hemisphere is creeping closer.
Andre, ZS3AG in Kimberley heard the control tower of Cape Town Airport with his vertical Yagi on the 12th of July. He tried to trigger repeaters in the ZS1 call area but was not successful. The antennas at Cape Town Airport are designed to be omni-directional and to have gain. I wonder how much power is used.
The East Coast and West Coast groups still have their skeds although there has been little activity.
Peter, ZS2ABF reports: Dave ZS5DJ,and I contacted each other direct along the Coast last Monday 9/07/18 over a distance of 320 KM. The Hepburn charts show very poor, to very bad, and nil propagation along our South East Coast for the next week.
We were only able to make contact via Morse Code. I do not fully understand Morse, and my bad hearing distorts the sounds, I use my Smart Phone to send Morse to Dave, and he replies in Morse. This method is used during predicted poor conditions just to get us started. Then we both change over to voice to have a QSO.
Last Monday, Dave could just hear my voice, but I could not hear his voice, but I recognized that it was him calling me.
We will both be watching the Hepburn Charts, and if there are any openings, we will come up on frequency, 144.300 MHz USB,Horizontal.
Old habits never die and amateurs remain friends even though the band conditions are poor. Let us blame the cold and not the amateur spirit when the bands are dead.
A number of beacons are being heard, however we do not know who heard which beacons and was it on Meteor Scatter or Tropo.
It also seems as if the 23cm group is growing.
Did you know that FT8 now has a chat mode? You can now chat like you used to on RTTY and PSK31.
We have previously reported on the TEC or Total Electron Count where ionisation is measured by monitoring and the distortion of the GPS signals. There are also maps on the NASA JPL website where you can get near live updates on the TEC. Apparently a new more accurate system is about to be tested when a new UHF GPS satellite will be launched. A very accurate receiver is required to be able to monitor the changes in the frequency and to be able to forward these variations to the research team in the US.
Amateurs may be able to help and apparently the SKA team have already indicated that they will participate as well. How accurate is your UHF receiver and can you improve the accuracy?
We believe and trust that the Tutorials broadcast on Amateur Radio Today and also placed on the SARL homepage will encourage someone to become active or even don the pioneering shoes to explore digital modes on long distance FM with 30 Watt maximum and good antennas.
Thank you, Pieter V51PJ for these interesting news snippets. Great to have you online again.
Please send your news snippets and information about activities on VHF and Above including information for the tutorial to email@example.com.
The text version of Focus on VHF and Above is available on the SARL home page as well as this audio file. Focus on VHF and above is edited and presented for Amateur Radio Today by Brian Jacobs ZS6YZ.