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Bredhurst Receiving and Transmitting Society

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Using VHF

The other day a (relatively) recently successful M3 candidate mentioned that whilst information on the band plan showed that there were various frequencies allocated that it was not until he started to operate that he fully appreciated what was what.

He commented further that he would like to see a page on the web site that helped to give more information.

This page has been written to provide some more information.

Firstly Antenna polarization- FM vertical SSB horizontal :

No where in the syllabus does it make any reference to polarization of antennas relative to the mode / frequency that is being used.

When you are on the 2m band the polarization of the Antenna for FM use is vertical and for SSB use is horizontal.

To mix up the polarization and use vertical when the other station is using horizontal will result in great attenuation of the signal to such an extent other than very close stations you may not be able to hear.

Secondly the Band Plan and the Calling Channel

If you look at the Band plan for 145MHz (2m) you will see the frequency 145.500 against it you will see V40 and FM calling channel.

The V40 means channel 40 and the calling channel means that is where you tune your rig onto so that you can listen to the calling channel for stations or where you call CQ your self.

If the above sound familiar it is as it has been copied from another part of the course.

Even today the channel numbering such as V40 has not been universally adopted as this is the numbering that has been brought in to give double the number of channels on the FM segment of this band with 12.5kHz channel spacing rather than the older 25kHz channel spacing. If you look at the band plan you will see channels from V16 to V46 (which is in fact shown with 25kHz channel spacing but the "V" numbering gives you the hint that other channels exist in between the other.

To equate those numbers to the channels that older users of the band know you have to divide the channel number by two. Thus V40 become channel 20, V32 becomes channel 16 and so on.

The calling channel know to many is thus thought of as channel 20. When someone suggested that you go up one channel from 20 which was also called "S20" this will mean not going up to 145.5125MhZ but going to 145.525MHz - unless you have a set with a narrow filter for 12.5kHz and thus will be able to cope with the narrow step between band and also not spread out over the adjacent channels.

This will sound most confusing to most of you so it will be best to sit down with a pencil and paper and work it out, or take a look at the graphic below.

Frequency animation

Do not use frequencies above 145.800MHz as that is the satellite band also do not use 145.200MHz and 145.225Mhz as these are reserved for emergency use only.

You will also see from looking at the Band plan more information about how the band is used so it is recommended that you take your time to look through it and anything that you do not "fully" understand ask your lead instructor for more interpretation.

When operating SSB

This is rather different from operating FM as the calling channel is 144.300MHz. Like FM you need to move off the calling channel and here the general rules of thumb is to more 25kHz or more up or down or away from other signals. To fail to do this will mean that you QSO will be interfered with by another and also you will interfere with the other QSO.

Thirdly joining an existing QSO

If you have already read through the "Using HF section" then some of this may seem familiar to you but joining a QSO on VHF is different from joining a QSO on HF.

If you are tuning across the bands and hear an interesting QSO in progress please do not think that you can boldly just call in between overs. Think of conversation like any other between two persons. If you think that you have something of interest to say wait until there is perhaps a pause in the conversation and then call in using -

"Break please this is ........( your callsign)

Say no more. If the stations wish to acknowledge you then they will but if they choose to ignore you then that is a sad reflection on them but it does happen.

So when called in to the QSO make certain that what you have to say is totally relevant to their conversation and perhaps it is best to start with

.....(their callsign) this is ..... (your callsign) I thought that you might like to know that in .... (give your location) your signal reports are to .... (callsign and give RST) and to ..... (callsign and give RST) and that ......... (give a very short comment on their previous QSO topic).

Then give the transmission back to the station who gave it to you.

So back to ..... (Callsign) this is .......(your callsign).

You will have then given interesting information to them in the form of the accepted report of RST and a short snippet of information. If the station swish to continue with you in the QSO then transmission will be again given to you but do not expect to be called in again.


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