VKs, Weston Electronics (Sydney)! Transceiver

Discussion in 'Wireless & RF Design' started by Art, Feb 26, 2014.

  1. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    Hi Guys,
    I expected the transmitter to be bung but it seem the problem is audio.

    With a top speed of 10MHz :D this Radio Telephone will "Ahem" Propagate!
    [​IMG]

    and a question.. Why don't we throw all UHF & VHF transceivers in the bin,
    and just use AM/SSB.
    I don't understand the excitement of using other machines on hills that are more
    powerful than the initiating machine to communicate long distances.
    Could someone please explain it to me?
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    am and ssb can be used on vhf and uhf also. the question seems to be " why not use short wave instead of vhf or uhf"? vhf and uhf are usefull when you dont need long distances, and when people in other countries a long way away would interfere with local comunications. Since there are a fixed number of frequencies available on short wave, how many could use it at the same time? vhf and uhf have a lot more frequencies available, and since the range is shorter, weveral people could use the same frequency if they were a distance apart.
     
  3. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
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    In my country (Aus) you can only transmit with AM below a certain frequency which I think would be around 30MHz.

    While I understand that, I still don't understand the "excitement" over using external machinery, more powerful than yours to do the real communication.
    We are doing that right now over the internet, with servers everywhere sending and retrieving this text data, and also with telephony.

    I brought this one back today, good receiving on all bands including AM broadcast :)
    I just don't have anything to load the antenna for transmission, but it is my feeling everything is fine.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
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    ham radio operators are still using am, although not as much now as it was used before ssb came along and proved its supererority. the external machinery you are mentioning is probably repeaters, which are used to extend the range of mobiles and handhelds for vhf and uhf. it all has its uses, even the internet has its uses, I suppose. there are many modes allowed on ham radio, and these days the liscense isnt as hard to get, they did away with the morse code requirement quite a long time ago.
    cliff
     
  5. vk6zgo

    Active Member

    Jul 21, 2012
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    AM is not very common above 30MHz,but is used for Aviation around 120MHz or so.
    It is a legal mode on all Amateur Radio Bands,but is not often used.

    SSB has the advantage of narrower band occupancy,& more efficient use of transmitter power.
    Where there are fairly narrow allocations with fixed channels like in Flying Doctor Radio,& the HF network used by 4WD users in the Outback,these become very attractive points.

    Within cities,VHF with Repeaters or remote bases means that the mobile device can be smaller,with a less efficient antenna than would otherwise be the case.
    HF would mean larger vehicle antennas,& normally,larger radios.----have you seen the big antennas on country Cop cars?

    There are only a finite number of channels allocated to each service,so multiple use of one channel becomes necessary.

    FM exhibits a characteristic known as the "capture effect",where the receiver responds to the stronger signal.
    With AM,there would be constant heterodyne squeals on a busy channel.
    Back in the 1970s,the CB "AM" call channel was like that.

    Even with SSB,you would still hear interference from other stations.

    The combination of "capture effect" & VHF/UHF also allows for the reuse of channels in more nearly adjacent geographical areas.

    Hams use Repeaters in a similar way,but they also use Simplex transmissions,as well as accessing distant Repeaters.

    For instance in WA,it is not unusual to access country 2m Repeaters hundreds of km away during "Summer Tropo ducting".

    Another point against Simplex HF AM/SSB for normal Business & Commercial use,is that the coverage is extremely variable,not just by season as with VHF/UHF,but hourly or less during the day.

    If,say,I wanted to talk to someone in the next suburb on 28MHz,I might be OK for a while then he might be in my "skip zone" & barely readable,but I may be able to work Japan with ease!

    These problems were solved in the past (& still are) for Small Ships, Military,Firefighters & the like,by having several HF Bands on their radios,but that would be difficult for taxidrivers,etc.
    (Even the old AM taxi radios were channelized VHF)
     
  6. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    By the way,Art,you probably already know this,but I've heard of one Ham who got caught out.

    The tuning control on that Weston isn't a transmit VFO--it's just for the receiver.
    The transmitter has a number of crystal locked channels,so you need the correct crystals to give you a number of spot frequencies.

    If your radio has the original marine crystals in it,you could innocently put out an illegal transmission.

    The idea of the tunable receiver is that Coastal Radio stations often operated "split".
    You needed a transmit crystal for their receive frequency,but you could tune the receiver to their transmit one.

    It also meant you didn't have to buy twice as many crystals.

    Of course,a bonus was,at sea,you could listen to MF & HF Broadcasts for entertainment.
     
  7. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
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    Interesting, and thanks :) All except for the bad news about the transmitter!
    At a later stage, perhaps one of the crystals could be replaced with a digital circuit that oscillates,
    but of course that would be modifying a transmitter, which would be some time in the future for me.
     
  8. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
  9. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
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    With all respect, I'm not sure I believe you! :D
    Or will at least take some further explanation.

    There are two rows of crystal sockets of five each,
    one of which is fully populated, while the other row contains three Xtals.
    Yet there are only five selectable channels on the channel rotary switch.

    [​IMG]

    This could be explained by there being five selectable channels on HF1, and another five on HF2,
    so that each row of Xtals is selected by the band selector.

    But then what I'd find inconsistent is that you can power the unit up without Xtal lock selected,
    and on either HF band the RF output valve section is powered with valve filaments lit.

    [​IMG]

    Then if I move the switch to Xtal lock, I loose reception of whatever the tuning gang was tuned to, and hear static.
     
  10. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,363
    Please note that you will need a license to operate the transmitter.
     
  11. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
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    Not to mention something to load the antenna socket, and more than a battery I borrowed from my UPS :D

    Of course, just waiting for my trainer to turn up at club again.
    Meanwhile I can transmit here in the presence of a licensed operator
    using the training prefix followed by his sign.

    I already have a UHF/VHF handheld for air time training.
     
  12. vk6zgo

    Active Member

    Jul 21, 2012
    677
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    That sounds suspiciously like Weston provided for crystal locking of the receiver,so it's a bit more sophisticated than I thought.

    It looks like you have 5 xtal locked transmit frequencies & 3 out of a possible 5 xtal locked receive frequencies.

    As the Tx section is always xtal locked,there is no need to switch it to that state,but the Rx is tunable,so when you switch it to Xtal lock,your tunable local oscillator is replace by the xtal oscillator.

    Do you have a dummy load?

    If so,you could find out what output frequency corresponds with which Tx xtal.

    They are probably at the output frequency,but maybe not.

    The Rx ones will in that case,have a frequency offset by the frequency of the IF.

    PS: I went Googling to see if I could find some more info on the Weston.

    All I could find was this: http://www.macnaughtonart.com/40am.htm

    As you will see,there are quite a few AM enthusiasts around,& one actually has (among other stuff) the same radio you have.---He's a VK4,too!
     
    Last edited: Mar 1, 2014
  13. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    Ok I get you.. That does limit it with regard to usability without modification though.

    Nice site, I will look a little further into it. It's hard to find much info on a lot of old radio stuff.
     
  14. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
    Ok, I found it, pity he isn't picturing it, but I suppose it's worth trying to get hold of him,
    and thanks again I will listen at the scheduled time with a SW receiver known to be sensitive.
     
  15. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    I followed up and it appears you're correct, which is the way it should work,
    just not the way I wanted it to be.

    [​IMG]

    Made a mistake, there are only four Xtals in one row or the other (Rx/Tx).
    Where there are pairs they are 455 Khz apart which of course sounds like the IF.
    THey are outside the range of foundation licence, even if not still allocated.
     
    Last edited: Mar 1, 2014
  16. vk6zgo

    Active Member

    Jul 21, 2012
    677
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    Bummer!

    You could probably get 80m xtals that would work.
    It only really needs Tx xtals,as you could use the tunable Rx.(may be a bit "drifty",but probably not too much problem with AM)

    USA NTSC colour carrier xtals are within VK allocation,& are often used by Hams.
    Sometimes valve oscillator circuits provide too much drive to the xtal & may cook the smaller packages.,so that may be a problem.

    If you had an advanced licence,you could probably tune it down to 160m.
    (Lots of AM there in the ES-----zilch in VK6)

    ACMA may see fitting new xtals as "modifications",so you may need to pick up the Standard Licence.

    Apparently,it isn't a hard upgrade.
     
  17. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
    I found these on eBay which happens to be the frequency the "AMers" (that group you linked me to earlier)
    meet up on Wed and saturday mornings.
    http://www.ebay.com/itm/FT-243-40-M...509?pt=LH_DefaultDomain_0&hash=item485a4d2cdd
    So long as 7125 kHz (7.125 MHz) Tx Xtal freq is the actual Tx freq for the radio.

    I could use a modern PLL radio as backup for the receive,
    and will listen in next time just to make sure they are still active.

    I'll have to look into the rules with my trainer regarding swapping crystals.
    I think it's a bit tight if it is not allowed to swap crystals, or insert a new one.
    It's possible someone could have purchased the radio that way.


     
    Last edited: Mar 1, 2014
  18. debe

    Well-Known Member

    Sep 21, 2010
    947
    184
    Heres the Owners manual ( I used to repair HF marine stuff 30Yrs ago) Will try & scan the Circuit diagrams later as they are quite large.
     
  19. debe

    Well-Known Member

    Sep 21, 2010
    947
    184
    Rest of the manual..
     
    Last edited: Mar 2, 2014
  20. debe

    Well-Known Member

    Sep 21, 2010
    947
    184
    Circuit of the Marina 60
     
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