[ardf] For 2m: Use HTs or Build a Transmitter?

[Kuon & Dale Hunt]

>For 80m, I'm getting ready to build some ON7YD ATX-80s:
>http://www.qsl.net/on7yd/atx80.htm, which seems to be a "standard".

    Just be aware that there is a glitch in the circuit - if
    you key the transmitter without turning on the oscillator
    the final transistor draws a LOT of current.  There are a
    couple possible fixes, and it needn't be a big problem
    depending on how you hook it up and what controller/options
    you use.


>
>But for 2m, it seems most people use HTs.  I noticed at his website
>(http://www.qsl.net/on7yd/ardfbrew.htm) that ON7YD also has a 2m design
>(http://www.qsl.net/on7yd/atx2.htm).  (That's the only 2m transmitter
>suitable for ARDF that I've found---Are there any others?)
>
>Has anyone had experience with this design?  It appears there is no board
>for it, but I'm up for that....


     If I recall, this used a stock 16.000 MHz crystal on the 9th
     overtone, which puts it a bit above the lower band edge.
     This may or may not be a good frequency in your local area.
     You can try the common crystals for 16.384 MHz instead, which
     puts it around 147.46 MHz, otherwise you probably will need
     to have some crystals custom ground for your desired frequency.

     By the way, if you have questions on the transmitters you can
     email Rik and ask him directly - he came to the first IARU
     Region 2 Championships back in 1999 here in Portland, and has
     been quite supportive of our efforts to develop ARDF.

     The WB2HOL or VE3EMM transmitters might be a better choice,
     both are available on the web.

     But crystal-controlled transmitters have an inherent limitation
     on the ability to change frequency.  If the 2m band is sparsely
     populated in your area, or if there is an established transmitter
     hunting frequency locally, then it isn't such a bad approach.
     But it can represent a substantial investment if you have to
     shift the boxes to another frequency due to interference.

     We usually use 146.565 MHz for hunts here locally, but there are
     some folks across the river in Washington State who hang out
     146.56 simplex and get quite upset when someone uses THEIR
     frequency. If I am going to be operating close to the river
     (and especially from a hilltop) then I can choose a different
     channel.

     When synthesized HTs are $25 at hamfests, it doesn't make
     much sense to build your own crystal controlled transmitter
     from scratch!  (Actually price I paid for working IC2AT.)
     And if the receiver isn't working you can often get a
     good transmitter for even less.  But if you luck onto a
     pile of inexpensive crystal-controlled transmitter boards
     you can put them all on 147.456 MHz for about a buck apiece
     in stock baud-rate crystals while you are deciding on a more
     permanent frequency to buy crystals for.  (And because the
     computer interference is so bad around that frequency,
     there likely is little regular usage.)


>The ARDF R1 rules say 1-to-5W Output Power for 80m and 0.25-to-1W ERP for
>2m.  Is it pretty standard to just use whatever power the HT puts out?
>Several people mentioned doing mods to allow adjusting the finals.  What
>power do you run?

     I almost always run them at low power.  At 5 watts they can
     get pretty warm.  Somewhere in the 0.5 to 1.0 watt range
     seems quite adequate, but even a quarter watt is sufficient.
     With most HTs I get a dead battery pack, remove the innards,
     and buid a regulator into the case.  I can adjust the output
     power in most cases by reducing the voltage to the radio
     (within reason) without affecting the synthesizer (which is
     probably on its own regulator.)  You only need to hear the
     transmitter from 2 to 3 miles away, and that doesn't take
     too much power unless you put it in a gully.

     On 80m the higher power levels may be needed with inefficient
     antennas and/or primitive receivers.  I've heard my 1 watt
     signal at a gas station in an industrial area 7 miles away,
     but the Chinese PJ-80 or Ron Graham RX-4 may not be able to
     hear it that far, and the extra power will help folks
     who are using such receivers.


>
>The R1 rules also specify 144.5 to 144.8 MHz.  The text for the ATX-2
>tranmitter only mentions 144.06 to 144.09.  I'm assuming that's an
>intermediate step, but he doesn't say anything else.


    I think Rik Strubbe ON7YD was trying to make due with stock
    frequency crystals, which is why he ended up at the bottom
    of the band.  At one point the R1 rules read 144.5 to 145.8,
    basically between the weak signal frequencies at the bottom
    of the band and the satellite band at the top.  (Their band
    only goes up to 146 MHz.)

    Frequency choice is one of the biggest problems we face,
    particularly on 2m.  Folks from Region 1 (and to some
    extent Region 3) may have equipment that only tunes up to
    146 MHz.  (Some of the Japanese Mizuho receivers have an
    internal dip jumper to cover 146 - 148, and the Altai
    receivers will tune up to about 146.6 with a fresh 9V
    battery.)  But for local practices the simplex frequencies
    from 146.4 - 146.6 and 147.4 - 147.6 are probably some of
    the best choices, especially if the 145.5 - 145.8 and
    144.9 - 145.1 ranges are filled with packet as they often
    are in populated areas.  All depends on the local band
    plan and usage, of course.

    This is another advantage of synthesized transmitters - you
    can adjust them to local conditions wherever you are
    setting the course.

    For practice sessions there is no need to worry about the
    Region 1 frequency limitations.  (I think the latest rules
    simply say, "in accordance with local band plans" or
    something like that.)  If you are putting on a major event
    and expect folks from Region 1, my suggestion is to
    contact the owner of one of a repeater in the 145 MHz
    range and ask if they can take the repeater off the air
    for a few hours (especially if it is mid-day on a week
    day.)  That gives you two channels, one for the
    hidden transmitters and one for the homing beacon.


      - Dale WB6BYU


---
[This E-mail Scanned for viruses by Onlinemac.com]