Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Opinions please...  (Read 2139 times)
KE6PKJ
Member

Posts: 256




Ignore
« on: April 20, 2005, 12:26:11 PM »

I was thinking of designing some fox transmitters/tracking beacons for the various ham bands from 50 through 928 mhz (or higher), and would like to get everyone's thoughts and opinions. This would be a "blue sky" type engineering project so I'd like to hear what people really want. Some of my own questions are:
 
1. Size, does it matter? Weight, ultra miniature?
 
2. Enclosed case, or open circuit board?

3. How much RF output power? Adjustable?

4. DC power source? Should it run from a single AA cell? 12 volts? Or something in between?

5. On/Off keying? FSK? Tone modulated, Or FM for voice?

6. If it's FM, should it be Line level, Mic level, an onboard Voice Recorder Chip? Any or all combinations?

7. Any particular frequency or bands?

8. Should it be radio commandable, to remotely turn it on or off?

9. Connections to the unit? Fixed connectors? Flying leads? Solder pads only? Or some combination?

10. And anything else anyone can think of?
Logged
WB6BYU
Member

Posts: 13287




Ignore
« Reply #1 on: April 27, 2005, 04:02:36 PM »

> I was thinking of designing some fox transmitters/tracking beacons for
> the various ham bands from 50 through 928 mhz (or higher), and would
> like to get everyone's thoughts and opinions. This would be a "blue sky"
> type engineering project so I'd like to hear what people really want.

   First, I presume you have researched what is currently available.
   Here are some existing designs that may give some ideas:
   http://homepage.ntlworld.com/daburleigh/atx80boxs.jpg
   http://homepage.ntlworld.com/daburleigh/atx80pcbs.jpg
   http://www.users.bigpond.net.au/vk3yng/foxhunt/80m_fox_or/80m-fox-or-tx.html
    http://www.silcom.com/~pelican2/PicoDopp/MICROHUNT.htm
    http://www.marecek.sky.cz/
    http://www.qsl.net/ve2emm/pic-projects/mt525fox/mfx525-e.html
    (KE6HTS has some low power transmitters similar to this, but
     without the final amplifier.)

  Or for controllers to plug into existing transmitters:
    http://www.byonics.com/piccon/
    http://www.qsl.net/ve2emm/pic-projects/mtfoxctr/mtl_fox.html

   Also WB8WFK (wb8wfk@worldnet.att.net) is working on a set that
   includes AM or FM modulation and some other interesting features

Besides the frequency range, it may be good to consider why any of
these would not work for your needs.

> Some of my own questions are:

> 1. Size, does it matter? Weight, ultra miniature?

I certainly like to use small transmitters.  I have a set of the
small 2m ones from KE6HTS (about 30mW, and the board is half the
size of a 9V battery) and have built a few of my own over the
years.  These are much more convenient than my ammo boxes when I
want to do a quick demo or test some equipment, also easier to
carry a set of 5 of them at time when I set them out.  For
longer hunts, they can be put in a box with a larger battery
(and an amp if needed).  Because such transmitters are often
very specific to the particular hunt circumstances, the best
approach seems to provide the parts that others can put together
as needed.



> 2. Enclosed case, or open circuit board?

Open circuit board, but designed to fit a commonly-available case.
(Or available in the case as an option.)


> 3. How much RF output power? Adjustable?

Something around 10 to 20mW is a good level when hunters are using
body shielding to find it.  Can be heard a couple hundred yards away
across a park, but still huntable reasonably close.  This is a great
way to get people started with transmitter hunting.  And for many
situations (balloon launches, practice sessions, hunts in small
areas) this is plenty of power and batteries last a long time.

The next level up I find myself using is around 1 watt (often an
HT.)  This has been enough for most of our county-wide 2m hunts
(though some could have used a bit more power!)  I have some of
the Hamtronics synthesized transmitter boards and it is difficult
to turn the power DOWN to this level without a significant increase
in the level of spurious outputs.

So an exciter board at, say, 20mW and an amp board that would bump
that up to 1 to 2 watts is a good start.  Then folks can add an HT
amp if they need more power... or just use their mobile rig with a
noisemaker plugged into the mic jack.


> 4. DC power source? Should it run from a single AA cell? 12 volts?
> Or something in between?

  Design the exciter to run from +5 volts through a low drop-out
  regulator, then it will work from 6 to 15 volts input.  For
  small size, this could be a 9V battery or a pair of lithium camera
  batteries.  Higher power will run from the main battery rather than
  through the regulator, allowing the use of 12V gel cells or packs
  of rechargable or alkaline cells.


> 5. On/Off keying? FSK? Tone modulated, Or FM for voice?
> 6. If it's FM, should it be Line level, Mic level, an onboard
> Voice Recorder Chip? Any or all combinations?

  One thing you might consider is making the audio generator unit
  separate from the transmitter itself.  Circuits like the PicCon
  are popular because they can be plugged into the mic jack of any
  radio - this is usually a less-expensive option than buying a
  transmitter just for hiding.  I often see old HTs like the IC2AT
  available at a hamfest in working order for $25, and it is
  difficult to build a synthesized transmitter for that price.
  Tone modulation (with programmable sequences) makes the transmitter
  distinctive to the hunters.  A voice recorder chip provides a
  simple way to record a callsign (and various other announcements
  and/or annoying noises) without the bother of programming CW.
  I like having the option to record two different sets of audio,
  with one repeating for most of the time and the second played at
  the end of a transmission for the ID.

  The modulation will depend on the purpose of the transmitter.  Most
  VHF/UHF hunts will be on FM, so that is a common option.  The
  international ARDF hunts specify AM tone modulation with a keyed
  carrier.  This can be accomplished with a switching transistor in
  the power lead to the final amp for both keying and modulation.

  The 80m transmitters used for ARDF all use CW.

  The Montreal Controllers by VE2EMM have outputs for audio, PTT,
  and key.  (PTT is on for 1 minute, key goes on and off with the
  tone keying.)  I use a 5-pin DIP header to add ground and a spare
  pin that can carry receiver audio back to the controller (because
  I used the same cables I had made for my PK232.)

> 7. Any particular frequency or bands?

   International ARDF uses 2m and 80m.  The British like 160m, and
   10m used to be popular for evening hunts when the band tended
   to be closed.  2m is probably the most common band for hunting,
   but 6m, 220 and 440 are also used at times.  And some folks hunt
   ATV on 1215 MHz.  There may be other uses, such as telemetry or
   beacons that you might want to consider in the design.


> 8. Should it be radio commandable, to remotely turn it on or off?

   This is easy if you have an HT for the transmitter, since it
   also provides receive capability.  But if you are building the
   transmitter, you would have to build an additional receiver to
   have this ability.

   A simpler approach is to have a timed turn-on delay.  Most of
   my controllers have this option but I've never used it, as I
   never trust that it is really set to come on properly.  So I
   use a toggle switch to disable the transmitter while letting
   the controller run to maintain timing.  After setting the
   transmitter in place I turn it on.  Seems to work for me.

> 9. Connections to the unit? Fixed connectors? Flying leads? Solder pads only? Or some combination?


    Connectors on the box, solder pads on the circuit board. Or
    perhaps a header on 0.1" spacing so wires can be soldered
    into individual holes, or a header can be used with a connector.
    I like the connectors for being able to swap parts around when
    something fails, but reliability is better with soldered wires.

> 10. And anything else anyone can think of?
 
    FREQUENCY AGILITY:  crystal control is good for simple rigs, but
    the cost can get excessive if you can't use standard frequencies.
    Colorburst crystals have become the norm on 80m, but a second
    frequency for the finish beacon sometimes takes some scrounging
    through old junkboxes to find a suitable crystal.  There are a lot
    of baud-rate crystal frequencies that multiply up to 147.456 MHz,
    but any other frequency in the 2m band is more difficult to
    find.  (Having an audio source that can be plugged into an existing
    radio simplifies this greatly, since most folks already have a
    synthesized radio for the frequency they are using.)

    Unfortuantly there isn't a common 2m frequency for the whole US.  
    I give talks and demos in different areas, and it is hard to find
    a frequency that is acceptable in this corner of the state.  So
    some type of frequency agility is required.  The ICS 525 chips
    used by VE2EMM and KE6HTS are a good start, as they can be set
    by DIP switches or soldered jumpers.  The programming is a bit
    quirky, so better done on the workbench rather than in the field.
    The next step up is a full-fledged synthesizer with keypad entry
    or digital switches.

    Perhaps a reasonable alternative would be the "programmable
    oscillator" modules available now from many standard suppliers.
    These are the usual "canned" oscillator modules programmed to
    your desired frequency (well, within 15kHz or so).  These are
    relatively inexpensive (maybe $5 or so?) so it would be possible
    to have a couple options in your pocket.  They are usually
    available up to 100 or 125 MHz and have a pretty good odd
    harmonic output: if you order one for a odd sub-harmonic of
    your frequency, then a double-tuned circuit should be able
    to extract the desired frequency and pass it to the following
    amplifier stage.  This might be a good solution to building a
    circuit board that would work on multiple bands.  The oscillator
    would be in a socket, then the filter and following amplifier
    (perhaps an MMIC) would be chosen for the desired band.

    Actually the ICS525 would probably be even better, since it will
    generate a wide range of frequencies with a single non-critical
    crystal between 5 and 20 MHz.  Rubbering the crystal provides
    fine-tuning of the output frequency, an option that is not
    available with the canned oscillators.  The board could be made
    to permit either DIP switches or soldered jumpers, depending
    on how often the frequency was going to be changed.  Since
    this also puts out a square wave it should be easy to extract
    harmonics on various bands (perhaps with an active multiplier
    on the higher bands.)  A single board design should work
    from HF up to at least 440 and maybe higher.

    The other option would be to design a synthesizer that operates
    over a smaller range of frequencies and beat it against a crystal
    oscillator to put it in the desired frequency range, or the
    synthesizer could be designed so different crystals could be
    used to set the output frequency range.  You still may need
    some multipliers for the higher bands, but you should be able
    to standardize the board design.


    ON/OFF timing.   Most transmitter hunts I've been on haven't left
    the transmitter on continuously.  This saves battery power (and
    heating in the final), as well as giving those who get lost or
    stuck in a ditch a chance to call for help.  Having a variable
    ON and OFF times would be good, whether it is set by trimpots
    on a 555 timer or digitally programmed in a microcontroller.

    SYNCHRONIZATION.  The ARDF competitions typically use a set of
    5 transmitters on the same frequency, each of which transmits
    for one minute and is off for 4 while the others cycle.  And
    for practice sessions it is helpful to be able to adjust the
    number of transmitters in a cycle.  (There are also standard
    CW sequences for each transmitter in the cycle.)  Generally
    these are synchronized before being hidden, and should be able
    to maintain synchronization within a couple seconds over 8 hours
    (though I know of some folks who would like to set them out
    the day before and have them maintain synchronization for 24
    hours or more.)

    REFINEMENTS.  These are some clever featuers that OK2BWN used on
    the transmitters at the last World ARDF Championships.  First was
    an extra tone element added at the end of each transmitter cycle
    when the battery voltage was above some threshold.  If this tone
    disappeared, then you had about 15 minutes of battery life left,
    so you'd better hurry and change it.  The transmitters had internal
    batteries as well as external packs, so it was possible to change
    the external pack while the transmitter was running without
    interupting the synchronization.  Jiri's transmitters also were
    capable of operating on both 2m and 80m, and used a DIN plug
    for both antenna connector and bandswitch simulataneously.  So
    the plug for an 80m antenna was wired to tell the transmitter
    to transmit on 80m.  With no antenna plugged in, the transmitter
    didn't transmit, through it kept synchronization and programming.
    So switching to a backup transmitter was simply a matter of
    moving the antenna plug from one to the other, and there was no
    danger of transmitting into the wrong type of antenna.


Hope this helps to give you some ideas.  And if you
come up with a design, I may be interested in some.

- Dale WB6BYU
 
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!