[Lowfer] Ultimate LOWFER Transmitter?

Tue, 12 Mar 2002 21:39:50 -0600

Maybe just offer a kit of parts for a reasonable price. I homebrew most of
my equipment to keep costs down.

Mike>WE0H
http://www.geocities.com/we0h/index.html

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Mark W1EOF
Sent: Tuesday, March 12, 2002 2:02 PM
To: [email protected]
Subject: RE: [Lowfer] Ultimate LOWFER Transmitter?

Jon,

As someone who has had some experience gaining FCC approval some years ago,
I can't imagine him recovering his cost with relatively small market size of
Lowfers. I also believe a high percentage of that small market are people
who actually prefer to homebrew their own equipment.

If one really had a notion to help this group, I would think a better
approach would be to create a good source of parts and kits applicable to
experimentation. At any rate I would not think that it's going to be a
money-maker.

Also as John pointed out many of the ideas you put forth don't really make
sense when thought-through. For instance an FCC approved device in PCB form
(without an enclosure).

Anyway.... assuming that you are not a troll, or do not have any ulterior
motives and are being 100% honest, I'd suggest you and your buddy re-think
this venture. IMHO :-)

73,

Mark W1EOF

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of W2MXW
> Sent: Tuesday, March 12, 2002 1:20 AM
> To: [email protected]
> Subject: [Lowfer] Ultimate LOWFER Transmitter?
>
>
> Hi everyone,
>
> A Part 15 'colleague' of mine, Keith Hamilton of Hamilton Printed Circuit
> Board (PCB) Design, who manufactures FCC Certified Part 15 100 mW AM
> broadcast transmitters recently expressed the idea that he would like to
> manufacture a LOWFER transmitter based on his very successful AM
> transmitter design. Basically he would (within reason) like to make The
> Ultimate LF Transmitter.
> His decision to do this would be predicated on being able to sell enough
> units to at least recoup the cost of FCC Certification (Type Acceptance)
> and so I am presenting this here so that you all might comment on
> what you
> would like to see in an LF transmitter that you would consider
> purchasing.
> Remember, unlike any other presently-available commercially-made LF
> transmitter this unit would be fully FCC Certified, which gives a measure
> of legal security over non-Certified equipment in that being tested for
> compliance it would be most likely to pass muster without
> nitpicking in the
> event of an FCC inspection.
> Of course aside from legal issues it would be a full-featured,
> plug-n-play
> standalone LF unit which in and of itself would be desirable to many
> operators I'm sure.
> The present features available on the current AM unit are as follows (not
> all of them would perhaps carry over to an LF unit and the LF unit we
> expect will have others not listed here - that is what we want
> your input for):
>
> 1. AM capability of 120% upward modulation (AM capability would remain in
> the LF setup because we anticipate some broadcast applications
> for this as
> well as LOWFER use, and because there isn't any other AM-capable LF rig
> besides the North Country kit available "out there").
> Modulation is via transformer - as the present units are designed
> for Part
> 15.219 100 milliwatt use even though the trans. is purposely
> over-rated at
> 400 mW for extra safety factor its value would need to be
> increased for the
> 1 watt input level.
> 2. On-board final tank/antenna tuning network (originally designed to
> resonate with the 8-1/2 foot whip antennas we use in AM service) which
> consists of an Amidon T-106-2 toroid RF transformer (I'm thinking
> this core
> would have to be changed to #3 material for LF if this design were
> desired??) which is multi-tapped on its secondary with the taps
> shunt-jumper selectable for tuning; the secondary is hi-Z naturally for
> tuning the whip; the primary is fixed at 4 turns (although he
> could make it
> tapped and jumper-selectable as well) and is lo-Z for matching to the
> paralleled MOSFET finals. Fine tuning is accomplished with a 10
> pF sapphire
> dielectric high-voltage trimmer across the coil secondary to ground. I
> suspect in an LF version this value would need to be made roughly
> up to 100
> pF or so, perhaps using a parallel bank of fixed high voltage NPO ceramic
> caps which are jumper selectable. Something like a parallel bank of
> 50-20-10-10-5-5-2-2 pF perhaps where one can add-in as many as needed (in
> other words select more than one cap simultaneously, in fact all
> if needed,
> with the jumpers).
> LOWFERS may also want to use their own big external loading coils so
> perhaps the present design with the on-board lo-Z to hi-Z toroid
> transformer may not be wanted (it serves the same purpose)
> although leaving
> it out would detract from the 'plug-n-play' philosophy somewhat,
> and while
> perhaps not *the* most efficient design possible compared to the HUGE
> Lowfer coils is still very efficient nonetheless, and a good deal more
> legal in the face of strict rules interpretations. That toroid coil has a
> pretty high Q.
> Would you like to see a very lo-Z output from the finals directly
> instead?
> A match from the very-lo-Z of the finals to 50 ohms nominal? Or
> some other
> design suggestions that would be popular?
> 3. The antenna output has a 1.5 kV gas tube arrestor to ground.
> This may be
> okay for LOWFER CW/QRSS/WOLF etc. use @ 1 watt but may need to be higher
> rated for AM modulation peaks at this level. There is also a
> static bleeder
> resistor across the ant. and a HV blocking cap to keep DC off the final
> tank. Volt rating of the latter is 3 kV and may need to be
> increased somewhat.
> 4. The finals are presently 3 paralleled Zetex MOSFETs with a combined
> dissipation of 3 watts (yes, Keith likes to over-engineer, his
> products are
> very reliable as a result) but for LF at a full watt may need to be made
> larger dissipation-wise or more added in parallel for extra
> safety margin.
> They are protected in the present AM design by a fast 40 volt Schottky
> diode across the drains. He can probably design the finals to operate in
> your choice of classes (C? D?)
> Are there any 'pet finals' you would like to see?
> 5. There are on-board metering jacks for final current and
> voltage to make
> final input power compliance measurements, but an on-board meter
> itself is
> also possible.
> 6. The oscillator is normally fundamental xtal-controlled (10 ppm xtals)
> but these are expensive at LF and many LOWFERs might not want to be
> rockbound; a PLL design, or PLL/divider, or something else, are also
> possible. The osc. chip is presently a 4000 cmos. There is an optional
> trimmer for setting xtal freq. exactly. Any special taps or
> inputs/outputs
> desired in the osc. stage?
> 7. Buffer stages are presently 4000 cmos. Basically, the design of the
> whole unit is all-digital in the RF train.
> 8. Modulator is LM386, with on-board mod. level pot, and as mentioned the
> mod. transformer. This IC may need to be upgraded to a huskier
> model along
> with the transformer. Audio input is 600 ohms balanced also via a
> separate
> transformer. The audio quality of these units has gotten rave
> reviews from
> many of Keith's customers. This of course may not be an issue for
> strictly
> LOWFER use but we are keeping broadcast functionality too, remember.
> 9. There is an optional on-board NE570 compressor stage (which can be
> jumpered).
> 10. Power regulation for finals and all other circuitry is via separate
> on-board regulators; the final volts reg. is adjustable to make
> it easy to
> trim power input. The voltage for all the rest of the circuits is fixed.
> Regulators may need to be beefed up a tad, and/or have larger heat sinks.
> Power input is protected by a PolySwitch (tm) auto-resetting fuse and an
> MOV, and a reverse-polarity protection diode. Nominal power input in the
> present model is 11-15 VDC.
> 11. The unit is built on a double-sided plated-through-hole FR4 board. I
> assume that won't change. :-)
> 12. It comes in a nice fiberglass-epoxy weatherproof enclosure with
> gasketed lid and SS hardware  -but this adds to the cost. I assume most
> LOWFERS will want just a bare board to use with their own choice
> of enclosure.
> 13. These units in the original design are capable of multi-unit
> synchronization- in other words, you put up a cluster of 4 or 5 units at
> one location, one has the xtal and is the 'master' and sends it's
> RF signal
> to the others which are "slaves", each is a separate transmitter
> in its own
> enclosure with its own antenna but all units share RF drive from the
> "master", power and audio. Since each unit shares a common freq. source
> there are no heterodynes. Each unit incl. the master has on-board
> provision
> for both coarse and fine phase delay adjustment to assure the relative
> phases of the radiated fields match thereby summing the radiated power
> without mutual cancellation. This allows one to get a 6 dB
> increase (double
> the range) over one unit and is perfectly legal. So in essence
> the cluster
> functionally acts as if it were one unit of 4 times the power.
> Now, this feature is expensive and the phasing tricky to adjust w/out a
> calibrated FIM so I'm assuming it won't be wanted in LOWFER circles (and
> impractical for LF hobby broadcasting because of the much larger antennas
> compared with mediumwave), but if I'm wrong please correct me!
> 14. Power/audio input/ant./gnd./sync in/out are all via captive PCB screw
> terminal blocks. Is this good or would other connections be preferred?
> Are there any special features (which could be made standard or optional)
> that would "put you over the top" so to speak if you were "on the fence"
> about purchasing this unit? Any special considerations for LOWFER
> modulation/keying  requirements, IDers, etc?
> Remember this is going to be a stand-alone unit not a PC card type thing
> and there is no direct interface with a computer.
> I cannot comment on the price as it is dependent on the features
> we wind up
> with except to say that it probably will be a couple to a few hundred
> dollars. This may seem expensive but remember this will be a
> professionally
> engineered, highly reliable stand-alone rig, not a kit, and will be FCC
> Type Accepted, (which ain't cheap! :-)
> Keith will naturally try to keep the cost as low as possible, but as you
> can see from the specs of the present AM broadcast unit he does not
> sacrifice quality and reliability.
> Sorry to go on for so long here but remember, YOUR input will help design
> this rig!
>
> 73, Jon W2MXW
>
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