DEEP VOICE LONGWAVE PROJECT

Below is a spreadsheet analysis of an unlicensed system on 175 kHz operating under FCC §15.217.

The DC input power allowed at the final r-f amplifier of the transmitter in this low frequency band is 10 times that allowed in the AM broadcast band under §15.219. Even though the radiating length of the antenna system permitted in this band is 15 meters, it has only about 1/3 of the radiation resistance of a 3-m radiator at ~1600 kHz. Also the loading coil needed to resonate the 15-m antenna has higher loss at this low frequency, and probably the resistive loss in the r-f ground connection is greater, also.

So the net result is that the radiated power from the Part 15 low frequency system is less than the typical value from a Part 15 MW system, and the usable coverage area for a 175kHz system would be smaller. Radio noise levels also are higher at these low frequencies.

The loaded Q for this low-frequency system is not very high, but the 3 dB r-f bandwidth of the antenna system in this example is only 2.7 kHz. The audio bandwidth at the output of an AM receiver would be 1/2 that, so this system be would be far from "hi-fi" to an average listener.

While installing a Part 15 LW setup would make an interesting and challenging project, system performance probably will be less than expected by those hoping to serve listeners using conventional AM receivers.

Rich's contribution makes a good 2nd post for this subject, like saying...

This looks like a 50-story building but the stairs only go half-way up to the 2nd floor.

Anyone who remains interested in Part 15 longwave after knowing the huge size of everything compared to the almost imperceptable result will need to be insane with radio.

We'll go on talking about it, design it on paper, and probably postpone physical involvement.

Tuning the blank static on my four LW radios is what makes me want to put something on the air, but procrastination could easily take precedence.

SIZE THIS UP

Courtesy of Barry Blue Bucket Radio

Interested parties have begun checking in for the re-kindling of the Deep Voice LW Transmitter Project, and various specifications have been set forth for discussion.

As a matter of procedure, not all the communication on this matter is made here in the forum, there are also e-mails and other communications submitted for consideration.

It is urged that the Deep Voice LW Transmitter be designed with output power of 7-Watts, even though Part 15 use requires no more than 1-Watt to the final RF stage. The reason for the extra power capacity takes into account the heat generation expected by driving a massive coil and tall antenna. An output stage operating below its full power rating will prove cooler than a smaller circuit built to less tolerance.

A question remains as to the need for an RF Low Pass Filter on the Final Output Stage, given the liklihood that a large loading coil will itself provide sufficient filtering, designed to establish antenna "Q" and eliminate harmonics in higher bands.

Meanwhile, we've compiled five low pass filter circuits at 170, 190, 200, 290, and 420 kHz, using standard parts, if needed.

"... It is urged that the Deep Voice LW Transmitter be designed with output power of 7-Watts, even though Part 15 use requires no more than 1-Watt to the final RF stage. ...  The reason for the extra power capacity takes into account the heat generation expected by driving a massive coil and tall antenna.  An output stage operating below its full power rating will prove cooler than a smaller circuit built to less tolerant specifications. ..."

That's a choice for the system designer/operator, of course.

However if the d-c input power to the final r-f stage is set to 1 watt as legally permitted by FCC §15.217, then the use of a transmitter "designed with output power of 7-Watts" would make little difference in the useful field strengths that such a (legal) system would produce -- other things equal.

The performance of such a system compliant with FCC §15.217 was shown in the spreadsheet of Reply 2 of this thread.

I have always enjoyed Rich's numbers and 

this time was no exception.  Rich's numbers 

say that this longwave project will not have

much range, and I agree. 

But the thing is to have fun, so if this is your

thing, then do it.   

In 1974 or there abouts, a "Part 15" friend of

mine built a 1 watt amplitude modulated

Part 15 160 to 190 kHz vacuum

tube transmitter from plans in an electronics

magazine.  There is a whole story, of course,

but it shakes out like this:

My buddy spent a lot of money and time, and metal work

on what turned out to be a beautiful Part 15 transmitter

for this band.  We didn't even have any receivers for the

LW band to test range, except for a Drake SW-4A, and

that sat in his cellar and received the test transmissions.

Which sounded great.  Again, the home built transmitter

was very nicely made, sort of on par with Neil's homemade

Part 15 AM BCB vacuum tube rig, which we have all admired.

So, yup, the longwave transmitter was hooked up to a 50 foot

long wire antenna.  My friend got a broadcast cart machine from

somewhere, and ran a loop announcement that gave details of

the experiment, and where to send reports for a QSL card.  This

loop ran for many weeks, or months, even?  (That cart machine

must have taken a beating.)   

The amount of reception reports received: none.

Did we regret doing it?  Nope, it was a blast getting

it running and we knew we were doing something

that hadn't been done too much at the time.

I didn't build the transmitter, but I helped with the rest of

the project, and I would do it again.

Actually, I would do a lot of things again.  If I could.

Brooce, Messing around with Part 15 in West Hartford

P.S.  Oh, yeah - receiving on 160 to 190 kHz and the

surrounding RF "area" isn't easy either.  You need a

top notch receiver and if you want to skip a bunch of

steps in the receiving installation you can do what I

did and just take the whole thing outside in your

back yard until you find a place where, hopefully,

there is not much RF noise, or none at all.

I have heard several European LW broadcast stations

and a few other stations that are cool, including Morrocco (sp?)

on 171 kHz and Iceland (easily my favorite longwave BC catch)

on 189 kHz.   (I actaully set the receiver and batteries down

in the middle of the backyard and transmitted the received audio

back into the house with a Part 15 FM transmitter.)   I'm extremely

fortunate because I'm in Connecticut, so this happened to work.

From what I've seen and heard, the only way one can

hear a Euopean LW BC station inside a house on a fairly good

radio and no external loop or wire is to be on the

edge of the Atlantic ocean. 

Mr. Rich in # 5 allowed a 7-Watt design, run at Part 15 level, would offer no advantage so far as range, and that happens to be true.

However it's odd to mention since no such range advantage was implied in the earlier description.

It was clearly stated that the purpose of over-designing the RF output would come from cooler operation. Yet Mr. Rich made no comment on this aspect.

I would say he went off thread.

I have built some low powered ham 

transmitters and they were all so simple that

they required a 50 ohm load.

That's the kind of load you get from using

a dipole, as we know.  

In my early days as a ham, I didn't know that.

I built a very popular and very dangerous one

tube ham transmitter for the 80 meter band.

Again, this project was from an electronics magazine.

I had a crystal for 3723 kHz.  That was "MY CHANNEL."

However, because of my inexperience with RF, I connected

the transmitter to a random wire.  Even though tests with

a lightbulb dummy load had been OK, the transmitter went

crazy into the wrong load and went into parasitic oscillation.

So all the TV channels were covered up with a big mess, and

you can bet I turned that thing off REAL FAST!

But yaknow, that wasn't even my point.  Here it is:

Another time I built a 500 mW input ham transmitter -

2 transistors - for 40 meters - 7040 kHz.  The final

transistor was a 2N2222A.  Those of us who find it

interesting to remember such things will know that

a 2N2222A will not tollerate a mismatch for long at that

power level.   

In fact - the antenna connection fell off the transmitter

and the 2N2222A fried.  If the transmitter had been

built conservatively, maybe the final transistor would

have survived my goofy transmitting tests.  

That way one can mess around with different antennas

and coils and maybe not have to replace the final 

RF section every once in a while.

I have to say, that is one of the really great things

about ham radio.  One can build the most minimal

transmitters that they chose to (as long as they are

RF clean) and try to make contacts with them.  

I have had some fun doing just that.  Morse code, 

of course.  But you don't need to need to be a 

really good code operator just to run some short

transmitting tests.  My cw is horrible.  I still like

doing it, though.

Brooce

Held a brief conversation with a project follower regarding antenna options for the Deep Voice Transmitter, and agreed that for getting started an end-fed would be quickest and easiest.

In another project thread MRAM 1500 describes his end-fed antenna at 13.560 MHz shortwave.

With these things in mind we chanced upon a very attractive end-fed product from Palomar Engineering that might be adaptible to the 15-meter length limit of this project.

Palomar Ed-Fed Antenna

"...It was clearly stated that the purpose of over-designing the RF output would come from cooler operation. ...

If this 15-meter monopole antenna system is resonated at 175 kHz, then virtually all of the r-f output power of the transmitter is dissipated in the ohmic resistances of the external loading coil and r-f ground reference -- not in the final r-f amplifier.

Said: "If this 15-meter monopole antenna system is resonated at 175 kHz, then virtually all of the r-f output power of the transmitter is dissipated in the ohmic resistances of the external loading coil and r-f ground reference -- not in the final r-f amplifier."

Although such a transmitter will probably run cool while the antenna is at resonance there could be out-of-resonance circumstances during which heat could and likely would build up at the RF final stage. The "over-design" will contribute to the preservation of the output stage under mis-match situations.

After spending some attention scrolling though the past thread linked at the outset of this one, I was reminded of all the work we'd already done in 2011 & 2012 to draft a proposed LW transmitter design.

Of great surprise was the rediscovery of a Simulated RF Final Stage submitted then by Neil Radio8Z.

http://www.part15.us/forum/part15-forums/general-discussion/170-khz-final-simulation

This project might be already complete except for the physical build.

"... This project might be already complete except for the physical build."

Which project also includes the design, installation, and optimization of the complete antenna system for that installation -- if an important goal of the project is to provide a useful radiated signal for the greatest area around the transmit site.

Probably because of a shifting parallel universe incident I have departed from the universe in which the RF Final hadn't been finished and entered this one where Radio8Z Neil did submit a Final RF design retroactively.

Updates have appeared at the project web page but seem to lack a current parts list.

http://kdxradio.com/deepvoice.html

What Rich just said does bring us to the stage of considering antenna configuration which could result in modifications to the schematic circuit.

For example, in cases where a loading coil is custom designed for use with a 15-meter antenna the low pass RF output filter would likely be omitted.

Retention of an RF output filter would be advisable when feeding an antenna without a loading coil.

Other than those two differences at the output the only other modification that comes to mind is the question of "over design" mentioned earlier, designing an output stage capable of greater than part 15 power for reasons previously expressed.

I'll be looking for improvements to add to the project web page, attentive as always to incoming comments.

"...Other than those two differences at the output the only other modification that comes to mind is the question of "over design" mentioned earlier, designing an output stage capable of greater than part 15 power for reasons previously expressed."

FCC §15.217 is silent on the maximum output power rating of the transmitter.

The only requirement there is that the (unmodulated) d-c input power to its final r-f amplifier legally cannot exceed 1 watt.

This observation already was posted in the following clip from Reply 5, above:  "That's a choice for the system designer/operator, of course."

PS:  Where are you gaining your new recognition of these issues, and why didn't they apply to your previous posts?