SF author needs help with radio transmitter questions

[RJAWriter]

A few months ago I joined this forum and asked some questions to help me develop a book I've been working on, a contemporary science fiction novel for teens which is scheduled for publication early next year. Now I'm back again, with some more specific (and hopefully, better informed) questions.

Here's what I'm working with: my heroine Niki, who is a teenaged electronics engineering genius, has been asked to build a radio transmitter capable of sending a transmission to a wormhole located some forty million kilometres from Earth. (I've described this briefly in the book as "An X-band RF transmitter with QPSK capability" - hopefully that's legit). Once constructed, the transmitter is going to be used in conjunction with the largest radio antenna in Canada (a dish 150 feet in diameter, on an equatorial mount) to send the signal.

Niki has to build this transmitter as quickly and cheaply as possible from parts she's ordered off the internet, and she also doesn't want her parents to notice that she's doing it, so she's doing most of the necessary work at her local (southern Ontario) hackerspace. However, she also doesn't want the folks at the hackerspace to know what she's doing because she's afraid it will raise a lot of awkward questions, so she's told them she's building the transmitter as a present for her dad, who is an amateur radio enthusiast and wants to do a moonbounce.

What I want to know is:

1. What technical things might Niki do in the course of building the transmitter that would impress the hackerspace guys and convince them she REALLY knows what she's doing?

2. What quality or qualities about this transmitter, if any, might tip off the hackerspace's resident amateur radio expert that what Niki is building is WAY too sophisticated/powerful for just a moonbounce? Is there any particular detail he might notice as he watches the building process that would make it clear to him that she's building something capable of deep space communications?

3. What legal and regulatory complications might be involved in building such a device, that Radio Guy might perhaps be concerned about?

4. Would it be possible to calibrate and briefly test the device in an well-populated area without attracting a lot of notice and swiftly bringing the wrath of the federal authorities down on one's head?

That's all for now! I appreciate any help or insight you might be able to give. Thanks in advance.

 

[cowboybob]

Here's what I'm working with: my heroine Niki, who is a teenaged electronics engineering genius, has been asked to build a radio transmitter capable of sending a transmission to a wormhole located some forty million kilometres from Earth.

If I may, since to me it's important: 40 million Kms is about the distance to Mars (at it's closest (56 million Kms). Not very far.

I point this out since radio transmissions for this distance would not require much in the way of power nor sophistication.

But, your call. Worm holes don't have to be gazillions of miles away.

(I've described this briefly in the book as "An X-band RF transmitter with QPSK capability" - hopefully that's legit).

That's fine. Although I'm curious why the message being sent needs that level of data density.

Once constructed, the transmitter is going to be used in conjunction with the largest radio antenna in Canada (a dish 150 feet in diameter, on an equatorial mount) to send the signal.

Again, not necessary at the distance you've chosen. See alternate idea in answer to your first question below.

Niki has to build this transmitter as quickly and cheaply as possible from parts she's ordered off the internet, and she also doesn't want her parents to notice that she's doing it, so she's doing most of the necessary work at her local (southern Ontario) hackerspace. However, she also doesn't want the folks at the hackerspace to know what she's doing because she's afraid it will raise a lot of awkward questions, so she's told them she's building the transmitter as a present for her dad, who is an amateur radio enthusiast and wants to do a moonbounce.

Fine.

1. What technical things might Niki do in the course of building the transmitter that would impress the hackerspace guys and convince them she REALLY knows what she's doing?

She builds her own Xband transmission horn out of, say, a Pringles can. And builds her antenna disk out of a metal flying saucer snow sled (with other mounting stuff from ACE HARDWARE).

2. What quality or qualities about this transmitter, if any, might tip off the hackerspace's resident amateur radio expert that what Niki is building is WAY too sophisticated/powerful for just a moonbounce? Is there any particular detail he might notice as he watches the building process that would make it clear to him that she's building something capable of deep space communications?

With your stated distance, a moon bounce rig would do the trick - no need to hide it.

3. What legal and regulatory complications might be involved in building such a device, that Radio Guy might perhaps be concerned about?

It might be easiest for Niki to already have, or acquire, the necessary Ham license for this. Would eliminate any questions.

4. Would it be possible to calibrate and briefly test the device in an well-populated area without attracting a lot of notice and swiftly bringing the wrath of the federal authorities down on one's head?

See answer to question 3.

ALL my thoughts are predicated on the distance you have chosen for the transmission to reasonably traverse.

 

[RJAWriter]

Hi, Bob --

Thanks so much for your quick reply! I can change the distance out if I need to, but my primary concern was the time it would take to send the signal and receive a confirmation. If I put it way out by Neptune, for instance, they'd be waiting eight+ hours for an answer and there goes my dramatic suspense. So I picked something closer to Mars' orbit instead.

I should also mention that this transmitter is being deliberately built with way more power and sophistication than it needs for this particular project, so that it can be traded to the folks at the antenna for use in their own future deep space communications, instead of Niki and friends having to pay them hundreds of dollars an hour to hire the use of the antenna.

As for data density, the message is being sent to an alien computer on the other side of the wormhole, telling it to shut down (against the wishes of the aliens running it on the other side). Niki's software guy / partner is also an alien, so he knows how to do that.

The idea of the Pringles can and/or snow sled made me grin, but that sounds more like a lighthearted middle-grade novel thing. I'm more interested in things Niki might do in the course of populating the circuit boards and doing the wiring that an expert might notice. I suppose I could always have them be dazzled by her soldering speed or technique, but I was looking for more transmitter-specific ideas if possible...

 

[cowboybob]

OK.

I didn't realize that there would be a signal back from the ETs. So we're looking at a transceiver.

Google "Software-based transceivers".

And currently, the rave systems are Software based. Take a look at this one, for example:

https://www.electro-tech-online.com/custompdfs/2012/09/g11specs.pdf

I think this 20W unit could easily be declared a 1,000W unit (5,000, 10,000?? for the story and would suffice for testing AND interfacing to the 150m dish. Given the limits on Ham output power, she should could keep the test signal to a few watts (software based control don't forget) - it would be unlikely anyone who might care would even notice.

You might note the complexity: well, welcome to the real world of what you're suggesting she do. The biggest prob is the PCB. I suppose she could get a large, copper clad PCB, draw out the traces with a fine point marker, etch it, drill the holes, etc.. This, too, would fly if she (and you) has the time. And this activity doesn't have to be spot on accurate.

Keep in mind that for XBand (or ANY sufficiently high frequency RF), due to inter-wiring capacitances (causing unwanted oscillations, signal degradation, etc.), there is precious little "hand wiring" used in a device of this sort. A carefully laid out PCB (especially for the RF sections) is really the only reasonable choice.

Note that for the G11 rig all the specs, schematics, etc. are laid out. You can easily fudge the frequency (just simply state that the unit handles the XBand needed).

I'm not suggesting Niki buy one, just use it as a framework for her unit. The SMT parts can be hand soldered, but very carefully (I've done it) and for realism just have her sitting behind a magnifying glass as she does the work (sneakily, of course). And with a really fine point, low wattage soldering pencil and a HUGE amount of patience (and solder wicking stuff).

And Niki's "software guy" can, obviously, do the coding (PC and/or IPad and the G11) needed.

And although not exactly true (actually, not true at all...), the parts needed could be had right away from a Radio Shack (or Digikey, Mouser, etc., a lot MORE true, except have to be ordered). And you could use the G11's plans for actually naming some of the pieces-parts she'll have to order/use. Great realism.

And none of any of this (I wouldn't think) should raise anyone's curiosity levels above normal (normal, that is, for someone of this age and level of experience, whatever that is ).

 

[RJAWriter]

Great input, Bob -- really appreciate the thoughts and attention to detail. Thanks for the link to the G11 rig specs, I'll definitely take a closer look at those as I work on the two remaining "tech stuff goes here" sections in the manuscript. Complexity and mad PCB skills are exactly what I'm looking for, so that's no problem, and I've already mentioned that she rush-orders a lot of the parts she needs from online sources. Thanks for the help! I'll certainly be mentioning you in the book's acknowledgments.

 

[RJAWriter]

Quick additional question: I see that units combining a transmitter and receiver are called "transcievers" if they share common circuits, but "transmitter-receivers" if they don't. Which would be more likely in the case of what Niki's trying to build? Or does it make any difference?

 

[cowboybob]

Quick additional question: I see that units combining a transmitter and receiver are called "transcievers" if they share common circuits, but "transmitter-receivers" if they don't. Which would be more likely in the case of what Niki's trying to build? Or does it make any difference?

Transceivers share commom "sub-circuits", i.e., a tuning array (to select what frequency to transmit and/or receive on [generally the same]). There are a number of such arrays that serve a common purpose in transceivers.

As such, no need to duplicate those circuits.

 

[RJAWriter]

And another question -- in the previous thread, RadioRon suggested in this post that Niki would need a spectrum analyzer and a vector network analyzer to build the necessary hardware. Would that recommendation still apply in the case of the transciever we're discussing? Or am I getting my wires crossed here?

 

[cowboybob]

And another question -- in the previous thread, RadioRon suggested in this post that Niki would need a spectrum analyzer and a vector network analyzer to build the necessary hardware. Would that recommendation still apply in the case of the transciever we're discussing? Or am I getting my wires crossed here?

RadioRon has a point. These devices are generally used to check a circuit for "correct" operation, i.e., is it tuned properly or, is it oscillating at the right frequency or, is the data being handled appropriately, etc., as it is being constructed and once completed.

Since a software based transceiver would (ideally) merely respond to the digital commands, it could easily be inferred that it (the transceiver) would only produce signals that adhere to the commands given.

For instance, if commanded to produce a 7.23342GHz signal, then that's what it'll produce. There would be no need to "back" check the signal's frequency with an analyzer. Or, for that matter, check to see if there were any spurious harmonics being produced (the spectrum analyzer's job). Similarly, data streams, again software controlled, could do nothing more than mimic, exactly, what had been commanded. In other words, The "loop" programming tools (software) would constantly monitor the output(s) desired and bring them into compliance when (if) they drifted, thus maintaining accuracy.

It's the combining of the hardware to the software that would, for the sake of the story, obviate the need for what would actually be needed to accomplish the transceiver's construction. AND give you a plausible literary device that even I, as a reader, would accept.

It sort of depends on how "deeply" you want to explicate Niki's expertise. A lot of real world design and fabrication of a transceiver does, in fact, involve a great deal of analyzing (and calibration, troubleshooting, component replacement, de-soldering, re-soldering, cursing and drinking...). Your call on how much time (writing) you devote to this aspect of the story (and your understanding of the process).

By combing the hardware (Niki's expertise), the software (her ET bud) and whatever antenna system you prefer you can, I think, create a believable comm system that is very flexible and robust, and does not take half the story to complete and put into use.

 

[RJAWriter]

Thanks for the explanation, cowboybob.

What I should have asked instead, I suppose, is whether I need to take the bits about Niki using the spectrum analyzer and VNA out of the story, because they're in there already. What I'm doing now is just some last-minute fact checking and adding more specific details before I turn the manuscript in to my editors on Monday morning.

So if it still makes sense to have Niki using those instruments to double-check her handiwork, despite the software-based nature of the transciever, then I'll save myself the trouble of changing it. As long as it's not actually wrong (or at least obviously unnecessary) for her to use those instruments under the circumstances. If it just implies that she's being really careful and thorough, then great. They're only mentioned briefly in passing, anyway.

 

[cowboybob]

Nah. Leave it in. I know I appreciate (as with Tom Clancy's work) specificity of equipment nomenclature.