Practical Information
Correspondence to other Consultants?

Updated:  Monday, December 14, 2015 04:46 AM

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As a result of the circuits and articles that have been published, I have been contacted by engineers who are either already consultants or who are thinking about it. Most want to know how I became a consultant, why I remain a consultant and secrets of my success. I am including some representative excerpts from my responses to this kind of correspondence. Perhaps some of these letters contain information that you might find useful. They should give you some insight into the real world of consulting. All the warts and concerns are left intact. I encourage your comments about the consulting profession.

Letter 1     Letter 2    Letter 3     Letter 4

Dear Jim,

Thanks for taking the time to respond to the information packet I sent you. People give me so little feedback that I often feel I'm talking to the walls. You are the exception.

I couldn't tell if you were kidding or not about the job in Ohio. However, I'm not so desperate that I would take the first job that came my way. It is true that I sometimes get tired of the constant uncertainly of the consulting business, but every year I seem to manage to make enough money to pay the bills. Sure, if an interesting job was offered, with a fair wage, I would certainly consider it. But, so far I haven't had any decent offers. It is not that I haven't tried. Over a ten year period I sent out perhaps a thousand resumes all over the country. However, not a single company ever expressed any interest in hiring me. Not one. I think one of the dangers of becoming a consultant is that after a period of time you are committed to staying a consultant. You can't go back to being an employee again. I guess companies are just not willing to take the risk. They must think that after being on your own you would not be able to play by their rules and be a "company man". The only real possibility of permanent employment is that you may do such a great job for some company as a consultant that they want to hire you full time. So far, after perhaps 500 consulting projects, that hasn't happened. So, my advice is, you better be sure consulting is what you really want to do, because you may get your wish and you may later find yourself unemployable, as I am. I'm not bitter, I just wish I had some more choices. Perhaps I should count my blessings. I know a lot of guys that tried consulting and lost a lot of money in the process. It took them so long to find a permanent job again that they went deep into dept. Also, I don't know of any consultant here in the Denver area, (I know perhaps 100 consultants) that is doing booming business. Most are like me, just getting by. I also know some consultants that have some fantastic years followed by next to nothing. The biggest danger is having one or two major clients that demand so much of your time that you have no time to prepare for a time when the work for them stops. My hope is that I can get something going on the side that can generate some extra cash. If you have any ideas on how to make some extra money I would like to hear them.

I'm hoping I can sell some copies of my book on through-the-air communications, whenever I finish it. I've also been thinking about some kind of some product I can develop and sell. I have made a little money selling circuits and articles to some magazines. But construction projects for magazines like Popular Electronics is not a very good investment. I sold a simple construction project article ("Build a 1 amp current injector") to Popular Electronics a few years ago. I figure it took me about 100 hours of time to generate all the stuff for the article. You can't write the text, take the photographs and design the printed circuit board artwork over night. For all that work, I only got $300 from the magazine. That means I got a return of $3.00 per hour for my invested time. My hope was that is was somehow going to generate some consulting business. But, that never happened.

I do a little better with circuits for magazines like EDN and Electronic Design. They pay $100 for each circuit published and an additional $100 to $150 if the circuit is voted by the readers as the best of the issue. Since it takes me about 6 to 12 hours to prepare those, I get a wage between $8 and $42 per hour. But, you may have to submit two or three circuits to get only one published. The guy at EDN told me that he gets about 600 circuits to review each week. But, just like the Popular Electronics article, the published circuits have not produced any consulting business.

Thanks for your kind comments on the my "Views and News of Imagineering" newsletters. I sent out thousands of them for awhile. The idea was to give some potential clients something to read which would also keep my name in their mind. It was a way to promote my consulting business. But, the effort did not produce enough business to justify the effort. Also, I hardly got any kind of response from the readers. With the first several hundred newsletters I sent out, I included a post-paid questionnaire. On it I wanted to know if anyone was interested in subscribing to the newsletter if offered, and how much they were willing to pay. Out of several hundred newsletters that went out with the questionnaire I got only one returned, and he didn't think it was worth anything. So, I gave up on the whole idea. The amount of time and materials needed to produce the newsletter cost me much more than could ever have been paid for, even with some limited advertisements.

I think the Tec Spec newsletter has a better chance since people would be more likely to buy some parts from Allegro Electronics than to hire a consultant. All Allegro has to do is to average one order for parts from each subscriber per year to justify his effort. But, I do like the idea of some kind of forum or newsletter for exchanging ideas. Author's note. Tec Spec and Allegro Electronics are no longer in business.

I've looked at some computer BBSs, but they all seem to have some limitations. Uploading and downloading schematics seems to be a big problem. Most engineers use programs like Orcad, Schema or Tango to generate their schematics. I use Orcad. Unfortunately, to transfer the schematics between different CAD programs you have to generate a DFX or IGES file which can create very large files, too large to be practical to send by a slow modem.

Have you sold any of you music software and hardware? What else do you like working on? Give me some idea of your interests.

What do I like working on? I guess I like working on things that are unique. Lasers and Tesla coils draw too many people. That's why I like working on long range optical communications, not many people are experimenting with it.

Yes, I may be interested in some neon. Well, something like a short neon sign. I think I did send you a drawing for a special xenon discharge tube I been trying to get built. One of the biggest problems in long range optical communications is finding a low cost and powerful light source. Infrared LEDs are cheap but they have a fairly low efficiency (typically 0.5% at 5 amps). Lasers are faster and can form tighter light beams but they are expensive and not yet powerful enough. Sure, some of the old GaAs laser diodes can be pulsed to produce 25 watts but you pay a price for the short pulses (50ns) they launch. To go long distances you really need several watts, 100 watts would be great. My long range prototype, which has a range of about 10 miles, uses just 20 cheap infrared LEDs. Collectively they launch only about 3 watts of peak light with a divergence angle of about 1 degree (half angle). Lasers could produce tighter divergence angles but angles smaller than 0.3 degrees cause some real alignment problems. I wanted to experiment with modulated xenon discharge lamps. I think I could get maybe 10 watts of light with a tight divergence angle from a simple glass lamp. To my knowledge nobody has built a communications system using a xenon source.

Xenon discharge tubes are not bad in terms of efficiency. They have a lot of nice emission peaks in the infrared and convert about 10% of the electrical power into useable light power. That means they are about 20 times more efficient than infrared LEDs. But, most lamps are designed for exciting lasers or taking photographs and not for communications. To get the most from the lamp you need the have the space between the electrodes small. Keeping the electrode gap narrow helps reduce the inductive reactance of the gas plasma. The idea is to pulse the discharge tube with narrow current pulses, at low duty cycles. According to some information I got from EG&G, the shortest practical pulse for xenon is about 1us. EG&G and some other manufactures do have some lamps with narrow gaps that can dissipate about 30 watts of average power. These lamps use tungsten electrodes and a quartz envelope. If you can keep the discharge pulses to about 1us and have a repetition rate of about 10,000 pulse per second (1% duty cycle) (good for voice audio communications) then you should be able to put about 3,000 electrical watts into the lamp for each pulse and get about 300 watts of light out. With a narrow gap, the light emitting area would be small and you should be able to use some inexpensive flashlight mirror reflectors to produce a tight exit angle. With a good reflector and 300 watts you should be able to go all the way to an orbiting satellite some 150 miles away. But, if you want higher data rates you will have to sacrifice range. With pulses as short as 1us you can go as high as 500,000 pulses per second (50% duty cycle). But, a 30 watt lamp would not be able to launch more than about 6 watts of light at such a pulse rate. Still, 6 watts will go 10 miles easily.

There are many ways to modulate the lamps. If you can stand a higher average power dissipation, a simmer circuit works best. The simmer circuit is a low power discharge that is maintained through the lamp continuously. A few hundred volts at a few milliamps usually will do the trick. A little neon gas added to the xenon gas inside the lamp helps lower the simmer current needed. The discharge provides a continuous ionization path that a high current pulse can ride on. Since there is already plenty of ions from the simmer discharge there is no pre-ionization time delay. Therefore, the optical rise time when pulsed at high currents is fairly fast. But, it does take some time for the higher ionization to die down after the current pulse. This "long tail" effect is lessened with narrow electrode gaps. The disadvantage of the full simmer circuit is that it might double the average lamp dissipation, thereby lowering the overall efficiency.

To increase the efficiency, a "pseudo-simmer" circuit could be used. It is a little more complicated than the continuous simmer circuit but it can drop the average power dissipated. The pseudo-simmer circuit works the same was as the full simmer circuit except the low current discharge is turned on just prior to the big power pulse and is not turned on again until the next pulse. However, at high pulse rates I think the pseudo-simmer method would need a third trigger terminal on the xenon lamp. External triggering through the glass envelope using several thousand volts would not be practical at high pulse rates. I built few simmer circuits but I haven't tried a pseudo-simmer circuit. If you have any ideas, let me know.

For wide area optical communications it is hard to beat a cheap fluorescent lamp. I sent you a simple circuit that works fine for the miniature 1 watt lamps. However, larger lamps with dual cathodes need a completely different circuit. I've tested many kinds of lamps at 10,000 pulses per second and I know I can get about 25 watts of modulated light from some small 9 watt "U" shaped lamps. However, I haven't yet worked out a good overall circuit that has a nice lamp starting circuit.

I enjoyed your descriptions of nitrogen spark gaps in Tech Spec. Unlike xenon, nitrogen sparks can be very short. I can imagine a variety of application of such light sources if you can figure out how to miniaturize them. Light pulses of 10ns or less would be great for time-of-flight distance measurement devices, like optical radar. At low duty cycles a small light source could launch maybe 100,000 watts of light (figuring about 10% electrical to optical conversion and a 0.01 joule pulse). No laser could come close to that much power at a low cost and compact size. But, to be practical you would need to get the spark gap down to about 1mm or less so a simple reflector could be used to produce a tight light beam. For distance measurements you would not need a high pulse rate. Even for applications like an optical police radar gun a pulse rate of 20 pulses per second should work fine. Let me know if you have any interest in this stuff.


David Johnson


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