FCC Certification (US) for Vintage Transmitter Kit - Page 1
Forum section: electronics / rf-microwave

author: Cyberdragon
author_rank: Super Contributor
timestamp: September 28, 2016, 04:58:43 am
content: I bought an old HAM transmitter kit a while ago because I was thinking of getting into ametuer radio. Unfortunately, college and things have gotten in the way. But when I do get around to getting a radio liscense I want to get it going. Yes, I know I should probably buy a working transmitter to start with, but that would be no fun.The problem arises in the fact that when I looked inside..., horrible assembly, gobs of parts soldered to terminals going nowhere or dangling and cold joints galore.Given it's a kit with manuals, I stripped it down to bare parts. But it's not just any normal kit like heathkit...it's a corrospondance school kit...Which means you don't just build it, you work through labs to put it together in sections. It also means that I'm missing alot of parts that went with some of the labs, and while I can work around some of it, others are used to calibrate certain the sections. Meaning I'll have to use my own equipment and substitutions to make sure it works properly. I also want to install a small digital frequency counter and a geared dial because the current tuning is just a small direct-drive knob.I'll have to scour the manuals for specs like range and watts, but I'm pretty sure those things will vary a bit given that it's a kit.The problem is how do I make sure that something I built is a certifiable HAM transmitter?

author: AG6QR
author_rank: Frequent Contributor
timestamp: September 28, 2016, 07:18:24 am
content: That's the beauty of getting a ham license. You don't have to get a transmitter certified. You are allowed to home-brew any sort of transmitter you desire, and you can then legally transmit using it, as long as it meets the emissions standards of Part 97, subpart D. Furthermore, even if you buy a commercially manufactured radio, you, not the manufacturer, are the one responsible for making sure it meets those technical standards of Part 97, subpart D.There are standards in subpart D for harmonic suppression and bandwidth, as well as for total power. And of course, standards for what frequencies and emission modes you may use.There are no testing methods prescribed in Part 97 regulations. To really verify that your transmitter meets the standards, you probably need at least a spectrum analyzer, which most hams do not own. In practice, most hams don't test their gear thoroughly against the standards. If you can tune a receiver to the transmitter's 2nd and 3rd harmonics, and not hear anything, that's probably better than most hams do. If you look at the transmitter output on a bandscope (a waterfall display on a SDR receiver) and see that the bandwidth is reasonable, that's another good test that most hams don't do.Note that I'm only speaking of USA regulations, since I'm in the USA and it looks like Cyberdragon is, too. I think rules are broadly similar in many other countries, since I know many hams around the world build their own gear, but I don't know the details of rules around the world.

author: joeB
author_rank: Contributor
timestamp: October 05, 2016, 11:57:36 pm
content: You may want to consider building a kit that is still in production for your first build. There are quite a few available. I had been out of ham radio for about 30 years and when I got back into it earlier this year I had the urge to build a transceiver. After some searching on the internet, I wound up building an Elecraft k1. I found quite a few kits to chose from in varying price ranges.In the case of the k1, the build instructions provided tests to be run throughout the build process and alignment procedures to be done after completion to help ensure that the transceiver would function properly.

author: retrolefty
author_rank: Super Contributor
timestamp: October 06, 2016, 12:22:57 am
content: Really no excuse to not get your licence right away, it's never been easier, no morse code requirement. There are on-line practice tests that let you see how you are doing. I upgraded 2 grades from Technician grade to Extra class grade after two weeks of quiz practice.

author: VK5RC
author_rank: Unknown
timestamp: October 09, 2016, 05:44:54 am
content: +1 re the licence first, even I got one so it can't be that hard.Re the kit I am sure you will be able to complete but it may be a longish project, some of the guys here and or Soldersmoke blog (who are devoted to homebrew transceivers) I am sure will help.In AUS (as it sounds like in USA) it just comes mostly down to harmonic suppression, being on frequency and power levels. It will require some test gear of ingenuity in place of Spec Anal, e.g. SDR or maybe line level receiver with some good attenuators and or pass band filters. If you become a Ham your local amateur radio club is another resource.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: October 09, 2016, 09:27:22 am
content: While S-meters on receivers aren't that well calibrated you can work out how many dB each S unit represents by having an RF signal generator and a calibrated step RF attenuator (easy enough to build from a bunch of switches and resistors). Set things up so that the meter is reading (say) S9 with the attenuator switched out. Then flip the switches of the attenuator so that the meter goes down to S8. Read off how much attenuation is in. Do the same for every S-point. That will allow you to tell how many dB each S-unit is. This could be handy if checking how many dB harmonics are attenuated by.I would suggest tidy up the construction so it's built properly as per the manual.There's several signal defects an old transmitter could have. Some you can live with. Others (which cause interference to others) you cannot and need to fix.I will go through them and suggest a fix.1. Frequency drift. Unlikely if it's a crystal controlled transmitter. Quite possible if it's a free-running VFO. Provided you don't drift out of band this is an inconvenience to the station you're working more than something which could cause interference. You can measure this on a stable test receiver. Fixes include better shielding between the VFO and the rest of the transmitter, better voltage regulation of the VFO and better isolation between the VFO and subsequent stages. Others will comment if it's severe but it's unlikely to get you into trouble with the FCC (who are underfunded and generally only do enforcement actions on more severe abuses).2. Chirpy keying (if a Morse transmitter). Slight chirp is tolerable but severe chirp makes your signal much less readable. You can detect this on a nearby receiver with its antenna removed or gain wound back so your signal does not over power it. Fixes include modified keying arrangement, better voltage regulation of the VFO, backing off power a bit, better isolation between stages etc. It is not good practice to key a variable frequency oscillator as this will almost certainly produce chirp.3. Clicks (again Morse transmitters). If your transmitter has this you really need to fix this since it can cause interference to stations 5, 10 or more kHz either side. You need to smooth the rise and fall of your signal. Something as simple as a capacitor across the Morse key might help. Or some clever timing circuitry.4. Harmonics. Can cause interference to others. Eg you may be unknowingly transmitting on 14 MHz even though you're aiming for 7 MHz. Can be caused by over-driving of stages, poor adjustment or insufficient filtering. Additional pi network low pass filter sections can help. If you don't want to modify the transmitter it's OK to build an outboard low pass or band pass filter and have this inline between the transmitter and the antenna. If only one harmonic frequency is a problem then it's easy to make a filter from a section of coaxial cable cut to 'short out' the offending frequency. This can be installed in the antenna line with a coax T-connector.5. Parasitic oscillations. Can cause interference to others. Can be unstable and drift in frequency especially when adjustments are made. Or it could be broadband hash. May be audible only with certain settings of controls. Can cause interference to others. Detectable by tuning across the spectrum with the key down. Good shielding, neutralisation (of tube amplifiers), shunt resistors, bypass capacitors and use of RF chokes (in some cases with a resistor in parallel) can all help.

author: Cyberdragon
author_rank: Super Contributor
timestamp: October 09, 2016, 08:43:37 pm
content: Quote from: vk3yedotcom on October 09, 2016, 09:27:22 am1. It's single crystal reference2+3 won't be doing morse4+5 My biggest concerns, as I don't have a spectrum analyzer. I do have several frequency meters, but I'll have to use a tuned S-meter or something like you said to find the harmonics. They should have instructions on wire and component placement to prevent parasitics (hopefully).

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: October 10, 2016, 11:13:12 am
content: Quote from: Cyberdragon on October 09, 2016, 08:43:37 pmAmateurs built clean transmitters for years before anyone had spectrum analysers. A test could be to have the transmitter on while tuning around with nearby receivers, including broadcast AM, FM, analogue TV and HF. If you don't hear strong squiggles across the spectrum and harmonics are well down then it's likely your transmitter is clean.