13 Ways NOT to Design a 432MHz Transverter Kit

  1. When designing a UHF transverter, start from a 50MHz design. You already stretched it to 144MHz, so everything is sure to stretch a little bit farther. What could possibly go wrong?
  2. Do not leave a continuous groundplane underneath the PC board. Beneath any UHF striplines, be sure to create gaps in the groundplane by routing IF and DC tracks underneath as well. This will ensure that important 432MHz, 404MHz (LO) and 28MHz IF signals are all freely shared around the entire board.
  1. Wherever there is groundplane both above and below the board, take care not to use too many RF grounding vias between them.
  1. Spread yourself out – make all leads and traces nice and long, especially if they are carrying UHF signals.
  1. When using chip capacitors for critical UHF bypassing, be sure to use thin ‘thermal relief’ connections to add some extra inductance between the capacitor and the groundplane.
  1. Even though you are pre-installing some SMD devices in areas of the board that are carrying UHF signals, include plenty of larger, less suitable, wire-leaded components in these areas as well.
  1. If one of your pre-installed SMD devices is a PHEMT with a very fragile gate (like the ATF-34143) be sure to provide a grounding link for the gate. But then require the kit builder to remove this link, to exchange it for a slightly different-shaped piece of wire. This will greatly increase the chances of successful ESD damage.
  1. When ordering overtone crystals, always choose the highest frequency available – in this case, 404/3 = 134.67MHz. Use this crystal in a simple one-transistor oscillator (which specifically requires 9mm long leads on the transistor in order to oscillate) and do the frequency-tripling in the collector circuit of the same transistor. Pass the output through a single tuned circuit at 404MHz and then use the hottest possible modamp to amplify what comes out.

Don’t ever pause to question why everyone else does it differently. Other reputable designers use 101MHz crystals in more complex oscillator circuits, followed by two frequency doublers. But you’re an innovator, so you don’t need to do that.

  1. Do not analyze the gain distribution… or if you do, ignore the fact that NF Analyzer instruments only measure the NF of the transverter itself. It’s always safe to assume that the NF of the following HF receiver will be zero (even if you also happen to manufacture a matching range of HF transceivers with an NF of at least 15dB).
  1. To achieve the best possible gain distribution, do not include a RX IF stage between the transverter and the transceiver. Also do not include an LPF at this point, as it will impede the rich two-way flow of signals and harmonics that is so necessary to produce birdies.
  1. When installing a Mitsubishi PA module, use only a small piece of 1/8in aluminium as a “heat spreader”. Do not use a finned heatsink – the bottom panel of the box will do just fine. Do use a fan, but nothing larger than 40x40mm (choose the loudest possible). In the assembly manual, emphasize the need for washers to separate the mounting flange of the PA module from the underside of the board. Anywhere around the PA module, keep the number of RF-grounding vias to an absolute minimum.
  1. Where metal-to-metal contact is required for shielding panels, be sure to use tough grey paint.
  1. And finally: if someone posts warnings about any or all of the above problems (eg http://tinyurl.com/ydynjb5n), ignore them. On no account change anything in your original design.

 

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