What diode for harmonic generator to check LNBs?

  • I need a way to test LNBs for RX. The idea is to use an nonlinear element (diode) to generate the xx harmonic from the rf from a signal generator on a lower frequency. The diode is soldered to a sma forming a very small antenna (several om's have published this idea before but cant find the articles). This is to be used for tests over a few meters only.


    What (available) microwave diode should/could I use?

  • Hello,


    like Heiner (DD0KP) said the easiest way is to take the 24th harmonic of a 70cm signal (e.g. from an handheld). 437.075 gives you a 10GHz signal at the upper beacon.

    Just hold the handheld close to the LNB and push PTT ;-)


    (If you have a BAOFENG UV5R you will see also the "processor-spikes" few kHz lower than the beacon frequency)


    73 de Johannes

  • I don't press PTT. In RX mode there is enough signal at the 24th harmonic.

    Beware that some (older versions) go into an alternating 'on off mode', but that can be circumvened (for a while) by pressing the menu button.

  • I don't press PTT. In RX mode there is enough signal at the 24th harmonic.

    Beware that some (older versions) go into an alternating 'on off mode', but that can be circumvened (for a while) by pressing the menu button.

    ...because of this I push the PTT ;-)

    ..and if you have not a BAOFENG the 24th harmonic (while pushing the PTT) works also with any other 70 cm TX :-)


    73 de Johannes

  • Any diode will do (e.g. 1N4148 etc etc). Besides a Baofeng I use my R&S signal generator tuned to 953.6 MHz (around +3 dBm) to produce 10489.600 MHz as 11th harmonic.

    Isn't the 1N4148 diode too slow for switching on say 3496 MHz ( my adf 4351 could be set at 3496 to drive the diode harmonic generator).

  • If you want a weak source the 1N4148 is fine. A more exotic diode will be better, but it's not necessary at 10 GHz which is a relatively low frequency these days. Don't feed it with a Baofeng, you won't know which spurii is which.


    For a strong source, find a packaged mixer with a highish LO/RF/IF capability, split the source and feed it into the IF and LO ports at high level but being careful not to exceed the ratings. E.g. 1296 MHz x8 gives 10368 MHz. Seems to work.


    Mike

  • When you've enough level (and the 4351 hasn't) it wasn't too slow (for me) since the late 80's (last century).

    What level is typically needed with an 1N4148 PA3FYM ? The ADF4351 says it can deliver approx +4dBm?

  • The level (formally) needed is around the forward voltage (for Si diodes 0.6 - 0.7 V, so around 5 mW).


    Cf the datasheet the 4351 may deliver +5 dBm (approx 3 mW) but I never realized that with these cheap Chinese boards. However, with my signal generator 3 mW is enough to let (partially) saturate the diode, and hence, produce harmonics.


    With +7 dBm the 11th harmonic of 953.6 (10489.600 MHz) is utterly strong, reducing the 953,6 MHz level also reduces the amplitude of the 11th harmonic. However, there will be a moment that the signal is 'suddenly' gone, because the P/N transition in the diode will not conduct anymore.


    It's worth a try anyway : -)