I just picked up a small spectrum analyzer to check out some transceivers I have. They are 10 meter ham units and put out anywhere from 4-12 watts @ 50 ohms. The new spectrum analyzer can handle a maximum of 10 dbm. What size voltage divider would I need to reduce the transceiver wattage to less than the 10 dbm for the analyzer? Thanks.
1 watt is 30 dBm. 4 watts would be 36 dBm. 12 watts would be about
In order to avoid driving the spectrum analyzer into overload, I'd suggest keeping the input signal at about 1 milliwatt (0 dBm). This will also give you some safety margin to avoid exceeding the 10 dBm limit.
40 dB of attenuation would take you down from 12 watts, to 1.2 milliwatts, so that's a good figure to shoot for.
So, you'd want either one 40 dB attenuator, or two 20 dB attenuators in series. Make sure that the attenuator is rated to handle the full output of the transmitter, or you'll cook it.
A single 30 dB attenuator would keep you under your 10 dBm worst-case limit if you feed it with 4 watts, but you'd be a hair over the limit at 12 watts. So, I'd stick with 40 dB of attenuation.
Make sure these are 50-ohm attenuators, of course, since that's what the transmitters will expect (and want) to see.
Tried the loop around the coax, just a prior loop I had made up one time for RG-8 (this is RG-58 I'm using now). It's not tight around the RG-58 of course, but output stays well within the analyzer limit. However, harmonics vary depending on where I move the loop. Maybe I should make a tight single loop around the coax?
Ok, as I already had a 20:1 voltage divider, which brought levels down to 10 dbm, I simply added another one in series. I've been testing out a TinySA handheld unit about the size of a cigarette pack. After watching some videos on it, it is recommended to keep levels at -30 dbm to prevent false spurs and harmonics. My voltage divider added in series does just that at just under -40 dbm.
Here's a question I can't seem to find the answer to: what are the harmonic emission requirements for spectral purity for HF radio transceivers in the US? I *think* its either -30 or -40db below, but it's been years since I've used these transceivers. Thanks.
(d) For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission. For transmitters installed on or before January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must not exceed
50 mW and must be at least
40 dB below the mean power of the fundamental emission. For a transmitter of mean power less than 5 W installed on or before January 1, 2003, the attenuation must be at least 30 dB. A transmitter built before April 15, 1977, or first marketed before January 1, 1978, is exempt from this requirement. (e) The mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency between 30-225 MHz must be at least 60 dB below the mean power of the fundamental. For a transmitter having a mean power of 25 W or less, the mean power of any spurious emission supplied to the antenna transmission line must not
40 dB below the mean power of the fundamental emission, but need not be reduced below the power of