Having done repairs on a ton of older service monitors, and having my hand in SDR, this is amazing! There's a huge amount of machining and hardware to make a service monitor, but with desktop CNC, cheap PCBS, and jelly bean components that go into the 10s of GHz, the sky's the limit.

I'd add a heat sunk 100 watt DC-5Ghz 20dB fixed attenuator, 0-110 dB switched attenuator, 5 ghz low pass filter, 7-12 Ghz local oscillator/mixer up/down converter, and it would make a small, very high performance service monitor good to 5 Ghz. 8)

▲

Eduard 3 hours ago | parent | next [-]

Service monitor?

	▲	mikewarot 3 hours ago \| parent [-]
		A Communications service monitor is a tool for servicing radios. Until recently, most large organizations used VHF/UHF FM radio for communications on dedicated channels. A service monitor is a tool that can usually absorb the full output power of these radios while measuring power, frequency, distortion, etc. They can also generate a variety of signals for aligning receivers. Most of the older, affordable models go from almost DC to 1 Ghz. I've got an IFR 2947a, which goes up to 1.05 Ghz. Here's an example from ebay. https://www.ebay.com/itm/168770412399 Here's a specification sheet for the one I have, a pdf https://www.testmart.com/webdata/mfr_pdfs/aerofl/2947a.pdf

▲

octoberfranklin 5 hours ago | parent | prev [-]

Why 4ghz?

	▲	mikewarot 5 hours ago \| parent [-]
		I've edited it, but generally you don't want to have problems with mirror images getting through and creating spurious responses. Real world RF filters don't have infinitely steep edges, so initially I figured a 4 Ghz low pass filter would have enough loss by 5 Ghz to get the job done. I revised to to a 5 Ghz low filter, and a 7-12 Ghz Local Oscillator to give the filter an easier job. Also, the lower the swing in percentage terms for a VCO, the easier it is to work with. So the signal path in receive mode would be: N connector / 20 dB 100 watt pad / Switched attenuator / Low pass filter / Front End diodes / Mixer / Router board for DSP Alternatively, there's usually a second path that skips the attenuator, with a lower maximum power level. The reverse path would work for generating signals from DC (almost) to 5 Ghz.