Hi all, Has anyone got any good tips on broadband (HF->UHF) somewhat physically compact directional coupler SWR / directional watt-meter designs? I'm also looking for equations or quantitative design parameters relating to their design and operation. Two use cases are of interest: 1) Specifically for weakly coupled power / SWR probe operation, I'd like somewhere very generally in the region of 1% to 0.001% coupled power. The probe coupler should not to impose much load or power limitation on the primary line which may be operating with 0.001W to 1000W kinds of powers, though 0.1 to 10W would be most commonly of use / interest. I'd like to cover all of HF, VHF, and UHF with one simple design *if* that's practical, though having one for each band wouldn't be a bad compromise if it greatly simplifies or improves the design. 2) Low insertion loss, highly directive circulator / isolator functions at modestly high power levels (e.g. 0 to 1kW), and good operational characteristics over a single specific narrow band of operation. The cases of HF, VHF, and UHF are most relevant since other techniques are applicable above or below those ranges. For (1), the weakly coupled power probe, I've seen designs using just a ~1/100th wavelength probe alongside a transmission line. I haven't references for the coupling ratios achieved with such a small probe line length, but I'd guess it's in the 0.1% range in order for it to be useful for its purpose. I question the directivity these are achieving, and would welcome some quantitative information on the subject. I wonder how much smaller than 1/100th of a wave long one could make the coupling probe line and still get good directivity and achieve around 0.1% coupling ratio? Has anyone any references relating to design types or design performance parameters? I understand that 1/4 wavelength is the optimum length for a secondary directionally coupled line, though in that case I'd expect there'd be a very high percentage of directionally coupled power, well in excess of what I'd need for a measurement. For (1), the weakly coupled power probe, I've seen designs using ferrite coupled transformers for the HF frqeuencies that are surely much smaller than 1/100th wavelength in physical size, though I am not aware of specific details of their performances or maximum achievable bandwidths. I'm inclined to be skeptical as to whether such a ferrite transformer design could work well for HF + VHF + UHF, or which could easily work with higher power levels at any frequency.