[Lowfer] 2040 kHz issue resolved

[Michael Sapp]

Jay & All:  I found my missing 20 dB or so of missing IP2 performance. It was there all along. The issue was (mostly) a combination of local rectification and re-radiation of the 1020 kHz 50KW signal from nearby conductors (utilities, cable TV lines at street, house wiring, etc.) ,  as well as some common mode ingress of those re-radiated 2040 kHz harmonic signals into the transmission lines used to deliver the signals from the e-probe antenna to my receiver. 

I moved the e-probe antenna to my front porch picnic table, allowing only 12~15 feet of RG-179 (mini RG 59) from the DC injector. This change removed 40~50ft of RG6 from the e-probe system (between the e-probe antenna and DC injector). With 1020 kHz at full scale on the FT-847, (about 6,000uV or -30 dBm)  the 2040 kHz signal went from about S7~S8 on the FT-847 to S2 (figure 3dB per S unit).  Then, DeOxIt cleaning the center pin and barrel of the BNC at the DC injector as well as one in-line BNC barrel used to join two 25 foot lengths of double shielded RG-223/U cable brought the 2040 kHz signal down to S0 in the FT-847. At this point I started flexing BNC connectors at their unions and could hear the 2040kHz signal attenuate further as added mechanical pressure to the connectors was applied. Taping each of those connectors tightly (three of them) reduced the 2040 kHz signal several dB.  At the FT-847, I have a short jumper to the antenna input with ten type 31 beads as a common mode choke.  Touching that union from the common mode jumper to the RG-223/U with my hand introduced enough body capacitance to all but null out the remaining 2040 kHz signal getting to the FT-847.   Nothing really wrong with the e-probe, just a harsh noise environment making measurements rather challenging for me.

Earlier in the day when I had a higher IP2 signal level, I tried a higher voltage and bias to the e-probe.  With about 20 Volts at 60ma the 2040 kHz signal was reduced 3dB, perhaps slightly more. However, that power level represents 1.2W, which is real close to maximum dissipation level of the two J310s in parallel.   

Thank you for asking the right question at the right time Jay, that was a good learning experience for me.....(reading Clifton Labs pdf on e-probe IP measurements was worthwhile as well).

73,  Mike, wa3tts








>Thanks for the measurements ... but something doesn't seem right. From your numbers I calculate IP2 
>at about +23.5 dBm whereas I consistently measure IP2 in the mid +50 dBm range. Maybe the 847 was 
>generating its own IP2 ... or 1020's second harmonic isn't that well attenuated! Recall Steve 
>Ratzlaff also measured the pair J310 modded Amrad mid + 50 dBm IP2 a number of years back.

>Anyway, thanks for taking a look!

>Jay W1VD WD2XNS WE2XGR/2