[Lowfer] 2040 kHz issue resolved

Sun Jul 7 19:18:15 EDT 2013

I have a 50 kW and 20 kW within 1.4 miles, plus a similar pair about 4 
miles away!  Severe garbled AM intermod every 10 kHz from below 100 kHz 
to above 7 MHz.  Everything to antenna relays to GOK because same no 
matter what receiver I use or how much attenuation I put in front of 
it.  I'm sure that very little of it is within my own equipment.  I can  
receive LF navigation beacons with LPF at   400 kHz but the intermod 
lines are still there, just not as strong.  I can hear a couple with 50 
ohm termination on my NRD-535D or my IC-756PROIII!

Ed

W6IZJ

jrusgrove at comcast.net wrote:

> Mike
>
> Thanks for looking into 'things' and the followup report. Your current 
> results are more in line with what I would have expected.
>
> Your results, and those of others, would lead one to question whether 
> 'out of this world' IP2 specs are really required in very many 
> installations. You're located 4.5 miles from a 50 kW AM station and 
> the IP2 is SØ. I'm at 11 miles from a 50 kW and the IP2 is 
> undetectable. Guess those stations that are located closer than 4.5 
> miles, or have multiple BC stations that close or closer in, would 
> need to go with the higher IP2 e probes. Not sure there are very many 
> folks in that situation. Might be like 100 dB dynamic range receivers 
> ... not many folks really need that level of performance but it sure 
> makes for good bragging rights.
>
> Jay W1VD  WD2XNS  WE2XGR/2
>
>
>
>
> ----- Original Message ----- From: "Michael Sapp" <wa3tts at verizon.net>
> To: <lowfer at mailman.qth.net>
> Sent: Sunday, July 07, 2013 4:55 PM
> Subject: Re: [Lowfer] 2040 kHz issue resolved
>
>
>> 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 comm
>> on 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
>>
>>
>>
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