[Lowfer] 2040 kHz issue resolved
jrusgrove at comcast.net
jrusgrove at comcast.net
Sun Jul 7 19:58:41 EDT 2013
Ed
My sincere condolences ... is HF, at least, unaffected?
Jay W1VD WD2XNS WE2XGR/2
----- Original Message -----
From: "Ed Phillips" <evp at pacbell.net>
To: "Discussion of the Lowfer (US, European, &UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Sunday, July 07, 2013 7:18 PM
Subject: Re: [Lowfer] 2040 kHz issue resolved
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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