[Lowfer] 2040 kHz issue resolved

Ed Phillips evp at pacbell.net
Sun Jul 7 20:09:16 EDT 2013 

Not really.  As I mentioned, problems through 40 meter band but no worse 
than foreight QRM.  I've gave  up on 1750 a long time ago and the days 
when I could hear as many as 9 beacons in the Nevada/Arizona/California 
are at once are gone for 30 years......  Have to pick frequencies on 80 
and 160 is almost a no go.  Didn't used to be with one 10 kW and reduced 
power after sundown but now all I can hear is scrambled Chinese and 
whatever all over the band.

Ed

jrusgrove at comcast.net wrote:

> 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, &amp;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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>>
>>
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