[Lowfer] W1VD my attempt at an e-probe

Sun Jul 7 10:50:10 EDT 2013

Mike

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

----- Original Message ----- 
From: "Michael Sapp" <wa3tts at verizon.net>
To: <lowfer at mailman.qth.net>
Sent: Saturday, July 06, 2013 6:01 PM
Subject: Re: [Lowfer] W1VD my attempt at an e-probe

> Jay & All:
>
>>Wonder if you could take a signal strength measurement (output from the e probe ... >preferably in 
>>dBm) at 1020 and 2040? I'm interested in both the signal level at 1020 and how far >down the IP2 
>>product is. At this location the strongest signal is a 50kW 1080 about 11 miles away. The signal 
>>at 1080 is -50 dBm and the 2160 is -140 dBm (limit of Perseus SDR >sensitivity).
>
>>Thanks in advance for your time on this.
>
>>Jay W1VD  WD2XNS  WE2XGR/2
>
>    OK. My HP141T has the 8555 RF Deck 10MHz~18GHZ head, so it's not real useful at 1 ~ 2 MHz.
>
>     What I did was use my FT-847, preamp off, AGC fast, 300Hz InRad CW filter.  Fifty feet of of 
> double-shielded RG-58 from the e-probe injector to my Telonic 0 to 50 dB step attenuator, 10db per 
> step. A double shielded rg-58 jumper to the FT-847 with ten Type31 beads on the jumper for common 
> mode isolation.  Handful of 10, 6, 3, and 1 dB stick attenuators. Zero beat the AM carriers on 
> 1020 and 2040 kHz to be certain the BFO offset was at 650.0Hz with ARGO....
>
> The Technical Supplement for the FT-847 states that receiver sensitivity is 20uV for 500 kHz to 
> 1.8 MHz and 2uV for 1.8 to 28MHz for AM, so it essentially has a 20 dB attenuator in-line in the 
> AM band. Taking that into consideration, the e-probe output at 1020KHz just pins the S-meter scale 
> at +60.  I need 55 ~ 56 dB of step attenuation to get to S7 range with one S-meter display segment 
> of modulation wiggle.  Now when I go to 2040 kHz, the signal is also S7 range with one S-meter 
> display segment of modulation wiggle.  I re-tested with an additional 10dB attenuator in line and 
> the relative S-meter measurement differences repeated at 55 ~ 56 dB down.
>
> Keeping in mind the FT-847 adds 20dB of attenuation in the AM band, I would have to say the 2040 
> kHz signal is 75 ~ 76 dB down.
>
> Voltage at the battery powering the two J310s in the e-probe 12.5VDC and 37.6 ma total current 
> draw. The J310s run just above body temperature at that bias setting, which avoids having to heat 
> sink them.....(I decided that would be a "safe" starting point for initial e-probe testing).
>
> Using my old Wavetek 132 as a signal source, 6000uV (-31.5 dBm) pins the S-meter on the FT-847 in 
> the AM mode at 1020 kHz with the preamp off. 5,500uV just comes off the top FS level.  I have to 
> run 15~16 dB of attenuation between the e-probe output and my FT-847 to be just at full scale 
> S-meter level for the on-air 1020 kHz signal in the AM mode.
>
> Unfortuneately, I dont have a narrowband generator.  I have to rely on my attenuators for 
> referencing the output of my (checked) HP-435K-05 dual power 0dBm 50MHz power reference source to 
> calibrate the Boonton CA-91 RF voltmeter.  That said, I could be a dB or two off, but close enough 
> for amateur radio purposes......
>
> Powering the e-probe with a 24V battery pair and (a well bypassed) LM317 adjustable regulator 
> would likely be worthwhile to take a few 2IP measurements at different voltages at some point. 
> But I think the next few nights I will just sip some coffee and spin the knobs on my old boat 
> anchor receivers now that I have something better than the (noisy) rain gutter and downspout on my 
> front porch as an rx antenna......:)
>
> Regards,  Mike wa3tts
>
>
> Mike,  wa3tts
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