[Hi-zreceivingarraydiscussions] BC IMD

[Paul Christensen]

Yes.  The 160m 8-circle worked great last night.  For about three minutes, VU2GSM was an honest S7 on the K3 S meter.  S5 about 10 minutes before and after the peak.  Copy was from the NE as expected.  No copy at all in the N and E directions.  

F/B from W1AW last night was better than 40 dB.  S9 NE and nothing heard in the SW position.  All switch positions are definitely working.  

This afternoon, N4CC and I just finished re-deploying radials for the "T" top transmit antenna.  Sure wished it was ready yesterday!  100 ft vertical section and a flat T top that is between 80-100 ft.  We could not remember the length as we discussed it today.  I do want to validate 100 ft to ensure there's little or no interaction with the 40m Yagi.  

IMD update:  clean for the last 48 hours.  I did adjust the power supply current threshold on an HP lab supply and validated system voltages.  Nothing conclusive though.  We'll see how it goes.  

Paul, W9AC

-----Original Message-----
From: Hi-zreceivingarraydiscussions <hi-zreceivingarraydiscussions-bounces at hizantennas.com> On Behalf Of dan edwards
Sent: Wednesday, November 11, 2020 9:59 AM
To: Hi-Z Receiving Array Discussions <hi-zreceivingarraydiscussions at hizantennas.com>
Subject: Re: [Hi-zreceivingarraydiscussions] BC IMD

 paul, was that what you heard VU2 with the other night??
my LAST zone, IF i ever get it
73, w5xz, dan

    On Monday, November 9, 2020, 07:45:17 AM CST, Paul Christensen <w9ac at arrl.net> wrote:  
 
 Sorry folks.  This was meant only for Lee, not the list.  I'm not paying attention this morning.  

-----Original Message-----
From: Hi-zreceivingarraydiscussions
<hi-zreceivingarraydiscussions-bounces at hizantennas.com> On Behalf Of Paul Christensen
Sent: Monday, November 9, 2020 8:39 AM
To: 'Hi-Z Receiving Array Discussions'
<hi-zreceivingarraydiscussions at hizantennas.com>
Cc: n4cc at windstream.net
Subject: [Hi-zreceivingarraydiscussions] BC IMD

Lee,

N4CC and I installed the new Hi-Z preamps on our 160m 8-cicle array.
Balance is better than with the old preamps and while listening last night, F/B was excellent with no signs of skewing.  However, starting at 6:15am this morning, I heard significant broadcast band IMD every 10 kHz on 160m.
We have a Hi-Z HPF between the controller and Hi-Z final preamp.  

The main culprit seems to be WBOB-AM.  In a prior life I was Director of Engineering at the station.  It operates with 5KW on 600 kHz.  ND daytime, and 5-tower DA inline array at night with a very narrow lobe to the east, right over Jacksonville.  Our site is about 15 miles NW of WBOB-AM and as such, the nighttime pattern has very little effect on us.  But the ND daytime field strength is very strong.  I don't recall the post-sunrise switch time for the month of November, but I'm guessing it's at 6:15 am.

I see that Jeff, AC0C is using a notch filter right at each Hi-Z whip antenna preamps.  I will do some more investigating but if it turns out that we need the filters, do you supply these?  Any impact on system balance with these filters?  Also, I am not sure if 600 kHz is the only Jacksonville station causing a problem.  It's certainly the main cause at the moment.
Others that are potential candidates in Jacksonville are at 690 kHz and 1460 kHz.  

By the way, I don't recall having the BC IMD issue with the prior antenna preamps.  Just an observation.

Paul, W9AC


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