Power Down/Signal Up

[cyberdad]

A couple of recent posts in other threads got me thinking....

Do any of you guys have experiences where a local groundwave AM signal is stronger where you are at night than in the daytime when the station is actually operating at higher power? I'm talking about groundwave only, not skywave.

My best example of this is WOKY. During its Top-40 "glory days" in the late 1960s. The 5kw directional daytime signal in the town where I grew up was fair at best due to a broad null to the south to protect WBAA (which would be audible from time to time....especially on a car radio). When WOKY powered down at night to 1kw, the signal would instantly "pop," and go from fair to good. WOKY was still protecting WBAA, but sent a nighttime lobe southwest....right at me. Being situated at 920, a lot of people stumbled upon on it at night when tuning back and forth between WLS and WCFL....and liked what they heard. Now, of course, the channel is more crowded, I'm about 12 west from where I grew up, and WOKY is audible but unlistenable at night. Despite still throwing more juice in my direction.

Do any of you have similar examples that come to mind?

 

[gr8oldies]

Good topic, unfortunately I can't think of any of the top of my head, either in current or previous locations.

 

[Schroedingers Cat]

CFCO 630 10/6 DA-2/U4 is a good example. Shallow null to the NW in Daytime pattern. Maximum to NW in Nighttime pattern. There are numerous other examples. Any DA-2 station can have nulls in different directions and increase IDF in some directions even when power is reduced. A 5/1 DA-N/U2 station with a three or four tower pattern may even increase in IDF in the maximum direction over nondirectional operation.

 

[1L6E6VHF]

Go to Oak Park, Michigan for an extreme example. WRDT goes from 500 W DA to 14 W ND at sunset. But their day site is in Monroe (30+ miles distant), while their night site is less than 3 miles away from the tallest tower in all of USA AM broadcasting!

Two cases where the night signal gets stronger with no change in power:

WXYT (AM1270) Has a deep, broad null to the SW in its day pattern (protecting Defiance, Ohio on 1280), the night pattern is much looser. WXYT is a "nighttimer" In southern Monroe County.
WSPD (1370) Toledo beams oddly southeast (away from Toledo) at night. I've met many a DXer who's told me they are listenable at night in the Carolinas.

 

[Schroedingers Cat]

Lots of stations send their power in the opposite direction from the City of License. It looks like a lot of them were the very early directional antennas where they went from 1000 watts nondirectional to 5000 watts directional Nights. It it mainly those stations with transmitter sites that are in the "wrong" direction to send the major lobe logically toward the City of License. Besides WSPD, in this region, the old WWJ antenna and site, WKZO, and WKMI come to mind. Other stations probably would have had much better Night facilities today if they had just figured out the correct direction to locate their site back when they first came on.

 

[HGR1290]

Although we did not reduce power, we had two different patterns on 600 WSJS in Winston Salem, NC the day pattern is a broad "squished oval" oriented NW/SE. 5kW into 3 towers.

At night, we added a fourth tower, and pointed a majority of the power east.

The night signal was generally better than day over most of the "important" cities of the market.

The area had abysmal ground conductivity, so even at the low end the signal quickly evaporates as you leave the site,

Daytime intensity was roughly 30-60mV/m in Winston Salem, Nights was 40-80mV/m. By the time we reached Greensboro, you were happy to see 3-4mV/m. That type of signal was fine back in the 70's and even in the 80's but as the 90s came about, and then the 00's 3-4 mV/m became mostly un-listenable due to noise etc. The night pattern would bump it up to around 5-6mV/m over Greensboro---still not really useful these days

Of course the people out west did not like our night pattern very much!

 

[cyberdad]

KHMO, 1070, in Hannibal, MO was discussed recently in another thread. The night pattern is 1kw aimed north-northwest from a six-tower site in an area with very good ground conductivity. Although my college location in the late 60s was 90 miles away, the 1kw night groundwave signal aimed right at me was essentially as good as the 5kw day signal. Alone and with minimal fades. Very listenable. Of course, reduced power local signals being every bit as good at night as they are daytime is nothing unusual. But 1kw being as good as 5kw at 90 miles out is undoubtedly quite rare.

 

[rfry]

KHMO, 1070, in Hannibal, MO was discussed recently in another thread. ... the 1kw night groundwave signal aimed right at me was essentially as good as the 5kw day signal. ... But 1kw being as good as 5kw at 90 miles out is undoubtedly quite rare.

Yes, but likely the nighttime signal of KHMO at that location/bearing 90 miles away was mostly their skywave -- which would have much less path loss than their daytime or nighttime groundwave at that receive location.

I see the same effects or better for a terrestrial path length of ~90 miles for the day/night signals of KMOX in that general direction, and they radiate the same power toward all az-el bearings, 24/7.

PS to cyberdad: Thanks for your followups on the reception of CKLW.

 

[cyberdad]

Yes, but likely the nighttime signal of KHMO at that location/bearing 90 miles away was mostly their skywave -- which would have much less path loss than their daytime or nighttime groundwave at that receive location.

I certainly defer to your expertise on this one. I originally had thought skywave was responsible myself. But what caused me to wonder is that the signal was so steady and reliable. Night after night, with few, if any fades. And in an area with fabulous ground conductivity.

And thanks for the kind words regarding my CKLW posts. Speaking of which (and skywave), I thought I'd try for it around midday today. Went to a noise-free area of the back yard with the GE Superadio II. No trace of it. I have heard it during daylight hours here northwest of Chicago on occasion, but no doubt via daytime skywave. My thinking in trying for it today was that if I had heard it, there might be something up with their day pattern.

 

[rfry]

[RE: KHMO in Iowa]... I originally had thought skywave was responsible myself. But what caused me to wonder is that the signal was so steady and reliable. Night after night, with few, if any fades. And in an area with fabulous ground conductivity.

I had a look at the day/night groundwaves for KHMO shown at Radio Locator, and see where your observations might be accurate, based on their 0.5 mV/m groundwave contours that fall near Keokuk and Burlington. But a 0.5 mV/m (and less) nighttime signal on 1070 kHz probably would have quite a bit of co-channel under it.

And thanks for the kind words regarding my CKLW posts. (etc)

Thanks for the followup. I had few more observations on this, and posted them in the original thread about CKLW nighttime coverage.

 

[cyberdad]

I had a look at the day/night groundwaves for KHMO shown at Radio Locator, and see where your observations might be accurate, based on their 0.5 mV/m groundwave contours that fall near Keokuk and Burlington. But a 0.5 mV/m (and less) nighttime signal on 1070 kHz probably would have quite a bit of co-channel under it.

Actually, in the mid and late 60s, not so much. KNX and the CBC station in New Brunswick were a long way off, and the Midwest 1070s were all pretty much aimed away from where I was (WKOW, WIBC, WDIA, CHOK, KFDI to name a few). Sometimes I'd hear something under KHMO, but usually it was alone. It wasn't a spectacular signal by any means, but very reliable and essentially fade free. Probably a much different scenario today.

 

[mimo]

The last time I was in Southeast Iowa (2001) KHMO had a decent night time signal. No fading but their was some noise underneath. It was the same strength as day time, and we know just how good conductivity is in that part of the world. It probably was groundwave that we were getting.