Re: [IRCA] DSP radios near transmitter sites

[Stephen Airy <pianoplayer88key@xxxxxxxxx>]

How close to the MW transmitters?  If I can do it, I'm hoping to take my PL-606 (and maybe my PL-380 as well as my SRF-59, and if I can fit it in my backpack with my Select-A-Tenna (yes I will be testing the PL-606 at the utility pole with the SAT tuned to 1170 ;)), the GE Superradio III) to 32°53'37.8"N 116°55'40.4"W or thereabouts sometime today.  About 300 feet from there is the nearest tower of a multi-tower array for 50kW 1170 KCBQ, shared with 5kW 910 KECR.  I may also check out some other spots in the general vicinity, including reading the signal strengths on the two stations (as well as 760 KFMB and 1130 KSDO whose transmitters are a few miles to the southwest), from various spots on other roads in the area.
 
I generally notice little modulation splatter beyond 10 kHz or so, but what I'll be looking at is the effects of desense, among other things.  Also when the dBµ meter is very high, like 98 dBµ, I do usually hear the station intermodulating on other frequencies.
I've noticed that when KCBQ does its day/night power change, it is usually off the air for several seconds.  Their night power is 2.9 kW, with a slightly different pattern (and tighter nulls in some directions at night than during the day).  Some day soon I hope to take advantage of this and make a recording of a nearby frequency (like 1150 for example) right at the time KCBQ is making its switch.  It won't be today, and maybe not this month, as I also want to scout around to find the nighttime signal readings of the two stations at that site.  I'm hoping to find a place where 760, 910 and 1130 are no more than about 60-63 dBµ or so, 1170 is at least 87-89 dBµ daytime and no more than about 51-57 dBµ or so nighttime, and do the sunset (or maybe sunrise) recording from there.
 
Speaking of using the SAT + utility ground and the PL-606 together ...  here's an example of what happens with 1170 in the daytime about 9.3 miles south of their transmitter. :)  http://www.youtube.com/watch?v=-w49RVGQzFc ; Maybe this should give some idea of what to expect closer to the site? ;)
Also has anyone else besides me tested a DSP radio this close to a transmitter site? ;)  https://picasaweb.google.com/118228966367965758611/TecsunPL606#5597872520572769682
 

________________________________
From: Guy Atkins <dx@xxxxxxxxxxxxx>
To: Mailing list for the International Radio Club of America <irca@xxxxxxxxxxxxxxxx>
Sent: Thursday, October 20, 2011 8:30 AM
Subject: Re: [IRCA] DSP radios near transmitter sites

The 600kw transmitter mentioned in the original post is of course far more
massive than the 50kw stations in the USA. However, the email exchange below
may be of interest regarding the D96L's front end. Gary, Kevin, myself, and
a few others did some tests in July 2009 with the Kchibo D96L. We found the
radio to be surprisingly resistant to overload when close to MW
transmitters.
73,

Guy Atkins
Puyallup, WA


--------------(below is from July 2009)----------------------------


The trip I took at noon today with the D96L to locations near three local MW
transmitters was enlightening. I stopped by Kelsey Creek Park in Bellevue,
and then had time left over to get even closer to the transmitters. I parked
near a campus of office buildings, as close as I could get to the north
boundary of Mercer Slough Nature Park (If I had consulted a map first I
could have gotten within about 500 ft. of the KKNW transmitter!

Below are the results from the two testing locations. The 1 kHz filter was
used in all instances:

>From Kelsey Creek Park

880 kHz, KIXI  (50 KW); 1.5 miles away
87 dBu on the meter
some moderate splatter +/- 10 kHz from 880
no splatter when tuned +/- 13 kHz from 880

1150 kHz, KKNW (10 KW); 1.6 miles away
89 dBu on the meter
some moderate splatter +/- 10 kHz from 1150
no splatter when tuned +/- 13 kHz from 1150

1540 kHz, KXPA (5 KW); 1.2 miles away
87 dBu on the meter
Splatter barely noted at 10 kHz +/- from 1540
no splatter when tuned +/- 12 kHz from 1540


from north end of Mercer Slough Nature Park

880 kHz, KIXI  (50 KW); 0.6 miles away
93 dBu on the meter !!
moderate splatter +/- 10 kHz from 880
no splatter when tuned +/- 13 kHz from 880

1150 kHz, KKNW (10 KW); 0.6 miles away
90 dBu on the meter !!
moderate splatter +/- 10 kHz from 1150
no splatter when tuned +/- 13 kHz from 1150

1540 kHz, KXPA (5 KW); 0.3 miles away
90 dBu on the meter !
moderate splatter at 10 kHz +/- from 1540
no splatter when tuned +/- 13 kHz from 1540

There you have it...this radio (and likely other SiLab chipped radios) have
an amazing front end. I didn't think to check for signs of images further
above and below the fundamental; I was concentrating on selectivity and
resistance to splatter near a local. There would probably be a hint of image
signal like John discovered with his biggie loop antenna slightly picking up
one of his Vancouver flamethrowers.

73,

Guy



-------------------------------------------------------------------

I tried last night, getting KOM0-1000 on the D92L at about 93-94 dB with my
active loop almost at oscillation.  The bandwidth sounded narrower than the
1 khz filter, and cycling through the bandwidths made almost no difference.
And of course, no overloads!
I will check tonight on how close I can come, but I think 20 khz is usually
pretty splatter free on the narrower bandwidths.

Kevin



-------------------------------------------------------------------

Hi Guy,

Thanks for running the detailed selectivity tests on the D96L at Kelsey
Creek Park in Bellevue last week, which were much appreciated.

In testing the D96L's ability to limit the splatter from local pest
KSUH-1450, I have checked it against both the G8, and a Murata CFJ455K5
filter modified C.Crane SWP Slider.

The apparent winner in limiting splatter was the D96L on its 1 kHz
selectivity setting, limiting KSUH's upper splatter to about 4 kHz, when the
pest was nulled. The G8 limited the splatter to about 5 kHz, while the SWP
Slider limited it to about 7 kHz.

Unfortunately, the D96L's ability to limit KSUH splatter doesn't seem to
give it the ability to receive either KARR-1460 or KUTI-1460 in the null of
KSUH. KARR-1460 can be received on both the stock G8 and the Slider SWP in
the null of KSUH in the daytime, and KUTI-1460 can also be received on the
Slider SWP (which of course has a longer, externally mounted loopstick). My
impression is that the D96L has rather modest nulling capability in
comparison to the G8 and other Ultralights, possibly related to the
loopstick's position in the cabinet. And as John and I found out at
Grayland, these type of domestic splatter tests don't necessarily translate
into superior 9-kHz split selectivity performance.

73, Gary



--------------------------------------------------------------------

Hey Guy/all:
I just checked on the D96L, and my observations match yours: with
uber-strong locals, 12-13 khz away there is no splatter with the 1 khz
filter.

On the "lowly" PL-300WT, I need to go 15-16 khz away to be splatter-free.

So, these filters do have skirts!  Man, there are some really corny jokes
that could made right now...

Kevin
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