[NLRS] Is there published data on tree foliage ...

[Dr. Gerald N. Johnson]

HDTV stations have developed a bit of frequency agility. In central 
Iowa, everybody went UHF while they converted their old analog hardware 
to digital at lower power. 5, 8, 11, and 13 moved back to their original 
RF frequencies. 17, 19 and 23 are spread over about 6 RF channels. With 
my dual band 2m and 70cm ham antennas on the roof tripod I have seen 
video from Cedar Rapids and Bradgate and with the inside antenna I 
sometimes see other channels in the Ames and Newton ares but only about 
once per month. The 70 cm antenna has to be about 45 degrees from the 
direct path to get 500 and 600 MHz signals.

Single strength at VHF and UHF does vary a great deal on even short 
paths hour to hour and day to day. I've not correlated signal strength 
with weather conditions, but I suspect its a function of refraction from 
density and humidity gradients. 4/3 earth radius is based on density 
gradient from the pressure of the air column above the elevation without 
humidity gradient. High winds tend to homogenize the lower atmosphere 
and reduce that refraction while stagnant conditions under a stalled 
high pressure dome tend to increase the refraction due to radiant 
cooling at night of the lower layers leaving warm air above cold to get 
a temperature inversion. Non sotrmy mornings tend to be better for the 
same reason.

I used to see at least 40 dB (on a generous S-meter in a FT-726R) 
variations on a 40 mile path on VHF or a 25 mile path on UHF on packet.

Historically UHF TV receive antennas have had a tendency to be very much 
narrower in frequency response than the width of the band, to the point 
that at one point UHF broadcasters sued receiving antenna manufacturers.

TV transmit antennas tend to have a narrow elevation pattern, that's how 
they get gain to cut their electric bill. Sometimes they don't include 
down tilt of the elevation pattern so close in viewers get a poorer 
signal than more distant viewers. So they can be shooting over you at a 
few miles distance and it will take a better antenna and feedline than 
further away.

TV coax can have considerable loss as the frequency rises, made worse by 
impedance mismatches. If might be significant benefit to abandon RG-59 
and RG-6 going to RG-11. Its going to take adapters for RG-11 to fit F 
connections. Belden 8213 is better than plain RG-11 for loss, but it 
isn't very flexible having a solid copper center conductor.

Most of the HDTV antennas on the retail market today are primarily UHF 
probably with much of the same limitations as those that were sued 
decades ago. I saw some a couple nights ago at wallyworld that claimed 
coverage from 54 to 88, 176 to 210 and 470 to 700 MHz on the boxes. I've 
not looked up their spec sheets yet. RCA models were ANT1600F and 
ANT1052F. GE number 34763.

Switching supplies and processing circuitry in my digital converter box 
does QRM the analog TV, so probably QRM themselves if the antenna isn't 
separated a significant distance from the converter and wall wart and 
connected with well shielded coax, like LMR.

I spent a couple afternoons in the ISU library in the last week 
researching on millimeter wave multipliers and clutter reduction for 
weather radar. Some of the articles I downloaded (now I have months of 
reading on the thumb drive) promised to discuss weather effects on radar 
signal refraction that can apply to this topic and to our long distances 
worked on microwave. I'll list them later, the downloaded file names 
generally are essentially encrypted to a number sequence so I'll have to 
read them and rename the files for future reference. Last I looked there 
were about 95 of them.

73, Jerry, K0CQ

On 7/10/2014 10:34 AM, Chris Elmquist wrote:
>
>
> On Thursday (07/10/2014 at 11:10AM -0500), Paul Husby wrote:
>>
>> Chris, I'm glad to hear that you have trouble too.  I'm only 4.5
>> miles from the towers and also have a view of them in winter.  I
>> just don't understand why I can't get enough signal sometimes.  It
>> hasn't always seemed to correlate with wet/dry conditions, but now
>> that I know it isn't just me, I will pay closer attention.
>
> I have stood down on the issue recently but this dicussion will probably
> light a fire here to dig in again.
>
> I am not sure if my problem is attentuation or multi-path.  I have
> multiple different receivers (TVs, USB tuners, ethernet connected tuners)
> and each are affected differently.
>
>> Ch4 always seems solid, Ch5 much more of a problem, as is Ch9 also.
>> I have wondered if it is significant that Ch4 has no subchannels,
>> while Ch5 has many?
>
> CH5's subchannels are the ones I have the most trouble with.  CH5s
> broadcasts are on 599 and 659 MHz.  KSTP-DT1 and -DT2 are on 599 MHz
> while -3, -4 are on 659.  I usually do not have issue with the stuff
> on 599 MHz.
>
> I also have little trouble with any of the KTCA stuff, which
> is on 527, 563 and 593 MHz or KMSP on 189 MHz or KARE on 201 MHz.
>
> Some trouble here with WCCO, which is on 581 MHz.  Go figure.
>
> So, not surprisingly, I think my trouble is a function of both frequency
> and transmitter power level.  The KSTPDT-3, -4 are lower power signals
> from the old channel 45 analog transmitter.
>
> Chris N0JCF
>