Snow ground cover induced multipath

jsb_hburg

DTVUSA Jr. Member
#1
Hello,

I believe that wet snow on the ground is causing multipath problems for WPMT.

My antenna system includes a Digitenna UXF (30 ft high), Digitenna 5 element VHF, Winegard 2870 Preamp, Pico 8 way splitter, 73 ft run of Belden RG6 to the splitter, individual RG6 runs from splitter ranging from 40 ft to 85 ft with a 3 dB attenuator on the shortest run, ground block before interior entry, mast grounded and splitter grounded.

I used a Digiair to peak both antennas for WPMT on the UXF and WGAL RF 8 on the 5-VHF. My house sits low and the antennas point over a line of arborvitae and to the left of a couple of pines.

treeline2.jpg I took the treeline photo while standing in front the chimney and aiming in sync with the antennas.

I had used some other antennas in the past to try to get WPMT and WGAL in the past and gave up, including an old style CM 8 bay for UHF. Recently, I tried again and I got WGAL 8 solidly (please ignore the other WGAL translators that have not been built yet on the TV Fool report below). Before the snow ground cover, I thought I had achieved success with WPMT.

Here is my current TV Fool Report. WPMT is 2Edge. Digiair reported 43.3 dBuV. According to my EyeTV One, the signal strength is 71% and signal quality is 100% without snow ground cover and 10% with snow ground cover with occasional signal lock.

I played around with TV Fool and noticed if I moved the antenna about 10 ft to the roof peak (and actually closer to the line of arborvitae), path improves to 1Edge with height increasing to 37 ft assuming the use of a tripod. Here is the alternative TV Fool Report.

antennaarray.jpg The alternative spot is the peak about 10 ft to the right of the chimney in the photo.

First, I'm surprised about the change in path status. Second, I noticed the improved noise margin and power. Could the fix for snow ground cover induced multipath be as simple as moving the antenna 10 ft over?

Any thoughts? Please advise. Thanks, Joe
 
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#2
Hi Joe,

I would first try raising the antenna in 6 inch increments at it's present mounting location. My gut feeling is that something has changed the sweet spot for that particular channel. I've seen as little as a 2-3 inch adjustment make a world of difference with even stronger UHF signals.

I too notice that snow affects my reception, but only while it is actually snowing. Only VHF suffers, but not sure why??? UHF is not affected.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#3
:welcome: Joe,

I live in a very difficult reception area and I had to design and build three separate antenna systems to receive most of the channels predicted by TVFOOL as available here. I also beat the odds on two channels which are theoretically out of range. My results may be atypical, but I have not had any seasonal reception changes do to vegetation and no changes do to snowfall, including the signal from one of the 'out of range' channels, KVOS-12 (35) Bellingham, 2-edge (or more) 75 miles away. This antenna 'looks' at two enormous evergreen trees, the first being about 10 feet away.

One of the channels I receive requires a 'cut-to-channel' Yagi to be located within a two foot range at about 18 feet above my roof peak: any higher or lower and I cannot receive the channel. Another four channels 'sweet-spot' is within a six inch height range roughly at my roofline on a mast mounted in my back yard, forty feet away from the front mast. This antenna when pointed west for other channels is within a foot of a large broad leaf maple tree.

One thing I noticed about your antennas is they are very close to each other and they are probably interacting. I ran the math a while back and at channel 35 (600 MHz) minimum recommended spacing is 36 inches. The lower the real channel, the greater the recommended seperation.

Does your Winegard pre-amp have separate VHF and UHF inputs? If not, the antennas must be combined with a UVSJ and not a 'standard' splitter.

It will be interesting to read what others have to say and suggest.

Jim
 

jsb_hburg

DTVUSA Jr. Member
#4
Thanks for the welcome!

The antenna separation is/should be 36 inches. The preamp has separate VHF and UHF inputs. I may have up to three inches of play considering the location of the bottom chimney strap. The roof would have to clear before I would adjust the bottom chimney strap. Ok, time to go on the roof.
 
#7
Joe,

Since that didn't help I'm now wondering if some of the stronger locals are overloading the pre-amp? I have much better signal distribution success with a distribution amp versus a preamp when strong locals are in the mix.

A similar scenario here was resolved by swapping the highly tolerant Winegard HDP-269 pre amp with a Channel Master distribution amp. My friend wanted the signal split to 4 TV's while preserving the more distant (45 miles) Baltimore channels at the same time. The difference was night & day. The only attenuation required was an FM trap before the input of the amp.

Post amplifier attenuation is rarely necessary & will not likely reverse the effects of preamp input overload.
 

jsb_hburg

DTVUSA Jr. Member
#8
Joe,

Since that didn't help I'm now wondering if some of the stronger locals are overloading the pre-amp? I have much better signal distribution success with a distribution amp versus a preamp when strong locals are in the mix.

A similar scenario here was resolved by swapping the highly tolerant Winegard HDP-269 pre amp with a Channel Master distribution amp. My friend wanted the signal split to 4 TV's while preserving the more distant (45 miles) Baltimore channels at the same time. The difference was night & day. The only attenuation required was an FM trap before the input of the amp.

Post amplifier attenuation is rarely necessary & will not likely reverse the effects of preamp input overload.

Before the snow ground cover, the signal quality for WPMT was 100%. So, might the snow ground cover cause the strong local signals to be even stronger due to reflection; thus, creating the overload in the preamp, which, in turn, is knocking out the weak UHF signal from WPMT?

If I have time in the morning, I will take the MacBook and the EyeTV on the roof and tap directly into the UXF to test this.

Thanks,
Joe
 

jsb_hburg

DTVUSA Jr. Member
#9
This morning, the initial reading was 10% signal quality and then one hour later before going on the roof, the reading is at 100% signal quality and holding firm at 72% signal strength. Figures! The sky is clear. Would multipath be more severe with the combination of overcast skies and snow ground cover?

I'm going to see if I can get an HDP-269 and a Pico UVSJ, locally, before the next storm hits.
 

Chips

DTVUSA Member
#12
I hesitate to reply to this, because I have nothing to offer from a technical aspect. But on some station my signal is greatly affected by weather. Not so much from snow as much as high and low pressures. For example right now I am picking up WNYO, I rarely receive that station, but since it has been cold, I have been able to get it for about a week now. WNYO is a very directional signal transmitting in the opposite direction from my location. Now you might think that it is the cold weather, but there are days we have been in the teens, 13 to 18 and the sun is out and WNYO is also out, right now it is snowing and 14 out and WNYO is there. I also get WGRZ it is one of my more solid stations, however when a high pressure or a strong weather front moves in, WGRZ becomes unstable. When WGRZ becomes unstable I often start to pick up the analog stations out of Toronto, about 120 air miles north of me. These conditions affect me wether there is snow or not and temperature is not always a factor, I suspect it is just the UHF signal and it's characteristics.

This morning, the initial reading was 10% signal quality and then one hour later before going on the roof, the reading is at 100% signal quality and holding firm at 72% signal strength. Figures! The sky is clear. Would multipath be more severe with the combination of overcast skies and snow ground cover?

I'm going to see if I can get an HDP-269 and a Pico UVSJ, locally, before the next storm hits.
 

jsb_hburg

DTVUSA Jr. Member
#13
When the weather clears, I am going to move the antennas to the spot predicted by TV Fool to have better reception for WPMT. I was hoping to avoid a tripod.
 

jsb_hburg

DTVUSA Jr. Member
#14
I resolved the issue. I should not have had this issue in the first place. Unfortunately, my preferred browser, Safari for Mac, does not present the option to show lines pointing to each transmitter on the TV Fool website. Using Firefox, I found the right spot to install the tripod to have a clear shot for WPMT.

Long story short, I am getting WPMT at 83% signal strength and 100% signal quality despite a 2Edge path and a 27' AGL antenna install. This a relief since it is the Fox affiliate - timing is everything! And there is nothing like incentive.

As suggested, I did increase the spacing between the two antennas to about 42". I really appreciated everyone's comments to tackle what was an avoidable multipath issue.
 
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