FM Signal strength - When to take action?
 

Curios as to if I have enough FM filtering for my future antenna setup. Been working and getting ready for some upgrades before football season and before I get things all put together I was just wondering if one FM trap is enough for my location.

My primary station I have issue with is 34, which we have chatted about before and they went to half power along the way. I've finally gotten high enough to get to 2 Edge vs Tropo. Future setup will also have Kitz Tech - KT-500 amp with an FM filter built in.

http://www.tvfool.com/?option=com_wr...82302a495e1279

FM Fool Report
http://www.fmfool.com/index.php?opti...pper&Itemid=29

It is necessary to post the image of the FM Fool report, that tool does not provide a means to linking to the report.

You'd also need to obtain specifics on the FM filter in the KT amp since there are no published data for it.

Keep in mind at the TVFool modelling engine is ONLY an approximation and is based on data of limited resolution. There are inherent limitations in it that make the results of small changes in the input height pretty much an exercise in futility and that will probably make those results useful for entertainment purposes only. The real data comes when you actually put the antenna up in the air and probe at different levels to see what signal is actually there.

Sorry about the post mistake.

Here is the image of the FMFool, which has a fair number of LOS transmitters. I'm just not familiar enough with the signal strengths to know what might be too much.


http://i878.photobucket.com/albums/a...psyap1ynjb.jpg


Here is what the KitzTech KT-500 looks like on the inside - don't know if there is anything that looks familiar there. What I should have done was offer to drop ship it to you for "official" testing.

http://i878.photobucket.com/albums/a...psc93c3748.jpg

Kitz would need to provide you with a graph of the FM filter's performance, a photo reveals nothing about the filter's parameters. Sure, I can test it if you'd like. Haven't seen a sample of that model.

I'd just throw a HLSJ (cap the L input with a terminator) on the front end of the pre-amp and be done with it since you don't have any low-VHF to worry about.

FM usually causes problems on high-VHF first, but an amp, in the presence of any strong signal, can go into compression and cause weak signals to be lost. It's simply better to keep the strong signals out of the amplifier in the first place.

ADTech, if I buy another one as a backup, I will touch base with you for testing of the KT-500.

The fog is kind of clearing now with the concept of the HLSJ to truly scrub out those signals. I'll have two separate antennas, one UHF and one VHF-Hi combined via UVSJ. So the actual sequence will be (UHF antenna - KT-500 #1) and (VHF-Hi antenna HLSJ ran "backwards" fed into the combined, cap with terminator on VHF-Lo, then VHF-Hi outputt into KT-500 #2). Coax #1 & Coax #2 combined properly with UVSJ for my viewing pleasure.

Guess I'm ordering an HLSJ and not putting up the VHF today, which is fine. Next weekend is a Holiday and if it does not rain :mad: then I might get everything done.

Thanks for the input!

Thinking - does the HLSJ pass power on both sides in either direction? Or is that like the UVSJ's where it depends upon the brand?

Your sequence is wrong, plus you only need one amp.

Connect the two antennas with a UVSJ, insert the HLSJ as the high pass filter, then feed filtered signal into the amp.

ADTech made some measurements of 2 HLSJs and I added some notes to the results to help me understand them. This might help clear the fog:

http://forum.tvfool.com/attachment.p...8&d=1435520228

ADTech quoted:
http://www.digitalhome.ca/forum/81-o...ml#post1396123

comments by holl_ands:
http://www.avsforum.com/forum/25-hdt...l#post30726945

Holland specs:
http://www.hollandelectronics.com/ca...-Diplexers.pdf

There is a long thread here about FM filters:
http://www.avsforum.com/forum/25-hdt...fm-filter.html

post #23 of 124 has curves of the MCM FM Filter:
http://www.avsforum.com/forum/25-hdt...l#post29973297

http://www.mcmelectronics.com/produc...-FM-88-/33-341
.

Ok, let me make another run at this with a bit more understanding and more clarity.

As my UHF and VHF antennas will be separated by necessity by about 20' I'll have to amp them individually. The UVSJ that I have is a Blonder Tongue and feeds power on the VHF side for reference.

So...

UHF #1 - KT-500 #1 - power inserter #1 - UVSJ "A" (High Side)

VHF #2 - (HLSJ in on High side - out on combined, terminate Low side) - KT-500 #2 - power inserter #2 - UVSJ "A" (Low Side), then the combined signal out of UVSJ "A" leads to TII Lightning Surge Protector w/ Ground Block feeding main incoming coax for viewing enjoyment.

Better?

Power inserters #1 and #2 are outside?

If the UVSJ passes power on the low side, why is the power inserter for the VHF preamp between the preamp and the UVSJ?

... Well yes, the inserters are outside but in an enclosure at the base of tower with power and a ton of other "stuff".

I'll have to go see about re-cabling to place the VHF inserter on the house side of the UVSJ. Is there a worthwhile reason for me to get that switched around now?

You're probably making this much more difficult than it needs to be. I doubt you actually need to amp UHF and VHF separately. 20' of RG6 coax only attenuates VHF signals by about .6 dB which is pretty close to nothing in the grand scheme of things. Based on your chart, KOMU and KRCG should have ample margin to tolerate that little extra bit of insertion loss. Plus, you completely omitted the factor that you'd then need TWO HLSJ devices as high pass filters, one for each amp.

Here's my specific recommendation:

Mount UHF antenna where it needs to be and the VHF antenna where it needs to be. Run a cable from the VHF antenna to the UHF antenna's location and combine them using the UVSJ. Run that into the capped HLSJ to eliminate everything below channel 7, then immediately amplify with the KT500. Install the power inserter at the other end of your lead-in and you're done.

Your proposed scheme adds the cost of a second amp, a second cable run, a second FM filter, and double the amplifier power consumption all in a effort to save 6/10ths of a dB of signal on the VHF band. Therefore, I have to ask you, do you really need that?

Follow the K.I.S.S principle.

ADTech, good suggestions/recommendations, I always respect your opinion. Probably should have thought of that before now, but alas I did not. The 20' separation is up. As in to accomplish that my bellybutton will need to be above my 80' tower and after I make my way around 7 different receivers/dishes/mounting hardware etc.

http://i878.photobucket.com/albums/a...psqrlpbypa.jpg

So I land in the complicated category.

Now trying to wrap my mind around the 2 HLSJ's. So, your suggesting that the UHF needs this also? I will have a FM filter of unknown capabilities in the KT-500 on the UHF and that will also pass through the High side of the UVSJ, after it is amplified. (certainly not as good as your suggestion) Which I take as a bad thing. I have a similar setup on a 60' tower all UHF without VHF and UHF antenna with the KT-500 is 95% on WDAF/34. So, I have to hope my more powerful new UHF with higher gain peaked on that channel will work. It is all theory for now.

What are you using for your UHF and VHF antennas respectively?

Strong FM signals will still be picked up by almost any antenna. The 91XG, for example, with its 8' boom, picks up a LOT of FM from the side via non-intuitive means.

Suppression of extraneous signals must be done PRIOR to amplification, otherwise, they can either mix with other signals (creates unwanted products) or drive the amp into compression which reduces the amp's sensitivity to weak signals.

That makes things more clear now. I had ordered an extra HLSJ anyway. So I will need to cut that in ahead of the UHF outside that weatherproof amp enclosure and protect with mastic tape, a pain yes, but doable. What I need is decent weather.

Antennas - well... the UHF is a DBGH20 optimized for max gain on 34 with a null for 14 at the rear with gain lobes for 17 & 22 at the rear, so I can only have one UHF and get signals in both directions. The UHF is a GH6. These are of the 4NEC optimized optimized type via nikiml's site.

UHF - as seen on top of picture
http://clients.teksavvy.com/~nickm/dbgh_u.html

VHF - is complete and awaiting mounting
http://clients.teksavvy.com/~nickm/gh_n_vV.html

With those antennas, you'd have to work out what they might do with nearby FM, there isn't any data on that.

Agreed. I'll put it ahead of the amp on both.

I can see about running a freq scan on the lower ranges to see what they might be susceptible to.

On the UHF gain to the rear is higher by about 1 db. That would be in the general direction of the most powerful FM, at that freq of 92.3 I would be around 3.86 gain max, it will be off to the side of that, but I need to look at the max.

On the VHF, max gain is also off the backside and in this case it seems pretty blind to FM. Max gain projected on that signal of -10.5 The most it does is -8.51 around 80mhz at the rear.

My way of thinking is I need the filter more on the UHF antenna ahead of the amp, over the VHF.

Thanks again. Must say the 4nec modeling is kind of fun when you can check all the spec's out yourself.

UHF reception patterns do not translate to FM patterns as the antenna will often have very different behaviors outside of its design band. They may well be very, very different .. or not. The antennas probably need to be modeled across the FM band to see what to expect... or just install the high-pass filters and don't worry about it.

Nice tower photo, Flint Ridge.

It isn't just the fundamental overload from KSDL at -14.0 dBm you need to be concerned about, but also second harmonics from FM signals in the VHF-High band:

Testing for DTV Interference
http://www.tvtechnology.com/expertis...ference/202503

ADTech, I did model them looking at 80 - 110 mhz to see what it was doing on the FM bands, that is where I got my info. And yes, install the high pass filter is the safe bet for sure.

looks like rabbit73 gave me a reading assignment which looks interesting and well help clear some more fog.

The tower is very nice. If I ever get everything done, I should post a retrospective in going after weak signals. But if you look long enough you can find towers "cheap".

double post

Do you happen to have the gain, VSWR, and polar plots for that simulation?

Do you want it on both antennas? The GH6 is so much simpler so that run does not take long. Here is the VHF antenna, is this what you were looking for?

SWR
http://i878.photobucket.com/albums/a...psmexcm22b.jpg

Gain across FM - looks like I shaved the freq off the bottom, should be enough to go by.
http://i878.photobucket.com/albums/a...psn4pak8gx.jpg

Basic Plots 80 - 90 - 100 - 110 Freq is in upper left corner. Front of antenna is to the right.
http://i878.photobucket.com/albums/a...psixgmtwld.jpg

http://i878.photobucket.com/albums/a...psmcewssyj.jpg

http://i878.photobucket.com/albums/a...psllcbskg6.jpg

http://i878.photobucket.com/albums/a...psp167fb8o.jpg

Guess I should start a run on the UHF and come back later and check it.

UHF - Higher FM gain to the rear. Any questions or need more info, let me know.

http://i878.photobucket.com/albums/a...psppp6urpv.jpg

http://i878.photobucket.com/albums/a...psytgfnw4t.jpg

http://i878.photobucket.com/albums/a...psaklcsszm.jpg

http://i878.photobucket.com/albums/a...psbczxwzru.jpg

http://i878.photobucket.com/albums/a...psry2dffca.jpg

Finally received the HLSJ today, with a heat index of 104, who knows when I get it mounted. Just to be certain and not engage in more wasted time etc.

Antenna in on HLSJ high side, out on combined, cap low side?

Thanks,

Flint

That sounds right to me.

I agree with ADTech.

I do have a minor concern about HLSJs. If you put one in front of a UHF amp, will the high side, which is a high pass filter, introduce any significant insertion loss for the high end of UHF? It was never really designed for that task, and the specs of some say passes 170 to 600 MHz.
http://www.hollandelectronics.com/ca...-Diplexers.pdf
http://www.nsccom.com/productpdfs/btl/dsv.pdf

ADTech:
Please comment on my concern.

Perfect. Thanks guys, now I just need to get it all together, mounted, aimed etc. Nice part is I am not disturbing my existing setup, so I can do a side by side and see what I have "gained".

Again, thanks.

I tested the Pico and the Holland HLSJ units several years back. The specs are simply incomplete, there's negligible insertion loss up in UHF land. I'll see if I can dig up either the old data and/or the samples I had from back then and rerun them using my much newer and more accurate gear.

Google to the rescue. See this post: http://www.digitalhome.ca/forum/81-o...ml#post1265531

Holland HLSJ measured, Pico similar.

http://i1203.photobucket.com/albums/...SJFreqResp.gif

I ended up the the Blonder Tongue, just to confuse the matter.

If you are concerned I might be headed into a bad direction. I could proceed without them and then see the results and if needed, head back up and splice them in ahead of the amp.

Thanks for the data. I'm feeling better already.

http://forum.tvfool.com/attachment.p...1&d=1437012689

Well, weather broke. Was able to get it hoisted up and secured. Did not play around with the variable amp much, but it all works and is solid. Time will tell as always. SNR ratios on my old 194 pound Sony CRT indicates 28 - 32 SNR on these two channels. Can check for more detail on my Aero-M once it is not recording. Does what I needed.

Filter in front of amp, I've got it going through my new gear, but then also scabbed into my existing setup with another UVSJ hooked to my existing UHF. More upgrades in the weeks ahead... Thanks all, very helpful as always guys pointing me in the right direction. I really appreciate what you do.

http://i878.photobucket.com/albums/a...psmniyluh0.jpg

http://i878.photobucket.com/albums/a...ps0t7cliqd.jpg

SNR on my weak #13 is 24 and 28 on #8

Glad that we were able to help, but you did all the work.:)

The GH6 looks very impressive up there, and it sounds like it is living up to its computer modeling predictions.

I like your photo of the GH6 with the car which shows how big it is. I couldn't resist the urge to add a caption; hope you don't mind.
Which callsigns, KRCG CBS NM 7.9 and KOMU NBC NM 14.4 dB?

The photo work is fine. And yes the call signs are KOMU for ch#8 at around 14NM and KRCG for #13, which is really #12 which always confuses me. Makes me wonder if I cut the balun for the right channel. It's NM is all over the place, meaning depending on height. Supposedly it is best at ground level? Through trees etc. I think I'm around 6.4 at my height, but at ground it might be another 1.5 db. Seems to be holding well today. Did see it blip off once with a bunch of errors early in the day. Might be useful for me to actually work with the variable amp and see if it is at the best SNR, might be pushing it too hard. Are single digit VHF really hard to pull in?

If there's local electrical noise, yes. Otherwise, not that much. I can routinely pick up KOMU from our family farm about 56 miles ESE of Columbia, NM in the mid negative single digits with nothing more than our VHF dipole kit and a preamp.... unless the power lines within several hundred yards are radiating. The electrical noise, which is plainly visible on the spectrum analyzer, wipes out the very weak KOMU signal. KRCG is about 15 miles closer with an estimated NM of around 15 dB and doesn't get affected at the tuner.

I need to fine tune the amp to eliminate that out of the mix. It randomly cut out again with tons of errors. Of course it is going through a highband filter an amp and then two UVSJ's. I could bypass some of my prep work I guess.

It confuses a lot of people. If you cut it for the frequency of the real channel, you're OK. Even if you didn't, you're still OK. Calaveras, who wanted the lowest loss balun possible, cut his half-wave coaxial baluns for his stacked 91XG UHF antennas for the middle of the UHF band. Then, he wanted to eliminate the combiner loss and connected the two 75 ohm lines in parallel, which gave 37.5 ohms. That was converted back to 75 ohms with a quarter-wave 50 ohm matching section.
http://www.aa6g.org/DTV/ABD/Antenna_Block_Diagram.html

The real channel is what the transmitter uses, and it determines what antenna you should use. The virtual channel number is a holdover from analog TV days, and is retained by the station to maintain continuity of identity for the viewer. Sometimes the real channel number and the virtual channel number are the same if the station stayed on the same channel.
.
To avoid confusion, an experienced user like you should only use the real channel number. If you use the virtual channel number, it should be in decimal form as, for example, 13.1. Some of the stations on a TVFOOL report don't even have a virtual channel number listed, only a real channel number.

The real channel number is for techs like us; the virtual channel number is what is displayed on the TV for the viewer.