: Splitters, Attenuators, Filters, Diplexers, Other Signal Gear
2010-11-12, 03:55 PM
Update to Post #1140: Mini Circuits ZFRSC-2075 is not good for the CM4228HD hack.
I tried the idea, bought 2 used ZFRSC-2075 on eBay, added 3 bnc-f converters and swapped this splitter from a CM splitter. Failed miserably. Even counting the insertion loss I added by using bnc-f adapters, this splitter should have been better, but it was worse. Failed... but now I know ! :D
2010-12-18, 03:26 PM
I have a 2-way splitter. The only information on it is "Wesline DM 772." (It is from my rural antenna setup from 1983.) I realize, depending on the quality and loss characteristics, the splitter could be a weak link.
Is there a splitter that is recommended?
And, if I was to combine two antennas, could I use a 2-way splitter between them or is there a better device? Some antennas have a box that snaps in place under the balun that has VHF and UHF inputs.
2010-12-19, 05:41 PM
I've tried many different splitters including the Winegard joiner (reverse splitter).
The best splitter I found is the Nexxtech "High Performance" 2-way splitter- it is quite the block and expensive.
2010-12-20, 10:55 AM
And, if I was to combine two antennas, could I use a 2-way splitter between them or is there a better device?
To combine VHF and UHF antennas, use a band combiner such as a UVSJ (or some pre-amps and as you said antennas, have one built in). If both antennas cover the same band(s) a reverse splitter can be used, but there are a bunch of disadvantages to this technique.
2010-12-27, 10:30 PM
With the impending conversion, many good stations in my area will be going digital on VHF. Unfortunately, I appear to have a rather strong electrical interference problem on VHF. The issue disappears during rain or humid conditions. I've done the AM radio check (using a low unused part of the AM spectrum), and I've also checked my own home (turning off power to entire house except TV and preamp).
I've concluded that the issue is likely with the aerial hydro lines around my home. I'm in an older area, and the hydro plant is likewise old (still using the separate 3-wire system, and not the braided single drop lines).
Of course I intend to contact the utility to see what, if anything, they will do to help. In the time being, I'm researching other alternative solutions to the issue.
One possibility I'm exploring is the use of a high-pass filter. This filter would effectively eliminate RF and noise below channel 7 (the interference is worse below 7). Yes, it will kill channel 6 Paris for me. However, this won't be an issue as the Toronto Global station is and will be easily received.
Has anyone with a similar issue had any success with a high-pass filter?
My logic here is that this interference appears to "roll up" the band, and if I can filter the majority of it out, then perhaps the high-VHF channels will clean up.
Ideas? Thanks in advance...
2010-12-27, 11:29 PM
I think we may discussed this before. Sounds pretty similar to what I see once in a while.
Where in my case I was thinking it could be from the FM tower down the Rd from me.
Everything is above ground around here too, so I suppose it could be that also.
It was a bit windy today and I was seeing the same signs during the PM for a while.
Anyhow, is it possible to hookup an extra antenna to an extra TV for testing there? Sumthin directional like a yagi? Maybe could use that to try zeroing in on the source with the yagi on the ground, and no pre-amp hooked up. Would it still be there? Or do ya think it's only able to be picked up by the sensitive antenna system w/pre-amp? I like the HPF idea, but squashing at the source is obviously ideal. Let me know what ur thinking for a decent HPF source (vendor, make, P/N, etc).
BTW, I was thinking of getting a diff pre-amp to test sometime. Something with decent NF, but only enough gain to overcome my JMPR + Downlead + Splitter losses. HDP-269 would probably be good enough for me. On the off chance that reducing the gain might help it.
2010-12-28, 12:12 AM
Yes, Majortom, I recall the discussion. In my situation, where I considered FM as a possibility, the fact the problem disappears in wet conditions made me suspect electrical interference instead. Windy conditions also appear to worsen the problem for me.
Removing the pre-amp does not fix the issue. And I've used a few different VHF antennas over the past year...so it's not a balun or connection to the antenna, as I replace coax whenever I change out equipment.
In terms of equipment, I'm considering having Tin Lee in Toronto build one for me. But I'd like to do more research first to determine if my logic is sound with regards to capturing most of the noise...or if the noise will still be present in channels 7-13 nonetheless.
2010-12-28, 12:24 AM
This image shows what I see:
2010-12-28, 10:09 AM
What Channel is that?
I've done the AM radio check (using a low unused part of the AM spectrum)
Did you hear anything in the AM radio when u were using it as a detector?
Did you roam the neighborhood at all with the AM Radio? And/Or...
Can u hear anything in your Car's AM radio when cruising around the neighborhood?
If it's electrical in nature, from the power lines, I'd suspect we'd be able to nail down the source somehow. I know ya checked ur house, but what about ur neighbors?
Keep in mind with a pre-amp, it could be quite a bit further away than we think. That's why
I was asking if it could be seen without the preamp. Sounds like it can be, so I think it's gotta be pretty close/nearby. Especially since it's able to disturb ur local Analog Reception. Don't have any strong local analog here to compare but when it does occurr,
definitely can see it in the VHF band more than the UHF band, like ur seeing. Might go up to around UHF CH 25 here...
My guess is the power company won't be of much help (I've never tried), unless you have pinpointed the source. Kinda doubt they'd go trolling the entire neighborhood looking for one guy's hunch of an interferer.
Here's what mine looks like on TVO UHF 19, real intermittent. Still pretty windy out today.
I just threw an unused output to the spec an/comm test set, turn on the AM/SSB detector to
see if I can hear any pops when it happens. BTW, If ur in to building stuff / protyping. If ya wanna try the High Pass Filter
route I'm sure we can design something, maybe like a 5 element chebyshev, with a decent amount of
attenuation in the stop band. Lower in freq the easier the design should be to build.
2010-12-28, 12:11 PM
the image Jase shows is what I experience when my girls use the hair dryer upstairs. I do experience issues on channel 6 analog. I suspect power lines cause those.
2010-12-28, 02:13 PM
here's a short movie clip (https://docs.google.com/leaf?id=0B1k4YjsB3lG6ODZiN2NjZDEtZDRjNi00NmQ0LWI0YWYtY2ZhN2V kZTJmNTk4&hl=en&authkey=CIPxsLkJ) of mine via google docs, on a spectrum analyzer, tuned to CHCH VHF 11 Audio Carrier.
Look at around 6 or 7 seconds in to it, u'll see the spike in the Noise Floor.
Can D/L it and play it back with VLC or sumthin.
2010-12-28, 08:22 PM
Majortom, the problem seems much worse in your area...judging by the pic. You may also have some impulse noise from a transmitter. Any hams in your area?
2010-12-29, 01:25 AM
Not that I'm aware of. Could very well be though, can't say I've sniffed the neighborhood
with a spectrum analyzer & a yagi. But they can be mobile too...
For kicks I went with a 7th order Chebyshev / 1dB ripple HPF
design with a cutoff freq of 156 Mhz (4 tuning coils, 3 caps = 7th order).
Theoretical / ideal attenuation in the FM band would be ~ 48 dB.
Obviously would be something less than that using real world components.
Free sample Tuning Coils on the way from Coilcraft.
We'll see if I can build it:) Fortunately I don't watch the Analog stations.
Doesn't really bother the digital much if at all.
That don't do anything, can try putting 2 Meters more in the stop band,
sacrificing a little VHF HI.
2010-12-29, 04:02 PM
Majortom: The image I posted is of channel 9 (CFTO) Toronto analog--about 57 miles away. Channel 11 Hamilton shows finer artifacts of the interference, but likely not enough to cause reception degradation once it goes digital (I'm LOS to Hamilton's tv tower).
I suppose the big question is how much noise can DTV (8VSB) tolerate before degradation appears? I suppose it depends on the tuner. But I'm working on the assumption that if you can hear ripple in the audio, it's probably going to negatively impact 8VSB modulation.
During a discussion with Tin Lee earlier this year, he indicated that 40+ dB of attenuation is desirable for FM. Most pre-amps with an FM trap only attenuate by 20dB or less. He did provide me with a quote for a sharp FM notch that would still allow channel 6 video and audio reception. But as I don't need channel 6, the VHF-HI HPF looks to be a better option both in price and performance.
Keep me posted on your experiments! I'm tempted to purchase a Spectrum Analyzer myself to do some tinkering...
2010-12-29, 04:04 PM
That don't do anything, can try putting 2 Meters more in the stop band,
sacrificing a little VHF HI.
You're probably close enough to channel 7 that strong attenuation wouldn't kill it completely for you...
2010-12-29, 06:06 PM
You're probably close enough to channel 7 that strong attenuation wouldn't kill it completely for you... Yeah, I'd say so...
Keep me posted on your experiments!
Will do. The design/attenuation characteristic I chose from normalized Chebyshev LPF tables, then ya transform to a HPF, and frequency scale it.
From there I went to the Coilcraft site to find suitable tuning coils, and ordered my Free Samples (love free stuff). I have the schematic drawn up in Eagle. Gonna use that for the PCB Layout also. I have all the stuff needed for PCB Etching here. Small Etching tank, heater, etc. Haven't used it in a really long time. But my etching solution is brand new. All we really need is time:)
I'm tempted to purchase a Spectrum Analyzer myself to do some tinkering... I don't think having a spectrum analyser is a requirement for building a Filter.
A plus for sure...Mine is pretty crappy, gotta be at least 30 years old, but it works (barely).
PS- I cracked open this old RF Circuit Design book I have, ISBN-0-672-21868-2.
My manual design, lines up identical to one of the online filter design scripts (http://www-users.cs.york.ac.uk/~fisher/lcfilter/) I saw,
when plugging in the same criteria, so it's a good manual verification.
BTW - I do think I know what causes it here. On that FM Broadcast tower, there's an OMNI stick, roughly 20-30 ft length, tough to say for sure, cause it's so high up.
It's side mounted approx 2/3 of the way up the structure. So, I'm thinkin it's traffic from that combining with the FM Broadcast (& or the AM that's co-located), or like u said, just spewing trash whenever they key up. Judging by yesterday & today it calms down after 5pm, so it's probably for some local business that's only open during the day. Also explain why it doesn't bother me much, cause I'm normally never home during the day. Wish I knew what freq it was on.
2011-01-03, 10:30 PM
Anyone wanna check out this high pass filter?
Schematic, Board layout is done in Eagle, trying to use
Thin Film SMD Caps, 5 mm tuning coils.
Quick hack job, little less than 3 inches long. Wasting a lot of real
estate, I'm no board designer...The tuning Coil Free samples
showed up today:) Find a source of caps next.
The Eagle project, Schematic and Board Layout,
as well as some .PDF Printout Docs included for anyone not
familiar with Eagle.
7th Order Chebyshev High Pass Filter VHF HI (https://docs.google.com/leaf?id=0B1k4YjsB3lG6NjQ4NzQ5NGMtYmY5NS00MjUwLThiYTMtM2VlMDR mNDU1MjYx&hl=en&authkey=CL6zsqIL)
2011-01-04, 12:00 AM
The board layout will probably work well, but could be made better I think if you desired:
-traces don't look like they are 75ohm impedance, probably just a random thickness decided upon.
-the ground plane should extend right to the inductors if possible. the traces to the ground plane add some nH of inductance to the inductor, which may not be desirable. Furthermore, the shielding of the inductor will be less effective
-I would have routed this on one layer of the board, and if you had the 2nd layer to spare, you could have left it as a ground plane, and pepper some via's around the board to tie the two ground planes together. If you are having this made at a PCB house, you can do a perimeter gnd stitch around the board
2011-01-04, 12:51 AM
no, not trying to be professional about it at all. just a quick hackjob for the basement. More for fun than anything else.
the extra L from traces may actually work out, since the tuning coil samples I have aren't shielded. Inadvertantly, I asked for the wrong ones...Though they'd probably send me some of those too if I requested 'em.
The cans tend to decrease the L and Q, shifting tunable range somewhat...so maybe between the lack of the cans, and some extra trace inductance, might fall within the range i'm lookin for a lil better. We'll see...shrunk it down a lil more already anyhow, so it's still changing.
2011-01-05, 01:13 PM
2. You need a UVSJ splitter, used as a filter.
Here's a pic that might be interesting.
Configuration for all traces is 1' of Belden 7916A on each side of UVSJ, connected between Tracking Generator out and Spectrum Analyzer in.
Green trace is with VHF port terminated with 75Ohm Terminator.
Yellow trace is with VHF port unterminated.
But... oh what games we play... Red trace is with a 6" unterminated stub connected to VHF Port.
What's the point? You can optimize a little bit by playing some games.
Look at the green (terminated) case first. The major null occurs at 217MHz, just above Ch 13. That means across the Hi-VHF band the loss goes from about 26dB at Ch 7 (174MHz) to something around 40dB at Ch 13.
In contrast, consider the red (6" unterminated stub) case. The losses here start at go from about 20dB at Ch 7 to about 30 dB at Ch 13.
Noteworthy, is that the yellow unterminated case is pretty useful. E.g. the "out of the box" and "don't put anything on the VHF port" case. Its about a 23 to to 30 dB loss across Hi-VHF, 29 to 34 dB loss across the Lo-VHF band, and a 40 db++ loss at FM.
So..... if your VHF is really strong maybe just inserting a UVSJ does the trick. But if you find its too much attentuation, you can cut the losses back, for example at Ch 13, by popping that stub onto the VHF port...