| Author |
Message |
Jeff Rife
Guest
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 Posted:
Thu Nov 10, 2005 5:41 am Post subject:
Re: a simple request... an OTA HD PVR |
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Sal M. Onella (salmonella@food.poisoning.org) wrote in alt.tv.tech.hdtv:
| Quote: | I'm worried that I'll clobber two or three channels on either side of the
channel
I notch out with a stub. I don't want to do that. I think I'd like to
notch out Ch 55
(KFMB-DT, San Diego) and leave Ch 53 (KABC-DT, Los Angeles).
|
If you find that it is too wide centered at 55, try building the stub for
somewhere around channel 56-58.
--
Jeff Rife |
| http://www.nabs.net/Cartoons/PaperOrPlastic.gif
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Sal M. Onella
Guest
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| Posted:
Thu Nov 10, 2005 5:41 am Post subject:
Re: a simple request... an OTA HD PVR |
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"John in Detroit" <blanked@blank.net> wrote in message
news:0Ulcf.2402$p37.292@newssvr17.news.prodigy.com...
| Quote: | Channel cut filters pricy? Wow... Guess you are not an electronics
tecnichian.
|
Bad guess. 43 years, mostly Navy Combat Systems. FCC General Commercial
License since 1983. Oh, yeah -- BS in Electronics, and a ham ticket.
I considered stubs, but they aren't very steep-sided. That is, they're not
very good
in a characteristic that's sometimes referred to as "skirt selectivity."
Commercial notch filters (for over $200.00 retail) will take out one channel
and
leave everything else.
I'm worried that I'll clobber two or three channels on either side of the
channel
I notch out with a stub. I don't want to do that. I think I'd like to
notch out Ch 55
(KFMB-DT, San Diego) and leave Ch 53 (KABC-DT, Los Angeles). I will try
a stub; although I have my doubts, I will happily announce any success
here.
Do you happen to know if a quarter wave open stub is more or less effective
than an shorted half-wave stub for notching? |
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John in Detroit
Guest
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| Posted:
Thu Nov 10, 2005 6:11 pm Post subject:
Re: a simple request... an OTA HD PVR |
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Sal M. Onella wrote:
| Quote: | "John in Detroit" <blanked@blank.net> wrote in message
news:0Ulcf.2402$p37.292@newssvr17.news.prodigy.com...
Channel cut filters pricy? Wow... Guess you are not an electronics
tecnichian.
Bad guess. 43 years, mostly Navy Combat Systems. FCC General Commercial
License since 1983. Oh, yeah -- BS in Electronics, and a ham ticket.
I considered stubs, but they aren't very steep-sided. That is, they're not
very good
in a characteristic that's sometimes referred to as "skirt selectivity."
Commercial notch filters (for over $200.00 retail) will take out one channel
and
leave everything else.
I'm worried that I'll clobber two or three channels on either side of the
channel
I notch out with a stub. I don't want to do that. I think I'd like to
notch out Ch 55
(KFMB-DT, San Diego) and leave Ch 53 (KABC-DT, Los Angeles). I will try
a stub; although I have my doubts, I will happily announce any success
here.
Do you happen to know if a quarter wave open stub is more or less effective
than an shorted half-wave stub for notching?
|
I have used stubs with good results but It has been a while.. I believe
I used a quarter wave
Which is better I don't honestly know... (in my case I wished to peak a
given frequency rather than notch one so I used a quarter wave shorted)
I prefer a shorted stub to an open one for safety reasons (A shorted
stub presents near zero resistance at DC voltages and thus will act as a
static discharge for the antenna Of course use of a proper grounding
block and/or lightening arrestor is also strongly suggested) |
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John in Detroit
Guest
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| Posted:
Thu Nov 10, 2005 6:13 pm Post subject:
Re: a simple request... an OTA HD PVR |
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Sal M. Onella wrote:
| Quote: | Do you happen to know if a quarter wave open stub is more or less effective
than an shorted half-wave stub for notching?
|
Note: The stub goes AHEAD of the pre-amp. not in it's output power line
(I know you know this but others might be reading too)
Note: 2 If it does not work... Odds are you made it out of scrap so you
are not out anything but a very few minutes of your time
I won't bore you with dimension calculations... Looks like you can do
them as easily as I My FCC license is a bit older than yours but
non-commericial |
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Dave Platt
Guest
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| Posted:
Fri Nov 11, 2005 2:32 am Post subject:
Re: a simple request... an OTA HD PVR |
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In article <2oAcf.41$MN.32@fed1read07>,
Sal M. Onella <salmonella@food.poisoning.org> wrote:
| Quote: | Bad guess. 43 years, mostly Navy Combat Systems. FCC General Commercial
License since 1983. Oh, yeah -- BS in Electronics, and a ham ticket.
I considered stubs, but they aren't very steep-sided. That is, they're not
very good
in a characteristic that's sometimes referred to as "skirt selectivity."
Commercial notch filters (for over $200.00 retail) will take out one channel
and
leave everything else.
|
I can suggest the Tin Lee company in Canada (www.tinlee.com) as a good
source for notching filters. They have a line intended for home use
which will solidly notch out one channel, weaken the immediately-
adjacent channels, and pass all other channels. The price should be
quite a bit less than the $200 you cite.
I bought one of their special-purpose filters (bandstops the 144-148
MHz 2-meter frequencies) in order to ensure domestic tranquility... it
keeps my 2-meter radio from bleeding into the over-the-air TV antenna
and saturating the distribution amplifier and causing herringbones on
all OTA channels. It works like a charm. They're the only company
I've found who seems to make such specialized filters available.
I share your suspicion that an ordinary stub may have too broad a
notch to be acceptable in your situation. You might want to consider
trying to construct a small helical filter of some sort. Or, see if
you can find somebody selling a surplus UHF duplexer at a hamfest, and
see if you can re-tune one of its notch cavities for the video-carrier
frequency of the station you want to notch out.
--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads! |
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Dave Platt
Guest
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| Posted:
Fri Nov 11, 2005 2:37 am Post subject:
Re: a simple request... an OTA HD PVR |
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| Quote: | Do you happen to know if a quarter wave open stub is more or less effective
than an shorted half-wave stub for notching?
|
The stub-filter guru I've spoken with at one of the local ham clubs
has a strong preference for using shorted stubs. He says that they're
easier to tune and to keep stable in operation.
"Open" stubs don't actually have an infinite, nonreactive impedance at
the end. There's always some capacitive reactance from end effects,
and this tends to be difficult to predict and not terribly stable
(wave the end of the stub near something and it'll de-tune). A short
circuit doesn't suffer from this... there's a bit of inductive
reactance from the short but it is low in value and tends to be quite
stable.
His feeling is that a longer, shorted stub will work better than a
shorter, open-ended stub, especially if one uses a heavy-gauge
low-resistive-loss cable to increase the Q.
--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads! |
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Sal M. Onella
Guest
|
| Posted:
Sat Nov 12, 2005 12:58 pm Post subject:
Re: a simple request... an OTA HD PVR |
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|
"Dave Platt" <dplatt@radagast.org> wrote in message
news:11n7bsnrj00fo4c@corp.supernews.com...
| Quote: | Do you happen to know if a quarter wave open stub is more or less
effective
than an shorted half-wave stub for notching?
The stub-filter guru I've spoken with at one of the local ham clubs
has a strong preference for using shorted stubs. He says that they're
easier to tune and to keep stable in operation.
"Open" stubs don't actually have an infinite, nonreactive impedance at
the end. There's always some capacitive reactance from end effects,
and this tends to be difficult to predict and not terribly stable
(wave the end of the stub near something and it'll de-tune). A short
circuit doesn't suffer from this... there's a bit of inductive
reactance from the short but it is low in value and tends to be quite
stable.
His feeling is that a longer, shorted stub will work better than a
shorter, open-ended stub, especially if one uses a heavy-gauge
low-resistive-loss cable to increase the Q.
--
Dave Platt
|
Thank you! I did a little experimenting with a quarter wave stub but
not to any great effect. I tuned my STB to Ch 55 and started trimming
to see the effect, but I didn't see much change. Each bar on the signal
strength meter is about 3 dB, based on my tests with fixed coaxial
attenuators. 10.5 cm is a 1/4-wave at Ch 55 and with an RG-59 velocity
factor of 0.66 I need a stub about 7 cm long. I think I was too long,
since I assumed a velocity factor higher than that. Back to
the workbench at first light!
I really need a spectrum analyzer and maybe a wideband noise source,
so I can see the effects of my stubs. Too bad I'm not rich.
[This thread is way off topic. My apologies for causing some of it.] |
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John in Detroit
Guest
|
| Posted:
Sat Nov 12, 2005 7:45 pm Post subject:
Re: a simple request... an OTA HD PVR |
|
|
Sal M. Onella wrote:
| Quote: | "Dave Platt" <dplatt@radagast.org> wrote in message
news:11n7bsnrj00fo4c@corp.supernews.com...
Do you happen to know if a quarter wave open stub is more or less
effective
than an shorted half-wave stub for notching?
The stub-filter guru I've spoken with at one of the local ham clubs
has a strong preference for using shorted stubs. He says that they're
easier to tune and to keep stable in operation.
"Open" stubs don't actually have an infinite, nonreactive impedance at
the end. There's always some capacitive reactance from end effects,
and this tends to be difficult to predict and not terribly stable
(wave the end of the stub near something and it'll de-tune). A short
circuit doesn't suffer from this... there's a bit of inductive
reactance from the short but it is low in value and tends to be quite
stable.
His feeling is that a longer, shorted stub will work better than a
shorter, open-ended stub, especially if one uses a heavy-gauge
low-resistive-loss cable to increase the Q.
--
Dave Platt
Thank you! I did a little experimenting with a quarter wave stub but
not to any great effect. I tuned my STB to Ch 55 and started trimming
to see the effect, but I didn't see much change. Each bar on the signal
strength meter is about 3 dB, based on my tests with fixed coaxial
attenuators. 10.5 cm is a 1/4-wave at Ch 55 and with an RG-59 velocity
factor of 0.66 I need a stub about 7 cm long. I think I was too long,
since I assumed a velocity factor higher than that. Back to
the workbench at first light!
I really need a spectrum analyzer and maybe a wideband noise source,
so I can see the effects of my stubs. Too bad I'm not rich.
[This thread is way off topic. My apologies for causing some of it.]
There was an article in QST some time back (1970's perhaps) on a gated |
noise source for use in tuning VHF/UHF receivers. Two authors, one was
Ted Hartson, I think his call was WB8ULG but I'm not sure.
Ted build his for less than fifteen bucks... Very useful tool |
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Sal M. Onella
Guest
|
| Posted:
Sun Nov 13, 2005 5:41 am Post subject:
Re: a simple request... an OTA HD PVR |
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|
"John in Detroit" <blanked@blank.net> wrote in message
news:4mmdf.11041$Lv.8600@newssvr24.news.prodigy.net...
| Quote: | There was an article in QST some time back (1970's perhaps) on a gated
noise source for use in tuning VHF/UHF receivers. Two authors, one was
Ted Hartson, I think his call was WB8ULG but I'm not sure.
Ted build his for less than fifteen bucks... Very useful tool
|
Thank you. |
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