Tetra
 

I have a Tetra filter before my indoor amp, which i beleive also has a
Tetra filter built in.

Are there any Pros or Cons to this setup.

Im thninking that two filters only make the sides of the Filter
steeper,


thanks

gaz

Tetra
 

"Garry" wrote in message
...
I have a Tetra filter before my indoor amp, which i beleive also has a
Tetra filter built in.

Are there any Pros or Cons to this setup.

Im thninking that two filters only make the sides of the Filter
steeper,


thanks

gaz


Do you suffer from TETRA interference?

There's nothing wrong with what you've done.
I expect a specific tetra filter will be tighter than that built into your
amp.

I can't remember whether 2 simple filters in series will increase the
drop-off rate or not. I think it does. It will also increase the
attenuation in the pass-band. If you have sufficient signal, that's
probably OK.

Stagger-tuning certainly does, as in old IF strips.

I have quite specific channel-pass filtering before my distributuion system,
and it certainly does not cause problems.

--
Ron

Tetra
 

"Ron Lowe" ronATlowe-famlyDOTmeDOTukSPURIOUS wrote in message
...
"Garry" wrote in message
...
I have a Tetra filter before my indoor amp, which i beleive also has a
Tetra filter built in.

Are there any Pros or Cons to this setup.

Im thninking that two filters only make the sides of the Filter
steeper,


thanks

gaz


Do you suffer from TETRA interference?

There's nothing wrong with what you've done.
I expect a specific tetra filter will be tighter than that built into
your amp.

I can't remember whether 2 simple filters in series will increase the
drop-off rate or not. I think it does. It will also increase the
attenuation in the pass-band. If you have sufficient signal, that's
probably OK.

Stagger-tuning certainly does, as in old IF strips.

I have quite specific channel-pass filtering before my distributuion
system, and it certainly does not cause problems.

--
Ron



Two filters in series will not change the slope of the attenuation
unless the filters have different characteristics. The filter will be
made up of capacitors and coils (inductors.) They can be made to act as
a filter at the same frequency using different values of both
components.

If the same component values are used in each filter then you will get
the same filtration as one filter but will have more loss on the signal
you want to use.

If different values are used then you may well get more filtration, but
again at the cost of more loss in the wanted signal.

I know this may sound daft, but do you actually have a problem with
Airwave (a specific system and frequency band as against a type of
transmission (Tetra) that can be used in any band) or are you just
hedging your bets? If you don't have a problem don't filter it.


--
Woody

harrogate three at ntlworld dot com

Tetra
 

In article , Woody
writes
"Ron Lowe" ronATlowe-famlyDOTmeDOTukSPURIOUS wrote in message
. ..
"Garry" wrote in message

...
I have a Tetra filter before my indoor amp, which i beleive also has a
Tetra filter built in.

Are there any Pros or Cons to this setup.

Im thninking that two filters only make the sides of the Filter
steeper,


thanks

gaz


Do you suffer from TETRA interference?

There's nothing wrong with what you've done.
I expect a specific tetra filter will be tighter than that built into
your amp.

I can't remember whether 2 simple filters in series will increase the
drop-off rate or not. I think it does. It will also increase the
attenuation in the pass-band. If you have sufficient signal, that's
probably OK.

Stagger-tuning certainly does, as in old IF strips.

I have quite specific channel-pass filtering before my distributuion
system, and it certainly does not cause problems.

--
Ron



Two filters in series will not change the slope of the attenuation
unless the filters have different characteristics. The filter will be
made up of capacitors and coils (inductors.) They can be made to act as
a filter at the same frequency using different values of both
components.

I was thinking the same myself but after winding back a few years I have
changed my mind:

Take 2 identical filters and assume that they pass 100% in the pass
band, so adding 2 in series gives 100% in the pass band.

Change the frequency until there is a 6dB loss per filter. Filter 1 sees
0dB level and attenuates it to -6dB. Filter takes the -6dB level and
attenuates it a further 6dB giving -12dB.

So we have that 2 filters in series attenuate twice as much as a single
for a given out of band frequency and therefore have a steeper cutoff.

As I was thinking of this I was reminded of 1 and 2 stage audio filters
with their 6 and 12dB per octave cutoff so I think it makes sense.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

Tetra
 

Im thninking that two filters only make the sides of the Filter
steeper,

I can't remember whether 2 simple filters in series will increase the
drop-off rate or not. I think it does.

Two filters in series will not change the slope of the attenuation
unless the filters have different characteristics.

I was thinking the same myself but after winding back a few years I have
changed my mind:

Take 2 identical filters and assume that they pass 100% in the pass band,
so adding 2 in series gives 100% in the pass band.

Change the frequency until there is a 6dB loss per filter. Filter 1 sees
0dB level and attenuates it to -6dB. Filter takes the -6dB level and
attenuates it a further 6dB giving -12dB.

So we have that 2 filters in series attenuate twice as much as a single
for a given out of band frequency and therefore have a steeper cutoff.

As I was thinking of this I was reminded of 1 and 2 stage audio filters
with their 6 and 12dB per octave cutoff so I think it makes sense.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs


Yes, that was my basic reasoning too.
That's why I said I think it does.

I * really* don't want to go dig up my old university textbooks.
I resisted opening them then, and I'm not really that keen on changing that.

They are up on a shelf here, glowering down at me...

I also think that stagger-tuning a series of filters can make the cutoff
rate much steeper.

--
Ron

Tetra
 

The message
from fred contains these words:

In article , Woody
writes
"Ron Lowe" ronATlowe-famlyDOTmeDOTukSPURIOUS wrote in message
. ..
"Garry" wrote in message

...
I have a Tetra filter before my indoor amp, which i beleive also has a
Tetra filter built in.

Are there any Pros or Cons to this setup.

Im thninking that two filters only make the sides of the Filter
steeper,


thanks

gaz


Do you suffer from TETRA interference?

There's nothing wrong with what you've done.
I expect a specific tetra filter will be tighter than that built into
your amp.

I can't remember whether 2 simple filters in series will increase the
drop-off rate or not. I think it does. It will also increase the
attenuation in the pass-band. If you have sufficient signal, that's
probably OK.

Stagger-tuning certainly does, as in old IF strips.

I have quite specific channel-pass filtering before my distributuion
system, and it certainly does not cause problems.

--
Ron



Two filters in series will not change the slope of the attenuation
unless the filters have different characteristics. The filter will be
made up of capacitors and coils (inductors.) They can be made to act as
a filter at the same frequency using different values of both
components.

I was thinking the same myself but after winding back a few years I have
changed my mind:

Take 2 identical filters and assume that they pass 100% in the pass
band, so adding 2 in series gives 100% in the pass band.

Change the frequency until there is a 6dB loss per filter. Filter 1 sees
0dB level and attenuates it to -6dB. Filter takes the -6dB level and
attenuates it a further 6dB giving -12dB.

So we have that 2 filters in series attenuate twice as much as a single
for a given out of band frequency and therefore have a steeper cutoff.

As I was thinking of this I was reminded of 1 and 2 stage audio filters
with their 6 and 12dB per octave cutoff so I think it makes sense.

That's exactly right! Saves me pointing out the bleeding obvious to
Woody. ;-)

--
Regards, John.

Please remove the "ohggcyht" before replying.
The address has been munged to reject Spam-bots.

Tetra
 

The message
from "Ron Lowe" ronATlowe-famlyDOTmeDOTukSPURIOUS contains these words:

Im thninking that two filters only make the sides of the Filter
steeper,

I can't remember whether 2 simple filters in series will increase the
drop-off rate or not. I think it does.

Two filters in series will not change the slope of the attenuation
unless the filters have different characteristics.

I was thinking the same myself but after winding back a few years I have
changed my mind:

Take 2 identical filters and assume that they pass 100% in the pass band,
so adding 2 in series gives 100% in the pass band.

Change the frequency until there is a 6dB loss per filter. Filter 1 sees
0dB level and attenuates it to -6dB. Filter takes the -6dB level and
attenuates it a further 6dB giving -12dB.

So we have that 2 filters in series attenuate twice as much as a single
for a given out of band frequency and therefore have a steeper cutoff.

As I was thinking of this I was reminded of 1 and 2 stage audio filters
with their 6 and 12dB per octave cutoff so I think it makes sense.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs


Yes, that was my basic reasoning too.
That's why I said I think it does.

I * really* don't want to go dig up my old university textbooks.
I resisted opening them then, and I'm not really that keen on changing that.

They are up on a shelf here, glowering down at me...

I also think that stagger-tuning a series of filters can make the cutoff
rate much steeper.

You're thinking of the IF _amplifier_ strip using simple LC tuned
circuits where this was indeed a common practice, especially in the case
of the 10.7MHz IF strips used for wideband FM.

However, when using bandpass filters which have a nominally flat
bandpass across the whole of the required range, there is no need for
'stagger tuning' to recreate a flat bandpass effect.

In either case, the skirt response would be steepened resulting in
better adjacent channel rejection performance.

--
Regards, John.

Please remove the "ohggcyht" before replying.
The address has been munged to reject Spam-bots.

Tetra
 

"Woody" wrote in message
...
Two filters in series will not change the slope of the attenuation unless
the filters have different characteristics. The filter will be made up of
capacitors and coils (inductors.) They can be made to act as a filter at
the same frequency using different values of both components.

If the same component values are used in each filter then you will get the
same filtration as one filter but will have more loss on the signal you
want to use.

Nay lad! Suppose the through loss is 3dB (average across the channel) and
the loss 8MHz away is 16dB. With two filters in series the through loss will
be 6dB and the loss 8MHz away will be 32dB. So the slope will have gone from
13dB/8MHz to 26dB/8MHz. That, unsurprisingly, is twice the rate of
attenuation.

I'll give thee a practical example. I recently built a system that used VSB
modulators for the in-house channels and carried the off-air analogues and
muxes on their received channels. Since the mods were VSB I could if I
wished have used every channel, in theory. I didn't use the channels one
above any of the off-air ones though, because there's no way passive filters
will have any worthwhile effect on the video carrier frequency of the next
channel up. I was using passive filters for the off-airs to keep costs down,
by the way. If I'd used 'smart' filters I could have filled every channel
from 21 to 68 if I'd wished. Anyway, imagine my dismay when some of the
in-house channels one below an off-air channel showed signs of CCI,, which
could be removed by unpowering the aerial's masthead amp. Bugger! Obviously
the slope of the passive filters wasn't enough to attenuate the video
carrier of the next channel down sufficiently. I thought it would be enough,
but I had underestimated the amount of crap the aerial would suck in on
certain channels. And you can be sure that if there's a little bit of CCI
visible on anormal day it will be wipeout time when there's a lift. I was
clean out of channels, so I couldn't just move off the affected ones. I put
another set of 11 single channel filters in front of the existing ones. So
instead of three tuned stages I now had six. I connected a noise gen in
place of the aerial and tuned the filters very carefully. I didn't want any
roll off that might kill the nicam and I wanted the muxes to be reasonable
flat, and I wanted a sharp cut off acrss the adjacent lower channel. I was
prepared to add strategic notch filters, but I didn't need to. It worked
without.

Bill

Tetra
 

On Oct 29, 2:20*am, "Bill Wright"
wrote:
"Woody" wrote in message

...

Two filters in series will not change the slope of the attenuation unless
the filters have different characteristics. The filter will be made up of
capacitors and coils (inductors.) They can be made to act as a filter at
the same frequency using different values of both components.

If the same component values are used in each filter then you will get the
same filtration as one filter but will have more loss on the signal you
want to use.

Nay lad! Suppose the through loss is 3dB (average across the channel) and
the loss 8MHz away is 16dB. With two filters in series the through loss will
be 6dB and the loss 8MHz away will be 32dB. So the slope will have gone from
13dB/8MHz to 26dB/8MHz. That, unsurprisingly, is twice the rate of
attenuation.

I'll give thee a practical example. I recently built a system that used VSB
modulators for the in-house channels and carried the off-air analogues and
muxes on their received channels. Since the mods were VSB I could if I
wished have used every channel, in theory. I didn't use the channels one
above any of the off-air ones though, because there's no way passive filters
will have any worthwhile effect on the video carrier frequency of the next
channel up. I was using passive filters for the off-airs to keep costs down,
by the way. If I'd used 'smart' filters I could have filled every channel
from 21 to 68 if I'd wished. Anyway, imagine my dismay when some of the
in-house channels one below an off-air channel showed signs of CCI,, which
could be removed by unpowering the aerial's masthead amp. Bugger! Obviously
the slope of the passive filters wasn't enough to attenuate the video
carrier of the next channel down sufficiently. I thought it would be enough,
but I had underestimated the amount of crap the aerial would suck in on
certain channels. And you can be sure that if there's a little bit of CCI
visible on anormal day it will be wipeout time when there's a lift. I was
clean out of channels, so I couldn't just move off the affected ones. I put
another set of 11 single channel filters in front of the existing ones. So
instead of three tuned stages I now had six. I connected a noise gen in
place of the aerial and tuned the filters very carefully. I didn't want any
roll off that might kill the nicam and I wanted the muxes to be reasonable
flat, and I wanted a sharp cut off acrss the adjacent lower channel. I was
prepared to add strategic notch filters, but I didn't need to. It worked
without.

Bill

Thanks for the Answers, No im not suffering from Tetra, So i think ill
remove and see what its like.

Gaz