Maker Pro
Maker Pro

Front End (TUNER)

J

Joerg

Jan 1, 1970
0
Frank said:
Frank said:
Phil Allison wrote:
[lot of snip]
** What the **** does that mean ?
But what really miffed me was this: Placed the antenna on a mast after
re-roofing the house. So, I equipped it with a nice preamp, splitter,
postamps with eight outputs .....
** And then this ASS blames his TV set's tuner for the bad outcome.
Pathetic really.
....... Phil
I presume you meant to say that the performance of most preamps would
limit linearity, and would dominate IP3, etc. over the tuner. That's
true, although I've seen some that don't ... I've designed some that
don't; maybe Joerg used a commercial model.

Well, yeah. If a lab grade receiver works just fine and the TV on the
same antenna is turning into a hopeless pile of intermodulation it's
pretty clear that the TV isn't up to snuff. Which didn't surprise me. I
just didn't expect it to be this bad.


Agreed. Did you do any tests on the TV tuner? IP2, 2-tone IM, etc.?
Did it use a solid state tuner or a "can"?

I did back in the 90's. Shook my heard and discarded the tuners
afterwards, then cracked out a Mini-Circuits DBM to build the receiver.
In the 80's they were better but there I used tuners scrapped out of
older TVs. Probably the older engineers still knew how to do it. One had
Ge-Transistors (AF239?) and was, well, somewhat ok. The other one had
two tubes and was quite excellent.

And sure enough the TV where that tube tuner came out of was the best
(until it's flyback XFMR went up in a plume of smoke one fine day). When
a powerful pager system was installed near our home almost all "modern"
transistorized TVs fell off the rocker. This signal was even
out-of-band, BTW. Telecom came out with lots of expensive Rhode&Schwarz
gear, determined that poor tuner design was to blame so they were not
legally obliged to do anything about it yada, yada, yada.... Lots of
negative PR mounted and then they agreed to supply notch filters for
free. I mounted a lot of these for neighbors because installation was
not included.

Besides the transistor versus tube thing there was another major
difference: The tube tuner had a ganged variable capacitor while the
transistor version used varicap diodes. I did not investigate the tuners
in our current sets. Not really worth it. Not just because of lousy RF
performance but except for an occasional old movie and the evening news
there ain't much to watch anyhow.

Even the old tuners were "in a can", except that those cans were the
size of a small paperback book. Very nicely done. For example, they had
thin copper foil on a rubber cushion to make sure that the lid was
RF-tight. They don't make'em like that anymore :-(
 
R

Rich Grise

Jan 1, 1970
0
Frank said:
"Joerg"
Phil Allison wrote:
[more snip]
But what really miffed me was this: Placed the antenna on a mast after
re-roofing the house. So, I equipped it with a nice preamp, splitter,
postamps with eight outputs .....
[still more snip]
I presume you meant to say that the performance of most preamps would
limit linearity, and would dominate IP3, etc. over the tuner. That's
true, although I've seen some that don't ... I've designed some that
don't; maybe Joerg used a commercial model.

Well, yeah. If a lab grade receiver works just fine and the TV on the
same antenna is turning into a hopeless pile of intermodulation it's
pretty clear that the TV isn't up to snuff. Which didn't surprise me. I
just didn't expect it to be this bad.

Did you try an attenuator? Every TV I've had had an exquisitely sensitive
front end - it's almost amazing what an ordinary $39.00 table model can
pluck out of the noise. I can see how shoving the output of an antenna
preamp or distribution amp into it could overwhelm it.

Thanks,
Rich
 
J

Joerg

Jan 1, 1970
0
Rich said:
Frank said:
"Joerg"

Phil Allison wrote:

<insulting garbage, as usual>
[lot of snip]

[more snip]

But what really miffed me was this: Placed the antenna on a mast after
re-roofing the house. So, I equipped it with a nice preamp, splitter,
postamps with eight outputs .....

[still more snip]
I presume you meant to say that the performance of most preamps would
limit linearity, and would dominate IP3, etc. over the tuner. That's
true, although I've seen some that don't ... I've designed some that
don't; maybe Joerg used a commercial model.

Well, yeah. If a lab grade receiver works just fine and the TV on the
same antenna is turning into a hopeless pile of intermodulation it's
pretty clear that the TV isn't up to snuff. Which didn't surprise me. I
just didn't expect it to be this bad.


Did you try an attenuator? Every TV I've had had an exquisitely sensitive
front end - it's almost amazing what an ordinary $39.00 table model can
pluck out of the noise. I can see how shoving the output of an antenna
preamp or distribution amp into it could overwhelm it.

That's what I ended up doing, losing a few channels :-(

Thing is, the old ones didn't need that yet were sensitive enough to
recognize the noise increase when an antenna was connected. That's how
it ought to be but is no more.

BTW it's the same with radios. Two classic examples: My old Becker car
radio always worked. Good old dial with string and pulleys. Then I
bought an Audi and it had their, ahem, high-end radio (called "Gamma").
Horrible. In half of our town all you heard was "deedle dit deeee deedle
dee". The newly installed paging system, on every FM channel. Yuck.

The other was here in the office. Nice "modern" stereo fell apart every
night on the AM band. A cacophony of noise. Out it went. In came ye olde
tube radio from the 50's and it works just fine, night and day. Oh,
Phil, you'd like this: The well-performing tube radio was made in
Australia, it's an Astor BPJ. The enclosure is IMHO ugly but it sure
works nicely.
 
G

Gary Tait

Jan 1, 1970
0
Thank you so much for the information.
Now I managed to find an application note for a DVB-T Tuner from
infineon.
I intended to expand my scope of knowledge. (not in depth in RF)
What I am interested there is how to configure the settings for
respective blocks in the tuner.

Reverse encgineer the tuner. Of find a datasheet on it.
I am quite eager to know how the I2C serial bit stream is recognized
by different control blocks in the front module.

It isn't. I2C only controls the PLL IC, which may have GPIO to control
band selects.
And I wish to know the scheme that the processing unit sends commands
to the front end module, and how it understands the commands from the
programming point of view.
With RF receiving system, I understand the basic block diagram but
wish to know more about it.

In a nutshell, it is a couple voltage tuned filters, feeding a mixer
supplied by a voltage tuned oscillator. The PLL IC, via I2C, tunes the
voltage tuned oscillator, and by proxy, the tuned filters. The output of
the mixer goes into an IF strip, and a video detector. There may be a
number of bands using different coils in the tuned filters, selected by
PIN diodes, which are controlled by GPIOs on the PLL chip, or discrete
inputs on the module.
I am not going to design a front end module but I am interested in the
power supply (usually 5 to 33V boost converter) of it.
I would like to have the relationship between the power supply
specifications and the tuner performance.
However, now I have one applications notes which encourages me to find
more information on it.
Thans for your initiation.
Regards
As said, the 33V is just to tune the varicaps. It requires a higher
voltage to tune higher frequencies. It only needs to be a few ma for
that. The 5V can be a standard 5V supply, although if your project has
sigificant digital, it should be a separate analog 5V.
 
Top