varicaps?

[Michael Terrell]

On Thursday, April 2, 2020 at 11:31:17 PM UTC-4, Phil Allison wrote:

Michael Terrell wrote:

----------------------


The electric bill for WACX TV in the late '80s was over $45,000 a month for their NTSC 130 KW Comark UHF transmitter. It was running at least 162 hours a week. That was just under $70 an hour.

** IOW absolute peanuts.

The receptionist plus coffee lady cost more in wages and overheads.

Are you ever going to grow up? Lets see you build and operate a station on peanuts. The annual operating costs were around $3,000,000 a year, you pathetic, inbred fool.

 

On Thu, 02 Apr 2020 16:21:17 -0700, Joerg <news@analogconsultants.com>
wrote:

On 2020-04-01 17:29, Rick C wrote:
On Wednesday, April 1, 2020 at 7:31:01 PM UTC-4, Phil Allison wrote:
Joerg wrote:

-------------

Up to about 30pf they'll likely remain. Skyworks and such. Those
with large capacitances lost their market.



** AM radio has disappeared ??

News to me.

My car doesn't even receive AM, only FM, Sirius XM and Slacker
Internet radio.


I would not want that radio in my car. I listen to AM most of the time
when driving, and not just then.


.. Oh, and bluetooth from your phone. But no AM radio.
I think they could do that 100% in software if they wanted to. It's
only 1600 kHz max frequency.


Well, they don't go that far but everything is PLL or DDS nowadays.
There simply isn't a need any longer for large capacitance varicaps to
run the local oscillator. As for the preselector (adjustable filter in
front of the mixer), that has fallen victim to the red pencil of the
bean counter, which has cost performance when in the vicinity of other
strong signals.

Selectivity ahead of the mixer was needed in the old days due to
mediocre mixers, usually a single transistor biased into
non-linearity. These mixers produced all kind of mixing products,
including images, mixing between all harmonics and letting RF and LO
frequencies through.

Using strong double balanced mixers (e.g diode rings), much of the
problems disappeared. By using a higher first IF, it is also easy to
get away with the image frequency response. Thus, fixed tuned high
pass filters below low end of the band and low pass above the band is
usually sufficient.

In battery powered equipment, in which the power consumption is the
premium issue, very strong mixers can't be used, but in car and mains
powered receivers the use of strong high power mixers is not a
problem.

 

[Phil Allison]

Michael Terrell is an Damn LIAR wrote:

-----------------------------

50 kilowatts of radiated RF must be expensive.


** Transmitters are rated in EIRP - not actual watts.

Antenna gain is added to the actual number used to get EIRP - it can be ten times higher with VHF and UHF.



5G will probably take
over everything at a huge energy saving.



** Laughably absurd crap.


Yes, you are.

** Let's see.

There are losses in the antenna system on the AM Broadcast band.
Gain in an antenna system comes from compressing the signal,
and reducing the coverage area.

** Completely wrong.

It comes from using directional antennas systems that avoid wasting RF power heading off into the ionosphere or space.

EIRP is the spec used to describe the licensed power rating of a broadcast station, be it AM, TV, FM or whatever.

I described this quite accurately while you stupidly misread.

Like you always bloody do.

Go fuck your pathetic self.




.... Phil

 

On Fri, 3 Apr 2020 01:32:48 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

Michael Terrell is an Damn LIAR wrote:

-----------------------------


50 kilowatts of radiated RF must be expensive.


** Transmitters are rated in EIRP - not actual watts.

Antenna gain is added to the actual number used to get EIRP - it can be ten times higher with VHF and UHF.



5G will probably take
over everything at a huge energy saving.



** Laughably absurd crap.


Yes, you are.


** Let's see.

There are losses in the antenna system on the AM Broadcast band.

While a full size 1/4 wave vertical is a quite good radiator, the
problem is often in the ground plane.

>> Gain in an antenna system comes from compressing the signal,

It just reduces the signal in some directions while moving i to other
directions.

>> and reducing the coverage area.

It moves the coverage area from one area to an other.

** Completely wrong.

It comes from using directional antennas systems that avoid wasting RF power heading off into the ionosphere or space.

Flattening the radiation pattern in the vertical direction helps
reducing fading (destructive interference) experienced by listener at
the fringes of the ground wave coverage area by suppressing NVIS sky
wave reflections into that area.

A station on a cost might want to also have some gain in the
horizontal plane by reducing radiation towards the empty sea and
instead aim more to listeners inland.

>EIRP is the spec used to describe the licensed power rating of a broadcast station, be it AM, TV, FM or whatever.

EiRP is also the parameter that directly affects the field strength
experienced by the listener antenna.

I described this quite accurately while you stupidly misread.

Like you always bloody do.

Go fuck your pathetic self.




... Phil

 

[Michael Terrell]

On Friday, April 3, 2020 at 4:32:53 AM UTC-4, Phil Allison wrote:

Michael Terrell is an Engineer wrote:


** Let's see.

There are losses in the antenna system on the AM Broadcast band.
Gain in an antenna system comes from compressing the signal,
and reducing the coverage area.


** Completely wrong.

Yes, you are.

It comes from using directional antennas systems that avoid wasting RF power heading off into the ionosphere or space.

EIRP is the spec used to describe the licensed power rating of a broadcast station, be it AM, TV, FM or whatever.

Not in the United States. EIRP is only used for FM and TV transmitters. RF field strength is used for AM and Shortwave stations. That can be affected by new buildings being built, or in one case I'm familiar with, a Mall was built next to a Rado station in Leesburg Florida. The land had belonged to the station, and the buired grounding sytem was partially under that land. They were only supposed to compact the soil and pave that area. The assholes used a bulldozer along the property line and cut the copper lines. That required that a new field map for FCC to show the new, lower signal strength in that direction. It could have cause the FCC to revoke their license for not covering the area they were licensed for.

I described this quite accurately while you stupidly misread.

Like you always bloody do.

You have never worked at a Radio or TV station. I have. In fact, I built a UHF TV station in Destin Florida in 1990. It was considered low power, but the 25KW transmitter had enough gain to emit 1.3 MW on the old Analog channel 58.

The first AM station that I worked at had a Gates BC250 transmitter which was fed into a center tapped dipole, on 980KHz. That wasn't the only oddity. It had a license from the FCC, but no assigned call letters. No set power level. It stated: "250 Watts, or as deemed necessary." The expiration date was, "Until no longer needed". The TV station was the same. I ran the TV transmitter at 650 Watts. We were exempt from most of the FCC regulations.

 

[Phil Allison]

Michael Terrell is a Bullshititng Ass wrote:

---------------------------------------------

** Let's see.

There are losses in the antenna system on the AM Broadcast band.
Gain in an antenna system comes from compressing the signal,
and reducing the coverage area.


** Completely wrong.

Yes, you are.


It comes from using directional antennas systems that avoid wasting RF power heading off into the ionosphere or space.


EIRP is the spec used to describe the licensed power rating of a broadcast station, be it AM, TV, FM or whatever.


Not in the United States. EIRP is only used for FM and TV transmitters. RF field strength is used for AM and Shortwave stations.

** Really.

I described this quite accurately while you stupidly misread.

Like you always bloody do.


You have never worked at a Radio or TV station.

** I would never wish to.

Might run into fucking assholes like you.

Broadcast Engineer = half trained monkey.

Snip whole pile of putrid Trumpet Blowing.



...... Phil

 

[Phil Allison]

upsid...@downunder.com wrote:

--------------------------------

Gain in an antenna system comes from compressing the signal,

It just reduces the signal in some directions while moving i to other
directions.

** So a directional antenna.

and reducing the coverage area.

It moves the coverage area from one area to an other.

** Yawnnnn....

** Completely wrong.

It comes from using directional antennas systems that avoid wasting RF power heading off into the ionosphere or space.

Flattening the radiation pattern in the vertical direction helps
reducing fading (destructive interference) experienced by listener at
the fringes of the ground wave coverage area by suppressing NVIS sky
wave reflections into that area.

** By avoiding the dam ionosphere.

EIRP is the spec used to describe the licensed power rating of a broadcast station, be it AM, TV, FM or whatever.

EiRP is also the parameter that directly affects the field strength
experienced by the listener antenna.

** FFS stop bloody over-explaining what has already been well explained.

Idiot.


....... Phil

I described this quite accurately while you stupidly misread.

Like you always bloody do.

Go fuck your pathetic self.




... Phil

 

[Gerhard Hoffmann]

Am 03.04.20 um 11:50 schrieb Michael Terrell:

> The first AM station that I worked at had a Gates BC250 transmitter which was fed into a center tapped dipole, on 980KHz. That wasn't the only oddity. It had a license from the FCC, but no assigned call letters. No set power level. It stated: "250 Watts, or as deemed necessary." The expiration date was, "Until no longer needed". The TV station was the same. I ran the TV transmitter at 650 Watts. We were exempt from most of the FCC regulations.

In Luxembourg, they used to have only maximum carrier power for ham
radio stations. That led to speculations how far one could get in SSB
with reasonable carrier suppression.

Gerhard DK4XP

 

[Jasen Betts]

On 2020-04-01, Phil Allison <pallison49@gmail.com> wrote:

Joerg wrote:

-------------

Up to about 30pf they'll likely remain. Skyworks and such. Those with
large capacitances lost their market.



** AM radio has disappeared ??

News to me.

No big problem, we can fix it in software



--
Jasen.

 

[Phil Allison]

Michael Terrell is Raving Psychopath wrote:

----------------------------------------

The electric bill for WACX TV in the late '80s was over $45,000 a month for their NTSC 130 KW Comark UHF transmitter. It was running at least 162 hours a week. That was just under $70 an hour.

** IOW absolute peanuts.

The receptionist plus coffee lady cost more in wages and overheads.


Are you ever going to grow up?

** How bloody hysterical.

Terrell is behaving like a 3 year old brat having a tantrum and pooing his diaper at the same time.

How fucking smelly.


..... Phil

 

[piglet]

On 02/04/2020 11:55 pm, George Herold wrote:

On Thursday, April 2, 2020 at 2:46:37 PM UTC-4, piglet wrote:
On 02/04/2020 6:05 pm, George Herold wrote:
On Thursday, April 2, 2020 at 12:02:46 PM UTC-4, piglet wrote:

Ah yes of course, we had fun last year disecting the AD310 parametric
input op-amp which used back to back transdiode (CB-E) bjts as varactors.

piglet

Ahh, parametric amps... be fun to build one.
Is there some easy way to make a (demonstration) para-amp from
the really crappy ceramic caps?

George H.


Varicap diode paramps (like the AD310 we enjoyed last year) have pF
scale capacitance and were driven in 00s kHz or lo-MHz but since the
ceramic caps with large voltage coefficient are uF range I like to think
one could get away with power line frequencies. Which opens up the
delightful steampunk idea I sketched here...

https://www.dropbox.com/s/jqubvy92xuc2788/mains_paramp_idea.pdf?raw=1

'Oh dear, piglet you're making my brain spin.'
said pooh.
I have trouble with all these transformer circuits,
doing modulation / demod (at 1/2 freq?) / and low pass detection..
Is that six diode bridge thing doing double duty?
No forget that part... let me ask about the front end.

So let's assume we have balanced the (vari)caps so at zero
V-in each C is the same. Then each 60 Hz 1/2 cycle there is the
some current flowing... I guess we'll want the caps to be the major
impedance limiting the current... then with voltage and unbalanced C's
there are different currents in each 1/2 cycle. And that looks like
some 2*f (120 Hz) 'modulation' that proportional to V-in... is that
close to right?

I must admit I never know exactly how to think about a transformer.

George H.


Of course if the input varactor caps aren't closely matched the offset
voltage could be of the order of volts but still the DC input bias
current is near zero! And 60Hz pump frequency rather limits GBW and
output slew rate!

piglet

Hi George, the four diodes can be thought of as switches driven by the
60Hz drive alternatly connecting the signal from the out-of-balance caps
in and out of phase to the output - or in other words being a phase
sensitive detector. Look up ring modulator or double balanced diode mixer.

However the input stage is probably wrong - I thought the hi-K caps
worked like varicap diodes but as Joeron and Whit3rd commented that
assumption is wrong.

piglet

 

[Phil Hobbs]

On 2020-04-03 03:56, upsidedown@downunder.com wrote:

On Thu, 02 Apr 2020 16:21:17 -0700, Joerg
news@analogconsultants.com> wrote:

On 2020-04-01 17:29, Rick C wrote:
On Wednesday, April 1, 2020 at 7:31:01 PM UTC-4, Phil Allison
wrote:
Joerg wrote:

-------------

Up to about 30pf they'll likely remain. Skyworks and such.
Those with large capacitances lost their market.



** AM radio has disappeared ??

News to me.

My car doesn't even receive AM, only FM, Sirius XM and Slacker
Internet radio.


I would not want that radio in my car. I listen to AM most of the
time when driving, and not just then.


.. Oh, and bluetooth from your phone. But no AM radio. I think
they could do that 100% in software if they wanted to. It's only
1600 kHz max frequency.


Well, they don't go that far but everything is PLL or DDS
nowadays. There simply isn't a need any longer for large
capacitance varicaps to run the local oscillator. As for the
preselector (adjustable filter in front of the mixer), that has
fallen victim to the red pencil of the bean counter, which has cost
performance when in the vicinity of other strong signals.

Selectivity ahead of the mixer was needed in the old days due to
mediocre mixers, usually a single transistor biased into
non-linearity. These mixers produced all kind of mixing products,
including images, mixing between all harmonics and letting RF and LO
frequencies through.


Using strong double balanced mixers (e.g diode rings), much of the
problems disappeared. By using a higher first IF, it is also easy to
get away with the image frequency response. Thus, fixed tuned high
pass filters below low end of the band and low pass above the band
is usually sufficient.

An arbitrarily strong mixer still needs selectivity to get rid of the
image frequency. SSB mixers help, but are a lot more complicated than a
tuned RF stage, and rarely have better than 30-40 dB rejection.

In battery powered equipment, in which the power consumption is the
premium issue, very strong mixers can't be used, but in car and
mains powered receivers the use of strong high power mixers is not
a problem.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 2020-04-02 19:10, Clifford Heath wrote:

On 3/4/20 1:28 am, George Herold wrote:
On Thursday, April 2, 2020 at 10:12:28 AM UTC-4, piglet wrote:
On 02/04/2020 14:29, jlarkin@highlandsniptechnology.com wrote:
On Thu, 2 Apr 2020 10:24:49 +0100, piglet <erichpwagner@hotmail.com
wrote:

On 01/04/2020 11:34 pm, John Larkin wrote:
On Wed, 1 Apr 2020 16:56:48 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-04-01 16:20, sea moss wrote:

I wonder if it's practical to use a MOSFET's Coss as a
varicap.  I haven't
seen it done.

Standard technique in ASIC design

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

Cool.  I should have googled it first, there's a few examples
out there.

There are pots of low-pF ones on Digikey.  The 1000-pFish ones
(MVAM108
etc.) are long gone, and the tens-to-hundreds range is
declining.  My
fave MV209 is a distant memory, but BB201s are still in stock.

Cheers

Phil Hobbs

According to my Boonton, a BFT25 c-b junction only goes from about
0.7
pF to around 0.65 from 0 to 6 volts. There's probably a bit of
fixture
capacitance too. Not a very good varicap.

I want a delta-c around 0.15 pF roughly, maybe 0.2. My dac+opamp
could
go to 20 volts.


You're going to need a bigger transistor. Try a BC847/2N3904 ?

piglet

I'm guessing that a varicap is doped to be, well, a varicap. They have
delta-c catios like 6:1 over some voltage range. Looks like transistor
junctions have much flatter c:v curves. So the tempco contribution
will be a lot higher if I use a transistor.

I've ordered some singles, Skyworks parts in the horrible SC79
package, and my 4-layer proto board should be here soon. If the board
house doesn't shut down.




Yes I think you're right about the flatter c:v curves. You only want
0.2pF swing so will have quite a lot of padding down.

I hooked up an SMD BC848C to the Boonton and got these:
Ccb (E open*)
0V 4.0pF
0.5V 3.2pF
1V 2.8pF
2V 2.36pF
3V 2.05pF
4V 1.85pF
5V 1.71pF
6V 1.60pF
7V 1.50pF
8V 1.42pF

Cceb (E tied to B)
0V 4.29pF
0.5V 3.54pF
1V 3.16pF
2V 2.69pF
3V 2.40pF
4V 2.20pF
5V 2.05pF
6V 1.92pF
7V 1.83pF
8V 1.75pF


A thru-hole version was Ccb (e open):
0V 5.35pF
0.5V 4.55pF
1V 4.12pF
2V 3.56pF
3V 3.19pF
4V 2.95pF
5V 2.72pF
6V 2.52pF
7V 2.33pF
8V 2.16pF

A thru hole RF part MPSH10 Ccb (e open):
0V 1.23pF
0.5V 1.09pF
1V 1.02pF
2V 0.94pF
3V 0.89pF
4V 0.86pF
5V 0.84pF
6V 0.82pF
7V 0.8pF
8V 0.79pF


A 4.3V 400mW zener was:
0V 211pF
0.5V 183pF
1V 168pF
2V 149pF

A junk box T1 red LED:
0V 28.4pF
0.5V 25.9pF
1V 24.4pF
2V 22pF
3V 20.4pF
4V 19.1pF
5V 18pF
6V 17.3pF
7V 16.6pF
8V 16pF

* I tried the NPN bjts Ccb-e and Cb-ce i.e. involving the base-emitter
junction - as expected the capacitance was higher at 12 to 16pF at zero
bias falling to 6-8pF at 6V (didnt go higher to avoid breakdown) but I
noticed that the low bias capacitance values looked jittery and only
settled down above about 2V.

My junkbox has some wire ended varicaps somewhere so next coffee break I
will try those too.

piglet

Fun,  If I can riff on the physics.  The variable C is caused by
changes in the depletion width.  So what sort of devices would have
a large variation?
PIN photodiodes?
maybe c-b junc of high voltage transistors?
What else?

High voltage rectifier diodes

Not so much. See e.g.
<https://datasheet.octopart.com/MMBD5004S-7-Diodes-Inc.-datasheet-13686563.pdf>

About than 10% variation from 1V-30V. 1N4007 is about a factor of 2 in
that range.

PIN photodiodes can be in the 7:1 range, but Q is probably going to be
disappointing on account of the epi sheet resistance. (The epi has to
be thin enough to be optically transparent.) Your basic BPW34 has about
50 ohms' series resistance. (That's for the Infineon ones. The Osrams
are much worse.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[George Herold]

On Friday, April 3, 2020 at 8:15:08 AM UTC-4, piglet wrote:

On 02/04/2020 11:55 pm, George Herold wrote:
On Thursday, April 2, 2020 at 2:46:37 PM UTC-4, piglet wrote:
On 02/04/2020 6:05 pm, George Herold wrote:
On Thursday, April 2, 2020 at 12:02:46 PM UTC-4, piglet wrote:

Ah yes of course, we had fun last year disecting the AD310 parametric
input op-amp which used back to back transdiode (CB-E) bjts as varactors.

piglet

Ahh, parametric amps... be fun to build one.
Is there some easy way to make a (demonstration) para-amp from
the really crappy ceramic caps?

George H.


Varicap diode paramps (like the AD310 we enjoyed last year) have pF
scale capacitance and were driven in 00s kHz or lo-MHz but since the
ceramic caps with large voltage coefficient are uF range I like to think
one could get away with power line frequencies. Which opens up the
delightful steampunk idea I sketched here...

https://www.dropbox.com/s/jqubvy92xuc2788/mains_paramp_idea.pdf?raw=1

'Oh dear, piglet you're making my brain spin.'
said pooh.
I have trouble with all these transformer circuits,
doing modulation / demod (at 1/2 freq?) / and low pass detection..
Is that six diode bridge thing doing double duty?
No forget that part... let me ask about the front end.

So let's assume we have balanced the (vari)caps so at zero
V-in each C is the same. Then each 60 Hz 1/2 cycle there is the
some current flowing... I guess we'll want the caps to be the major
impedance limiting the current... then with voltage and unbalanced C's
there are different currents in each 1/2 cycle. And that looks like
some 2*f (120 Hz) 'modulation' that proportional to V-in... is that
close to right?

I must admit I never know exactly how to think about a transformer.

George H.


Of course if the input varactor caps aren't closely matched the offset
voltage could be of the order of volts but still the DC input bias
current is near zero! And 60Hz pump frequency rather limits GBW and
output slew rate!

piglet

Hi George, the four diodes can be thought of as switches driven by the
60Hz drive alternatly connecting the signal from the out-of-balance caps
in and out of phase to the output - or in other words being a phase
sensitive detector. Look up ring modulator or double balanced diode mixer.

However the input stage is probably wrong - I thought the hi-K caps
worked like varicap diodes but as Joeron and Whit3rd commented that
assumption is wrong.

piglet

No problem piglet. I get the ring modulator/double balanced mixer part.
(I built an audio DBM once.. silly but fun.) I need read some in
Pippards "Physics of Vibration" (He does a nice job discussing para-amps.)
And then I'll have more to say/ ask. ... IIRC there is this threshold
condition for amplification and I'd like to remember the details.

Georg H.
(It's too bad all threads seem to descend into male pissing contests.)

 

Phil Allison <pallison49@gmail.com> wrote in
news:e473f661-b3be-4432-adad-dcfe6724e7bb@googlegroups.com:

Michael Terrell is an Damn LIAR wrote:

-----------------------------


50 kilowatts of radiated RF must be expensive.


** Transmitters are rated in EIRP - not actual watts.

Antenna gain is added to the actual number used to get EIRP -
it can be ten times higher with VHF and UHF.



5G will probably take
over everything at a huge energy saving.



** Laughably absurd crap.


Yes, you are.


** Let's see.

There are losses in the antenna system on the AM Broadcast band.
Gain in an antenna system comes from compressing the signal,
and reducing the coverage area.


** Completely wrong.

It comes from using directional antennas systems that avoid
wasting RF power heading off into the ionosphere or space.

EIRP is the spec used to describe the licensed power rating of a
broadcast station, be it AM, TV, FM or whatever.

I described this quite accurately while you stupidly misread.

Like you always bloody do.

Go fuck your pathetic self.




... Phil

His rotten molar fucked with his brain and his personal EIRP is now
measured in femtowatts.

 

On Fri, 3 Apr 2020 09:51:14 -0000 (UTC), Jasen Betts
<jasen@xnet.co.nz> wrote:

On 2020-04-01, Phil Allison <pallison49@gmail.com> wrote:
Joerg wrote:

-------------

Up to about 30pf they'll likely remain. Skyworks and such. Those with
large capacitances lost their market.



** AM radio has disappeared ??

News to me.

No big problem, we can fix it in software

A decent ARM, which typically includes a mediocre ADC, might, with a
PWM DAC for the audio, make a usable antenna-to-speaker AM receiver.
Could be a student project.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Michael Terrell]

On Friday, April 3, 2020 at 6:06:45 AM UTC-4, Gerhard Hoffmann wrote:

Am 03.04.20 um 11:50 schrieb Michael Terrell:

The first AM station that I worked at had a Gates BC250 transmitter which was fed into a center tapped dipole, on 980KHz. That wasn't the only oddity. It had a license from the FCC, but no assigned call letters. No set power level. It stated: "250 Watts, or as deemed necessary." The expiration date was, "Until no longer needed". The TV station was the same. I ran the TV transmitter at 650 Watts. We were exempt from most of the FCC regulations..

In Luxembourg, they used to have only maximum carrier power for ham
radio stations. That led to speculations how far one could get in SSB
with reasonable carrier suppression.

Gerhard DK4XP

50+ years ago, we would modify CB radios to supress most of the carrier, so that it put out a 100 mW when it wasn't modulated, but it would go up with modulation. It caused the S meters to go nuts on the receivers.

 

[Michael Terrell]

On Friday, April 3, 2020 at 10:42:55 AM UTC-4, Phil Hobbs wrote:

On 2020-04-03 03:56, upsidedown@downunder wrote:
On Thu, 02 Apr 2020 16:21:17 -0700, Joerg wrote:

On 2020-04-01 17:29, Rick C wrote:
On Wednesday, April 1, 2020 at 7:31:01 PM UTC-4, Phil Allison
wrote:
Joerg wrote:

-------------

Up to about 30pf they'll likely remain. Skyworks and such.
Those with large capacitances lost their market.



** AM radio has disappeared ??

News to me.

My car doesn't even receive AM, only FM, Sirius XM and Slacker
Internet radio.


I would not want that radio in my car. I listen to AM most of the
time when driving, and not just then.


.. Oh, and bluetooth from your phone. But no AM radio. I think
they could do that 100% in software if they wanted to. It's only
1600 kHz max frequency.


Well, they don't go that far but everything is PLL or DDS
nowadays. There simply isn't a need any longer for large
capacitance varicaps to run the local oscillator. As for the
preselector (adjustable filter in front of the mixer), that has
fallen victim to the red pencil of the bean counter, which has cost
performance when in the vicinity of other strong signals.

Selectivity ahead of the mixer was needed in the old days due to
mediocre mixers, usually a single transistor biased into
non-linearity. These mixers produced all kind of mixing products,
including images, mixing between all harmonics and letting RF and LO
frequencies through.


Using strong double balanced mixers (e.g diode rings), much of the
problems disappeared. By using a higher first IF, it is also easy to
get away with the image frequency response. Thus, fixed tuned high
pass filters below low end of the band and low pass above the band
is usually sufficient.

An arbitrarily strong mixer still needs selectivity to get rid of the
image frequency. SSB mixers help, but are a lot more complicated than a
tuned RF stage, and rarely have better than 30-40 dB rejection.


In battery powered equipment, in which the power consumption is the
premium issue, very strong mixers can't be used, but in car and
mains powered receivers the use of strong high power mixers is not
a problem.

Which is why dual or triple conversion is used in some designs, like the Telemetry receivers that we built at Microdyne. The Cable converters we used back in the '80s up converted the entire input up to over 1GHZ, then back down to Ch3 for the output. It was real fun replacing the transistor in the up converter. The leads had to be the exact length and bent to match the original pattern. This was long before surface mount, and the Japanese construction didn't lend itself to being repaired.

 

[Phil Hobbs]

On 2020-04-03 11:20, Michael Terrell wrote:

On Friday, April 3, 2020 at 10:42:55 AM UTC-4, Phil Hobbs wrote:
On 2020-04-03 03:56, upsidedown@downunder wrote:
On Thu, 02 Apr 2020 16:21:17 -0700, Joerg wrote:

On 2020-04-01 17:29, Rick C wrote:
On Wednesday, April 1, 2020 at 7:31:01 PM UTC-4, Phil
Allison wrote:
Joerg wrote:

-------------

Up to about 30pf they'll likely remain. Skyworks and
such. Those with large capacitances lost their market.



** AM radio has disappeared ??

News to me.

My car doesn't even receive AM, only FM, Sirius XM and
Slacker Internet radio.


I would not want that radio in my car. I listen to AM most of
the time when driving, and not just then.


.. Oh, and bluetooth from your phone. But no AM radio. I
think they could do that 100% in software if they wanted to.
It's only 1600 kHz max frequency.


Well, they don't go that far but everything is PLL or DDS
nowadays. There simply isn't a need any longer for large
capacitance varicaps to run the local oscillator. As for the
preselector (adjustable filter in front of the mixer), that
has fallen victim to the red pencil of the bean counter, which
has cost performance when in the vicinity of other strong
signals.

Selectivity ahead of the mixer was needed in the old days due to
mediocre mixers, usually a single transistor biased into
non-linearity. These mixers produced all kind of mixing
products, including images, mixing between all harmonics and
letting RF and LO frequencies through.


Using strong double balanced mixers (e.g diode rings), much of
the problems disappeared. By using a higher first IF, it is also
easy to get away with the image frequency response. Thus, fixed
tuned high pass filters below low end of the band and low pass
above the band is usually sufficient.

An arbitrarily strong mixer still needs selectivity to get rid of
the image frequency. SSB mixers help, but are a lot more
complicated than a tuned RF stage, and rarely have better than
30-40 dB rejection.


In battery powered equipment, in which the power consumption is
the premium issue, very strong mixers can't be used, but in car
and mains powered receivers the use of strong high power mixers
is not a problem.


Which is why dual or triple conversion is used in some designs, like
the Telemetry receivers that we built at Microdyne. The Cable
converters we used back in the '80s up converted the entire input up
to over 1GHZ, then back down to Ch3 for the output. It was real fun
replacing the transistor in the up converter. The leads had to be the
exact length and bent to match the original pattern. This was long
before surface mount, and the Japanese construction didn't lend
itself to being repaired.

Multiple conversions lead to a forest of spurs unless your frequency
plan is very clever or the tuning range is small. Since high frequency
gain is cheap these days, single-conversion with a very high IF is
usually a win.

A few years ago I did a proof-of-concept for a laser microscope based on
a 2D acousto-optic scanner. The two scan signals were both an octave
wide, 50-100 MHz, and the RX signal came back at

f_RX = 2f_X + 2f_Y.

Mixing that down to a fixed IF of 10.7 MHz was a bit of a puzzle--there
were all sorts of spurs crossing the IF. Putting a 1:1 PLL on the LO
output fixed it right up.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

On Fri, 3 Apr 2020 10:42:45 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Using strong double balanced mixers (e.g diode rings), much of the
problems disappeared. By using a higher first IF, it is also easy to
get away with the image frequency response. Thus, fixed tuned high
pass filters below low end of the band and low pass above the band
is usually sufficient.

An arbitrarily strong mixer still needs selectivity to get rid of the
image frequency. SSB mixers help, but are a lot more complicated than a
tuned RF stage, and rarely have better than 30-40 dB rejection.

The standard topology of LF/MF/HF general conversion receivers has
been for decades to use a high first IF e.g. 45 or 75 MHz, Due to the
high side LO, the images are up in the VHF range. A steep 40 MHz RF
input LPF will easily take out the image frequency.

If the RF amplifier is not sufficiently strong a strong input signal
may generate harmonics (mainly 2nd and 3rd), which could mix with the
LO and produce the IF. For this reason, some receivers use octave wide
fixed band pass filters, to filter out strong low frequency signal
harmonics from polluting the higher bands,

The first IF filter is often a crystal filter only 10-30 kHz wide,
This can then be mixed down to a low second IF without risk for image
responses in the downmix. Alternatively use zero-IF I/Q detection at
1st IF.

SDR works also surprisingly well with sampling at say 80 MHz sampling
frequency with only 14 bit ADC.

For AM (MW) only SDR receiver, sampling at 4 MHz should be sufficient.