"Jerry Stuckle" wrote in message
...
And yes, many inexpensive "modern" receivers suffer from poor front
ends. And since transistors (especially bipolar) typically generate more
noise than tubes,
noise can be a worse problem now than in the 60's. You can get low noise
transistors, but these are more expensive.

--

How did ou come up with transistors generate more noise than tubes ?

Most of my research into low noise has been above 50 mhz and the beter tubes
generate much more noise than transistors. The older U310 devices have a
noise figure less than 2 db at 150 mhz and a 6cw4 will have around 3 db.
Cheap gaasfets have noise figuers less than 1 db.

I seem to remember that most tube sets of the old days were stating about .5
uv senstivity on ssb, and many of todays ham trasceivers are way less than
that.



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On Fri, 24 Jan 2014 04:06:20 -0800 (PST), W5DXP
wrote:

On Wednesday, January 22, 2014 7:32:09 PM UTC-6, Jeff Liebermann wrote:
You're not radiating anything in receive.

Isn't part of the received signal re-radiated?

I have no idea. I guess it's possible for a received signal to
"bounce" off the wire and wander off elsewhere. With VSWR, the
reflected signal might be re-radiated if the source impedance is
mismatched. Dunno.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
Isn't part of the received signal re-radiated?

I have no idea. I guess it's possible for a received signal to
"bounce" off the wire and wander off elsewhere. With VSWR, the
reflected signal might be re-radiated if the source impedance is
mismatched. Dunno.

Interisting thought. When the signal hits the receiver I am sure there is
some mismatch and part of it is reflected back to the antenna. Now what
hapens. All of it is radiated, part radiated and part reflected back, all
of it reflected back to the receiver ?



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On 1/24/2014 10:58 AM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...
And yes, many inexpensive "modern" receivers suffer from poor front
ends. And since transistors (especially bipolar) typically generate more
noise than tubes,
noise can be a worse problem now than in the 60's. You can get low noise
transistors, but these are more expensive.

--

How did ou come up with transistors generate more noise than tubes ?


Almost 50 years of experience, including studying both tubes and
transistors in my EE courses back in the 70's. Plus measurements of
both received and transmitted signals, using lab-grade test equipment.

The easiest way of seeing it is looking at the output of both tube and
transistorized transmitters on a spectrum analyzer. You will see much
more hash on the transistorized transmitter.

Back in the 70's, I ran a CAP repeater from my home. Transmit and
receive antennas were separated by about 25' vertically. It was a
surplus Motorola tube rig, running 25W. I was able to run it without
any desense without duplexers. Yes, the channel spacing was 4.25Mhz,
but you can't do that with a transistorized rig.

Most of my research into low noise has been above 50 mhz and the beter tubes
generate much more noise than transistors. The older U310 devices have a
noise figure less than 2 db at 150 mhz and a 6cw4 will have around 3 db.
Cheap gaasfets have noise figuers less than 1 db.


Yes, nowadays, there are transistors with lower noise figures. But they
are relatively expensive, and you won't find them in the less expensive
receivers.

I seem to remember that most tube sets of the old days were stating about .5
uv senstivity on ssb, and many of todays ham trasceivers are way less than
that.


Plus or minus, that is about right. But that wasn't because of the
tubes; they could have done better but it would have required more
amplification and higher cost. Plus with a decent antenna, the
atmospheric noise was higher than that, so there was no need for more
amplification. It would have just been lost in the AGC circuitry.

Even back in the early 70's, commercial tube VHF radios could easily get
..15mv for 20db S+N/N ratio. Not much different than the transistorized
versions today.



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--
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Remove the "x" from my email address
Jerry Stuckle

==================

It seems to me to be the same as a multipath TV signal causing
ghosting. The signal that is not on the direct path hits a building
and is reradiated and arrives at the TV at a different time.

....and how about the reflectors and directors on a Yagi antenna?

....where does the signal go when it hits something? It is either absorbed
or re-radiated -- some of course is lost in heating, but there is always
a little left over.

Food for thought!

Irv VE6BP

--
Political correctness is a doctrine, fostered by a delusional, illogical
minority, and rapidly promoted by an unscrupulous mainstream media, which
holds forth the proposition that it is entirely possible to pick up a piece
of **** by the clean end.

Jeff wrote:

I'm sorry Jerry, but you don't know what you are talking about.

Smith Charts do not have anything to do with antenna efficiency or
resonance.
The only thing that Smith Charts does is explain what is happening
inside of a piece of coax X inches long. Note I do not use feet -
since that is too vague.

Whilst I agree with your first point, Smiths Charts do not "explain what
is happening inside of a piece of coax X inches long". They are an easy
way to plot impedances, and show what happens if you *change* the length
of coax, but more importantly they give you an easy way of working out
how to match impedances (with or without any length of coax involved).
They can also display other valuable quantities such as Q.

jeff

A Smith chart is a plot of reactance and resistance versus frequency and
can be used for just about anything, if you know how to use one.

In the case of an antenna, the chart shows what you have to match at any
particular frequency and the resonant frequency of the antenna, i.e. the
point where the reactance is zero.


--
Jim Pennino

On Fri, 24 Jan 2014 04:06:20 -0800 (PST), W5DXP
wrote:

On Wednesday, January 22, 2014 7:32:09 PM UTC-6, Jeff Liebermann wrote:
You're not radiating anything in receive.

Isn't part of the received signal re-radiated?

I have no idea. I guess it's possible for a received signal to
"bounce" off the wire and wander off elsewhere. With VSWR, the
reflected signal might be re-radiated if the source impedance is
mismatched. Dunno.

My recollection is that in the best of cases (good match, no
dissipative losses), half of the RF energy which impinges on the
antenna goes into the feedline. The other half is re-radiated.

AIUI, the received EM field induces a current flow in the
antenna... and this current flow itself causes another EM field to be
generated and radiated away.

"Jerry Stuckle" wrote in message
...
How did ou come up with transistors generate more noise than tubes ?


Almost 50 years of experience, including studying both tubes and
transistors in my EE courses back in the 70's. Plus measurements of both
received and transmitted signals, using lab-grade test equipment.

The easiest way of seeing it is looking at the output of both tube and
transistorized transmitters on a spectrum analyzer. You will see much
more hash on the transistorized transmitter.

Back in the 70's, I ran a CAP repeater from my home. Transmit and receive
antennas were separated by about 25' vertically. It was a surplus
Motorola tube rig, running 25W. I was able to run it without any desense
without duplexers. Yes, the channel spacing was 4.25Mhz, but you can't do
that with a transistorized rig.


I think you are mixing apples and oranges. For transmiters the tubes
usually have less broad band noise. One reason is not the tube, but the
tuned circuits are much more selective. With the high impedance of the
tubes it is easy to be very selective due to the circuit Q.
For a receiver, it is still all about the noise figuer and having enough
gain (which is not usually a problem) to overcome the noise of the other
parts of the receiver.

Yes, you could run the CAP repeater with seperate antennas with tubes where
you could not with the transistors. As above the circuit selectivity has
alot to do with it. Tube circuits are much more selective when it comes to
broad band noise. Many transistor receivers are broad band in the first few
RF stages. That gives two problems to over come. Broad band noise for the
transmitter (which I am not talking about) and the broad RF stages of the
receiver (Not noise of the transistor/fet but poor selectivity). The old GE
Mastr ll is one of the few that has a fairly narrow front end. I have one
of those on 2 meters.

What do you call relative expensive for a transistor/fet that has a noise
figuer of around 1 db ?

Even in some of the old ARRL repeater handbooks they are putting fet preamps
ahead of the tube receivers.

What tubes are you talking about that has an under 2 db noise figuer at 150
mhz ? I think there was a 417 and maybe a 416 that might make it, but they
were very expensive, especially the 416.



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On Friday, January 24, 2014 1:22:02 PM UTC-6, David Platt wrote:
My recollection is that in the best of cases (good match, no
dissipative losses), half of the RF energy which impinges on the
antenna goes into the feedline. The other half is re-radiated.

That is my recollection also. 73, Cecil, w5dxp.com

On 1/24/2014 2:24 PM, Ralph Mowery wrote:

"Jerry Stuckle" wrote in message
...
How did ou come up with transistors generate more noise than tubes ?


Almost 50 years of experience, including studying both tubes and
transistors in my EE courses back in the 70's. Plus measurements of both
received and transmitted signals, using lab-grade test equipment.

The easiest way of seeing it is looking at the output of both tube and
transistorized transmitters on a spectrum analyzer. You will see much
more hash on the transistorized transmitter.

Back in the 70's, I ran a CAP repeater from my home. Transmit and receive
antennas were separated by about 25' vertically. It was a surplus
Motorola tube rig, running 25W. I was able to run it without any desense
without duplexers. Yes, the channel spacing was 4.25Mhz, but you can't do
that with a transistorized rig.


I think you are mixing apples and oranges. For transmiters the tubes
usually have less broad band noise. One reason is not the tube, but the
tuned circuits are much more selective. With the high impedance of the
tubes it is easy to be very selective due to the circuit Q.
For a receiver, it is still all about the noise figuer and having enough
gain (which is not usually a problem) to overcome the noise of the other
parts of the receiver.


No, I am not mixing apples and oranges. Sure, the transmitter tuned
circuits have a higher Q, but that does not affect noise on nearby
frequencies (like 4.25Mhz apart on 2 meters - less than 3% of the
transmitted frequency).

Remember also that receivers also have tuned circuits for input; many of
the older receivers had preselectors to tune the input to the desired
frequency (and these circuits typically had higher Q than transmitter
output circuits).

Yes, you could run the CAP repeater with seperate antennas with tubes where
you could not with the transistors. As above the circuit selectivity has
alot to do with it. Tube circuits are much more selective when it comes to
broad band noise. Many transistor receivers are broad band in the first few
RF stages. That gives two problems to over come. Broad band noise for the
transmitter (which I am not talking about) and the broad RF stages of the
receiver (Not noise of the transistor/fet but poor selectivity). The old GE
Mastr ll is one of the few that has a fairly narrow front end. I have one
of those on 2 meters.


No, tubes themselves generate less noise, especially when running in a
non-linear mode such as Class C. But transistors definitely generate
more noise, as can be identified on a good spectrum analyzer.

What do you call relative expensive for a transistor/fet that has a noise
figuer of around 1 db ?


For manufacturers, anything over a couple of cents per device. But also
GAsFETs are also more susceptible to static charges from the antenna,
requiring additional protective circuitry at the front end.

Even in some of the old ARRL repeater handbooks they are putting fet preamps
ahead of the tube receivers.


Yes, and they also put tube preamps in front of the tube receivers.
FETs were real popular back then, mainly because they weren't tubes -
and didn't have the high power requirements associated. They also were
new, making them ripe for experimentation (quite popular at one time).

What tubes are you talking about that has an under 2 db noise figuer at 150
mhz ? I think there was a 417 and maybe a 416 that might make it, but they
were very expensive, especially the 416.


I don't remember tube numbers any more - that was over 40 years ago, and
I haven't touched a receiver tube circuit in at least 30 years But I
also remember having to design low noise RF circuits - and make them
work. Not easy to do even in the lab; much harder for manufacturers.
And when we were doing solid state amplifiers, it was much harder to get
a great noise figure.

--
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