On 7/2/2015 1:56 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...

Try this - connect the output of an HF transmitter to an SWR bridge.
Now connect a piece of 75 ohm coax such as RG-59 to the output of the
SWR meter, and connect that to a 75 ohm resistive load. Do you think
the SWR bridge will show a 1:1 SWR? Not a chance. It will be 1.5:1.



What you have described is a case of using the wrong swr bridge. You are
trying to use a 50 ohm bridge on a 75 ohm system. If a 75 ohm bridge is
used it will show a 1:1 SWR.

The real SWR is 1:1. With a 75 ohm line and 75 ohm load there is no
reflected power.



No, the SWR bridge is correct. The output of the transmitter is 50 ohms.

You are correct in that if a 75 ohm bridge is used, the indicated SWR
would be 1:1, because everything from that point on is 75 ohms.
However, the mismatch (and reflection) occurs on the transmitter side of
the bridge, not the antenna side. So the bridge will never see it. But
an accurate bridge will show lower power output due to the mismatch.

A mismatch is a mismatch, no matter where in the system it occurs. And
any mismatch will cause less than 100% power to be transferred. The
rest is reflected.

Just look at the specs of any amateur transceiver. They show an
impedance of 50 ohms. So a load of 50 ohms provides for maximum power
transfer; any other impedance causes a mismatch.

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

"Jerry Stuckle" wrote in message
...
On 7/2/2015 1:56 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...

You are correct in that if a 75 ohm bridge is used, the indicated SWR
would be 1:1, because everything from that point on is 75 ohms.
However, the mismatch (and reflection) occurs on the transmitter side of
the bridge, not the antenna side. So the bridge will never see it. But
an accurate bridge will show lower power output due to the mismatch.

A mismatch is a mismatch, no matter where in the system it occurs. And
any mismatch will cause less than 100% power to be transferred. The
rest is reflected.

Just look at the specs of any amateur transceiver. They show an
impedance of 50 ohms. So a load of 50 ohms provides for maximum power
transfer; any other impedance causes a mismatch.

--
The real impedance of the transmitter is not 50 ohms. It is whatever the
device is used in the final stage and the poewr level. For a 100 watt
transmitter it is in the thousand ohm range and for solid state devices it
is very low. The matching circuit is often fixed to be 50 ohms,but could be
made for most any impedance. The older tube circuits were adjustable by the
user for a range of somewhat bleow 50 ohms to around 200 ohms. Could be
more or less depending on the design.

The mismatch you are counting on for a 50 ohm transmitter and a 75 ohm
feedline and 75 ohm antenna is in the tuned circuits/matching circuit in the
transmitter. Whatever power comes out of the transmitter will make it to
the antenna minus the loss of the coax, but not additional loss due to swr.
The power comming out of a 50 ohm transmitter will be less due to mismatch,
but not because of swr of the antenna system which is 1:1.

On 7/2/2015 3:24 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...
On 7/2/2015 1:56 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...

You are correct in that if a 75 ohm bridge is used, the indicated SWR
would be 1:1, because everything from that point on is 75 ohms.
However, the mismatch (and reflection) occurs on the transmitter side of
the bridge, not the antenna side. So the bridge will never see it. But
an accurate bridge will show lower power output due to the mismatch.

A mismatch is a mismatch, no matter where in the system it occurs. And
any mismatch will cause less than 100% power to be transferred. The
rest is reflected.

Just look at the specs of any amateur transceiver. They show an
impedance of 50 ohms. So a load of 50 ohms provides for maximum power
transfer; any other impedance causes a mismatch.

--
The real impedance of the transmitter is not 50 ohms. It is whatever the
device is used in the final stage and the poewr level. For a 100 watt
transmitter it is in the thousand ohm range and for solid state devices it
is very low. The matching circuit is often fixed to be 50 ohms,but could be
made for most any impedance. The older tube circuits were adjustable by the
user for a range of somewhat bleow 50 ohms to around 200 ohms. Could be
more or less depending on the design.


Incorrect. The real impedance of the transmitter is 50 ohms. The
impedance of the final stage may be above or below that, and is matched
to the 50 ohm standard. What happens before the match is unimportant.
The only important part of the discussion is the 50 ohm output.

The mismatch you are counting on for a 50 ohm transmitter and a 75 ohm
feedline and 75 ohm antenna is in the tuned circuits/matching circuit in the
transmitter. Whatever power comes out of the transmitter will make it to
the antenna minus the loss of the coax, but not additional loss due to swr.
The power comming out of a 50 ohm transmitter will be less due to mismatch,
but not because of swr of the antenna system which is 1:1.



Incorrect. The connection between the 50 ohm transmitter and the 75 ohm
coax is also part of the antenna system. The system starts at the
transmitter output (actually the output of the final stage - but since
this is converted to the 50 ohm standard, you can effectively consider
the output of the matching network to be the start of the antenna
system), not the coax.

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

"Jerry Stuckle" wrote in message
...
The mismatch you are counting on for a 50 ohm transmitter and a 75 ohm
feedline and 75 ohm antenna is in the tuned circuits/matching circuit in
the
transmitter. Whatever power comes out of the transmitter will make it to
the antenna minus the loss of the coax, but not additional loss due to
swr.
The power comming out of a 50 ohm transmitter will be less due to
mismatch,
but not because of swr of the antenna system which is 1:1.



Incorrect. The connection between the 50 ohm transmitter and the 75 ohm
coax is also part of the antenna system. The system starts at the
transmitter output (actually the output of the final stage - but since
this is converted to the 50 ohm standard, you can effectively consider
the output of the matching network to be the start of the antenna
system), not the coax.

--


So with my Icom 746 with a built in tuner, where does the system start ?
Within a small range 3 or 4 to 1, the internal SWR meter will show a 1:1
match, an external SWR meter will show a differant SWR if there is a
mismatch. If I hook up a good 75 ohm load and 75 ohm coax I will have no
SWR by definition . A 50 ohm bridge will show 1.5:1 but the internal
tuner/bridge will show 1:1.

Which SWR meter is correct ?

On 7/2/2015 6:08 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...
The mismatch you are counting on for a 50 ohm transmitter and a 75 ohm
feedline and 75 ohm antenna is in the tuned circuits/matching circuit in
the
transmitter. Whatever power comes out of the transmitter will make it to
the antenna minus the loss of the coax, but not additional loss due to
swr.
The power comming out of a 50 ohm transmitter will be less due to
mismatch,
but not because of swr of the antenna system which is 1:1.



Incorrect. The connection between the 50 ohm transmitter and the 75 ohm
coax is also part of the antenna system. The system starts at the
transmitter output (actually the output of the final stage - but since
this is converted to the 50 ohm standard, you can effectively consider
the output of the matching network to be the start of the antenna
system), not the coax.

--


So with my Icom 746 with a built in tuner, where does the system start ?
Within a small range 3 or 4 to 1, the internal SWR meter will show a 1:1
match, an external SWR meter will show a differant SWR if there is a
mismatch. If I hook up a good 75 ohm load and 75 ohm coax I will have no
SWR by definition . A 50 ohm bridge will show 1.5:1 but the internal
tuner/bridge will show 1:1.

Which SWR meter is correct ?




A built in tuner is an entirely different story. The output from the
transmitter is not necessarily 50 homes at this point.

It's a shame they've dumbed down the exams so much that you don't need
to know anything to hold a ticket any more. Back when I got mine, even
the General Class was tougher than the Extra Class today - and it was
administered by the FCC, with no public question pool or cheat sheets.
You had to actually know something other than just memorizing a few answers.

And at the time, the Amateur Extra was harder than the First Class
Radiotelephone.

Nowadays, an 8-year-old can pass the Amateur Extra with virtually no
knowledge of math or electronics at all - just the ability to memorize a
few answers.

Learn something about electronics, AC power transfer and other theory.
Than maybe we can converse with a modicum of intelligence. As it is,
I'm tired of trying to teach an idiot who refuses to learn.

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

"Jerry Stuckle" wrote in message
...
On 7/2/2015 6:08 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...
It's a shame they've dumbed down the exams so much that you don't need
to know anything to hold a ticket any more. Back when I got mine, even
the General Class was tougher than the Extra Class today - and it was
administered by the FCC, with no public question pool or cheat sheets.
You had to actually know something other than just memorizing a few
answers.

And at the time, the Amateur Extra was harder than the First Class
Radiotelephone.


I had my First Phone at the age of 22 back in 1972. Passed the 2nd and
first the same day on the first try.

And back at you on trying to teach someone that will not learn. Seems that
several on here think you are wrong most of the time.

On 7/2/2015 8:51 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...
On 7/2/2015 6:08 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...
It's a shame they've dumbed down the exams so much that you don't need
to know anything to hold a ticket any more. Back when I got mine, even
the General Class was tougher than the Extra Class today - and it was
administered by the FCC, with no public question pool or cheat sheets.
You had to actually know something other than just memorizing a few
answers.

And at the time, the Amateur Extra was harder than the First Class
Radiotelephone.


I had my First Phone at the age of 22 back in 1972. Passed the 2nd and
first the same day on the first try.

And back at you on trying to teach someone that will not learn. Seems that
several on here think you are wrong most of the time.



I've got you there. First phone in 1970 at age 18 - before I started
college. Amateur I also passed Second and First the same day. My
Amateur Extra came 9 months later, but only because I had to hold a
General for two years before I could take the Extra exam.

Did you ever use your first phone? I was an engineer for one broadcast
station and chief engineer for another. I also repaired everything from
$40 cb sets to multi-million dollar mainframe computers. And even did
some digital design work back on the 70's.

But it's quite obvious from your updates that you have no idea what
you're talking about. You're an appliance operator with no
understanding of what's going on underneath the covers. And yes, I know
there are some idiotic trolls here who don't think I know what I'm
talking about. My EE professors would disagree with them.


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

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

On Thu, 02 Jul 2015 14:55:53 -0400, Jerry Stuckle
wrote:

It's easy enough to demonstrate that you're wrong.

1. Setup your favorite HF xmitter and attach a Tee connector to the
antenna connector, your favorite VSWR meter, a length of 50 ohm coax,
and a 50 ohm load.
2. Transmit and convince yourself that the VSWR is 1:1. Make sure
the transmitter is not into ALC.
3. Now, take another 50 ohm dummy load and connect it to the Tee
connector. The transmitter now sees 25 ohms, so the PA stage has half
the normal gain. You may need to increase the drive level to obtain
the same RF power as before.
4. Measure the VSWR again. It should also be 1:1.

Looking back towards the transmitter, the 50 ohm coax cable sees a 2:1
mismatch of 25 ohms (the alleged 50 ohms from radio in parallel with
another 50 ohms from the extra dummy load). I know this part works
because I've demonstrated it twice to the local non-believers.


Now, we go into uncharted territory and do it again with a 75 ohm coax
and a 75 ohm dummy load at the far end (antenna end) of the coax. Same
procedure.
1. Check the VSWR and it should be 1.5:1.
2. Connect a 50 ohm dummy load to the Tee connector, and measure the
VSWR again. It should still be 1.5:1.

Looking back towards the transmitter, the 75 ohm coax cable sees the
same 2:1 mismatch of 25 ohms. If you want to go further, I think it
can be demonstrated that almost any number of extra dummy loads at the
Tee connector will still produce the same 1.5:1 VSWR.

I'll try it on the bench, but I have other plans for the holiday
weekend. If I find time, and manage to get all the junk off my
workbench, I'll give try it.

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

On 7/2/2015 7:56 PM, Jeff Liebermann wrote:
On Thu, 02 Jul 2015 14:55:53 -0400, Jerry Stuckle
wrote:

It's easy enough to demonstrate that you're wrong.

1. Setup your favorite HF xmitter and attach a Tee connector to the
antenna connector, your favorite VSWR meter, a length of 50 ohm coax,
and a 50 ohm load.
2. Transmit and convince yourself that the VSWR is 1:1. Make sure
the transmitter is not into ALC.
3. Now, take another 50 ohm dummy load and connect it to the Tee
connector. The transmitter now sees 25 ohms, so the PA stage has half
the normal gain. You may need to increase the drive level to obtain
the same RF power as before.
4. Measure the VSWR again. It should also be 1:1.


Of course it will be. You have 50 ohms on one end. But you're not
measuring what the TRANSMITTER sees. The fact that you may have to
increase drive level indicates the circumstances have changed.

Looking back towards the transmitter, the 50 ohm coax cable sees a 2:1
mismatch of 25 ohms (the alleged 50 ohms from radio in parallel with
another 50 ohms from the extra dummy load). I know this part works
because I've demonstrated it twice to the local non-believers.


Sure. But you don't have power going from one resistor to the
transmitter and the other resister, so your measurement is meaningless -
and you are as full of crap as you normally are.

Stick your VSWR meter between the power source (the transmitter) and
BOTH loads (i.e. before the T). You will see a 2:1 SWR.


Now, we go into uncharted territory and do it again with a 75 ohm coax
and a 75 ohm dummy load at the far end (antenna end) of the coax. Same
procedure.
1. Check the VSWR and it should be 1.5:1.
2. Connect a 50 ohm dummy load to the Tee connector, and measure the
VSWR again. It should still be 1.5:1.

Looking back towards the transmitter, the 75 ohm coax cable sees the
same 2:1 mismatch of 25 ohms. If you want to go further, I think it
can be demonstrated that almost any number of extra dummy loads at the
Tee connector will still produce the same 1.5:1 VSWR.


Again, the dummy load is not producing any power, so adding something to
the other end of the T will have no effect. So once again your "test"
is meaningless and you are full of crap.

Now in this case if you connect the SWR bridge before the T, you will
show a 1.5:1 with one 75 ohm load, and a 1.3:1 SWR with two 75 ohm loads
(37.5 ohms).

SWR measurements are only valid when the VSWR meter is connected between
the power generator (transmitter) and the total load (one or both dummy
loads). Connecting between one leg of the T and the load only shows
VSWR for that leg - but not the entire system.

I'll try it on the bench, but I have other plans for the holiday
weekend. If I find time, and manage to get all the junk off my
workbench, I'll give try it.


Go ahead - continue to mae a fool of yourself. You're real good at it.

--
==================
Remove the "x" from my email address
Jerry, AI0K

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