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

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