Re: Coax to connect between exciter and SB-200
The best way to view the mismatch at the amp input is to look at a point on the Smith chart.? If the amp input impedance is not 50+j0, the point will NOT be at the center of the Smith chart.? It will be on a SWR circle going around the center.? This circle is centered on the center location of the Smith chart.? The distance the point moves on the circle is a function of its electrical length of the coax.? The SWR does NOT change along the coax unless there ls loss in the coax.? What does change is the reactance and resistance combination.? Assume the amp input impedance is on a 2:1 SWR circle.? Then the impedance could be 100+j0 ohms at a certain coax length or could be 25+j0 at another coax length.? In other words the real and imaginary combination change a lot but the point stays on the 2:1 SWR circle.? The SWR does not change.? ...Bill K3HZP
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Re: Coax to connect between exciter and SB-200
Thanks, Adrian – a very good explanation ! I wrote an article on SWR for AR magazine many years ago. Covered the same ground. ? Cheers, ? John ?
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From: [email protected] <[email protected]> On Behalf Of Adrian Fewster
Sent: Wednesday, November 1, 2023 6:52 AM
To: [email protected]
Subject: Re: [ham-amplifiers] Coax to connect between exciter and SB-200? Also ; On 1/11/23 08:43, Adrian Fewster via groups.io wrote: I would have thought such information would be in the public domain, if a web link etc, ... the reluctance to share to the group, I find odd.
Here is another interesting site on the subject ;??
73
vk4tux
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Re: Coax to connect between exciter and SB-200
John, Send me a personal email with the address to send it to. I got the address off of here, used this one... sent it but it bounced. Bob? W4JFA
Hi Bob – I would like to read that too, if you would put it on here or send it to me directly. ? Thanks ! ? John VK6JX ? ? Jim, I sent you an email directly. The address copied kinda strange so not sure if you'll get it or not. Let me know. You'll be interested in reading. Not that long. ? Jim, If a 50 ohm coax is NOT terminated into a 50R - j0 load, the impedance will change with length. Somewhat like using a 1/4 wave 75 ohm coax to match/change impedance of certain antennas. Now some will say that the impedance will change but the SWR does/should not. I have a little write up from a feed line expert explaining why the SWR does indeed change, just like your 3 foot to 6 foot example changed the SWR. Personally I've noticed this change more so on ten meters than lower bands. Makes sense because for example a 3 foot piece of coax is a larger percentage of a wabvelength on ten meters than on the lower bands. ? On Sun, Oct 29, 2023 at 2:43?AM Jim VE7RF <jim.thom@...> wrote: Watch out with length of coax between xcvr + input of the amp.? ? On all 4 of my Drake L4B amps, if coax is 3' long, input swr is flat on all bands.? ?But when I use a 6' jumper, input swr increases to aprx? 1.4:1? or? 1.5:1? ? and no amount of slug tuning will reduce it.? And the Q of the tuned input PI networks on the drake amps is a helluva lot higher? vs a SB-220.? (cap values are higher) ? On my big hb amps, they all use a manually tuned, PI tuned input.? Same deal, but at least I can tune it dead flat.? ? I still have not figured out why the interconnecting coax length affects? input swr.? ? Jim? ?VE7RF
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Re: Coax to connect between exciter and SB-200
Yep. Just to clarify, with 50 ohm coax/feedline, if the load is 50 ohms resistance with zero reactance, the SWR will not change. Bob? W4JFA
On Tue, Oct 31, 2023 at 12:37?PM Jim VE7RF < jim.thom@...> wrote: Tnx Bob.... got it.? ?Into a 50 ohm DL..... swr is 1:1? ? regardless of coax length.? My guess is since the C1 and C2 caps in the tuned inputs are fixed...and only the coil is adjustable, there is no real way to adjust it correctly.? It's probably off a tiny bit, and enough such that it's not 50 ohms + zero reactance.? Then when the cable length is changed, the values used on the tuned input are even more outa whack.??
On my hb tube amps, I use a manually tuned, PI tuned input, with a tapped coil, and a pair of broadcast caps.? ( both padded on 160m only).? Coax length is a non issue.?
?
On the next manually tuned, tuned input,? I'm going to use a 0 -? 4.4 uh? roller coil (8 ga wire used)..and a pair of broadcast caps? ( padded on 160m).? ?Then I can vary the loaded Q between extremes, on each band..... which is more of an experiment to see the effects on? IMD? vs loaded Q, and some other tests.?
?
Years ago, I used a pair of Arco trimmer caps ( padded on the lower bands) and a T-50 coil...... one assy for each band.? Simple tweak for flat swr. Again, cable length did not enter the equation.?
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Re: Coax to connect between exciter and SB-200
Tnx Bob.... got it.? ?Into a 50 ohm DL..... swr is 1:1? ? regardless of coax length.? My guess is since the C1 and C2 caps in the tuned inputs are fixed...and only the coil is adjustable, there is no real way to adjust it correctly.? It's probably off a tiny bit, and enough such that it's not 50 ohms + zero reactance.? Then when the cable length is changed, the values used on the tuned input are even more outa whack.??
On my hb tube amps, I use a manually tuned, PI tuned input, with a tapped coil, and a pair of broadcast caps.? ( both padded on 160m only).? Coax length is a non issue.?
?
On the next manually tuned, tuned input,? I'm going to use a 0 -? 4.4 uh? roller coil (8 ga wire used)..and a pair of broadcast caps? ( padded on 160m).? ?Then I can vary the loaded Q between extremes, on each band..... which is more of an experiment to see the effects on? IMD? vs loaded Q, and some other tests.?
?
Years ago, I used a pair of Arco trimmer caps ( padded on the lower bands) and a T-50 coil...... one assy for each band.? Simple tweak for flat swr. Again, cable length did not enter the equation.?
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Re: Coax to connect between exciter and SB-200
Hi Bob – I would like to read that too, if you would put it on here or send it to me directly. ? Thanks ! ? John VK6JX ?
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From: [email protected] <[email protected]> On Behalf Of Bob
Sent: Monday, October 30, 2023 8:44 PM
To: [email protected]
Subject: Re: [ham-amplifiers] Coax to connect between exciter and SB-200? Jim, I sent you an email directly. The address copied kinda strange so not sure if you'll get it or not. Let me know. You'll be interested in reading. Not that long. ? Jim, If a 50 ohm coax is NOT terminated into a 50R - j0 load, the impedance will change with length. Somewhat like using a 1/4 wave 75 ohm coax to match/change impedance of certain antennas. Now some will say that the impedance will change but the SWR does/should not. I have a little write up from a feed line expert explaining why the SWR does indeed change, just like your 3 foot to 6 foot example changed the SWR. Personally I've noticed this change more so on ten meters than lower bands. Makes sense because for example a 3 foot piece of coax is a larger percentage of a wabvelength on ten meters than on the lower bands. ? On Sun, Oct 29, 2023 at 2:43?AM Jim VE7RF <jim.thom@...> wrote: Watch out with length of coax between xcvr + input of the amp.? ? On all 4 of my Drake L4B amps, if coax is 3' long, input swr is flat on all bands.? ?But when I use a 6' jumper, input swr increases to aprx? 1.4:1? or? 1.5:1? ? and no amount of slug tuning will reduce it.? And the Q of the tuned input PI networks on the drake amps is a helluva lot higher? vs a SB-220.? (cap values are higher) ? On my big hb amps, they all use a manually tuned, PI tuned input.? Same deal, but at least I can tune it dead flat.? ? I still have not figured out why the interconnecting coax length affects? input swr.? ? Jim? ?VE7RF
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Gentlemen,
?
If you can spare the time, calibrate your
nanoVNA boxes and run some profiles
on various coax jumpers.
?
Setting up the IRIG-B network at work required
any number of coax jumpers between various
panelboard instruments because everybody
in the band hadda be on the same beat.
?
So one day it all had to be proof-tested by
a third party, just like most of the other
control widgets, and this guy showed up
with a R&S VNA with a bag full of factory
jumpers, and the tech ran a Calibrate between
all tests, and we could plainly see that $50
jumpers were nowhere near one another
on the curve screen.
?
So yes, using a longer chunka coax does make
a difference, especially if it’s premium flavor.
?
Hal Mandel
W4HBM
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Re: Coax to connect between exciter and SB-200
Phase angle.??
If the coax length does not matter, phasing lines would not work.?
Jim, If a 50 ohm coax is NOT terminated into a 50R - j0 load, the impedance will change with length. Somewhat like using a 1/4 wave 75 ohm coax to match/change impedance of
certain antennas. Now some will say that the impedance will change but the SWR does/should not. I have a little write up from a feed line expert
explaining why the SWR does indeed change, just like your 3 foot to 6 foot example changed the SWR.
Personally I've noticed this change more so on ten meters than lower bands. Makes sense because for example a 3 foot piece of coax is a larger percentage of a wabvelength
on ten meters than on the lower bands.
Bob? W4JFA
On Sun, Oct 29, 2023 at 2:43?AM Jim VE7RF < jim.thom@...> wrote:
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Watch out with length of coax between xcvr + input of the amp.? ? On all 4 of my Drake L4B amps, if coax is 3' long, input swr is flat on all bands.? ?But when I use a 6' jumper, input swr increases to aprx? 1.4:1? or? 1.5:1? ? and no amount of slug tuning
will reduce it.? And the Q of the tuned input PI networks on the drake amps is a helluva lot higher? vs a SB-220.? (cap values are higher)
?
On my big hb amps, they all use a manually tuned, PI tuned input.? Same deal, but at least I can tune it dead flat.?
?
I still have not figured out why the interconnecting coax length affects? input swr.?
?
Jim? ?VE7RF
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Re: Coax to connect between exciter and SB-200
Jim, I sent you an email directly. The address copied kinda strange so not sure if you'll get it or not. Let me know. You'll be interested in reading. Not that long. Bob? W4JFA
Jim, If a 50 ohm coax is NOT terminated into a 50R - j0 load, the impedance will change with length. Somewhat like using a 1/4 wave 75 ohm coax to match/change impedance of certain antennas. Now some will say that the impedance will change but the SWR does/should not. I have a little write up from a feed line expert explaining why the SWR does indeed change, just like your 3 foot to 6 foot example changed the SWR.
Personally I've noticed this change more so on ten meters than lower bands. Makes sense because for example a 3 foot piece of coax is a larger percentage of a wabvelength on ten meters than on the lower bands. Bob? W4JFA
On Sun, Oct 29, 2023 at 2:43?AM Jim VE7RF < jim.thom@...> wrote: Watch out with length of coax between xcvr + input of the amp.? ? On all 4 of my Drake L4B amps, if coax is 3' long, input swr is flat on all bands.? ?But when I use a 6' jumper, input swr increases to aprx? 1.4:1? or? 1.5:1? ? and no amount of slug tuning will reduce it.? And the Q of the tuned input PI networks on the drake amps is a helluva lot higher? vs a SB-220.? (cap values are higher)
?
On my big hb amps, they all use a manually tuned, PI tuned input.? Same deal, but at least I can tune it dead flat.?
?
I still have not figured out why the interconnecting coax length affects? input swr.?
?
Jim? ?VE7RF
|
Re: Coax to connect between exciter and SB-200
Jim, If a 50 ohm coax is NOT terminated into a 50R - j0 load, the impedance will change with length. Somewhat like using a 1/4 wave 75 ohm coax to match/change impedance of certain antennas. Now some will say that the impedance will change but the SWR does/should not. I have a little write up from a feed line expert explaining why the SWR does indeed change, just like your 3 foot to 6 foot example changed the SWR.
Personally I've noticed this change more so on ten meters than lower bands. Makes sense because for example a 3 foot piece of coax is a larger percentage of a wabvelength on ten meters than on the lower bands. Bob? W4JFA
On Sun, Oct 29, 2023 at 2:43?AM Jim VE7RF < jim.thom@...> wrote: Watch out with length of coax between xcvr + input of the amp.? ? On all 4 of my Drake L4B amps, if coax is 3' long, input swr is flat on all bands.? ?But when I use a 6' jumper, input swr increases to aprx? 1.4:1? or? 1.5:1? ? and no amount of slug tuning will reduce it.? And the Q of the tuned input PI networks on the drake amps is a helluva lot higher? vs a SB-220.? (cap values are higher)
?
On my big hb amps, they all use a manually tuned, PI tuned input.? Same deal, but at least I can tune it dead flat.?
?
I still have not figured out why the interconnecting coax length affects? input swr.?
?
Jim? ?VE7RF
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Hi Alek, I did consider that but I have some old AA5 radios, and an old Zenith floor radio to kinda restore so I will need it then. I said kinda restore because I don't really restore them, I just make them work reliably.? 73, Bob? W4JFA
Sounds like a true ham shack Bob. Congratulations.
Another thing to consider is the actual need for a tube tester.
How often do you use it and how often are you likely to use it in
the next 10 years?
You might find, like me, that the better option is to sell it or
pass it on to somebody that will use it.
73, Alek VK6APK.
On 27/10/2023 10:06 pm, Bob wrote:
Jim, My shack/shop inside is getting cramped! I
know it doesn't sound like it would save much space but it will.
Thanks, Bob? W4JFA
On Fri, Oct 27, 2023 at
9:55?AM Jim VE7RF < jim.thom@...>
wrote:
Store
it inside the home.? ?If you store it outside, it will end up
with mildew, condensation etc, on everything.? ?IF it has to
be stored outdoors,? I would put it in a sealed container,
packed with a ton of silica gel (desiccant).? Then change out
the silica gel once per year.
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Re: Coax to connect between exciter and SB-200
Hi fellas
For 24 out of my 41 years as an Electrical/Instrument Engineer, I worked in Alumina Refineries. Both of the refineries I worked in were owned by US companies. The first - Worsley Alumina, owned by Reynolds Metals, the second (3 sites) by Alcoa.
Hence, both companies used Honeywell process control equipment. When I started at Worsley in 1989, I was trained in the intricacies of the equipment and one thing that stuck in my memory (being a radio ham) was their recommendation that ANY coax jumper cable had to be at least 10 feet long (even if the distance between connections may have only been 1 foot) as the cable needed time to establish it's inherent impedance. This sounded like voodoo to me, but your comment on the different swr seen with different length coax jumpers brought back the memory.
Any comments ?
Cheers,
John VK6JX
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-----Original Message----- From: [email protected] < [email protected]> On Behalf Of Adrian Fewster Sent: Sunday, October 29, 2023 3:24 PM To: [email protected]Subject: Re: [ham-amplifiers] Coax to connect between exciter and SB-200 I think the reason different lengths of coax effect measured swr is because its not a purely resistive load and is effected by reactance. The type of swr measurement system would make a difference. Measured true power out compared to reflected would be better with more expensive meters. Some use an inline tuner to deliver dialled watts between amp and txcr. If you replace the amp input with a purely resistive 50 ohm dummy load, do you see the same shift in measurement from 6" to 3 feet coax patch length ? 73 vk4tux On 29/10/23 16:43, Jim VE7RF wrote:
I still have not figured out why the interconnecting coax length
affects input swr.
Jim VE7RF
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Re: Coax to connect between exciter and SB-200
Watch out with length of coax between xcvr + input of the amp.? ? On all 4 of my Drake L4B amps, if coax is 3' long, input swr is flat on all bands.? ?But when I use a 6' jumper, input swr increases to aprx? 1.4:1? or? 1.5:1? ? and no amount of slug tuning will reduce it.? And the Q of the tuned input PI networks on the drake amps is a helluva lot higher? vs a SB-220.? (cap values are higher)
?
On my big hb amps, they all use a manually tuned, PI tuned input.? Same deal, but at least I can tune it dead flat.?
?
I still have not figured out why the interconnecting coax length affects? input swr.?
?
Jim? ?VE7RF
|
Re: Coax to connect between exciter and SB-200
Don't we all know a million places we can buy jumpers if we want to ?
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Sounds like a true ham shack Bob. Congratulations.
Another thing to consider is the actual need for a tube tester.
How often do you use it and how often are you likely to use it in
the next 10 years?
You might find, like me, that the better option is to sell it or
pass it on to somebody that will use it.
73, Alek VK6APK.
On 27/10/2023 10:06 pm, Bob wrote:
toggle quoted message
Show quoted text
Jim, My shack/shop inside is getting cramped! I
know it doesn't sound like it would save much space but it will.
Thanks, Bob? W4JFA
On Fri, Oct 27, 2023 at
9:55?AM Jim VE7RF < jim.thom@...>
wrote:
Store
it inside the home.? ?If you store it outside, it will end up
with mildew, condensation etc, on everything.? ?IF it has to
be stored outdoors,? I would put it in a sealed container,
packed with a ton of silica gel (desiccant).? Then change out
the silica gel once per year.
|
Jim, My shack/shop inside is getting cramped! I know it doesn't sound like it would save much space but it will. Thanks, Bob? W4JFA
On Fri, Oct 27, 2023 at 9:55?AM Jim VE7RF < jim.thom@...> wrote: Store it inside the home.? ?If you store it outside, it will end up with mildew, condensation etc, on everything.? ?IF it has to be stored outdoors,? I would put it in a sealed container, packed with a ton of silica gel (desiccant).? Then change out the silica gel once per year.
|
Store it inside the home.? ?If you store it outside, it will end up with mildew, condensation etc, on everything.? ?IF it has to be stored outdoors,? I would put it in a sealed container, packed with a ton of silica gel (desiccant).? Then change out the silica gel once per year.
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I got some answers emailed direct saying leave it inside. I've had electronic equipment in a garage for years with no issues but I thought I'd ask about an old tube tester. It'll stay inside. 73, Bob? W4JFA
Hi all, I thought this would be the best group to get an opinion from. I have an old tube tester in it's wooden cabinet. I would like to store it in the garage/shed.
What do you all think about winter temperatures that can get to the middle 20 degrees fahrenheit?in the winter, and 95 degrees fahrenheit?in the summer??
It will be wrapped in plastic or in a plastic bag and then inside a cabinet drawer.
Thanks guys.
Bob? W4JFA
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Coax to connect between exciter and SB-200
Hi all
Today I found a pre-made 6-foot RG-58 cable at <> with UHF connectors.? USD$13.49 or thereabouts, soec-ed?at 66% velocity factor. ?
It's an easy and relatively cheap way to try one of these cables...not all of us have spare UHF male connectors for RG-58, and some fresh RG-58 hanging out. ?
Yes, they have 12-footers that can be cut into two?six-footers and a different connector added.? USD$16.99.
73 Jim N6OTQ
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No electronic equipment will do very well in an uncontrolled environment. ?Also, I certainly would not wrap it in plastic, which will trap moisture.? Cloth like a bedsheet would be a much better choice because it can breathe.? I used to work in a boat yard up way up North.? We would store boats for the winter under canvas tarps.? One year some idiot decided use plastic tarps, which was a total disaster. Wood boats developed severe cases of wood rot and the fiberglass boats had tons of mold on them. ? ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Bob
Sent: Wednesday, October 25, 2023 3:39 PM
To: Ham Amplifiers Ham Amplifiers
Subject: [ham-amplifiers] Tube testers ? Hi all, I thought this would be the best group to get an opinion from. I have an old tube tester in it's wooden cabinet. I would like to store it in the garage/shed. What do you all think about winter temperatures that can get to the middle 20 degrees fahrenheit?in the winter, and 95 degrees fahrenheit?in the summer?? It will be wrapped in plastic or in a plastic bag and then inside a cabinet drawer.
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Bill K3HZP
Bob
HaL Mandel