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75ohm Impedance question K3S and Antenna side.

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ae4pb

75ohm Impedance question K3S and Antenna side.

I'm about to pull the trigger on a Hustler 6BTV (6-Band, 80, 40, 30, 20, 15,
10 meters). It will be temporarily installed (with radials) about 200' away
from my house. I'd like to run CATV "hardline" but I'm not sure how to get a
2:1 UnUn with a wide enough bandwidth on the antenna side (the impedance
with 60ish radials should be in the 35ohm range). In addition I believe I
will be ok on the RIG side to just connect RG6 (75ohm) to the hardline and
direct to the rig since my K3S can match the impedance. Is this essentially
correct and is there a better way to do this? I'm trying to minimize losses
for the distance run and still have a decent transmitted signal.
Thanks in advance.
Yeah, I should know this stuff but I can't know everything 100%.

73 es
De AE4PB
..

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Vic Rosenthal

Re: 75ohm Impedance question K3S and Antenna side.

I don't think you need a unun because the additional loss due to SWR
running RG/6 at 2:1 is only 0.381 dB, and the unun itself would
certainly have some loss.
But the loss in 200' of RG/6 even at 1:1 is about 2.9 dB! That is almost
half your power. RG/8 would have only 1.9 dB loss, and with a probable
SWR of about 1.5:1 you would have a total loss of 2.2 dB.
Even better would be Belden 9913 or similar coax, which would give you a
total loss of 1.6 dB.
All these facts and more are available at
<https://www.qsl.net/co8tw/Coax_Calculator.htm>

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 31/03/2020 19:39, [hidden email] wrote:

> I'm about to pull the trigger on a Hustler 6BTV (6-Band, 80, 40, 30, 20, 15,
> 10 meters). It will be temporarily installed (with radials) about 200' away
> from my house. I'd like to run CATV "hardline" but I'm not sure how to get a
> 2:1 UnUn with a wide enough bandwidth on the antenna side (the impedance
> with 60ish radials should be in the 35ohm range). In addition I believe I
> will be ok on the RIG side to just connect RG6 (75ohm) to the hardline and
> direct to the rig since my K3S can match the impedance. Is this essentially
> correct and is there a better way to do this? I'm trying to minimize losses
> for the distance run and still have a decent transmitted signal.
> Thanks in advance.
> Yeah, I should know this stuff but I can't know everything 100%.
>
> 73 es
> De AE4PB
> ..
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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Vic Rosenthal

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by ae4pb

Forgot to add: I used 28 MHz for the calculations in my previous email.
Losses will be lower on lower bands.

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 31/03/2020 19:39, [hidden email] wrote:

Jim Brown-10

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by ae4pb

That CATV hard line is pretty low loss, so the excess loss from the
small mismatch isn't much. I wouldn't worry too much about the impedance
mismatch if your radio has the tuner installed. Hook everything up with
the CATV hard line, no Unun, and if the tuner makes the radio happy,
declare victory. Especially if the installation is temporary, don't
sweat 15M and above -- at the solar minimum, there's not a lot happening
on these bands for a few years.

Also, I suggest that you check the feedpoint Z with a good antenna
analyzer right at the antenna. Depending on your soil conductivity, 35
ohms is pretty optimistic.

73, Jim K9YC

On 3/31/2020 9:39 AM, [hidden email] wrote:
> I'm about to pull the trigger on a Hustler 6BTV (6-Band, 80, 40, 30, 20, 15,
> 10 meters). It will be temporarily installed (with radials) about 200' away
> from my house. I'd like to run CATV "hardline" but I'm not sure how to get a
> 2:1 UnUn with a wide enough bandwidth on the antenna side (the impedance
> with 60ish radials should be in the 35ohm range).

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ae4pb

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by Vic Rosenthal

The 200' run is Cable TV hardline (1/2") 75 Ohm, that's where the UnUn would go (maybe).

Jerry Moore
Cell: 803-431-1870

-----Original Message-----
From: Victor Rosenthal 4X6GP <[hidden email]>
Sent: Tuesday, March 31, 2020 1:58 PM
To: [hidden email]; [hidden email]
Subject: Re: [Elecraft] 75ohm Impedance question K3S and Antenna side.

I don't think you need a unun because the additional loss due to SWR running RG/6 at 2:1 is only 0.381 dB, and the unun itself would certainly have some loss.
But the loss in 200' of RG/6 even at 1:1 is about 2.9 dB! That is almost half your power. RG/8 would have only 1.9 dB loss, and with a probable SWR of about 1.5:1 you would have a total loss of 2.2 dB.
Even better would be Belden 9913 or similar coax, which would give you a total loss of 1.6 dB.
All these facts and more are available at <https://www.qsl.net/co8tw/Coax_Calculator.htm>

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 31/03/2020 19:39, [hidden email] wrote:

> I'm about to pull the trigger on a Hustler 6BTV (6-Band, 80, 40, 30,
> 20, 15,
> 10 meters). It will be temporarily installed (with radials) about 200'
> away from my house. I'd like to run CATV "hardline" but I'm not sure
> how to get a
> 2:1 UnUn with a wide enough bandwidth on the antenna side (the
> impedance with 60ish radials should be in the 35ohm range). In
> addition I believe I will be ok on the RIG side to just connect RG6
> (75ohm) to the hardline and direct to the rig since my K3S can match
> the impedance. Is this essentially correct and is there a better way
> to do this? I'm trying to minimize losses for the distance run and still have a decent transmitted signal.
> Thanks in advance.
> Yeah, I should know this stuff but I can't know everything 100%.
>
> 73 es
> De AE4PB
> ..
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net Please help support this email
> list: http://www.qsl.net/donate.html Message delivered to
> [hidden email]
>

Bob McGraw - K4TAX

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by ae4pb

So you end up with < 2:1 SWR on the line. Actually TLW shows the input
to the line SWR as 1.87:1, at the load 2.15 and the total loss at 28MHz
as 1.017 dB. Nothing wrong with those numbers. You don't need a 2:1
UNUN.

Keep the length of RG6 to a minimum as it has higher loss than the 1/2
inch 75 ohm CATV cable.

73

Bob, K4TAX

On 3/31/2020 11:39 AM, [hidden email] wrote:

Bob McGraw - K4TAX

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by ae4pb

You don't need an UNUN with the system. Connect the 1/2" CATV 75 ohm
hard line to the feed point on the antenna, and use a short jumper of
RG8X or RG6 between the hard line to the radio for convenience.

73

Bob, K4TAX

On 3/31/2020 1:06 PM, [hidden email] wrote:

> The 200' run is Cable TV hardline (1/2") 75 Ohm, that's where the UnUn would go (maybe).
>
> Jerry Moore
> Cell: 803-431-1870
>
> -----Original Message-----
> From: Victor Rosenthal 4X6GP <[hidden email]>
> Sent: Tuesday, March 31, 2020 1:58 PM
> To: [hidden email]; [hidden email]
> Subject: Re: [Elecraft] 75ohm Impedance question K3S and Antenna side.
>
> I don't think you need a unun because the additional loss due to SWR running RG/6 at 2:1 is only 0.381 dB, and the unun itself would certainly have some loss.
> But the loss in 200' of RG/6 even at 1:1 is about 2.9 dB! That is almost half your power. RG/8 would have only 1.9 dB loss, and with a probable SWR of about 1.5:1 you would have a total loss of 2.2 dB.
> Even better would be Belden 9913 or similar coax, which would give you a total loss of 1.6 dB.
> All these facts and more are available at <https://www.qsl.net/co8tw/Coax_Calculator.htm>
>
> 73,
> Victor, 4X6GP
> Rehovot, Israel
> Formerly K2VCO
> CWops no. 5
> http://www.qsl.net/k2vco/
> On 31/03/2020 19:39, [hidden email] wrote:
>> I'm about to pull the trigger on a Hustler 6BTV (6-Band, 80, 40, 30,
>> 20, 15,
>> 10 meters). It will be temporarily installed (with radials) about 200'
>> away from my house. I'd like to run CATV "hardline" but I'm not sure
>> how to get a
>> 2:1 UnUn with a wide enough bandwidth on the antenna side (the
>> impedance with 60ish radials should be in the 35ohm range). In
>> addition I believe I will be ok on the RIG side to just connect RG6
>> (75ohm) to the hardline and direct to the rig since my K3S can match
>> the impedance. Is this essentially correct and is there a better way
>> to do this? I'm trying to minimize losses for the distance run and still have a decent transmitted signal.
>> Thanks in advance.
>> Yeah, I should know this stuff but I can't know everything 100%.
>>
>> 73 es
>> De AE4PB
>> ..
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net Please help support this email
>> list: http://www.qsl.net/donate.html Message delivered to
>> [hidden email]
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

John K9UWA-2

Re: 75ohm Impedance question K3S and Antenna side.

Cut the hardline to multiples of 1/2 wavelength and the swr will be 1 to 1 on both
ends. 50 in 50 out. In this case the OP needs around 200 feet. Once your get the
velocity factor for the 1/2" hardline... that is ballpark 80 to 83%. for 3.540 mhz is
265 feet x .8 = 212 feet. If you don't have a piece of test gear to get it cut
correctly then put a 50 ohm dummy load at the far end keep cutting until your
wattmeter says 1 to 1 swr. 1/2 wave multiples will hit most of the ham bands. A
little high in the 30m band. Close enough.
73
John k9uwa
John Goller, K9UWA & Jean Goller, N9PXF
Antique Radio Restorations
[hidden email]
Visit our Web Site at:
http://www.JohnJeanAntiqueRadio.com
4836 Ranch Road
Leo, IN 46765
USA
1-260-637-6426

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Jim Brown-10

Re: 75ohm Impedance question K3S and Antenna side.

On 3/31/2020 8:52 PM, John K9UWA wrote:
> Cut the hardline to multiples of 1/2 wavelength and the swr will be 1 to 1 on both
> ends. 50 in 50 out.

Did you notice that this is for an all-band antenna?

73, Jim K9YC
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David Gilbert

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by Jim Brown-10

Very true, and in fact due to those ground losses the feedpoint
impedance might be higher ... and therefore provide a better "match" to
the 75 CATV line than if it was 35 ohms. The loss just shows up in the
ground instead of in the UNUN (they aren't lossless), on the line, or in
the rig tuner.

I agree with most of the comments here. I'd try it first without the
2:1 UNUN.

73,
Dave AB7E

On 3/31/2020 11:04 AM, Jim Brown wrote:
>
>
> Also, I suggest that you check the feedpoint Z with a good antenna
> analyzer right at the antenna. Depending on your soil conductivity, 35
> ohms is pretty optimistic.
>
> 73, Jim K9YC

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john@kk9a.com

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by ae4pb

You can also use coax to make matching transformer however I don't
know how either of these methods would work for AE4PB's 6 band vertical.

John KK9A

John K9UWA wrote:

Cut the hardline to multiples of 1/2 wavelength and the swr will be 1
to 1 on both
ends. 50 in 50 out. In this case the OP needs around 200 feet. Once
your get the
velocity factor for the 1/2" hardline... that is ballpark 80 to 83%.
for 3.540 mhz is
265 feet x .8 = 212 feet. If you don't have a piece of test gear to
get it cut
correctly then put a 50 ohm dummy load at the far end keep cutting until your
wattmeter says 1 to 1 swr. 1/2 wave multiples will hit most of the ham
bands. A
little high in the 30m band. Close enough.
73
John k9uwa
John Goller, K9UWA & Jean Goller, N9PXF
Antique Radio Restorations
k9uwa at arrl.net
Visit our Web Site at:
http://www.JohnJeanAntiqueRadio.com
4836 Ranch Road
Leo, IN 46765
USA
1-260-637-6426

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John K9UWA-2

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by Jim Brown-10

Ah YES I noticed it is for a multi band antenna.

2 wavelengths 3540 = 265'
4 wavelengths 7080 = 265'
6 wavelengths 10600 = 265'
8 wavelengths 14160 = 265'
12 wavelngths 21240 = 265'
16 wavelengths 28320 = 265'

Multiply the 265' by velocity factor of the coax and you will be someplace just a bit
over 200 feet.

the 10mhz band is off a bit. So OK... other than that 80, 40, 20, 15,10 are all
harmonically related. As I said 50 in and 50 out. If the OP runs this vertical on 17
and 12m then yes he will have maybe a 1.5 / 1 mismatch caused by the coax. But
the antenna isn't designed for 17 and 12.

I cut all the 3/4" CATV in my system with a Hewlett Packard HP 4815A Vector
Impedance Meter. Any 1/2 wave mult the the SWR is the same in as out. Any
ODD 1/4 wavelength multiple creates a transformation With Multiple 4 hi stacks of
yagi's I have many of those in the system as well. 75 ohm cable works well to put
pairs or quads of yagi's together.

The only thing that maybe won't be perfect is the actual vertical itself may not be a
50 ohm input. His vertical is a Hustler 6BTV.
73
John k9uwa

On 31 Mar 2020 at 22:39, Jim Brown wrote:

> On 3/31/2020 8:52 PM, John K9UWA wrote:
> > Cut the hardline to multiples of 1/2 wavelength and the swr will be 1 to 1 on
> > both ends. 50 in 50 out.
>
> Did you notice that this is for an all-band antenna?
>
> 73, Jim K9YC
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

John Goller, K9UWA & Jean Goller, N9PXF
Antique Radio Restorations
[hidden email]
Visit our Web Site at:
http://www.JohnJeanAntiqueRadio.com
4836 Ranch Road
Leo, IN 46765
USA
1-260-637-6426

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Bob McGraw - K4TAX

Re: 75ohm Impedance question K3S and Antenna side.

Based on TLW calculations for 1/2" CATV 75 ohm hard line, 200 ft at 28
MHz should show a 1.87:1 SWR at the transmitter. Assuming 35 ohms load
Z. This equates to 1.027 dB total loss with 0.207 dB being attributed
to the SWR on the line. Thus going through the efforts and matching
process would only net an improvement of 0.207 dB on 10 meters. Lower
frequencies would be less.

Since this is a 5 or 6 band antenna, I doubt the Z at the feed point
will always be 35 ohms. In order to determine what is actually needed,
one would need measurements for each band.

Conclusion: Feed it with 200 ft of 1/2" CATV 75 ohm hard line, use a
short jumper of RG6, or 8X or whatever to connect the hardline to the
radio and be done with it.

NOTE: I just noticed that the numbers below are somewhat in error.

468/3.540 = 132.2 which is 1/2 wavelength. Thus 132.2 X 2 = 264 ft
which is 1 wavelength, not 2 wavelengths as stated. I didn't run the
math on the others.

73

Bob, K4TAX

On 4/1/2020 7:28 AM, John K9UWA wrote:

> Ah YES I noticed it is for a multi band antenna.
>
> 2 wavelengths 3540 = 265'
> 4 wavelengths 7080 = 265'
> 6 wavelengths 10600 = 265'
> 8 wavelengths 14160 = 265'
> 12 wavelngths 21240 = 265'
> 16 wavelengths 28320 = 265'
>
> Multiply the 265' by velocity factor of the coax and you will be someplace just a bit
> over 200 feet.
>
> the 10mhz band is off a bit. So OK... other than that 80, 40, 20, 15,10 are all
> harmonically related. As I said 50 in and 50 out. If the OP runs this vertical on 17
> and 12m then yes he will have maybe a 1.5 / 1 mismatch caused by the coax. But
> the antenna isn't designed for 17 and 12.
>
> I cut all the 3/4" CATV in my system with a Hewlett Packard HP 4815A Vector
> Impedance Meter. Any 1/2 wave mult the the SWR is the same in as out. Any
> ODD 1/4 wavelength multiple creates a transformation With Multiple 4 hi stacks of
> yagi's I have many of those in the system as well. 75 ohm cable works well to put
> pairs or quads of yagi's together.
>
> The only thing that maybe won't be perfect is the actual vertical itself may not be a
> 50 ohm input. His vertical is a Hustler 6BTV.
> 73
> John k9uwa
>
>

John K9UWA-2

Re: 75ohm Impedance question K3S and Antenna side.

Supposedly the feedpoint impedance is 52 ohms ??? Yes, I question that a bit.
Read all about it here. Sorry I doubled the 1/2 wave mults.

https://www.dxengineering.com/search/department/antennas/section/hf-vertical-a
ntennas/brand/hustler-antenna/product-line/hustle

Hustler Antenna 6BTV - Hustler 6BTV 6-Band HF Vertical Antenna and DXE
Installation Guide Packages
Antenna, Vertical, HF, 6-Band, 80, 40, 30, 20, 15, 10 meters, 1.5 kW, 24 ft., +
DXE BTV High Perf. Guide, Each $241.99

Performance provided by the Hustler 6BTVs is better than any other antenna of
this type. Broad-banding is such that one measurement and setting permits both
phone and CW operation. The antenna provides nominal 52-ohm base
impedance when installed and tuned according to the instructions. The radiation
efficiency is equal to, or greater than, other trap verticals.

73
John k9uwa

On 1 Apr 2020 at 8:14, Bob McGraw K4TAX wrote:

> Based on TLW calculations for 1/2" CATV 75 ohm hard line, 200 ft at 28
> MHz should show a 1.87:1 SWR at the transmitter. Assuming 35 ohms load
> Z. This equates to 1.027 dB total loss with 0.207 dB being attributed
> to the SWR on the line. Thus going through the efforts and matching
> process would only net an improvement of 0.207 dB on 10 meters. Lower
> frequencies would be less.
>
> Since this is a 5 or 6 band antenna, I doubt the Z at the feed point
> will always be 35 ohms. In order to determine what is actually needed,
> one would need measurements for each band.
>
> Conclusion: Feed it with 200 ft of 1/2" CATV 75 ohm hard line, use a
> short jumper of RG6, or 8X or whatever to connect the hardline to the
> radio and be done with it.
>
>
> NOTE: I just noticed that the numbers below are somewhat in error.
>
> 468/3.540 = 132.2 which is 1/2 wavelength. Thus 132.2 X 2 = 264 ft
> which is 1 wavelength, not 2 wavelengths as stated. I didn't run the
> math on the others.
>
> 73
>
> Bob, K4TAX
>
>
> On 4/1/2020 7:28 AM, John K9UWA wrote:
> > Ah YES I noticed it is for a multi band antenna.
> >
> > 2 wavelengths 3540 = 265'
> > 4 wavelengths 7080 = 265'
> > 6 wavelengths 10600 = 265'
> > 8 wavelengths 14160 = 265'
> > 12 wavelngths 21240 = 265'
> > 16 wavelengths 28320 = 265'
> >
> > Multiply the 265' by velocity factor of the coax and you will be someplace
> > just a bit over 200 feet.
> >
> > the 10mhz band is off a bit. So OK... other than that 80, 40, 20, 15,10 are
> > all harmonically related. As I said 50 in and 50 out. If the OP runs this
> > vertical on 17 and 12m then yes he will have maybe a 1.5 / 1 mismatch caused
> > by the coax. But the antenna isn't designed for 17 and 12.
> >
> > I cut all the 3/4" CATV in my system with a Hewlett Packard HP 4815A Vector
> > Impedance Meter. Any 1/2 wave mult the the SWR is the same in as out. Any ODD
> > 1/4 wavelength multiple creates a transformation With Multiple 4 hi stacks of
> > yagi's I have many of those in the system as well. 75 ohm cable works well to
> > put pairs or quads of yagi's together.
> >
> > The only thing that maybe won't be perfect is the actual vertical itself may
> > not be a 50 ohm input. His vertical is a Hustler 6BTV. 73 John k9uwa
> >
> >
>
> ______________________________________________________________
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Don Wilhelm

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by Bob McGraw - K4TAX

Bob and all,

One problem is that you are using '468/fMhz' to compute the length of a
half wavelength. That is the common 'cutting formula' which includes an
end-effect factor of about 5% which reduces the length of a half wave
radiator. An actual half wavelength is longer.

The actual length (in feet) of a wavelength is 983.5712/fMhz which is
considerably longer than that computed using 468/fMhz times 2.

When dealing with a length of transmission line, the use of the '468'
factor should not be used - compute the actual wavelength and then apply
the velocity factor.

For those who work in meters instead of feet, the factor is 299.7925/fMHz.

See any antenna handbook which has essential characteristics of antennas
for validation of my numbers.

73,
Don W3FPR

On 4/1/2020 9:14 AM, Bob McGraw K4TAX wrote:

>
> NOTE: I just noticed that the numbers below are somewhat in error.
>
> 468/3.540 = 132.2 which is 1/2 wavelength. Thus 132.2 X 2 = 264 ft
> which is 1 wavelength, not 2 wavelengths as stated. I didn't run the
> math on the others.
>
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Lyn WØLEN

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by John K9UWA-2

Try this link instead:

https://www.dxengineering.com/parts/hsr-6btv

73

Lyn, W0LEN

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of John K9UWA
Sent: Wednesday, April 01, 2020 9:01 AM
To: [hidden email]
Subject: Re: [Elecraft] 75ohm Impedance question K3S and Antenna side.

Supposedly the feedpoint impedance is 52 ohms ??? Yes, I question that a
bit.

Read all about it here. Sorry I doubled the 1/2 wave mults.

https://www.dxengineering.com/search/department/antennas/section/hf-vertical
-a

ntennas/brand/hustler-antenna/product-line/hustle

Hustler Antenna 6BTV - Hustler 6BTV 6-Band HF Vertical Antenna and DXE

Installation Guide Packages

Antenna, Vertical, HF, 6-Band, 80, 40, 30, 20, 15, 10 meters, 1.5 kW, 24
ft., +

DXE BTV High Perf. Guide, Each $241.99

Performance provided by the Hustler 6BTVs is better than any other antenna
of

this type. Broad-banding is such that one measurement and setting permits
both

phone and CW operation. The antenna provides nominal 52-ohm base

impedance when installed and tuned according to the instructions. The
radiation

efficiency is equal to, or greater than, other trap verticals.

73

John k9uwa

On 1 Apr 2020 at 8:14, Bob McGraw K4TAX wrote:

> Based on TLW calculations for 1/2" CATV 75 ohm hard line, 200 ft at 28

> MHz should show a 1.87:1 SWR at the transmitter. Assuming 35 ohms load

> Z. This equates to 1.027 dB total loss with 0.207 dB being attributed

> to the SWR on the line. Thus going through the efforts and matching

> process would only net an improvement of 0.207 dB on 10 meters. Lower

> frequencies would be less.

>

> Since this is a 5 or 6 band antenna, I doubt the Z at the feed point

> will always be 35 ohms. In order to determine what is actually needed,

> one would need measurements for each band.

>

> Conclusion: Feed it with 200 ft of 1/2" CATV 75 ohm hard line, use a

> short jumper of RG6, or 8X or whatever to connect the hardline to the

> radio and be done with it.

>

>

> NOTE: I just noticed that the numbers below are somewhat in error.

>

> 468/3.540 = 132.2 which is 1/2 wavelength. Thus 132.2 X 2 = 264 ft

> which is 1 wavelength, not 2 wavelengths as stated. I didn't run the

> math on the others.

>

> 73

>

> Bob, K4TAX

>

>

> On 4/1/2020 7:28 AM, John K9UWA wrote:

> > Ah YES I noticed it is for a multi band antenna.

> >

> > 2 wavelengths 3540 = 265'

> > 4 wavelengths 7080 = 265'

> > 6 wavelengths 10600 = 265'

> > 8 wavelengths 14160 = 265'

> > 12 wavelngths 21240 = 265'

> > 16 wavelengths 28320 = 265'

> >

> > Multiply the 265' by velocity factor of the coax and you will be
someplace

> > just a bit over 200 feet.

> >

> > the 10mhz band is off a bit. So OK... other than that 80, 40, 20, 15,10
are

> > all harmonically related. As I said 50 in and 50 out. If the OP runs
this

> > vertical on 17 and 12m then yes he will have maybe a 1.5 / 1 mismatch
caused

> > by the coax. But the antenna isn't designed for 17 and 12.

> >

> > I cut all the 3/4" CATV in my system with a Hewlett Packard HP 4815A
Vector

> > Impedance Meter. Any 1/2 wave mult the the SWR is the same in as out.
Any ODD

> > 1/4 wavelength multiple creates a transformation With Multiple 4 hi
stacks of

> > yagi's I have many of those in the system as well. 75 ohm cable works
well to

> > put pairs or quads of yagi's together.

> >

> > The only thing that maybe won't be perfect is the actual vertical itself
may

> > not be a 50 ohm input. His vertical is a Hustler 6BTV. 73 John k9uwa

> >

> >

>

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John Goller, K9UWA & Jean Goller, N9PXF

Antique Radio Restorations

[hidden email]

Visit our Web Site at:

http://www.JohnJeanAntiqueRadio.com

4836 Ranch Road

Leo, IN 46765

USA

1-260-637-6426

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Jim Brown-10

VF Varies With Frequency

In reply to this post by Don Wilhelm

On 4/1/2020 7:58 AM, Don Wilhelm wrote:
> When dealing with a length of transmission line, the use of the '468'
> factor should not be used - compute the actual wavelength and then apply
> the velocity factor.

There is yet another variable -- VF varies with frequency. At low
frequencies, it is lower (slower), increasing until it converges to the
published value at VHF. For this reason, matching sections and stubs
must be measured at or near the operating frequency with an analyzer or
as a stub placed in line with a generator and receiver. They should be
cut long, then trimmed so that the null in that generator/receiver
circuit is heard, or the analzyer reads a short or open.

How much is this variation? For typical transmission lines, it's on the
order of 1% from 80M, a bit more for 160M as compared to the published
value. If what you're building is a stub to kill harmonics, it's the
difference between the CW and phone bands on 80M.

73, Jim K9YC

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Edward R Cole

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by ae4pb

I agree with those who say just try it with TV cable connected,
direct. Tuner will keep the transmitter happy. If you can cut the
run to integrals of half wave that might be marginally better on
Tx. Back before WWII hams never worried about SWR and just maxed RF
current. Open-wire transmission line was popular (and low loss).

In 1980 I bought a TS-180S and a 4BTR with 80m coil-whip addition. I
attached the base direct to the front bumper of my 4x4 and operated
mobile with no radials or tuner. Heard Antarctica on 20m from Eagle,
AK. Should have kept the antenna.

Sold the radio after losing the finals (driver still output
10w). Before my K3 the best radio I owned was a FT-840. I traded it
for a FT-847 which was great on VHF/UHF but nowhere as good on HF
(and part of the reason for getting the K3).

73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
[hidden email]

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k6dgw

Re: 75ohm Impedance question K3S and Antenna side.

In reply to this post by John K9UWA-2

Ummm ... not quite. A "perfect" half-wave transmission line will
reproduce the impedance of the load [which has been alleged to be 35
ohms but this is an all-band antenna so that may vary some] at the
source [TX] end. The real line will come close, its loss will have a
small effect. His ATU will see whatever the feedpoint complex impedance
is, not necessarily 50 ohms.

I'd suggest a good common-mode choke at the feedpoint too which might
mean a short pigtail of RG-8 ... not sure if there are ferrite toroids
that will fit the CATV hardline. Jim, K9YC, has probably the best
source of data on chokes, ferrites, et al at k9yc.com/Publish.htm

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 3/31/2020 8:52 PM, John K9UWA wrote:

> Cut the hardline to multiples of 1/2 wavelength and the swr will be 1 to 1 on both
> ends. 50 in 50 out. In this case the OP needs around 200 feet. Once your get the
> velocity factor for the 1/2" hardline... that is ballpark 80 to 83%. for 3.540 mhz is
> 265 feet x .8 = 212 feet. If you don't have a piece of test gear to get it cut
> correctly then put a 50 ohm dummy load at the far end keep cutting until your
> wattmeter says 1 to 1 swr. 1/2 wave multiples will hit most of the ham bands. A
> little high in the 30m band. Close enough.
> 73
> John k9uwa
>

Elecraft mailing list

Re: VF Varies With Frequency

In reply to this post by Jim Brown-10

Requested technical comment from a long established coaxial cable manufacturer on this topic.

This was the response:

The Vp is not measured at any frequency and is independent of frequency. The only variable in play is the dielectric constant. The Vp represents the speed at which a signal transmits along the cable as a % of the speed of air. Air/vacuum will be the fasted medium to use to transmit an RF signal. The thing is, air is usually not practical since there is nothing to support the center conductor, can be easily crushed and is susceptible to the ingress of moisture.

We use foamed dielectrics and expanded tapes to get as close to air as possible. Vp will vary based on the specific dielectric used. The vast majority of our cables range in velocity of propagation from 76% to 86%. For a given cable, the Vp will likely not vary more that +/- 1% over it’s length but as I mentioned earlier, it would be best to use +/-2% for planning purposes.

End response

Regards,

Mark, K1RX

> On Apr 1, 2020, at 1:43 PM, Jim Brown <[hidden email]> wrote:
>
> On 4/1/2020 7:58 AM, Don Wilhelm wrote:
>> When dealing with a length of transmission line, the use of the '468' factor should not be used - compute the actual wavelength and then apply the velocity factor.
>
> There is yet another variable -- VF varies with frequency. At low frequencies, it is lower (slower), increasing until it converges to the published value at VHF. For this reason, matching sections and stubs must be measured at or near the operating frequency with an analyzer or as a stub placed in line with a generator and receiver. They should be cut long, then trimmed so that the null in that generator/receiver circuit is heard, or the analzyer reads a short or open.
>
> How much is this variation? For typical transmission lines, it's on the order of 1% from 80M, a bit more for 160M as compared to the published value. If what you're building is a stub to kill harmonics, it's the difference between the CW and phone bands on 80M.
>
> 73, Jim K9YC
>
>
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