Re: Dummy Antenna and FM Alignment
I remember a form of low loss cable that was popular in the 1980-90's the size of rg-8 (can't remember the brandname). It had a spiral plastic dielectric and I used a run of it for a UHF antenna.? One day I walked in the shack, only to find water on the floor.? It had rained that night and the outdoor connection to the antenna had a leak.? Water easily found its way in the outdoor leak and down the center of the coax.?? I called this my "garden hose feedline".
Joe, K1ike
toggle quoted message
Show quoted text
On 4/7/2025 6:09 PM, Jim Lux via groups.io wrote: You want low epsilon of the dielectric and foam tube or a spiral of plastic meets the requirement nicely.
|
Re: Dummy Antenna and FM Alignment
exactly. You want low epsilon of the dielectric and foam tube or a spiral of plastic meets the requirement nicely. To that extent it's like minimizing dielectric losses in microwave cables, but for a different reason.
I asked a coax mfr about options for a custom coax for an application in a spacecraft receiver for low frequencies. We wanted something shielded for a run about 10-15 cm long get from point A to point B with minimum capacitance.
toggle quoted message
Show quoted text
-----Original Message----- From: < [email protected]> Sent: Apr 7, 2025 1:51 PM To: < [email protected]> Subject: Re: [nanovna-users] Dummy Antenna and FM Alignment Maybe that explains an automobile antenna I found once in the past. I was surprised that what looked like coax was actually a piece of plastic tubing, maybe 1/4" I.D., with a thin wire running through the center. Joe, K1ike On 4/7/2025 1:05 PM, Jim Lux via groups.io wrote: The big requirement for coax on voltage probes is low capacitance - you generally don't worry about impedance.
|
Re: Dummy Antenna and FM Alignment
Maybe that explains an automobile antenna I found once in the past.? I was surprised that what looked like coax was actually a piece of plastic tubing, maybe 1/4" I.D., with a thin wire running through the center.
Joe, K1ike
toggle quoted message
Show quoted text
On 4/7/2025 1:05 PM, Jim Lux via groups.io wrote: The big requirement for coax on voltage probes is low capacitance - you generally don't worry about impedance.
|
Re: Dummy Antenna and FM Alignment
The big requirement for coax on voltage probes is low capacitance - you generally don't worry about impedance.
That's because the antenna is largely capacitive (so it looks like a voltage in series with a capacitor), and shunt C at the receiver reduces the signal level (think of it as a capacitive voltage divider).
In some ways, this is similar to high performance audio cables with high Z sources and amplifier inputs.
toggle quoted message
Show quoted text
-----Original Message----- From: < [email protected]> Sent: Apr 7, 2025 9:31 AM To: < [email protected]> Subject: Re: [nanovna-users] Dummy Antenna and FM Alignment The high-Z coaxial cable is more for the AM portion of the radio. On AM frequencies, especially the European version, the "stinger" antenna is nothing but a capacitive probe. Consequently, it presents an extremely high impedance. The loss in the 93-ohm line is considerably less at the AM broadcast frequencies than a standard 50-ohm cable would offer. However at FM broadcast frequencies, the external "stinger" antenna is a reasonable portion of a wavelength, although still a bit short. Therefore, it offers something more manageable considering losses. If you're just doing FM alignment, 88 to 108 MHz, a 50-ohm source/load is appropriate. Some older units may have a 300-ohm balanced input. In that case you need a transformer/balun to convert from 300-ohms balanced input to an unbalanced 50-ohm load. That's the purest approach and theoretically correct. HOWEVER, if its 300-ohmsbalanced input, just take a visit to Home Depot, Lowe's or any big-box distributor and buy a cheap 300-ohm to 75-ohm converter and use your 50-ohm equipment. Dave - WØLEV On Mon, Apr 7, 2025 at 2:43?PM AArnaud via groups.io wrote: Hey everyone,
True beginner in RF here for a classic alignment question. Sorry if this
is inappropriate or the wrong group, I'm not sure where to ask such
question. I suppose the NanoVNA would be a great tool to solve the question
and you guys seem to know a thing or two about RF.
I'm working on FM alignment for Citroëns car radios from the late 80s and
early 90s. For this I would suppose matching the alignment to the OE
antenna and cable are ideal for best tuner performance and sensitivity.
Therefor I also suppose it would mean making something such as a dummy
antenna/aerial or a network so that the RF generator looks exactly like the
antenna does to the radio, right?
I have the cable, base and antenna of the car taken out. I also have
access to a bunch of cars if averaging is necessary.
My particular generator is 50ohm. I have no clue what the OE antenna and
cable impedance are, as nothing is printed on them. Reading online it seems
most automotive radio cable are 93 or 100ohms?
For the extra information: there are two models I would like to align, a
Blaupunkt which would have a 150ohm impedance, but the other which is a
Clarion does not give any information regarding its impedance... it just
says to plug the generator into the radio and voila.
Thanks for looking into my question.
-- *Dave - WØLEV* -- Dave - WØLEV
|
Re: Dummy Antenna and FM Alignment
What I would do is use a NanoVNA to measure the impedance over 88-108 MHz right at the connector that plugs into the radio. Average the measurements for several cars. Then design a network that approximates the average when driven by a 50 ohm generator. To ensure generator flatness, make the network show 50 ohms to the generator. Network loss shouldn't matter since you can set the generator level so resistors are fine.
Brian
|
Re: Dummy Antenna and FM Alignment
The high-Z coaxial cable is more for the AM portion of the radio. On AM frequencies, especially the European version, the "stinger" antenna is nothing but a capacitive probe. Consequently, it presents an extremely high impedance. The loss in the 93-ohm line is considerably less at the AM broadcast frequencies than a standard 50-ohm cable would offer. However at FM broadcast frequencies, the external "stinger" antenna is a reasonable portion of a wavelength, although still a bit short. Therefore, it offers something more manageable considering losses. If you're just doing FM alignment, 88 to 108 MHz, a 50-ohm source/load is appropriate. Some older units may have a 300-ohm balanced input. In that case you need a transformer/balun to convert from 300-ohms balanced input to an unbalanced 50-ohm load. That's the purest approach and theoretically correct. HOWEVER, if its 300-ohmsbalanced input, just take a visit to Home Depot, Lowe's or any big-box distributor and buy a cheap 300-ohm to 75-ohm converter and use your 50-ohm equipment. Dave - W?LEV On Mon, Apr 7, 2025 at 2:43?PM AArnaud via groups.io <a.cabiyaud= [email protected]> wrote: Hey everyone,
True beginner in RF here for a classic alignment question. Sorry if this
is inappropriate or the wrong group, I'm not sure where to ask such
question. I suppose the NanoVNA would be a great tool to solve the question
and you guys seem to know a thing or two about RF.
I'm working on FM alignment for Citro?ns car radios from the late 80s and
early 90s. For this I would suppose matching the alignment to the OE
antenna and cable are ideal for best tuner performance and sensitivity.
Therefor I also suppose it would mean making something such as a dummy
antenna/aerial or a network so that the RF generator looks exactly like the
antenna does to the radio, right?
I have the cable, base and antenna of the car taken out. I also have
access to a bunch of cars if averaging is necessary.
My particular generator is 50ohm. I have no clue what the OE antenna and
cable impedance are, as nothing is printed on them. Reading online it seems
most automotive radio cable are 93 or 100ohms?
For the extra information: there are two models I would like to align, a
Blaupunkt which would have a 150ohm impedance, but the other which is a
Clarion does not give any information regarding its impedance... it just
says to plug the generator into the radio and voila.
Thanks for looking into my question.
-- *Dave - W?LEV* -- Dave - W?LEV
|
Dummy Antenna and FM Alignment
Hey everyone,
True beginner in RF here for a classic alignment question. Sorry if this is inappropriate or the wrong group, I'm not sure where to ask such question. I suppose the NanoVNA would be a great tool to solve the question and you guys seem to know a thing or two about RF.
I'm working on FM alignment for Citro?ns car radios from the late 80s and early 90s. For this I would suppose matching the alignment to the OE antenna and cable are ideal for best tuner performance and sensitivity. Therefor I also suppose it would mean making something such as a dummy antenna/aerial or a network so that the RF generator looks exactly like the antenna does to the radio, right?
I have the cable, base and antenna of the car taken out. I also have access to a bunch of cars if averaging is necessary.
My particular generator is 50ohm. I have no clue what the OE antenna and cable impedance are, as nothing is printed on them. Reading online it seems most automotive radio cable are 93 or 100ohms?
For the extra information: there are two models I would like to align, a Blaupunkt which would have a 150ohm impedance, but the other which is a Clarion does not give any information regarding its impedance... it just says to plug the generator into the radio and voila.
Thanks for looking into my question.
|
Re: NANO VNA H4 , Implausible measurement results?
If you used this BNC to Banana adapter, you are adding about 2 pF or so of shunt capacitance across the feed point of your test dipole. At 500 MHz for example, this is about Xc = 159 ohms. This is significant and will impact where the min SWR will be.
Not sure if this was mentioned above or not. Sorry.
I determined that many of these adapters disrupt the characteristic Z. I came across this years ago as I have old GR bridges. GR, I think, set the spacing at 0.75 inches many decades ago and it was even significant when tinkering with EFHW antennas (the feed point is on the order of 3000 ohms so even a few pF at HF can be significant).
There are different versions of these BNC/Banana adapters and different mfrs so your adapters might be better or worse. I use them mainly for low frequency applications.
|
Re: Measurement correction for Zc Coax caracteristic Impedance
This is the part of LF model that don’t work basically because is the wrong frequency region…
toggle quoted message
Show quoted text
On 6 Apr 2025, at 1:49?PM, Team-SIM SIM-Mode via groups.io <sim31_team@...> wrote:
Hi Patricio
Thanks for clarification , I do not understand this graphic zone circled on red color below
73's Nizar
<Capture d_????cran 2025-04-06 174532.png>
|
Re: Measurement correction for Zc Coax caracteristic Impedance
Hi Patricio
Thanks for clarification , I do not understand this graphic zone circled on red color below
73's Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
This chart shows the typical behaviour of a loosy coaxial cable over frequency. Basically there are two models , the low frequency model in this case the dielectric loose are very small then G tends to zero and is removed from the Zo formula. The serial equivalent loose resistor this is basically the resistance of the metallic boundary of the cable. It drops to lower frequency to a minimum this is determined by the conductor resistivity and uses to be very small but never zero , L goes up from the High Frequency model because appears magnetic fields inside de conductors… as frequency goes down the Zo goes up. In the other hand on high frequency region L an C are dominant on Zo formula and results on a more stable value. Skin effect reduces de magnetic field inside de conductor and L becomes defined basically by metallic boundaries.
At all this is not a problem in the practical world because the coaxial cables are used on high frequency regions , at audiofrecuencies becomes a shielded cable and Zo concept are irrelevant. In metrology these variations are taken to correct high precision measurements and standards characterization.
At very low frequencies where transmission lines are required usually higher Zo is adopted too . This is the frequency where LF and HF curves crosses are higher as Zo is lower. This is of course with the same materials on each case.
I?m sorry for my engllsh is not very good. If you have any difficulties to understand that I say please let me know.
Regardd, Patricio.
toggle quoted message
Show quoted text
On 6 Apr 2025, at 5:31?AM, Team-SIM SIM-Mode via groups.io <sim31_team@...> wrote:
Hi Patricio
I do not understand this chart, can you explaine it more pse.
73's Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
Hi
With same coax, same method, same NanoVNA H4 (1.2.40 DiSlord) surprisingly i have some different Zc values for 50Mhz & 100Mhz
50Mhz ---> Zc = 49.0 Ohm
100Mhz ---> Zc = 43.5 Ohm
73's Nizar
2Mhz ---> Zc = 52.6 Ohm
3Mhz ---> Zc = 52.5 Ohm
7Mhz ---> Zc = 52.0 Ohm
14Mhz ---> Zc = 53.0 Ohm
18Mhz ---> Zc = 53.0 Ohm
21Mhz ---> Zc = 54.0 Ohm
24Mhz ---> Zc = 54.0 Ohm
29Mhz ---> Zc = 52.0 Ohm
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
|
Re: Measurement correction for Zc Coax caracteristic Impedance
Hi Patricio
I do not understand this chart, can you explaine it more pse.
73's Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
Oops! I should have R >> jwL, not R >> jwC. My error.
73,
Maynard
W6PAP
toggle quoted message
Show quoted text
On 4/5/25 16:20, Maynard Wright, P. E., W6PAP via groups.io wrote: An interesting chart.? Note that below about 300 kHz, the imaginary component of the characteristic impedance can no longer be ignored and, if you are working on any cables at voice frequencies or where R >> jwC, the angle of the characteristic impedance will be around -45 degrees, which is characteristic of most telephone cable pairs (or any other transmission lines) at voice frequencies.
73,
Maynard
W6PAP
On 4/5/25 12:10, Patricio Greco via groups.io wrote:
?
On 5 Apr 2025, at 12:03?PM, Jim Lux via groups.io <jimlux@...> wrote:
Not unexpected
Zc is sqrt( (R+jomegaL)/(G+jomegaC))
Mostly determined by L/C, but the R is in there too, and it goes up as frequency goes up, because of skin effect. For HF the dielectric loss (G) is really tiny, so the R term dominates.
On Apr 5, 2025, at 05:34, Patricio Greco via groups.io <> <patricio_greco@... <mailto:patricio_greco@...>> wrote:
?Interesting , the Zo uses to rise a little when the frequency goes down.
On 5 Apr 2025, at 6:43?AM, Team-SIM SIM-Mode via groups.io <> <sim31_team@... <mailto:sim31_team@...>> wrote:
Hi
for same RG213? cable (25m length) loaded by a 50.3 Ohm resistor
I used the same?? circle methode centered on smith graph with the renormalized Z0 impedance ( option added by DiSlord)? for different ferquency's band (span always fixed? to 4 Mhz)? :
2Mhz?? --->? Zc = 52.6? Ohm
3Mhz? --->? Zc = 52.5 Ohm
7Mhz?? --->? Zc = 52.0 Ohm
14Mhz? ---> Zc? = 53.0 Ohm
18Mhz? ---> Zc = 53.0 Ohm
21Mhz? ---> Zc = 54.0 Ohm
24Mhz? ---> Zc = 54.0 Ohm
29Mhz? ---> Zc = 52.0 Ohm
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's? Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
An interesting chart. Note that below about 300 kHz, the imaginary component of the characteristic impedance can no longer be ignored and, if you are working on any cables at voice frequencies or where R >> jwC, the angle of the characteristic impedance will be around -45 degrees, which is characteristic of most telephone cable pairs (or any other transmission lines) at voice frequencies.
73,
Maynard
W6PAP
toggle quoted message
Show quoted text
On 4/5/25 12:10, Patricio Greco via groups.io wrote: ?
On 5 Apr 2025, at 12:03?PM, Jim Lux via groups.io <jimlux@...> wrote:
Not unexpected
Zc is sqrt( (R+jomegaL)/(G+jomegaC))
Mostly determined by L/C, but the R is in there too, and it goes up as frequency goes up, because of skin effect. For HF the dielectric loss (G) is really tiny, so the R term dominates.
On Apr 5, 2025, at 05:34, Patricio Greco via groups.io <> <patricio_greco@... <mailto:patricio_greco@...>> wrote:
?Interesting , the Zo uses to rise a little when the frequency goes down.
On 5 Apr 2025, at 6:43?AM, Team-SIM SIM-Mode via groups.io <> <sim31_team@... <mailto:sim31_team@...>> wrote:
Hi
for same RG213 cable (25m length) loaded by a 50.3 Ohm resistor
I used the same circle methode centered on smith graph with the renormalized Z0 impedance ( option added by DiSlord) for different ferquency's band (span always fixed to 4 Mhz) :
2Mhz ---> Zc = 52.6 Ohm
3Mhz ---> Zc = 52.5 Ohm
7Mhz ---> Zc = 52.0 Ohm
14Mhz ---> Zc = 53.0 Ohm
18Mhz ---> Zc = 53.0 Ohm
21Mhz ---> Zc = 54.0 Ohm
24Mhz ---> Zc = 54.0 Ohm
29Mhz ---> Zc = 52.0 Ohm
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
?
toggle quoted message
Show quoted text
On 5 Apr 2025, at 12:03?PM, Jim Lux via groups.io <jimlux@...> wrote:
Not unexpected
Zc is sqrt( (R+jomegaL)/(G+jomegaC))
Mostly determined by L/C, but the R is in there too, and it goes up as frequency goes up, because of skin effect. For HF the dielectric loss (G) is really tiny, so the R term dominates.
On Apr 5, 2025, at 05:34, Patricio Greco via groups.io <> <patricio_greco@... <mailto:patricio_greco@...>> wrote:
?Interesting , the Zo uses to rise a little when the frequency goes down.
On 5 Apr 2025, at 6:43?AM, Team-SIM SIM-Mode via groups.io <> <sim31_team@... <mailto:sim31_team@...>> wrote:
Hi
for same RG213 cable (25m length) loaded by a 50.3 Ohm resistor
I used the same circle methode centered on smith graph with the renormalized Z0 impedance ( option added by DiSlord) for different ferquency's band (span always fixed to 4 Mhz) :
2Mhz ---> Zc = 52.6 Ohm
3Mhz ---> Zc = 52.5 Ohm
7Mhz ---> Zc = 52.0 Ohm
14Mhz ---> Zc = 53.0 Ohm
18Mhz ---> Zc = 53.0 Ohm
21Mhz ---> Zc = 54.0 Ohm
24Mhz ---> Zc = 54.0 Ohm
29Mhz ---> Zc = 52.0 Ohm
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
Hi Jim Lux
"L , C & R exhibit some frequency-dependent variation; they do not have a perfectly flat response across frequency. This behavior depends on the dielectric material used, skin effect and the physical design of the coaxial cable. so theroritical formula is 1sft order modelisation , NanoVNA mesure them physically, just we should have the good method and practice at a reasonnable accuracy.
73's Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
Not unexpected
Zc is sqrt( (R+jomegaL)/(G+jomegaC))
Mostly determined by L/C, but the R is in there too, and it goes up as frequency goes up, because of skin effect. For HF the dielectric loss (G) is really tiny, so the R term dominates.
toggle quoted message
Show quoted text
On Apr 5, 2025, at 05:34, Patricio Greco via groups.io <patricio_greco@...> wrote:
?Interesting , the Zo uses to rise a little when the frequency goes down.
On 5 Apr 2025, at 6:43?AM, Team-SIM SIM-Mode via groups.io <sim31_team@...> wrote:
Hi
for same RG213 cable (25m length) loaded by a 50.3 Ohm resistor
I used the same circle methode centered on smith graph with the renormalized Z0 impedance ( option added by DiSlord) for different ferquency's band (span always fixed to 4 Mhz) :
2Mhz ---> Zc = 52.6 Ohm
3Mhz ---> Zc = 52.5 Ohm
7Mhz ---> Zc = 52.0 Ohm
14Mhz ---> Zc = 53.0 Ohm
18Mhz ---> Zc = 53.0 Ohm
21Mhz ---> Zc = 54.0 Ohm
24Mhz ---> Zc = 54.0 Ohm
29Mhz ---> Zc = 52.0 Ohm
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
Interesting , the Zo uses to rise a little when the frequency goes down.
toggle quoted message
Show quoted text
On 5 Apr 2025, at 6:43?AM, Team-SIM SIM-Mode via groups.io <sim31_team@...> wrote:
Hi
for same RG213 cable (25m length) loaded by a 50.3 Ohm resistor
I used the same circle methode centered on smith graph with the renormalized Z0 impedance ( option added by DiSlord) for different ferquency's band (span always fixed to 4 Mhz) :
2Mhz ---> Zc = 52.6 Ohm
3Mhz ---> Zc = 52.5 Ohm
7Mhz ---> Zc = 52.0 Ohm
14Mhz ---> Zc = 53.0 Ohm
18Mhz ---> Zc = 53.0 Ohm
21Mhz ---> Zc = 54.0 Ohm
24Mhz ---> Zc = 54.0 Ohm
29Mhz ---> Zc = 52.0 Ohm
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
Hi
for same RG213 cable (25m length) loaded by a 50.3 Ohm resistor
I used the same circle methode centered on smith graph with the renormalized Z0 impedance ( option added by DiSlord) for different ferquency's band (span always fixed to 4 Mhz) :
2Mhz ---> Zc = 52.6 Ohm
3Mhz ---> Zc = 52.5 Ohm
7Mhz ---> Zc = 52.0 Ohm
14Mhz ---> Zc = 53.0 Ohm
18Mhz ---> Zc = 53.0 Ohm
21Mhz ---> Zc = 54.0 Ohm
24Mhz ---> Zc = 54.0 Ohm
29Mhz ---> Zc = 52.0 Ohm
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's Nizar
|
