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The simple answer is "you don't".

As pointed out in another email, the AM car antennas are a hi-Z capacitive

probe free space.? They are highly capacitive, and measurement in a 50-ohm

system, the NANOVNAs, is senseless.

Dave - W?LEV

On Thu, Sep 7, 2023 at 4:43?AM Michael A. Terrell <
terrell.michael.a@...> wrote:

Old car radios had a tuned RF input, and an RF amplifier. I't's hard to
beat a '63 to late '70's? Delco AM car radio. They used a variable
inductor tuning system, with very good tracking between stages. Later
designs eliminated the tuned front? end which both lowers sensitivity
and noise rejection. This started with Japanese imports in the early
'70s. A factory radio was hundreds of dollars, but the crap design
import was $20.? I serviced hundreds, if not thousands of car radios in
the early to mid '70s. Ford and Chrysler radios were a joke, compared to

Delco. Ford even used Delco radios in their high end Lincolns. Ford
owned Philco, but they also used Bendix and Motorola radios. Chrysler
used pink plastic circuit boards that would melt when you tried to
repair them.

On 8/26/2023 10:22 PM, fbray@... wrote:

At the risk of being slightly OT, there are several reasons that AM

radios are disappearing.? One is the EMI problem caused by various

vehicle

charging and propulsion systems.? The EMI issue is a discussion topic on

forums frequented by public safety and commercial two-way radio techs.

European car makers have dropped AM because it has been supplanted by

DAB and AM stations are shutting down there, leaving little to listen

to.

Major US car makers disclaim any intention to abandon AM but we'll have

to

wait and see. In major US metro areas some of the AM stations are now
simulcasting on FM so that they don't lose their audience.

Many of us have noted that the AM radios in older cars with

traditional

external metal rod antennas work better than the in the glass antennas.

--

*Dave - W?LEV*


--
Dave - W?LEV

I don't like to be the bearer of bad news, but the dealership has no idea
what RFI is. They know the words and there is a problem with some Jeep
models, but that's as far as they go. Experience follows:

While somewhat of an esoteric problem with RFI: the "Water Hole"
surrounding 1420.405751 MHz. This is the emission line of celestial and
deep space hydrogen designated by HI. The Water Hole is protected spectrum
by international agreement, including the US. Well,......., read on.

We have a 2018 Jeep JL Rubicon. It, of course, includes the capability of
serving as a hotspot for the internet and making cell phone calls. As
such, it contains a cell modem as part of the electronics behind the video
display in the dash. That modem operates at nominally 700 MHz (I've easily
detected its fundamental frequency output on the spectrum analyzer) . The
second harmonic screams out of the assembly and blankets the hydrogen line
such that I can not do radio astronomy on that frequency. It ceases
"looking for mommie" - finding a cell tower as we have no cell coverage at
home - after sitting untraveled for 3 or 4 days. Does it track my
travels? Absolutely yes, but that's a different problem.

I have four times contacted the local dealership where we bought the
vehicle. They have absolutely no inkling of what I'm talking about other
than recognizing the term "Radio Frequency Interference". I've sent Jeep
in Toledo - their engineering department - three letters documenting,
screen grabs, the interference both as captured on the spectrum analyzer of
the second harmonic of the cell modem and in the time domain from my
receiver as captured on the laptop at 1420 MHz (after some downconversion
and detection). There has been absolutely no response from them, either,
other than a form email "thanking me for my interest in Jeep".........which
we already own. Thanks, but no thanks!

Frustrated......? Yes.......! There are instructions online on disabling
the cell modem, but since we camp off-grid in many...many locations which
do not have any cell coverage or amateur repeaters, I'm reluctant to do
so. In addition, it involves literally taking the whole dash apart which
I'm not into attempting.

All I can communicate is, "good luck"........and, there really is no such
thing as "luck". YMMV......?

Dave - W?LEV

On Sat, Aug 26, 2023 at 11:49?PM Glenn Little <glennmaillist@...>
wrote:

Take it back to the dealer and insist that they fix the problem.

The problem is poorly designed and implemented inverters for the battery
and electronics.
It probably does not meet part 15 FCC rules for unintentional radiators.

Glenn


On 8/26/2023 12:59 PM, Donald S Brant Jr wrote:

If you are describing a problem with AM reception, it could be EMI from

all of the inverters, etc. in the car, interfering with reception, rather
than an antenna issue. I had heard that car makers were trying to move
away from having AM to side step this issue. 73, Don N2VGU

--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIVwb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI, FRA, NRA-LM ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"

If you are describing a problem with AM reception, it could be EMI from all of the inverters, etc. in the car, interfering with reception, rather than an antenna issue. I had heard that car makers were trying to move away from having AM to side step this issue. 73, Don N2VGU

At the risk of being slightly OT, there are several reasons that AM radios are disappearing. One is the EMI problem caused by various vehicle charging and propulsion systems. The EMI issue is a discussion topic on forums frequented by public safety and commercial two-way radio techs.

European car makers have dropped AM because it has been supplanted by DAB and AM stations are shutting down there, leaving little to listen to. Major US car makers disclaim any intention to abandon AM but we'll have to wait and see. In major US metro areas some of the AM stations are now simulcasting on FM so that they don't lose their audience.

Many of us have noted that the AM radios in older cars with traditional external metal rod antennas work better than the in the glass antennas.

To further W0LEV’s point, a good friend of mine works for that manufacturer, specifically on that truck, and said that the EMI from the PWM controllers in powertrain and battery management system was a large consideration for the decision to disable AM on the radio stack. Additionally the radios are now SDR based and have highly sensitive basically wide open RF front ends.

My personal experience is that EV manufacturers struggle with EMI, some more than others. I’ve been totally “blown off the air” on 10m by a passing Rivian truck. I also know several hams with Tesla vehicles who don’t seem to be plagued by this issue. YMMV...

In my own truck, RAM 1500, a simple aftermarket upgrade has caused a mess of EMI while the engine is running. Who would have thought those performance coil packs would cause so much noise!!!

Anyway, I run the risk of diverting too far from the original post for this thread..

Larry, the central pin “is” the resonant element, as compared to the baofeng antenna. The body of the vehicle is the ground plane. So in measuring that antenna, you could unplug it from the radio stack where both conductors are present and use some sort of adapter to make the connection to your nanovna. A measurement of an antenna system should include the transmission line as well, right? By comparison, the baofeng antenna outer shield connects to the radio body and capacitively to your hand to make the ground plane. (or via a tiger tail, but that’s a different discussion)

For a receive only antenna, the impedance match is not super important. These antenna are all compromise antenna and suffer accordingly. The nanovna will provide data points for impedance etc., but its not very helpful for understanding the difference in reception. Furthering what W6PAP said, for receive you are best served by an S-meter or a spectrum analyzer. Heck you might actually be able to quantify potential EMI frequencies with the truck “on” verses “off” with the analyzer.

For some things to check, verify that the body panel the antenna is mounted on is properly bonded to the rest of the vehicle. Bad ground = poor ground plane. That can change the dynamics of the antenna for certain. Hope that helps and have a great day!

-Ben

Pasternack made a high quality product when the company I worked for used them about 20 years ago. Good chance it is still a high quality product, at a higher price.
Recently I have ordered components from Newark and Digi-Key. I have a higher level of confidence with them, compared to most of the products that overwhelm Amazon. For components like resistors, capacitors, etc I like to see data sheets and refer to the manufacturers website to see the entire product line. I don't want a generic part. Connectors and intra-series adapters require attention to detail. A high tolerance adapter good to 10 GHZ can be expensive. If you need just 10 MHz a less expensive one or even a generic one might be fine. Cables are a bit more murky. I recently purchased part number 250-086 from Digi-Key. Too soon to comment on durability.