[rabbit73]

You use a 1/2 Wave balun to get 300 Ohm unbalanced to 75 Ohm Balanced. I am looking to get 150 Ohm unbalanced to 75 OHm balance. So is it a simple matter to replace the 300 Ohm Resistor which a 150 Ohm restor ?

You have it backwards. The 1/2 wave coaxial balun converts 300 ohm Balanced to 75 ohm Unbalanced. Balanced means neither side is grounded like in a folded dipole. Unbalanced means one side is grounded like the shield of coax.

The 300 ohm resistor you see in the diagram is not an actual resistor that is part of the balun, it represents the 300 ohm impedance of the antenna for the simulation. The two diagrams above were originally posted on this forum by Brian Beezley K6STI.
http://ham-radio.com/k6sti/balun.htm

What are you trying to connect to 75 ohm coax?

 

[HRE]

I am trying to remove the balun on the CM4228HD. In theory it is a 150 Ohm when you combine two 300 Ohm impedances equaling 150 Ohm impedance. I am trying to take the 75 Type F and convert it to 150 Ohm to connect to the antenna terminals.

 

[HRE]

I am trying to hack a Channel Master CM4228HD by modifying the internal balun. I have a sneaky suspicion it is not matched correctly and everything I have read on line seems to state that. I want to match 75 Ohm Coax to the theoretical Impedance of the antenna which is 150 Ohms. 150 Homes represents two dipoles (CM4221 in parallel). I do have a N1201SA Vector Impedance Analyzer to match the antenna exactly. But what I need to know is how to design same to get started. I have 93 Ohm coax as well

 

[rabbit73]

I am trying to hack a Channel Master CM4228HD

Have you read the Temporary Page on hdtvprimer.com that describes the balun for the 4228HD?
Temporary page

Ken Nist, MSEE (ret), KQ6QV, created the hdtvprimer site.
HDTV Primer

Forum member holl_ands also has a low loss harness (HHH) for the 4228HD.
https://imageevent.com/holl_ands/multibay/8bayrefl

I do have a N1201SA Vector Impedance Analyzer to match the antenna exactly.

That looks interesting.

 

[HRE]

Actually I familiar with the Holland Harness and Ken Nist Suggestions. However I still believe that the original balun is the problem and that is supported by Ken Nist as he can not determine if the match is 150 Ohms or to 300 Ohms from the 75 Ohm Coax as done on a PCB. I would simply like to design a 2:1 Balun without using torroids. I do know the you are using 93 Ohm Coax and taking into account the Velocity Factor. I also realize now that I simply can not change resistor to 150 OHms as it does not exist. However, I presume that the 75 Ohm resistor does. So it seems that I am only lacking the knowledge of what wavelength creates what ratio. For instance you use 1/2 Wavelength with a coax velocity factor of about 0.83 to obtain a 300 Ohm conversion. I can find 1:1 coax baluns which can use a combination of 1/4 Wave and 3/4 or both but I have to date seen no transitions via coax, to transfer the 75 Ohm Coax to 150 Ohm for the antenna.

 

[rabbit73]

Actually I familiar with the Holland Harness and Ken Nist Suggestions.

You need to read Ken Nist's suggestions again for alternatives.

I want to match 75 Ohm Coax to the theoretical Impedance of the antenna which is 150 Ohms. 150 Homes represents two dipoles (CM4221 in parallel).

How were you planning to connect the two sections together to get 150 ohms? Even if the impedance of each feedpoint is 300 ohms, where they are combined might not be the 150 ohms you expect. The actual combined impedance will depend upon the characteristics of the feedlines that you use to combine them. In particular, the feedline lengths and the conductor spacing, which is the same problem that must be solved with a harness design.

I would simply like to design a 2:1 Balun without using torroids.

Then you have two choices: design a stripline PCB balun for that ratio or use two halfwave coaxial baluns, combine them in parallel for 37.5 ohms and use a 1/4 wave matching section to convert back to 75 ohms.

I also realize now that I simply can not change resistor to 150 OHms as it does not exist. However, I presume that the 75 Ohm resistor does.

No, there is also no 75 ohm resistor, only the 75 ohm impedance of the RG6 coax feedline.

So it seems that I am only lacking the knowledge of what wavelength creates what ratio. For instance you use 1/2 Wavelength with a coax velocity factor of about 0.83 to obtain a 300 Ohm conversion.

The coax for the halfwave coaxial balun must be an electrical halfwave for the required 180 degree phase shift. The VF for foam dielectric is not the same as for solid dielectric. When the current flows into one side of the feedpoint, it must flow out of the other side of the feedpoint.

I can find 1:1 coax baluns which can use a combination of 1/4 Wave and 3/4 or both but I have to date seen no transitions via coax, to transfer the 75 Ohm Coax to 150 Ohm for the antenna.

The way around that problem is to use a different approach.
Each 4-bay section has a nominal feedpoint impedance of 300 ohms. Use a 4:1 coaxial balun for each 4-bay. Combine them in parallel giving you 37.5 ohms. Convert that to 75 ohms with a 1/4 wave matching section of 50 ohm coax.

You will have two problems to solve. You must keep the ends of the coax sealed to prevent the entry of water, and the two 4-bay sections must be connected in phase. You have a 50-50 chance of getting it right. If they are not connected in phase, the main lobe will split in two with a null in the center of aim.

This will give you UHF only. If you want to use the 4228HD for UHF and VHF, you must use toroids. This also has the need to have the two 4-bay sections in phase.

 

[holl_ands]

Characteristic Impedance of an individual CM4221HD may be about 150-ohms....but ONLY above about 550-MHz. The "best" compromise Load Balun is more like 300-ohms, given that the Characteristic Impedance (Zohm in chart) is Very High Impedance [400-470-ohms] on the lowest Freqs vs Low Impedance [about 150-ohms] Mid-Band:
https://imageevent.com/holl_ands/multibay/4bayrefl/uhfnewcm4221hd

CM-4228HD's Original Horizontal Harness is ALSO an (imperfect) Impedance Transformer, resulting in a Characteristic Impedance (Zohms is Green Line) that hovers around 200-ohms mid-Band [SWR of 1.5 is Still Excellent with Mis-Match Loss = 0.18, IF applicable], rising to a Max of about 400-470 MHz on the lowest Freqs and dropping to Min of about 150-ohms at 698 MHz. So the "best" compromise Load Balun would also be 300-ohms:
https://imageevent.com/holl_ands/multibay/8bayrefl/cm4228hd

Given the CM4228HD's Excellent SWR of 1.2 to 1.5 Mid-Band, I don't really understand WHAT you hope to improve, other than possibly making SWR on the Lower Channels even worse. And bear in mind that Mis-Match Loss will ONLY be fully realized when the [Partial] NULLS that occur every Half-Wavelength down the Coax just happens to form on the END of the Coax going into your Tuner [fixable by adding short piece of Coax]....and will be at DIFFERENT positions along the Coax on Different Channel Numbers. So in practice the EFFECT will only occur very rarely. And BTW, if using a Mast Mounted Preamp, the Antenna-to-Preamp Coax Length "should" NOT be long enough to support SWR NULLS along it's length:
https://www.microwaves101.com/encyclopedias/voltage-standing-wave-ratio-vswr

BTW: My HHH (Holl_ands Horizontal Harness) adds some additional "Degrees of Freedom" which are OPTIMIZED to improve overall Gain (esp on lowest Freqs where original was deficient) and ALSO SWR, where Zohm hovers very close to 300-ohms across most of the band, eventually falling to 200-ohm at 698-MHz: [So it's easier & Better to FIX the Harness, rather than try to find or build a 2:1 Balun.]
https://imageevent.com/holl_ands/multibay/8bayrefl/newcm4228hdwithhollandshorizharness

CM4221HD WITH "BALUN FLIP" HACK IMPEDANCE:

CM4228HD "AS SHIPPED" IMPEDANCE:

CM4228HD "AS SHIPPED" SWR:

CM4228HD with HHH IMPEDANCE:

CM4228HD with HHH SWR:

CM4228HD "AS SHIPPED" vs RF COMBINER MOD vs HHH MOD:
[Does NOT include 0.5-1.5+ dB Loss in RF Combiner]

 

[morehp1]

Coax balun vs. manufactured balun

Guys wondering if any one can explain how a typical manufactured balun works..
the type with 2 small wire leads (which connect to the antenna's 2 feed points) running into a cylinder with a 75 ohm coax f connector on the output ...

I purchased a package of 10 baluns off Amazon and all 10 pieces show that there is electrical continuity between the 2 wire lead connectors (which is expected) checked with a Fluke multi meter set on ohms/continuity

BUT the surprising part was the outside of the threaded coax connection point also shows continuity with the 2 wire lead connectors...
IE the shielding on the coax cable running from the balun down the tower to the TV will be electrically connected to the feed points of the antenna once the balun is connected...

Is that correct?

typical 300 ohm to 75 ohm balun

When I made a coax balun to compare performance to a purchased balun
the instructions found online to make/calculate a coax balun clearly have the coax shielding isolated from the coax copper core and when checking for shorts with the multi meter the coax copper core is as expected isolated, from the coax outer shielding.. ie the feed points of the antenna are isolated from the exterior shielding of the coax cable

coax balun

 

[rabbit73]

Hello, morehp1

The halfwave 4:1 coax balun is different than most manufactured baluns. It is very low loss, but is only good for one of the three TV bands: UHF, VHF-High, or VHF-Low.

When you use your ohmmeter to make resistance measurements, it is the DC resistance. Any conclusions based on DC resistance are not valid, because manufactured baluns are wound on a ferrite core using various configurations. The advantage of the ferrite core balun is that it is suitable for all three TV bands. See this page by K6STI about baluns. It is titled about FM baluns, but the theory is the same for TV baluns:
Baluns for 88–108 MHz

Scroll down to 300Ω Ferrite Baluns, which are transformer type baluns.

This forum has a thread that is about baluns:
https://www.digitalhome.ca/forum/81-over-air-ota-digital-television/100512-baluns-brands-designs-losses-diy-loops-etc.html

The baluns on the most recent UHF TV antennas are PCB (printed circuit board) baluns. They are similar to the halfwave coaxial baluns, and are only suitable for one band. This is the UP2A PCB balun for the Antennas Direct UHF antennas:

More INFO here:
http://www.hdtvprimer.com/ANTENNAS/TemporaryPage.html

 

[morehp1]

Hi Rabbit

yes but are not all baluns a compromise... just like an antenna...
optimum for a specific frequency and less as you more farther up or down from the optimum frequency

most of my hard to pull stations are between channels 20-40 so I cut a coax balun for ch 30 and it worked great...
and yes the ch 10 came in strong but again I can get it with rabbit ears inside the house when nothing else comes in using rabbit ears indoors

I'm looking to squeeze out every last db of signal and keep it.. thus the reason for the highest gain antenna and a preamp for the long cable run into the TV

the Buffalo stations are 130 miles away but I routinely get 2.1 29.1 and 51.1 ..... these are more problematic 4.1 7.1
and on a good day get about 7 more US channels

I'm not quite done the new antenna set up... its up on the side of the tower and connected to the TV.. and it blows the doors of the DB8 it is replacing
I constructed Holl_ands NEW FF6 and did a vertical stack so the antenna is like 14 feet tall x 3 feet wide...

the question I had about the purchased balun is I was shocked to see the coax outer shield was electrically connected to the antenna feed points and the coax center conductor... I used the multi meter just to check for shorts.. not measuring resistance

 

[morehp1]

Rabbit

correct me if I'm wrong... but is not the TV tuner looking at the Voltage on the coax line...

the antenna is made of an electrical conductor (copper or aluminum)
and when you expose a conductor to a CHANGING magnetic field (ie the TV signal) you induce a voltage in the conductor...
and electrical current only flows if you close the circuit and I don't see how you can close the circuit to the elements on the antenna

and the TV does not use ground... as the TV only has a 2 prong connection to the electrical outlet on the wall
and the antenna's coax center conductor is not shorted to ground (if it did your antenna would be a big lightning grounding rod)

that's why I think the TV tuner is looking at the changing voltage on the coax cable...
and there are numerous different peaks at different frequencies to match the channel's frequency

sort of like when you use a VFD to control some motors speed.. you can introduce noise/harmonics into the power electrical feed which can play havoc with other motors

 

[rabbit73]

the Buffalo stations are 130 miles away but I routinely get 2.1 29.1 and 51.1 ..... these are more problematic 4.1 7.1
and on a good day get about 7 more US channels

I'm not quite done the new antenna set up... its up on the side of the tower and connected to the TV.. and it blows the doors of the DB8 it is replacing
I constructed Holl_ands NEW FF6 and did a vertical stack so the antenna is like 14 feet tall x 3 feet wide...

Your original question was about baluns, so the moderator moved it to the balun thread.

Now you are talking about a reception problem without giving a location or signal report.

the question I had about the purchased balun is I was shocked to see the coax outer shield was electrically connected to the antenna feed points and the coax center conductor... I used the multi meter just to check for shorts.. not measuring resistance

When you check for shorts, you are making a resistance measurement. Just because your ohmmeter gives a very low reading doesn't mean your balun is defective.

 

[rabbit73]

Rabbit

correct me if I'm wrong... but is not the TV tuner looking at the Voltage on the coax line...

I have been giving reception advice on four forums for about 10 years with a total number of posts at about 7,878 and many satisfied posters that I have helped. I started doing antenna experiments when I was 8; I'm now 86 and still learning. I have built many ham and TV antennas. I've been a ham since the early 1950s and have DXCC with a mobile setup. I have two signal level meters to make signal measurements and I also have a Fluke meter; they are very good.

Umm, I'm having difficulty following your train of thought and have no desire to engage in an argument...

 

[majortom]

@morehp1,
did you read rabbit73's reply? I'd say he is spot on with his reply.

Brian Beezley's (k6sti) page describes how the typical 300 ohm balanced to 75 ohm unbalanced transformer (Balun) works. It's not sumthing u can describe in a few sentences on an internet forum, and expect that every one will get it. There are entire textbooks and college courses dedicated to RF fundamentals. That's why he referred you to k6sti's web page which already does a decent job explaining... Much like when you read a book, you will have footnotes citing where the author may have taken certain information from.

Scroll down to "300Ω Ferrite Baluns"... read that and follow the example schematics of the various types you may run in to as you read.
Maybe even take one of them 10 baluns you have apart, and see how it compares to the variations shown on
k6sti's page. Then you will really know what it is that you have for a balun.

k6sti also explains the reasoning behind the common ferrite balun having it's windings configured as they are.
Please let us know if you find the section I'm referring to, then we'll know you read thru it thoroughly....

 

[testproggie]

DC Resistance AC Resistance

DC resistance is rarely the same resistance seen by an AC input. AC is affected by any capacitance, resistance and inductance along the path. DC see these totally differently. So when you measure a DC resistance with a multi meter the AC resistance can and will be quite different. AC resistance also varies by the frequency of the input. This explains why baluns that are constructed in different manners can have very different outputs - acting as bandpass, low pass, highpass, etc.

Robert

 

[rabbit73]

the antenna is made of an electrical conductor (copper or aluminum)
and when you expose a conductor to a CHANGING magnetic field (ie the TV signal) you induce a voltage in the conductor...
and electrical current only flows if you close the circuit and I don't see how you can close the circuit to the elements on the antenna

I read your questions several more times; I think I can answer that question. You are correct; there must be a return path for current to flow:

Sources:
http://kilyos.ee.bilkent.edu.tr/~koymen/chapter_8.pdf

http://www.hottconsultants.com/pdf_files/dipoles-1.pdf

and the TV does not use ground... as the TV only has a 2 prong connection to the electrical outlet on the wall
and the antenna's coax center conductor is not shorted to ground (if it did your antenna would be a big lightning grounding rod)

There is some controversy about that, but the NEC requires the coax shield and the mast be connected to the house electrical system ground with separate 10 gauge conductors. The theory is that if the mast is grounded, it will drain any buildup of charge to reduce the chance of a strike. The code is interpreted by the AHJ (Authority Having Jurisdiction), who is usually the electrical inspector. His interpretation becomes the local law that is binding on the local electricians and you.

If the antenna is outside, the coax shield should be grounded with a grounding block that is connected to the house electrical system ground with 10 gauge copper wire for electrical safety and to reject interference. For further compliance with the electrical code (NEC), the mast should also be grounded in a similar manner to drain any buildup of static charge which will tend to discourage a strike, but the system will not survive a direct strike.

It is true that most TVs have a two-wire plug instead of a 3-wire plug, but that creates a potential shock hazard. The antenna coax is connected to AC operated equipment. All AC operated equipment has leakage current. Just because you can't feel it, doesn't mean it isn't there; it's just below your threshold of perception. If there is a defect in the AC equipment, the coax shield can become energized. If the coax is grounded, the leakage current will be shunted to ground.

I have had three close calls with electrical shock. I bought a Leakage Current Tester to check my equipment and any equipment that I was calibrating for someone else.

Leakage current posts on this forum:

Getting A/C voltage on converter box's antenna input !
https://www.digitalhome.ca/forum/81-over-air-ota-digital-television/42186-atsc-converter-boxes-non-hd-non-recording-69.html#post1457594

Equipment Leakage Current
https://www.digitalhome.ca/forum/81-over-air-ota-digital-television/42186-atsc-converter-boxes-non-hd-non-recording-69.html#post1457668

 

[Sev]

So.
A gentleman posted these pictures and is claiming this is working as a substitution as a typical balun. He says he is getting much better results.
His concept is based on this first picture.
He is using RG59 as the short coax.
No ferrite beads are involved.
I am not seeing how he is actually converting from 300 to 75 ohm. Or how he is not getting phasing issues with the driven elements due to differences in metal velocities, resistance and lengths of materials.

I am aware there are methods for getting from 300 to 75 ohms. Calveras and others have for instance made various harnesses that get you there.

However this just not appear to be correct. Perhaps I am wrong.

The antenna itself is an Archer that has been modified to be similar to a Delhi SFA-1483. He has not mentioned doing any modeling.

Thoughts?
Observations?

 

[Sev]

Also.
The RG-59 has the shielding stripped off of it.

 

[rabbit73]

So.
A gentleman posted these pictures and is claiming this is working as a substitution as a typical balun. He says he is getting much better results.
His concept is based on this first picture.

Hello, Sev.

The information provided by the gentleman is incomplete and confusing. I wish there was a way to look at his original post.

 

[Sev]

Well Rabbit.
He had no explanation as to how he went about figuring what he did.
The model he is basing it on is a single solid element
The Archer is 2 separate driven elements being combined together using dissimilar materials.
The guy types like 91xg without the rambling.