Antenna Comparison A Stark Reality!

[sunwave]

I done a quick and easy antenna comparison using RSP Spectrum Analyser. MLA 30+ compared with my homebrew halfwave 27MHz vertical dipole. Can't say I am thoroughly surprised, but it will shine a light on the truth!

Behold:


MLA 30+ has a considerable higher noise floor than the half wave dipole. Less rf density than half wave dipole.

What is the proper antenna? The halfwave dipole or other than MLA 30+ for upper HF reception!

 

[prcguy]

There is no substitute for lots of wire in the air although a 1/2 ave dipole at 27MHz is not that much. Any active antenna will amplify noise along with signals. Why did you put a 9:1 balun on a 27MHz dipole?

 

[devicelab]

Neither of those antennas is anything special. The dipole should be using a 1:1 balun. I suppose if the dipole was mounted up really high then the impedance might be closer to 450 ohms but I seriously doubt it. Perhaps 200 or so. A 4:1 balun might give better results IF the vertical's feedpoint is mounted up high. So I'm thinking of heights at 34ft or 68ft -- (one or two wavelengths.)

I admit that would be an interesting vertical antenna to play with.

 

[prcguy]

Neither of those antennas is anything special. The dipole should be using a 1:1 balun. I suppose if the dipole was mounted up really high then the impedance might be closer to 450 ohms but I seriously doubt it. Perhaps 200 or so. A 4:1 balun might give better results IF the vertical's feedpoint is mounted up high. So I'm thinking of heights at 34ft or 68ft -- (one or two wavelengths.)

I admit that would be an interesting vertical antenna to play with.

A 27MHz dipole will vary from about 72 ohms at multiples of a wavelength and maybe 25 ohms horizontal really close to the ground. This is of course at 27MHz and it should never reach higher than about 72 ohms at any height at reaonance.

At other frequencies it will be all over the map like 54MHz probably over 2k ohms and at lower frequencies it should be much lower than 72 or even 50 ohms. At some low frequency like 1MHz and lower it becomes more of an E field probe and could become several thousand ohms.

if you were to dedicate a 27MHz dipole to general SW use I would feed it with ladder line all the way to the receiver then use a 1:1 balun right at the receiver. In the end it would not be the best SW antenna.

 

[Ubbe]

The MLA30 are using an amplifier that will also raise the noise floor at least 10dB. The 9:1 balun reduce the signal 9 times, almost 10dB. That makes the two antennas more or less receive the same noise level before the amplifier and balun voltage transformation.

The dipol are seen to have most of its signals at 10KHz steps but there are also other signals in between those channels. Are all signals actual transmissions or just some interferences? If you can receive a steady signal from a transmitter then switch antennas and compare how many dB between noise floor and top of signal, the signal / noise ratio, that are a more true comparison.

/Ubbe

 

[sunwave]

I knew you all would bark about it. I was talking about received signal density between MLA 30+ and vertical dipole. I get good reception on my dipole.

A balun: balanced to unbalanced is an electrical device that converts between a balanced signal and an unbalanced signal, or feed line. A balun can take many forms and may include devices that also transform impedances but need not do so.

You all are talking like it's an attenuator which is not the intended purpose!

Try again.

 

[prcguy]

I knew you all would bark about it. I was talking about received signal density between MLA 30+ and vertical dipole. I get good reception on my dipole.

A balun: balanced to unbalanced is an electrical device that converts between a balanced signal and an unbalanced signal, or feed line. A balun can take many forms and may include devices that also transform impedances but need not do so.

You all are talking like it's an attenuator which is not the intended purpose!

Try again.

A 9:1 balun is designed to match a 450 ohm impedance to 50 ohms and is good for matching a single random wire maybe 25ft long to over 100ft long. Your 27MHz dipole would be a low impedance over most of the HF band and a terrible mismatch for a 9:1 balun meaning its attenuating signals the way it’s being used.

 

[sunwave]

A 9:1 balun is designed to match a 450 ohm impedance to 50 ohms and is good for matching a single random wire maybe 25ft long to over 100ft long. Your 27MHz dipole would be a low impedance over most of the HF band and a terrible mismatch for a 9:1 balun meaning its attenuating signals the way it’s being used.

It is working as I intended. Did well on 9265 shortwave radiogram tonight.

Shortwave Radiogram Post-a-rama

On 11/2/2023 at 2330-0000utc I received WINB on 9265khz A.M. Shortwave Radiogram #328 Images (mfsk64) and Arabic text (mfsk32). Equipment used was MLA 30+ active loop, SDRPlay RSP1a. Software was SDRuno routed through Virtual Audio Cable Lite (free version) then to FLDigi. The signal was a fair...

forums.radioreference.com

 

[sunwave]

A 9:1 balun is designed to match a 450 ohm impedance to 50 ohms and is good for matching a single random wire maybe 25ft long to over 100ft long. Your 27MHz dipole would be a low impedance over most of the HF band and a terrible mismatch for a 9:1 balun meaning its attenuating signals the way it’s being used.

So I have just ordered a LDG 1:1 and pl-259 to sma adaptor from HRO.




I had to think about more that the 1:9 balun probably was good for the RTL-SDR and portables that easily overload. I am using it on the RSP1a which needs as much signal as possible. I got to run a balun on it because MW reception goes south without it with horrible router power supply noise. Yes, you all may be correct because transformers have a certain amount of loss.

 

[sunwave]

Update:

I received in the mail the LDG 1:1 balun with the sma-f to PL-259 accessory. Ran into a problem with the balun. While it is 1:1 it was worse than the Nooelec balun one nine v2.

The LDG 1:1 balun allowed the same RFI on much of the shortwave band except for what frequency the 1/2 wave dipole is cut for which is 27MHz. The same RFI and poor reception as I had before I even owned a balun! If you saw router power supply noise and the router it self's noise you would be astonished at the high RFI bumps from DC to about 7 MHz. More RFI humps all the way up to about 26 MHz.

The Nooelec 1:9 (not 9:1) balun greatly reduced RFI across the band. It allowed decent reception from 80m to 10m all the way on the same 27MHz dipole. Best reception 24-30MHz. Reeception on the MW band was a little lacking. That's what I bought the MLA 30+ amongst other purposes for.

So, the LDG 1:1 current balun isn't up to my expectation. I really doubt any 1:1 balun would suffice.
The Nooelec 1:9 balun v2 probably was designed for my intent. Dipoles do work on 1:9 baluns with the right type of transformer.

I now have first-hand experience on 1:1 balun from LDG. That's not happening again. Also based on this new experience I shall not give any benefit of the doubt to any discussion in the forums about baluns. The design Nooelec used works for reception!! The design LDG used is for transmission!! The loss in the Nooelec balun 1:9 v2 is negligible at best!!

 

[prcguy]

Update:

I received in the mail the LDG 1:1 balun with the sma-f to PL-259 accessory. Ran into a problem with the balun. While it is 1:1 it was worse than the Nooelec balun one nine v2.

The LDG 1:1 balun allowed the same RFI on much of the shortwave band except for what frequency the 1/2 wave dipole is cut for which is 27MHz. The same RFI and poor reception as I had before I even owned a balun! If you saw router power supply noise and the router it self's noise you would be astonished at the high RFI bumps from DC to about 7 MHz. More RFI humps all the way up to about 26 MHz.

The Nooelec 1:9 (not 9:1) balun greatly reduced RFI across the band. It allowed decent reception from 80m to 10m all the way on the same 27MHz dipole. Best reception 24-30MHz. Reeception on the MW band was a little lacking. That's what I bought the MLA 30+ amongst other purposes for.

So, the LDG 1:1 current balun isn't up to my expectation. I really doubt any 1:1 balun would suffice.
The Nooelec 1:9 balun v2 probably was designed for my intent. Dipoles do work on 1:9 baluns with the right type of transformer.

I now have first-hand experience on 1:1 balun from LDG. That's not happening again. Also based on this new experience I shall not give any benefit of the doubt to any discussion in the forums about baluns. The design Nooelec used works for reception!! The design LDG used is for transmission!! The loss in the Nooelec balun 1:9 v2 is negligible at best!!

You’re running a very unusual antenna for general SW use and I think you would be see better results with an end fed 1/2 wave for 27MHz (18ft continuous ft of wire) instead of 18ft center fed and feed that with a 9:1.

The RFI is a separate problem with several possible points of entry to your receiver. Direct pickup by the antenna would not be affected much by baluns or choking devices on the feedline. RFI riding on your feedline and making it to the antenna is another path and eliminating that at the radio end before it travels up the coax is usually more effective unless the coax is a radiating part of the antenna. In that case a good 1:1 choke balun at the radio end and one at the feedpoint can really cut down RFI that is not direct pickup through the air.

Since you are seeing a change in RFI when adding or changing different baluns it sounds like your RFI problem involves noise traveling up the coax. Many baluns are designed for impedance matching with no regard to choking or absorbing RF on the coax while others are specifically designed to eliminate RF on the coax. The LDG line of baluns is not advertised as having a lot of resistive choking impedance for reducing common mode currents on the feedline.

Finally, there are dipoles specifically designed to use a 9:1 transformer or balun and I own many. They are usually military designs for both transmitting and receive only, intended for wide band use usually 2-30MHz range and are long and intentionally non resonant. Some use resistors at the wire ends connected to ground rods for matching. Long being 100+ ft long with some being over 250ft and none that I’ve run across are less than 100ft.

 

[sunwave]

You’re running a very unusual antenna for general SW use and I think you would be see better results with an end fed 1/2 wave for 27MHz (18ft continuous ft of wire) instead of 18ft center fed and feed that with a 9:1.

The RFI is a separate problem with several possible points of entry to your receiver. Direct pickup by the antenna would not be affected much by baluns or choking devices on the feedline. RFI riding on your feedline and making it to the antenna is another path and eliminating that at the radio end before it travels up the coax is usually more effective unless the coax is a radiating part of the antenna. In that case a good 1:1 choke balun at the radio end and one at the feedpoint can really cut down RFI that is not direct pickup through the air.

Since you are seeing a change in RFI when adding or changing different baluns it sounds like your RFI problem involves noise traveling up the coax. Many baluns are designed for impedance matching with no regard to choking or absorbing RF on the coax while others are specifically designed to eliminate RF on the coax. The LDG line of baluns is not advertised as having a lot of resistive choking impedance for reducing common mode currents on the feedline.

Finally, there are dipoles specifically designed to use a 9:1 transformer or balun and I own many. They are usually military designs for both transmitting and receive only, intended for wide band use usually 2-30MHz range and are long and intentionally non resonant. Some use resistors at the wire ends connected to ground rods for matching. Long being 100+ ft long with some being over 250ft and none that I’ve run across are less than 100ft.

The Nooelec balun 1:9 v2 does work well for a long range of frequencies. Tuned into a lot of amateur radio rag chews, received Shannon Volmet on 5505khz upper side band, the CODAR network around 13400khz from the Mediterranean Sea somewhat between Italy and a small island, listened to the very weak pirate signals around 6900khz-6950khz. None of that would get through on the LDG Balun.

Noone asked about what type of coax I am using. RG-174. Another bag of worms. 33 feet of it. That's 0.5 db loss. Nothing to shake a stick at. As a matter of fact, reduces the chance of overload. I see Nooelec had reception in mind when they designed the balun. Kind of thinking it is acting like a choke balun. Sure does clear things up.

I am keeping the 1:1 balun for another purpose when I feel like spending money on more radio equipment. I am flat worn out on spending. I will continue using the 27mhz center fed with the Nooelec balun and the MLA 30+ for the lower bands.

Try to ease up the boxed in thinking when it comes to radio reception. Some strange antennas work that was not well received at first. Pun intended. They say to try different things with antennas. Even if it breaks tradition and conventional ways. See what works. Thats what I did.

 

[sunwave]

I am doing the right thing using a balanced antenna known as a center fed dipole. The Nooelec balun is designed for that. The Coilcraft WB-9 has a neglible loss of .5 db from longwave to 70MHz. A near flat curve measured at 3db

Nooelec Balun 1:9 v2 schematic and frequency response:

source:The NooElec Balun 1:9 v2

source: WB Through Hole Wideband RF Transformers | Coilcraft

source: Nooelec - Balun One Nine v2 Barebones - Small Low-Cost 9:1 HF Antenna Balun/Unun with Multiple Connection Options

 

[MavamQ]

>I now have first-hand experience on 1:1 balun from LDG. That's not happening again. Also based on this new experience I shall not give any >benefit of the doubt to any discussion in the forums about baluns. The design Nooelec used works for reception!! The design LDG used >is for transmission!! The loss in the Nooelec balun 1:9 v2 is negligible at best!!

I'm surprised by this response. A transformer is used to transform the impedance of an antenna to the impedance of the radio.
Your radio is generally 50Ω and a dipole is is 72Ω at the frequency it is cut for (at a reasonable height). The 50Ω to 75Ω mismatch
creates a minor loss, I think it is 0.2db. Now if you tune different frequencies than your antenna is tuned (cut) to the impedance can swing considerably. I suppose at some frequencies you 9 to 1 would be correct but that would be very hit or miss.
As someone else said your noise problem is a different issue. It can be eliminated using feed line chokes, ground breakers, burying the feed line, I have went to using Cat5 cable to eliminate feed line ingress. and I'm very happy with it. It is 100Ω impedance, so does require different transformation.
Your spectrum is 27MHz but then you mention 13MHz, 6Mhz and 5MHz signals
Seems like there are many better choices for a wideband SW antenna than a dipole cut to 27Mhz.
A wide band antenna will have a more stable impedance over frequency.
If I need to be corrected, I'd be happy to learn. Thanks.
Mikek

 

[sunwave]

>I now have first-hand experience on 1:1 balun from LDG. That's not happening again. Also based on this new experience I shall not give any >benefit of the doubt to any discussion in the forums about baluns. The design Nooelec used works for reception!! The design LDG used >is for transmission!! The loss in the Nooelec balun 1:9 v2 is negligible at best!!

I'm surprised by this response. A transformer is used to transform the impedance of an antenna to the impedance of the radio.
Your radio is generally 50Ω and a dipole is is 72Ω at the frequency it is cut for (at a reasonable height). The 50Ω to 75Ω mismatch
creates a minor loss, I think it is 0.2db. Now if you tune different frequencies than your antenna is tuned (cut) to the impedance can swing considerably. I suppose at some frequencies you 9 to 1 would be correct but that would be very hit or miss.
As someone else said your noise problem is a different issue. It can be eliminated using feed line chokes, ground breakers, burying the feed line, I have went to using Cat5 cable to eliminate feed line ingress. and I'm very happy with it. It is 100Ω impedance, so does require different transformation.
Your spectrum is 27MHz but then you mention 13MHz, 6Mhz and 5MHz signals
Seems like there are many better choices for a wideband SW antenna than a dipole cut to 27Mhz.
A wide band antenna will have a more stable impedance over frequency.
If I need to be corrected, I'd be happy to learn. Thanks.
Mikek

It doesn't matter since I am not transmitting. Reception is forgiving. Here is my video. This time the hardware chain is:

27MHz center fed dipole >> Nooelec Balun 1:9 >> Nooelec Flamingo FMBC bandstop >> Nooelec LaNA HF v2 (LNA) >> RTL-SDR Blog v4 >> SDR Sharp v1919

Clean reception of these wide ssb signals on 14.285MHz USB

The antenna is indoors because tenants here aren't allowed to mount antennas outside. I have to improvise for space constraints. This is the best way practical within the small confining space I have. It works!

 

[sunwave]

A balun serves two primary purposes:

1. Single-Ended to Differential Conversion: The balun plays a crucial role in converting single-ended signals, like those connected to SMA connectors on SDRs, into differential signals. This transformation is particularly useful when receiving signals from center-fed dipoles.
2. Impedance Matching for Center-Fed Dipoles: Center-fed dipoles often exhibit higher impedance (e.g., hundreds of Ohms) than the standard impedance of receivers (usually 50 Ohms). In such cases, a balun becomes essential to match the antenna's impedance to the lower impedance of the receiver. This matching process optimizes the efficiency of signal reception.