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Re: Cheap TV splitter on HF = fail

Roger Need
 

On Tue, Nov 24, 2020 at 01:01 PM, Chris Moulding wrote:

So what's the difference over just using a few cheap splitters? The first one is that the loss in the internal Owen splitter is balanced by a low noise amplifier so that the gain is near to zero overall. This allows up to five receivers to operate exactly as if the antenna was connected directly to each individual receiver. This is especially important on the VHF and UHF frequencies where the loss of a simple splitter would seriously degrade the performance of the overall antenna/receiver system.

The Multicoupler also has a 20,000 A gas discharge tube on the input with additional overload and electrostatic protection for the input to the amplifier. The outputs also have RF protection diodes that can provide protection in case transmitters up to 350 W inadvertently transmit into any of the outputs.


I agree that the 3.5 to 4 dB splitter loss (or higher with multiple outputs) can be significant when operating at VHF/UHF and above.  Active splitters are very useful at those frequencies.

For HF and below the splitter loss is not as much of a concern because the atmospheric and man made noise are much higher than the receiver noise floor unless you have a negative gain antenna with low signal output.

The use of an amplifier and/or RF protection diodes introduces non-linearity into the antenna system and intermodulation products and spurious signals are the end result.  The amplifier can be designed to have a high OIP3 with minimal effect but RF protection diodes operating in the 1V region have a poor OIP3.  That is why modern high-end receivers no longer use them in the front-end. 

In the end it all comes down to what the user is trying to achieve.  If operating at VHF/UHF or with multiple receivers (3 or more)  the active splitter fits the requirement.  If operating near transmitters some form of RF protection like diodes is necessary but it is nice to have a switch to disconnect them when not required.  For those with shallow pockets listening on HF frequencies a homebrew or CATV splitter will work well.

Roger


Re: Cheap TV splitter on HF = fail

Chris Moulding
 

It's all very nice looking at cheap TV splitters but I thought that I had better remind everyone that our most popular product at Cross Country Wireless is the range of Multicouplers that we have been manufacturing for quite a few years now.

We make three versions, the HF/VHF/UHF wideband version that is popular with radio amateurs and short wave listeners and the HF and VHF/UHF versions which tend to sell to professional users such as airports and the military.

So what's the difference over just using a few cheap splitters? The first one is that the loss in the internal Owen splitter is balanced by a low noise amplifier so that the gain is near to zero overall. This allows up to five receivers to operate exactly as if the antenna was connected directly to each individual receiver. This is especially important on the VHF and UHF frequencies where the loss of a simple splitter would seriously degrade the performance of the overall antenna/receiver system.

The Multicoupler also has a 20,000 A gas discharge tube on the input with additional overload and electrostatic protection for the input to the amplifier. The outputs also have RF protection diodes that can provide protection in case transmitters up to 350 W inadvertently transmit into any of the outputs.

If you have a series of very expensive receivers connected to your antenna all weathers 24/7 it's a good precaution to have something that can protect them.

Regards,

Chris



It is also designed to be connected to the station ground system in professional radio stations to help provide a path to ground for lightning.


Re: Cheap TV splitter on HF = fail

Roger Need
 

On Tue, Nov 24, 2020 at 05:14 AM, Martin - G8JNJ wrote:
Hi Roger,

OK your plots are good, especially from 5MHz upwards as specified.

Many are not that good (usually Chinese generic cast metal cases with different brand labels), so it's definitely worth measuring the performance if you can.

I agree. the cheap ones have horrible performance.  I use the ones that CATV companies install and have published specs.

BGI, Regal and Commscope are reputable manufacturers with published 75 ohm specifications that work OK with 50 ohm impedance.   Those that want the best performance use 50 ohm splitters and build their own or use the Mini-Circuits or Diamond products.

Roger


Re: Cheap TV splitter on HF = fail

Martin - G8JNJ
 

Hi Roger,

OK your plots are good, especially from 5MHz upwards as specified.

Many are not that good (usually Chinese generic cast metal cases with different brand labels), so it's definitely worth measuring the performance if you can.

Regards,

Martin.


I Killed my loop amplifier - Happy Ending

Paul Sayer
 

I had the original modified version and was very happy with it. I got used a lot. Then, while trying some antenna comparisons I managed to transmit into it and I killed it. After a few choice words about my stupidity I ordered the LAA+.

I am so glad that I did. I is a very big improvement over the old unit. The old one was good up to about 40m and better than my miniwhip. About equal on 20m and worse above this. 

The new one covers all of LF and HF very well with excellent SNR. I can even hear broadcast FM. Not tested on 2m or 6m yet. My loop is only 1m above the ground so it won't do too well. But I have a discone to cover that range.

Turned out to be a happy accident.

Many thanks to Chris for his help and excellent customer service.

Paul G0VKT


Re: Cheap TV splitter on HF = fail

Roger Need
 

Same CATV Splitter Return Loss (50 ohm impedance.).  Measured at input with output ports terminated in 50 ohms.


Re: Cheap TV splitter on HF = fail

Roger Need
 

On Mon, Nov 23, 2020 at 06:10 AM, Martin - G8JNJ wrote:
Be careful when measuring splitters.

One of the most important parameters is the isolation between the split ports and also the match Return Loss (RL) or SWR.

Ideally this should be greater than 20dB in order to avoid interaction between receivers and any other cables or devices connected to the splitter ports.

The ferrite in these TV & cable splitters is really optimised for the VHF & UHF bands and only provides very limited isolation below about 50MHz.

When just measuring the insertion loss you could just as easily be using a simple tee piece.

You are correct Martin.  I did not post the port to port isolation becasue the OP was concerned with Insertion Loss.  Here is the port to port isolation on the same CATV splitter.


Re: Cheap TV splitter on HF = fail

Martin - G8JNJ
 

Be careful when measuring splitters.

One of the most important parameters is the isolation between the split ports and also the match Return Loss (RL) or SWR.

Ideally this should be greater than 20dB in order to avoid interaction between receivers and any other cables or devices connected to the splitter ports.

The ferrite in these TV & cable splitters is really optimised for the VHF & UHF bands and only provides very limited isolation below about 50MHz.

When just measuring the insertion loss you could just as easily be using a simple tee piece.

Regards,

Martin


Source of Ferroxcube toroids for the loop counterpoise antenna design.

Chris Moulding
 

I've just had an email from Brian, 2E0TCU.

He has bought a batch of the Ferroxcube toroids recommended for my recent loop counterpoise antenna design in the RSGB RadCom magazine.

He is selling the slightly smaller toroid as the original one I specified sold out at the Ferroxcube distributors within a week!

His eBay listing is https://ebay.us/2iDh09

Regards,

Chris


Re: Cheap TV splitter on HF = fail

Ondřej Povalač
 

Hello Roger,
your comment regarding the title is right. It should be "Cheap TV splitter on LW = fail". Unfortunately I don't know how to change the title now. Sorry about misleading you with the title. I really wanted to point out the fact that it is useless under certain frequency more than the fact that is has a 4dB attenuation as this is normal for passive 2 way splitters.
Regarding the 4dB loss - you are right for the SNR ratio as soon as you don't reach the receiver's base noise (noise figure). In such case, the signal will drop 4dB but the receiver's noise will stay. This is why I mentioned "weak signals".
73, Ondrej


Re: Cheap TV splitter on HF = fail

Roger Need
 

On Sun, Nov 22, 2020 at 02:34 AM, Ondřej Povalač wrote:
Hello group,
today, I needed to split HF signal from my Wellbrook ALA-1530LN. First I wanted to use a cheap low noise TV splitter which I have here in my drawer. Fortunately, I decided to put in on the NanoVNA-F first. The 2dB loss is OK for passive splitter but it is useless below 350kHz!!!

These 4dB could be missed seriously in some weak signal analysis. Thank you.


Your post header says "Cheap TV splitter on HF = fail"  You were not testing the CATV splitter on HF.  You were testing it on 350 kHz. which is MF.  The label indicates that it is designed for 5 to 1000 MHz. 

I use a quality CATV splitter with the same 5 to 1000 MHz. specification.  I find it works well down to 2 MHz. even when used with 50 ohm devices instead of 75 which is the design impedance.

The 4 dB loss you referred to applies to the signal AND the noise (both drop) so the SNR remains the same after the splitter. So it will not affect reception if the noise level at the splitter output is at least 8 dB above the internal receiver noise.


Re: Loop height above gnd and 2 loops

Simon
 

Hello again..been refreshing my memory..

May have an issue..loops will need ( even 2.) to be in line with direction i wish to hear in..this i think here will be nigh on impossible..i can add loops broadside, next to each other along a perimeter hedge, but then they will at 90 degrees to direction i wish to hear.( even though loops facing direction..)

Imagine a straight beach..all loops on waters edge..all looking towards sea..that i can do l l l l
What i cannot do is have loops all in a straight line from waters edge to beginning of beach. - - - -

Did i explain that ok?

The lz1aq delay line looks good..but will not work with 2 loops as i can fit in garden ( see above.) i dont have the space to fit a 3rd in another corner.( thus getting 360 steerable.)

I could maybe use short active verticals, but the man made noise here??? Back to the cardioid loops??

My knowledge of phasing arrays is now exhausted..any suggestions would be welcomed..( never had space to do so, so never learnt about..) just read 3 papers on the subject..will be re reading them later..

Simon


Re: Loop height above gnd and 2 loops

Simon
 

Might need to make this clearer
when i say quad loops i mean see attached pic


Re: Loop height above gnd and 2 loops

Simon
 

Like the photo!!( military base?!!

Was looking at similar on Cornwall coast..ex or maybe still used massive towers..over looking sea..there is more than one..Mary even says yes to buying one!!( once we sell house here in london.not yet though...)

Dont have the space for lots of loops.nor wife permission..
Could get 3-4 small 1m up, but really closely spaced..all cardioid maybe..phase them together and then against another noise loop..( cardioid loops on own will not null out noise due to direction of local noise in relation to where i want them aiming.)
So how to combine 4 loops in phase without having massive loss and spending £££? (Google time.)

Martin  Chris any thoughts??

Also Chris..how about designing a higher (Lf) gain preamp optimised for the higher inductance cardioid loop?  (Aimed at low band users..)

Simon g0zen



On 22 Nov 2020, at 15:05, Martin - G8JNJ via groups.io <martin_ehrenfried@...> wrote:

On Sun, Nov 22, 2020 at 12:53 PM, Simon wrote:
Ps shame i cannot work out a way of combining my quad rx loops with the cardioid design Chris posted.( quad loops much more “gain” than single loop.)
Hi Simon.

The original C&S loops were used in lines of four or eight to form arrays, and I'm fairly sure they just combined them all in phase.

"Oh for a house on a beach with no neighbours!"

https://www.google.com/maps/@50.3887482,-5.1559668,3a,44.4y,120.9h,95.23t/data=!3m8!1e1!3m6!1sAF1QipNVq_hASA72zYEQa2UBsPB9Srmg6UANhw0v0SNd!2e10!3e11!6shttps:%2F%2Flh5.googleusercontent.com%2Fp%2FAF1QipNVq_hASA72zYEQa2UBsPB9Srmg6UANhw0v0SNd%3Dw203-h100-k-no-pi-0-ya166.44261-ro0-fo100!7i9728!8i4068

Regards,

Martin


Re: Loop height above gnd and 2 loops

Martin - G8JNJ
 

On Sun, Nov 22, 2020 at 12:53 PM, Simon wrote:
Ps shame i cannot work out a way of combining my quad rx loops with the cardioid design Chris posted.( quad loops much more “gain” than single loop.)
Hi Simon.

The original C&S loops were used in lines of four or eight to form arrays, and I'm fairly sure they just combined them all in phase.

"Oh for a house on a beach with no neighbours!"

https://www.google.com/maps/@50.3887482,-5.1559668,3a,44.4y,120.9h,95.23t/data=!3m8!1e1!3m6!1sAF1QipNVq_hASA72zYEQa2UBsPB9Srmg6UANhw0v0SNd!2e10!3e11!6shttps:%2F%2Flh5.googleusercontent.com%2Fp%2FAF1QipNVq_hASA72zYEQa2UBsPB9Srmg6UANhw0v0SNd%3Dw203-h100-k-no-pi-0-ya166.44261-ro0-fo100!7i9728!8i4068

Regards,

Martin


Re: Loop height above gnd and 2 loops

Simon
 

Hi Martin

Yes it seems to work very well, atleast on frequency that i wanted to use it on.1845-50khz

I do need to add gain to the noise antenna..currently it is 6s points down on the main antenna, but still removes the smpsu noise though!

Noise antenna is a loop hidden in the front garden hedge with an average/ crap loop amplifier..the loop amp either needs more gain or I add a preamp in input line to phaser( inside the phaser box.)
Loop in hedge is “ aimed” at the offending noise.

Being heard quite well on 160m ssb ( on the big mag loop) stateside now..( season opened) but still struggling to hear them..soooo..

Now that i know the phaser works well it is time to make another along with another quad loop and good amplifier..this to see if can get any better rx from usa on 160..( adding rather than nulling.)
Issue here will be second quad loop is going to be VERY near the big tx/rx qro loop..( no where else to put it,) and only 10m from the existing rx quad loop..
Will it couple to big loop? I think not. But will need some rf protection and good coax choking etc..

Oh for a house on a beach with no neighbours!

Simon..

Ps shame i cannot work out a way of combining my quad rx loops with the cardioid design Chris posted.( quad loops much more “gain” than single loop.)


Re: Loop height above gnd and 2 loops

Martin - G8JNJ
 

On Sun, Nov 22, 2020 at 01:50 AM, Simon wrote:
well been busy.. made a new phaser..old one was top of Martins page..the vk5 one..
it was always abit crap..but had nothing to compare it with..
Hi Simon,

Excellent that's really good news.

Your comments have given me an incentive to update my noise cancellation webpage, so thanks for prompting me to do that.

https://www.g8jnj.net/rfnoisecancellation.htm

Regards,

Martin


Re: Cheap TV splitter on HF = fail

Ondřej Povalač
 

Hello Chris,
as always, you are right - my mistake. I have done the measurement again with 50 Ohm termination and it shows almost 4dB indeed.
See photo.
These 4dB could be missed seriously in some weak signal analysis. Thank you.
Ondrej, OK2TOP


Re: Cheap TV splitter on HF = fail

Chris Moulding
 

Hi Ondrej,

Thanks for posting about the cheap splitter. I noticed that you didn't have a termination in the unused port so the loss will be even higher. Typically a two way splitter has a 4 dB loss.

Good to hear that you like the HF/VHF/UHF Multicoupler and thanks for the order for the new one!

Regards,

Chris


Cheap TV splitter on HF = fail

Ondřej Povalač
 

Hello group,
today, I needed to split HF signal from my Wellbrook ALA-1530LN. First I wanted to use a cheap low noise TV splitter which I have here in my drawer. Fortunately, I decided to put in on the NanoVNA-F first. The 2dB loss is OK for passive splitter but it is useless below 350kHz!!!


After that, I went and made order for HF multicoupler 

I already own the HF/VHF/UHF version which is excellent but works from 500kHz. Now I bought also the HF version which works from 50kHz to 30 MHz.

Looking forward to it.

Ondrej OK2TOP

Below, you can see what happens when using cheap TV splitter:

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