For receive purposes there is really very little difference between the two.

In practice neither the signal source (generator) or the receiver (load) are likely to be an exact 50 Ohm match, and in real life here will be some slight amplitude variations as a result of changes in mismatch loss across the required frequency range.

You can simulate the use of different coax types using tools like SimSmith.





If we model a 30m Length of RG58 to feed a 50 Ohm load from a 50 Ohm source we get this result.




The purple trace shows the line loss in dB relative to the 1w source on the left hand vertical axis, and the blue trace shows the SWR on the right hand vertical axis.

The loss is about 2.5dB at 30MHz and the worst case SWR is about 1.1:1

If we now swap the coax for 75 Ohm RG59 we see these changes occur.






The average loss over the 1-30MHz frequency range has increased slightly, but the loss at 30MHz has reduced by about 0.5dB.

The SWR is also noticeably worse, but doesn't exceed 2.2:1, which is still well within acceptable bounds for such excursions. It's really only when you get ratios above say 6:1, that the mismatch losses start to have a noticeable effect, with >3dB additional variation in signal levels.

If you can't see the graphs embedded in this post, I've added them to the "Antenna Noise reduction" album in the photos section.

Regards,

Martin

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Martin,?

I was thinking of asking about using 75ohm sat cable
when I saw your preference for this.

I have read elsewhere that such coax can be used
in lieu of standard 50hm.

How would you use it for rx and tx?

"Better" NewYear to all!

Michael
2E0IHW

Chris

The coax into plastic box injector sounds like a very early Wellbrook design that was used with a Wall Wart, later? injectors are in a die-cast box without potting compound, they have additional internal filtering, BNC output and come with a switching supply as our European Masters dictate.? I don't think Chris's problems are down to the injector at all.

One possibility is grounding the ALA100 feeder at the ALA100 end, a nastier way of injecting noise is to ground the loop at one point or to have unbalanced the loop by having a grounded fence, metal pole or chicken wire asymmetric to the loop. Another nasty would be water in the coax, when the braid corrodes it looses screening effectiveness before going open.

I would suggest that any KiwiSDR owner can do a few useful things for the future. Display the ? 0-30MHz Spectra (? outward pointing arrows and SPEC selected) then take a screenshot. Doing this at Noon? and Midnight or whenever you get QRM on and off? gives a good idea where noise levels are at these times.? It will make the kinds of QRM quite clear and give a baseline to investigate things. The Spectrum is far more valuable as it gives accurate signal levels and can show more detail, the waterfall can show on/off signals and you can adjust the speed of the water falling! Obviously you can zoom in on any interesting details and take more spectra.

Every month or two I like to measure the noise levels on all of the Ham bands, an easy way is to use the KiwiSDR built in WSPR mode then find the noise level for each band. That gives a very good indication of the QRM levels.? There is a much better way using a Kiwi, RPi4 and wsprdaemon software to decode WSPR, the software also can do noise charts/time for each WSPR band so 24 hour patterns are evident.? Over many years people have talked about QRM surveys, there are some very? elaborate schemes suggested however a KiwiSDR and a RPi? would be a very effective and low cost way of producing a package that goes from RF to Wi-Fi at low cost and at relatively low power consumption, there are thousands of KiwiSDR's and millions of RPi's all over the Planet that could perform a valuable service to our Hobby by mapping real noise levels.

73, Alan G8LCO

Another good series of articles on EMC testing and best design practice can be found here.

On Fri, Dec 31, 2021 at 11:42 AM, Simon wrote:

My go place for working out what common mode choke will work at which frequency is G3TSO common mode chokes page

Hi Simon,

Slight correction Steve's callsign was G3TXQ



Some supporting maths if you enjoy that :-)



Highly recommended reading.

Regards,

Martin

On Fri, Dec 31, 2021 at 12:09 AM, Andrew Ikin wrote:

For receiving applications, I doubt that most users could tell any difference.

?

What I can say is:

?

There is nothing wrong with RG58c. It has 95% coverage of the screen. Going
to a 100% screen isn't likely to make any difference with a long run of
cable; most noise current currents can be choke off with ferrite rings.

Hi Andrew,

My experience of standard coax cables such as RG58 seems to have been different to yours.

Although theoretically it is supposed to have 95% braid coverage, it often does not, and in some cases the copper (or whatever has been used that looks like copper) is so poor quality that the electrical connection between the overlapping strands of wire that form the braid is not consistent, and as a result the screening can be very poor, especially if there is some moisture ingress.

In addition I have found that even a reasonable quality single braid screened cable will pick up additional noise in the shack from items such as switched mode power supplies and other domestic electronics.

Ferrite rings can very effectively reduce the problem of common mode noise being carried on the outside of the coax screen, but if poor braid coverage allows it to permeate into the coax you may have problems that ferrite won't fix.

The term typically used is screening effectiveness or efficiency, but transfer impedance may be a better description to use.

In the articles linked below, it can be seen that single braided RG59 coax may only provide about 50 dB isolation, which may not be sufficient if it being run close to other cables in a bundle or near to noise sources, and a copper foil and braid screen can improve upon this substantially and can provide 30 to 50 dB better isolation than a single braid cable of the same type. This is pretty much in line with my own observations, both in my home and on the hilltop Kiwi sdr site at Weston? ? where the site admin has spent a lot of time replacing existing coax runs with double screened or solid outer Heliax, in order to get the receive system noise floor down as low as possible. This has also involved changing bayonet type BNC's for screw type N connectors, as these provide a much more reliable screen connection between mating surfaces.

Further reading.





Personally I now prefer to use 75 Ohm satellite TV coax with a foam dielectric and copper foil and braid with a solid copper inner conductor, as I have found this to be a cost effective cable with good electrical performance.

WF100 is one such type.



Regards,

Martin

Hi Martin..your pics did show..if you mean pic of cm chokes with house and end feed.

Hi Jeff..

Yes useful info, what he did not show is to maybe add chokes to the power to bias T and sdr, even one between sdr and bias t. Not always needed of course, but even a tiny bit improvement is helpful when its all added up..and I live in rf pollution hell here in London, so everything does help.

So Antennas cables and Ferrites ( or cores or whatever you wish to call them.

My go place for working out what common mode choke will work at which frequency is G3TSO common mode chokes page..google it you will find it..DOWNLOAD it.. I have no idea how long the site will have this info for..G3TSO is silent key ( big shame.)
The site gives lots of easy ( important) to understand info on said chokes..
These chokes work on antenna cables and power cables. Down side, if you need lots they start to get expensive if using 200 size cores.plus read cm choke for mains in to station.

Buying cores/ ferrites etc.. Dont buy “ genuine “ amidon etc usa made chokes from ebay unless you know the seller.
Ie plenty on ebay cheap but sold from China..hmmmmm you work it out..
Use Farnell, mouser, etc..

For general power cable ferrites I use ones ripped out of LARGE smpsu’s..10kw etc..they work well, BUT that was abit of a guessing game untill i found the ones that worked well. I also use them on all pc, monitor, rf patch leads etc..as i have a large source of these i used them, but to be safe use chokes recommended by g3tso.

Just using them on the internal wiring in my shack made a big difference.

Antenna cables..dont skimp. Buy good quality stuff..ie you can buy mil spec rg58 on ebay that’s totally rubbish, only thing mil about it is the mil printed on cable..( guess how i know?) OR you can buy good rg58 from ebay or elsewhere.
Ask seller to show you stipped off end to see the screening.
Buy just copper, no mixed metal cable, ( though may be just fine inside where no rain etc)
Always seal the plug sockets from water on anything that can get damp, especially if running voltage though to preamp.
I use cat5e as well as rg213 to my preamps. I prefer the cat5e.
Though this will start a discussion I suspect..
Whatever cable you use add common mode chokes at antenna and if possible at rx.
Lz1aq has cm choke design for cat5e on his web site that works well..tested and in use here.

Earthing of station equipment to single point..tricky one this..can make things better, sometimes worse plus there is electrical safety to consider ( plus earth loops etc.) maybe someone can add advice??

On Thu, Dec 30, 2021 at 05:52 PM, Steven Greenfield AE7HD wrote:

The list does not allow attachments. So you must post a link, or upload to the Photos section. Or files, for non-photos.

I was fooled because I can see the images I attached in the web version of the group in my browser.

I've now added them to a new folder in the photos section.

Regards,

Martin

Martin <martin_ehrenfried@...> added the album Antenna Noise reduction: Methods of reducing noise on receive

Hi Andrew..re rg58.. what i was meaning is ( which) i should have said, dont buy from ebay unless you seen it..very easy to end up with crap..

Simon

Hi Jari

What i mean by that is often, very often general rg58 coax is poor quality.
The screen on cable is very poor, allowing interference to get into cable.

Simon.

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Graig

There are two Wellbrook loops that use an 8/9dB push-pull Norton amplifier inside the Antenna Interface. These are the ALA1530S+ which is out of production and the ALA1530LNPro Imperium that is now back in production.

73

Andrew Ikin

Wellbrook

After some strange results with the Wellbrook loop comparison with an LZ1AQ loop, I finally found that my Wellbrook interface was in fact a 12db line amplifier.

Cheers.
Craig.

On Thu, Dec 30, 2021 at 09:10 AM, DX Pedro wrote:

Images seem not to be loading on my end. Is it just me?

The list does not allow attachments. So you must post a link, or upload to the Photos section. Or files, for non-photos.
?
--
Steve Greenfield AE7HD

Hi Dx Petro..

Thats what this thread all is about..WORKING answers to living in an urban/ noisey area..Some, know all the answers, many do not..

I am intending with help from others ( please, as i dont know it all( far from) to shed some light on this subject.

Will share my antenna experiences, what works ( FOR ME.) and what does not later..hopefully others in the know will also do so..NO GUESSING please..not tried it, please don’t post it..

But location location location most definitely decides antenna choice..

( under my 50 yr old range rover changing out steering box at moment..( not fun!) actually having a rest from, so laters..)

Simon

Good luck with the rg58…unfortunately quite often cb or taxi spec..ie 68% or so screening..ie pooh for dedicated rx antennas.

Simon