Looking for advise - Bandpassfilter - SO2R

Roland HB9VQQ

Mack

Stan VA7NF

Mike-VA3MW

Hi  Roland

Some good ideas

You didn't mention which radio you are using?  Like others have mentioned, a 6600 should fit the bill.

However, it is not related just to the radio, but good quality feedlines and RF chokes as well.  

I posted something last week about changing out some RG8X for LMR400 made an amazing difference in my station.  My noise floor got quieter and all my birdies disappeared.  You don't want any RF making it into the radio and quality well shielded feedline is a big contributor.

I talked to a good RF friend of  mine of Maple Leaf Communications (Bob, he used to be the chief designer at CushChraft) and highly recommend LMR240 for HF operations.  It isn't as heavy as LMR400 and costs much less.  Yet, its shielding properties are amazing.

Can you share your entire station layout including feedlines and lengths?  Isolation is not all in the radio, but the entire station layout.

Mike va3mw

Roland HB9VQQ

Mike-VA3MW

Hi Roland

The 6600 has over 60db of isolation, so adding more BPFs might not fix your situation.  Somehow the RF is making it in on a different path.   

What sort of feedline are you using?  Have you added chokes to the antenna end and the radio end of the feedline?

This is one filter I am aware of:  https://www.dxengineering.com/parts/kmi-bf-100 if you want to give it a try, but there is no guarantee it will solve your issue.

As well, take some time and review this document from the YCCC.  It is one of my bibles when it comes to RF Chokes and highly recommend that every HF ham read it.  http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf

Mike va3mw

Roland HB9VQQ

Roland HB9VQQ

Also I disconnected one antenna (vertical) at the feed point and trasmitted wit the other one (Spiderbeam). No more interferences. I did the same the other way around, disconnected Spiderbeam and transmitted with the vertical. Again no more interference.

Roland HB9VQQ

Mike-VA3MW

Hi Roland

It will be interesting if cascading band pass filters solve your issue.  Please keep us informed on how you make out.

Very nice looking QTH!

Mike

Roland HB9VQQ

NR4O

Hi Roland, We worked you in the contest last night, I believe on 40M. Had a little trouble decoding you due to a strong adjacent signal. Thanks for the QSO. I’m a relatively new Flex6600 owner , about 6 weeks now. I think my situation is similar to yours. I have a relatively small lot and not enough antenna separation. I have been using the Array Solutions Bandpasser II filters for a couple of years and found they worked well with my previous rigs, Yaesu Ftdx3000 and FT-991. I continued to use them when I installed the Flex and they do make an improvement allowing me to operate with high power. It’s easy to interface the filters to the Flex using USB to BCD cables plugged directly into the Flex USB ports. Another thing I found is that Bandpasser II filters also have a noticeable insertion loss on 15M that’s noticeable on transmit. I don’t see the same effect on the other bands. What I am finding is that the 2nd harmonic when transmitting on 80M and 40M is still causing a significant signal on 40M and 20M respectively. When operating at the low end of the bands that can put the harmonic signal within the desired receiver sub-band. The harmonic is still present even when operating low power, just a lower signal level. I plan to experiment with coaxial stub filters(quarter-wave shorted RG8 coax on 80M) to attempt to further reduce the harmonic energy by another 20-25dB. That’s relatively inexpensive compared to high power bandpass filters. There’s quite a few sources of info on the internet and Amateur handbooks for these. BTW...your QTH looks very nice. See you in other contests. Eric - NR4O

Roland HB9VQQ

N2WQ

Just like Mike said, start with the common mode chokes. A good common mode choke has well over 5K of impedance, ideally mostly active rather reactive or complex. Adding some beads to the end of the coax unfortunately doesn’t do anything, except fatter profits for the seller.

The W1HIS paper is over 10 years old and out of date. The concept is sound, but building consistently high performance chokes is quite difficult. Take a look at the K9YC cookbook on chokes. Here’s a picture of high performance chokes, the left for 160/80 and the right for 40/20/15/10:



We use high quality Teflon coax that is expensive, but delivers outstanding performance. Choke the antenna end and the shack end.

If you have an ATU, activate it even if you don’t need it to match your antennas. The ATU acts like a TX filter, albeit not a great one. Don’t forget to choke the rotator controller cable as well as the DC power supply and all other wires/cables on the shack. Consider switching to a wireless keyboard/mouse combo to remove unnecessary wires in the shack.

Stubs work great, but you won’t be able to apply them to both antenna fees points. The Spiderbeam being a tribander makes it unsuitable as tuning out 40 will also tune out 15. You can however install a stub at the base of the 40 antenna and tuning out 20.

Assuming you stay low power, you want to make sure you have TX filters as well, not just RX. Question for Mike- are the 6600 filters TX/RX or only RX?

You also want to make sure that the shields of both coax cables are bonded together and grounded, both at the antenna end and the shack end. Bond the shack equipment together and connect to the AC power ground.

I run 1500w and the second harmonic is not an issue as long you stay ~25 KHz away. Smack on top of the second harmonic its signal strength is S5.

The Array Solutions (Hamation actually) filters work very well. I use them between the radios and the amps; there are 4KW filters for each band after the amps as well.

Roland HB9VQQ

Thanks for all your input so far. Trying to replicate the issues since I did not have time during contest and see what I can do.

Kari Gustafsson SM0HRP

I could add to above that harmonics supression on the 1st harmonic is quite common and an effective solution is lump tuned stubs. They provide some 75-80 dBs of isolation.
What is this then? Nothing else than two stubs in parallell with a tuned coil inbetween. Not to difficult to built.
I have about 110 dB of isolation between my antennas for out of band signals. But the 40 m harmonic on 20 m is S9 without the lumped tuned stub. With the stub it almost dissipears. I am running a kW.
Not to forget also is rectification of signals in junctions (rotors, bearings etc). In my house I discovered that my LCD TV produced 20 m harmonics when sending on 40 m even with modest power (rectification inside the TV created double frequency signals). I pulled out the TV cord and all went away. It is very likely you may have this too.

Roland HB9VQQ

N2WQ

You will have to implement some sort of switching at the TX output. You may also want to read this book:

http://www.qrz.lt/ly2w/Ham%20Radio%20... and of course K9YC’s extensive work on stubs: http://audiosystemsgroup.com/StubPlac...

Chris DL5NAM

N2WQ

I would strongly advise against such simple articles on stubs as they omit some seriously important details, such as: 1) Stub placement 2) Calculating stub length for a specific frequency and your own coax 3) Trimming/tuning stubs for a specific frequency using an antenna analyzer Having cut quite a few stubs myself, I have learned that stubs take a lot more effort than snip-snip.

Chris DL5NAM

... but they come from the practice and they are in use and they do there job and that since many years ! Cant be so wrong.

Everything you can do better - that's real life :-)

Mark NS9N

Agreed, without proper test equipment, spectrum analyzer with tracking filter or graphical SWR analyzer it is going to be very difficult to get the desired results. Even with the equipment it can take hours of careful trimming.

N2WQ

The way I see it, it is all about return on time and effort. That is, my philosophy is do it right the first time. And make sure you understand what you are doing. For example, stub placement is rarely even mention. Ditto for how to connect multiple stubs properly. Another example is the choice of coax. The common wisdom is to use cheap coax which has a lower velocity factor so you use less coax. What this common wisdom forgets to mention is that the expensive coax, with a velocity factor of 0.87, produces longer stubs that are much more broadband. In other words, people have the option to decide on their own trade off of cost vs. broadband coverage.

Kari Gustafsson SM0HRP

Hi, as many below has said it is fairly easy to make one or double stubs and have them switched in line for different bands.
But as N2WQ points out you need to know WHERE you insert them. To complicate matters little bit more if you have PA you must know even more (what type of output network it has).
To make a long story short. You should insert a stub at a high impedance point along the coax line (the stub is a 0 ohm short at this point). If not the stub will not function properly. A OM2500A has a pi-L filter at output, with a high impedance at the 2nd harmonic, and here you may put a stub. For other PA it could be the opposite (low impedance). Next stub can then be placed on the next high impedance point (remembering that a stub produces a new low impedance point along the line).
A VNA is a must to measure the coax line properties. ARRL has free programs to analyse coax impedances as a funtion of length.
It is not complicated as it sounds but you need to do it in the right order as several has pointed it out.
An excellent artice is:Minimizing interstation interference by K9YC. It is on the web.
GL Kari SM0HRP

Roland HB9VQQ

DL4RCE

Isolation is "only" 70db or something like that. What do you expect? External BP Filter will not help. I tried all kind of, 4o3a, OM power, low/high power, before/after amp. You can only reduce to the inherrent isolation which should be enough to not dmg your Flex. Volker

Roland HB9VQQ

Well with only 5W into a dummy load directly at the TRX I would expect to see no traces on other bands.

Mike-VA3MW

No so.  You'll have to do the math on the minimal discernable signal the radio detects and how my RF your dummy load and coax is leaking.  

Roland HB9VQQ

There is zero coax involved just the dummy load.

Mike-VA3MW

I think you'll find that a dummy load will also radiate RF.  It is not able to turn all the RF energy into heat.   I don't know what the number is, but I know we did studies like this when I was in college.  It was impossible to not have any RF radiating.  

Roland HB9VQQ

So I consider my obervations to be working as designed.