6600M SO2R: Is external Bandpass filter needed?

Andy - KU7T

Using my 6600M and trying to do more SO2R. I have 1 unused Filtermax bandpass filter. I have ANT1 and ANT2 going to an outside 6 x 2 switch. For SO2R, the radio has already very good filters.

My question is, whether it still makes sense to put the FilterMax bandpass filter system inline with one of the two ANT coax?  And if so, would it be better sitting on the antenna where I am calling mostly CQ or on the S&P antenna? Asked differently, is an external filter more effictive in transmit or receive?

Thanks,
Andy
KU7T

Kari Gustafsson SM0HRP

Hi Andy, Difficult to say. My own situation could exemplify how complex a situation can be depending on the actual antenna characteristics and other factors. I have both bandpassfilters and high power bandpassfilters in line on my 6700 SO2R station. It yields some +90 dB out of bands isolation. So good so far but what I struggle with is inband harmonics. E g 40 m harmonics on 20 m and 80 m harmonics on 40 m. They are quite strong some 59+10 dB and only way to get rid of those is with "intelligent" tuned hybrid stubs that **** them. The challenge is where to put them. So if you do not suffer from inband harmonics and you already have some 70 dB of out of band supression you may settle with that. You are lucky ☺️ 73s Kari SM0HRP

Mack

Andy,

As Kari has already said it depends on MANY interrelated factors like; antenna separation, directional antennas, power, frequency. I own two of the Bandmaster IV filters and do not use them with my 6600. The 6600 offers greater than 50 DBm of isolation using the internal filters as long as you are NOT in wide mode. I can run legal limit on two bands simultaneously but I have great antenna separation on separate towers and directional antennas (40M-6M).

The only way to know for sure is to run some tests at your station. Begin running SO2R on two separate bands at low power (say 100W). Increase the power in 100W increments until you see signal degradation or overloading. 

Hope this helps.

73,

Mack
W4AX
Alpha Team

Mike-VA3MW

Hi Andy

Have you run things through the calculator?

https://www.flexradio.com/downloads/flex-6000-fdx-power-calculation-worksheet/

The 6600 has 7th order band pass filters as Mack mentioned.  What are you hearing when you try?  


Mike

Andy - KU7T

Michael,
thanks for the link. Will have to check this out. It seems that 2 values can be calculated for each antenna combination, internal and external isolation. Can you explain the difference?

Thanks,
Andy
KU7T

Eric-KE5DTO

If I understand your question correctly, the internal isolation is defined within the radio and is well understood.  The external isolation I would expect to be due to the location/orientation/proximity of the 2 antennas.  This is what the worksheet is designed to help identify to figure out whether additional filters may be beneficial.

Andy - KU7T

Let me ask more precisely. The worksheet at https://www.flexradio.com/downloads/flex-6000-fdx-power-calculation-worksheet/ has 3 calculation sections:

1. Full Duplex / SO2R External Isolation Worksheet
2. Antenna Coupling Worksheet
3. Full Duplex Internal Isolation Worksheet

It sounds like 2 is a temporary calculation that can be plugged into the calc 1. 

What I was trying to understand is what the numbers in 1 and 3 actually mean?  What is external vs. internal isolation?  Wouldn't internal isolation be dependent on the radio only, and therefore be the same for all non-defect 6600Ms?

73
Andy
KU7T

Al Dewey

Andy;

If I had only one external bandpass filter, I would use it on the S&P side as you describe above.  The reason is based more on my experience rather than the above referenced calculations.  My experience has been with the Dunestar D600 six band filter.

Here are my reasons:  1) If the CQ antenna is doing most of the transmitting, I would want the extra protection on the S&P side since it has to deal with the most RF.  2) My experience has been that the filters are better at filtering out harmonics (and other products) on the RX side than they are at suppressing them on the TX side.  3) Bandpass Filters often have some insertion loss.  With My Dunestars, I experience about a 10% loss which means my 100 watt radio actually puts out about 90 watts on the other side of the filter.  I have spoken to a few others in our area and they see the same loss.

73,

Al, K0AD

Steve-N5AC

Andy,

The worksheet mentioned here is designed as an aid to help you figure out what will and will not work at your station. The first worksheet (SO2R) is for SO2R operation (using one radio), the Antenna Coupling Worksheet helps you figure out the coupling between antennas that can affect operations and the final is used to determine if there is any kind of isolation issue in the radio that would affect you.

All of these assume that you've had some experience with the requisite problems and understand how you can get into trouble with station design. If these topics are unfamiliar, I would recommend reading W2VJN's book Managing Interstation Interference. If you understand the concepts and the worksheet is still confusing, let me know and I'll try to clarify.

Internal isolation is exactly what you suggested -- isolation inside the radio. There are a lot of variables that will determine if it is a problem, though. Bands, antenna spigots, preamp, etc. so the worksheet lets you calculate the specific isolation for your mode of operation. You might run the calculation once for no-preamp on 40 and transmitting on 20 and decide you're fine. Then you might run a calculation listening on 10 with a preamp and transmitting on 20 and decide you have a problem. The numbers will let you know how big of a problem you have. 

Mark Erbaugh

Question: Do I need to be concerned about half duplex operation with two antennas connected to my Flex 6700 (ANT1 and ANT2)? ANT1 is connected to a legal limit amplifier which is connected to a dipole. ANT2 is connected to a vertical antenna about 100' from the dipole.  Should I be concerned about transmitted RF from the dipole coming in to ANT2 and damaging the radio?  Same question when operating in diversity mode with the two antennas?

Andy - KU7T

These are the sort of questions I also have. We will have to go through the worksheet to make sure. Additionally, I am planning to put up a second tower and will now consider putting it up temporarily and then measure. Its will be an WRTC-style spiderbeam about 80 feet away from my main tower. So I could move it further away if needed without a lot of effort, but would lose some elevation... Andy KU7T