EMRFD Message Archive 11589

Message Date From Subject
11589 2015-09-06 18:22:46 Ken Chase BCI problems
Hi All
My first post with the group and I hope I'm in the right place.
All summer I've been trying to get on the air on 40m. The backyard is very restrictive on antennas. I have a LNR 40/20/10 end fed. I also built a stealth on my wooden fence.
In an attempt to tune the end fed with a friends analyzer, I could not get the SWR to settle, it just jumps around. This also goes for the stealth antenna.
I took the end fed and analyzer to a friend's place in the country. We put that end fed into every configuration imaginable, but the SWR was rock solid. I even took the end fed and TCVR camping and no problem with SWR. My friend and I decide I was getting near field interference. You can imagine my fristrstion not being able to operate.
Last weekend while calibrating my frequency counter to WWV 2.5 MHZ, I saw this whopping wide strong signal down around 2.46 MHZ. I moved over to it and it sounded like 2 or 3 AM stations on top of each other. Then I thought was 'what if these signals are adding to the amalyzer signal on reflected signal'. I found a quick and dirty BCI filter, inserted between the analyzer and the antenna. Wow what a difference. SWR was not jumping, rock solid.
Now that I figured out what was going, my questions is, will this cause a problem when I'm on the air. If I need a filter to RX, then I'm assuming I need one on TX.
I have no idea how to go about designing a filter to handle 10-20 watts. What size toroids to handle the power, etc.
Any info would be greatly appreciated and I don't expect anyone to design one for me. I have to learn.
11590 2015-09-06 23:17:30 Tayloe, Dan (Noki... Re: BCI problems
I have had the same problem.  I live half a mile from a mountain top of broadcast transmitters (South Mountain).  My MJF analyzer does not work here because it has a broad band detector that assumes any reading it gets is reflected power.  I.e., it assumes all received signals are small from outside sources.

This is where it would be nice if it had a DC receiver with a 2x Tayloe detector that has built in out of band rejection for the SWR detection.

- Dan

Sent from my Windows Phone

11591 2015-09-07 05:10:45 jwolczanski Re: BCI problems
You didn't mention your rig, but in my old Ten-Tec 525, I was able to break into the receiver line and bring a pair of connectors out to the rear panel.  From there, one can make a variety of receive filters, the best of which might be a notch, in your instance.

One other thing is to use a L-network tuner with the inductor as the shunt element - this has a high pass response.  Most couplers have a low-pass response.

My BCB "flame-thrower" is 3km away and a mere 22kW - not as severe as yours.

Good luck!

Warrenton, VA
11592 2015-09-07 07:05:29 Ashhar Farhan Re: BCI problems
this is why, what you need is a narrow-band tool like the N2PK VNA or a spectrum analyzer with a tracking generator. 
the wide-open detectors are bereft of all these problems.

- f

11594 2015-09-07 14:12:56 Ken Chase Re: BCI problems

Hi Jerry
My rig is not the problem, at least right now. The problem was the BCI interfering with the analyzer, which works fine with a filter.
I guess my question is, will i have BCI on TX, not RX?
BTW, my rig is a MST400 kit.
73 Ken VA3ABN
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11595 2015-09-07 14:20:21 w7zoi Re: BCI problems
Hi Ken,

No, I don't think you will have any BCI problems.    The measurement problem you encountered is because the detector portion of the MFJ instrument you used has a wideband response.    That is, it is nothing more than a diode detector (or similar IC) connected to an antenna.    If you attach that detector to an antenna, you will get a response.    That is probably what has happened.    So you probably do not need to build a higher power filter.

That said, you could build the same filter that you just built with 500 volt mica capacitors and air core inductors wound with about #18 wire, perhaps with a diameter of an inch or so and you would be fine at 100 watts.     Most of us, myself included, have no idea what that kit is that you mentioned, so we don't know if you are running 4 watts or 400 watts.

Good luck.

73, Wes

11596 2015-09-07 17:08:53 Ken Chase Re: BCI problems

Hi Wes
The MST400 is a 40m SSB kit by OZQRP dot com. Output is about 5 watts.
Sorry I should have mentioned the rig but I didn't think it relevant.
I thought the BCI was adding to the reflected power of the analyzer and filtering stopped that from happening.
So I guess I can go ahead and tune the end fed for 40m and I should see a similar SWR on my power meter with the rig.
If for some reason I needed a high power filter, I was looking at this but scaled to 40m
Thanks Wes, much appreciated.
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11597 2015-09-07 17:14:41 w7zoi Re: BCI problems
Hi again Ken,

Very good.    I don't do a very good job of keeping up with the many QRP rigs that are out there.   I'll have to take a look at this one.

That new filter that you show in that link looks like it would be great.    However, it is designed to allow operation on the 160 meter band while suppressing the broadcast band signals.     That's a severe combination of thing to do at the same time.   I bet this would be a difficult filter (although a fun one) to build.  If your transceiver is just for 40 meters, you would be just as well off with the simple design, if indeed any filter is needed at all.

Good luck with the experiments and with getting the rig going.    Should be great fun.

73, Wes

11599 2015-09-07 19:17:02 Ken Chase Re: BCI problems

Hi Wes
With all the trouble I've had with the antenna and analyzer, I've learned a lot. I should be on the air next weekend or the one after.
BTW, off topic, I enjoy the work you've shared with your publications.
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