Posts Tagged ‘balun’
In your ham radio adventures, you may have heard the words..choke balun, feedline isolation, common mode choke or a 1:1 balun. In my humble opinion different names for the same device. These devices for the most part are present in a system to control common mode currents. I am not an engineer just a simple ham guy trying to sometimes understand some very complicated and technical explanations.
I hope to keep the next bunch of lines understandable. Here we go...what are common mode currents! Most ham use some form of 52 ohm coax as it's very easy to route, secure and can within reason be placed anywhere. Ideally, RF will flow out on the OUTER SURFACE of the coax INNER CONDUCTOR and flow back on the INSIDE SURFACE of the coax shield. This is what happens in a perfect world but if a system is unbalanced RF current will return on the OUTSIDE of the outer coax braid. It does not return but it radiates.
This is when we hams can experience RFI issues and these issues vary with the amount of common mode currents flowing on the outside of the shield of the coax. How does one control this common mode current? One very effective way is to introduce a common mode choke, 1:1 balun, choke, feed line isolation or whatever else it could be called.
In a previous post, I did go over how I installed a 1:1 balun at the antenna feed point of my Hustler 4BTV and that seemed to satisfy my RFI issues but further reading informed me that a choke balun at the radio feed point would be very advantageous. I ordered 2 FT240-31 mix toroids as I decided to make a choke balun instead of buying one. The two common mixes for HF toroids are 31 and 43. The difference being the 31 mix is effective from 1-300 Mhz and 43 is effective from 25-300 Mhz. I chose to go with the 31 mix and purchased 2 from a reputable dealer as not all toroids are created equal. I would be very wary if you find toroids at a very low price....just remember you get what you pay for. I ordered mine from Mouser Electronics Canada, part number 623-2631803802 made by Fair-Rite for 13.00 each.
I used RG8X coax to wind around the toroid but the issue with using a ring toroid compared to a split bead is I had to remove the PL-259 to wind the coax around the toroid and then solder the PL-259 back on. I intended to make 10 loops and for some reason, I ended up with 11 turns through the toroid. I then soldered the PL-259 connector back on but not before placing the barrel and coax spacer on....how many of us have soldered a PL-259 on and then realized we forgot the spacer and barrel!
Another advantage to having a choke balun at each end of the coax is that it helps remove some RF noise that is picked up on the shield of the coax.
|Dont forget these BEFORE soldering the PL-259|
When I moved to the East coast from Ontario at the new QTH I purchased and installed an EndFed antenna and it worked great for me. It was a huge step up from the condo balcony mag loop antenna. The EndFed is a compromise-type antenna and does come with some issues. The main issue is (if you don't use a counterpoise) the coax shield is used as the counterpoise. This can cause some issues and an isolation balun is needed in the shack. I purchased a quality isolation balun from balun designs to take care of the feed line issues. In time I did install a counterpoise but it's not that effective when your Endfed goes from 10m-80m.
I still had some RFI issues in the shack that ferrites did an excellent job in looking after. I still had some off-and-on issues with our electronic washing machine, the motion sensor light on the shed and some Google home devices. I then moved from the EndFed to a vertical antenna the Hustler 4BTV antenna. In the manual for the 4BTV, it is advised if you have any RFI issues due to the coax radiating RF place an isolation balun at the antenna. It seemed as time passed I was issue free.
Drainage holes 1/16th
Now and then I started to notice while operating my Icom 7610 in CW mode I would have my N1MM contest program lock up. There was no rhyme or reason as to when this happened, what power level and what band I was on. I could make it through a CWops mini-test of an hour with no issues. The next CWops mini contest I had nothing but issues. I also noticed when using my VPN on the PC I would have the VPN disconnect and then reconnect messages coming up as I transmitted. I was reading online when coax radiates RF it can be very hit-and-miss as to when it happens and what is affected each time. This sounded like the issue I was having and I decided to place the isolation balun at the base of the 4BTV vertical.
I had to take into consideration some precautions when putting the isolation balun outdoors. It was recommended to drill 2 1/16 holes in the bottom so any condensation would not build up inside. Also around all PL-259 connections, I waterproofed them with self-amalgamating tape.
|20m without balun|
14.100 to cover the CW and digi section of the band. The local time was in around 22:37 and without Balun Designs 1:1 balun installed the section of 20m from 14.000 to 14.100 showed some what I called washout sections. I did notice around the 14.040 mark there is some RFI on the waterfall. When I moved the VFO over to that section the RFI was very faint. Also a very faint indication of RFI on the waterfall just past the
|20m with balun|
When the 1:1 balun was introduced the band cleaned up regarding the washed out sections. I was able to see digi signals, in the posted picture the digi signals are almost gone from the waterfall. There was some CW signals close to the noise floor that I was able to hear (not shown in the picture). I did notice the RFI what was in the waterfall without the balun installed is gone BUT after the balun was installed at 14.080 there was a stronger RFI signal and I could hear it very well when tuned to it. This RFI was not there all the time I would say it was on and off. Not sure what it is but that is not the purpose of this post.....save that for another post.
|20m RFI without balun|
|20m RFI with balun|
|30m without balun.|
Because it was later in the evening 40m seemed to really shine when I preformed the comparison with and without the balun installed. The span on 40m was 7.000 to 7.100. Without the balun there was some CW signals as well as some digi signals that I noticed. I was pleased with what I saw until I placed the balun in the picture. This cleared up the band and I was able to see more CW signals and the digi section was much more pronounced. I also noticed according to the S-meter with the balun was in around S-4 and without just over S-5.
I am very pleased how the balun has improved the reception end of things.
|30m with balun|
|30m digi signal with something to the right?|
|40m without balun|
|40m with balun|
I can hardly believe that 2 years exactly has passed where I hosted an erecting party, to install my new mast, antenna and rotator. The first year of the antenna was perfect I was able to find the DX weak signals pick them out and get heard over the majority of the European pileups. I had a great deal of fun. The antenna remained unchanged in that first year.
But suddenly over a period of 3 months I found the SWR was changing, and the antenna was becoming more and more deaf on 20m. Something clearly had changed on the antenna. My initial thoughts were water ingress in the Balun. I never really trusted the balun and found the construction of it crude. But in fact the balun was fine. I did however find that every clamp, bracket and connection on the antenna extremely corroded. “dissimilar metals” was the culprit.
A huge strip down clean and reassemble job was needed. And so this was completed with the antenna still in place, and although better the antenna still isn’t quite right. It really does need bringing down to earth and cleaning thoroughly and wrapping up in self amalgamating tape.
So 2 years on. What do I think ? the antenna is excellent. But do look closely at the spreader arms, clips and any screw terminal. You may need to buy some new hardware in order to achieve a compatible metal. Have a look at the chart below. For a cross match on metals used to clamp the antenna up. As a guide I had a stainless steel screw, brass washers, clamping an aluminum ring clip. Not a great combination.
Also make sure the clear acrylic tubes do indeed have a place for water to drain from. 2 of mine do not and I have the bottom bracket nearly half full of water at any given time.
Welcome once again to the Wonderful World of Linux in the Ham Shack. As indicated in the title, this episode is full of Sheer Hamshackedness. If you’re unsure what that is, we encourage you to pour yourself a nice glass of dark beer or a 100-proof spirit of your choice, put on your headphones and immerse yourself in the pure hedonism that is LHS. And if you believe any of that, we have a large vehicular conveyance over the East River in New York City up for sale as well. Anyway, we talk a little bit about Raspberry Pi computing, APRS, WSPR, Echolink, svxlink, Qtel and a bunch of other stuff in this episode. Hope you enjoy, as always.
73 de The LHS Guys