Antennas

Discussion in 'General Chat' started by skier, Feb 6, 2021.

  1. -mjk-

    -mjk- Moderator Staff Member

    Joined:
    Oct 2018
    Messages:
    2,382
    Likes:
    1,425
    From:
    Hukou Township, Hsinchu County, Taiwan
    Gear:
    DP-32, | 2A Mixer, A3440
    Yes, that's a good example. Being able to add them on cables can be a live saver.
  2. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    Hey you two! Is this on topic? And MJK, shouldn't you be sleeping??? Just sayin...

    Good for you Peter! Ask away!

    I'll just add to MJ's response that there's an aspect of "balance" with antennas, just as with audio. Some antennas, such as a dipole, are fed in the center. Such an antenna is really just two elements, whether copper wire, or copper or aluminum tubing, fed at their center point with the result that the antenna is the combination of those two elements and it radiates all the power.

    However, if the antenna is instead fed from an end, the other element might be created by connecting the coax shield to ground. In this case, not only the aforementioned elements are the antenna, but also the feed line from the radio to the antenna and the other devices connected between them (an antenna tuner to match the impedance, a possible amplifier to increase the power, etc.) So, the entire group of connected equipment in the station plus the feed line also become part of the antenna system. The problem with this is that, at the higher power levels, it often results with high voltages on the surfaces of the equipment cases in the station and can cause burns to our fingers - truly no joy! To avoid these nasty occurrences, a Ham will implement a choke by winding up from 4 - 12 loops of the feed line into the coils or add the ferrite snap-on chokes onto the outsides of the coax (as explained by MJ). This choke is implemented at some place in the feed line. It can be at the antenna or at some intermediate point. Such an intermediate point is usually where the coax, which is unbalanced (just like a 2 conductor audio cable with a center lead and a shield) transitions to a balanced line (like a 3 conductor cable with + and - conductors within a shield for a balanced mic input). There are many ways to match impedance and transition between unbalanced and balanced signals from transformers and different types of inductors to clever matching networks based on the wavelength.

    But there's something really important for you to keep in mind: The similarities between audio and radio are great. You already have knowledge that makes it easier to learn and understand how radio works and understanding one definitely helps in understanding the other. The distinctions are primarily the result of how the higher frequencies of radio behave differently than the low frequencies of audio and electric power ( at 50 or 60 Hz).

    I'm sorry for being long-winded; I hope the foregoing is more elucidating than confusing.
    Last edited: Feb 23, 2021
    -mjk- likes this.
  3. Peter Batah

    Peter Batah Well-Known Member

    Joined:
    Feb 2017
    Messages:
    1,027
    Likes:
    476
    From:
    Montreal, Canada
    Gear:
    DM4800 / MU1000
    skier and -mjk- like this.
  4. -mjk-

    -mjk- Moderator Staff Member

    Joined:
    Oct 2018
    Messages:
    2,382
    Likes:
    1,425
    From:
    Hukou Township, Hsinchu County, Taiwan
    Gear:
    DP-32, | 2A Mixer, A3440
    1. I moved those spurious posts.
    2. I dislike sleep. Such as waste of valuable time.
    3. And yes, everything is my fault. I take full (ir)responsibility.
    Peter Batah and skier like this.
  5. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    HA!

    1. I moved those spurious posts.

    Good! I want Arjan to be proud of me setting this straight.


    2. I dislike sleep. Such as waste of valuable time.

    I cannot disagree; unfortunately, I need my beauty sleep to perform even minimally.


    3. And yes, everything is my fault. I take full (ir)responsibility.

    Man, you must be the perfect husband! That is exactly what many a wife wants to hear. (Though, Arjan could nick me for following your errant post within Peter's "New PC Build" topic... maybe he won't notice. :rolleyes: )
    -mjk- and Peter Batah like this.
  6. -mjk-

    -mjk- Moderator Staff Member

    Joined:
    Oct 2018
    Messages:
    2,382
    Likes:
    1,425
    From:
    Hukou Township, Hsinchu County, Taiwan
    Gear:
    DP-32, | 2A Mixer, A3440
    I am. It's just that using the word "perfect" and "husband" together in the same paragraph is grammatically incorrect in Chinese.
    Peter Batah and skier like this.
  7. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    Man, your admitting everything is your fault likely means you are so much smarter than I more than anything else you've ever said. I just can't seem to resist the opportunity to tempt fate, and that could be my biggest weakness (out of the other few hundred, of course).
    -mjk- likes this.
  8. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    I love this response!
    Peter Batah likes this.
  9. Arjan P

    Arjan P Veteran

    Joined:
    Oct 2012
    Messages:
    1,414
    Likes:
    880
    From:
    Netherlands
    Gear:
    DM3200 IFFW
    You guys, what is going on here!? @skier: ofcourse I notice... :LOL:

    Now there's a neat antenna topic - removed from the original wrong place of Peter's new PC build - and here we are again with posts about being perfect and a husband at the same time? I give up... :cry:
    Peter Batah and skier like this.
  10. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    BUSTED! :oops:
    Arjan P likes this.
  11. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    upload_2021-3-8_22-8-1.png

    I thought members following this thread might enjoy seeing this ATU so large that you walk into it. I don't know for which station this unit serves, but it broadcasts a 250KW signal. The inductors and tank capacitors are some of the largest I've ever seen. The copper ceilings indicate that this room is a true Faraday cage.
    Peter Batah, Arjan P and -mjk- like this.
  12. -mjk-

    -mjk- Moderator Staff Member

    Joined:
    Oct 2018
    Messages:
    2,382
    Likes:
    1,425
    From:
    Hukou Township, Hsinchu County, Taiwan
    Gear:
    DP-32, | 2A Mixer, A3440
    If you don't know what you're doing, that ATU is a Death Chamber for certain.
  13. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    Absolutely no doubt about that. I presume that no one would ever go in there while the transmitter is powered, would they?

    There is an interesting video (well, at least to us nerds) of a 250KW Voice of America station in California which was dismantled and moved to the Antique Wireless Association museum in New York. I'm wondering whether or not the photo I posted is of that station - I don't believe there are very many 250KW AM transmitters; aren't they capped at 50KW? Regardless, I found it fascinating to see gear that big and how they cleverly solved problems, such as impedance matching, at this scale. Here's a link to that video:



    There were several signs posted telling all personnel to stay out of such spaces when the system was energized - if it's not the same one, I'm sure that is also true for the station ATU that I posted.

    Just wait until you see the curtain antenna system - I've never seen anything that large. It reminded me in a way of the massive Duga radar receiving antenna outside Mykolaiv in Ukraine. They're different, but so very large:

    Peter Batah and Arjan P like this.
  14. -mjk-

    -mjk- Moderator Staff Member

    Joined:
    Oct 2018
    Messages:
    2,382
    Likes:
    1,425
    From:
    Hukou Township, Hsinchu County, Taiwan
    Gear:
    DP-32, | 2A Mixer, A3440
    I'm so glad they turned that woodpecker off! That really used to mess me up on the 20m CW bands!

    I'm still an avid SWL (Short Wave Listener) and I have a white Sangean ATS909X, which is a local Taiwan brand radio. VOA is still on the air and quite listenable here in Taiwan. I have a flat roof and I made an SWL wire antenna. It works quite well.

    On a side note, during my last trip to Thailand in January/February 2020, I brought my SW radio with me. I was listening to the BBC and there were a couple of interesting segments on the (then) emerging pandemic. That broadcast showed just how much information was already known but being suppressed. I used my phone and recorded 2 short videos in which you can clearly hear the discussion.

    Re: the above ATU (Antenna Tuning Unit): the coils look kinda small, which makes me think it's HF, not MW. As for going inside, that would depend upon the radiation level. Back when I first started working in radio, we were left to our own discretion. Then the US FCC made guidelines and we had to measure the radiation field and put red lines on the floor in our facilities (like in front of the dinosaur cage in Fallen Kingdom, lol). After that, it would be illegal for a person to be in the red zone with the power on. That being said I've been inside some of the larger ATUs when they were hot, anywhere from 10kW to 50kW. I usually keep my hands in my pockets and remove them one at a time to do anything.

    Either here or perhaps another thread, but I have some cool stories on repairs I've been involved with related to ATUs and transmission lines.

    Thanks for posting those videos and photo Jerry.

    And yes, the domestic broadcast power limit in the USA is 50kW. Boston has several so-called "clear channel" 50kW stations. One of them, WBZ is actually directional because they are on the water. They basically do something of a "figure 8" and Grady told me that at night they are loud like a local in Miami.

    I've done a couple of published DX tests on several radio stations in the Boston area. Sometimes, with a new station buildout, I'd recommend doing a DX test and the owner would immediately jump on the idea. They always seemed really keen on knowing what would happen at night on full power.
    Arjan P and skier like this.
  15. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    That's very interesting, MJ! I find your stories fascinating, especially the one of DXing on the tower when it was off the air. I had always wondered about doing things like that, but not being in the field, I never knew.
    -mjk- likes this.
  16. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    Where were you living when the Duga system was interfering with your communications? I'm especially interested in knowing that because I'm curious as to the system's range. I do know it put out 10MW between 7MHz - 19MHz. That doesn't actually sound like a radar signal because those are long wavelengths - they couldn't have provided much resolution on the target at those low frequencies.
  17. -mjk-

    -mjk- Moderator Staff Member

    Joined:
    Oct 2018
    Messages:
    2,382
    Likes:
    1,425
    From:
    Hukou Township, Hsinchu County, Taiwan
    Gear:
    DP-32, | 2A Mixer, A3440
    Boston's north shore area. That thing was loud man. Sometimes it obliterated a section of the band.

    Remember, the woodpecker is an OTH radar system, so it has to propagate much differently than a high resolution, high frequency system. The resolution isn't great but it would give you an idea what was happening beyond the horizon. That's the nature of early warning systems (as you well know). So, it would put the high res systems on alert so they would be pointing in the proper direction to pick up a threat just as it came into line-of-sight range.

    ---
    Here are those shortwave videos I mentioned:

    https://photos.app.goo.gl/ptPtXs12ByRJvb5e8

    After listening to these broadcasts, I think the value of listening to shortwave broadcasts will be well made. These were recorded on January 25, 2020.
    Last edited: Mar 10, 2021
    skier likes this.
  18. -mjk-

    -mjk- Moderator Staff Member

    Joined:
    Oct 2018
    Messages:
    2,382
    Likes:
    1,425
    From:
    Hukou Township, Hsinchu County, Taiwan
    Gear:
    DP-32, | 2A Mixer, A3440
    I also have some fox hunt stories too. I really loved doing those. The best fox I ever heard of was created by John, WN9T and coincidently, it was done on the old WILD transmitter site property.
    skier likes this.
  19. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    I tried both of your videos, but they won't play; not sure why.

    Yes! I want to participate in some fox hunts. It's one of the reasons I'm getting a 2m radio. I went with my dad on CB fox hunts when I was 11 or 12. On those hunts, they were always at night and all the participants would meet at this diner and throw $2 into the pot (only the biggest finances for us). The person playing the fox would then go out in his/her car, had 30 minutes to find a place to hide and would call in when ready. The rules were that they had to leave their parking lights on and would broadcast their call sign every 5 minutes. The rest of us had to find them with only our knowledge of the area and the CB radio S-meter reading. A hunt generally took about an hour, and once found, the fox would announce the hunt was over, the winner's name, and we'd all go back to the diner for a cup of coffee and a piece of pie while the winner claimed the pot, the next fox went out to hide, and the remaining participants put two more dollars into the pot. While waiting for the fox to be ready, everyone would be telling stories of where they'd searched, what they were thinking, and where might the current fox be going (though the latter was often intentional mis-direction to the others). After the 2nd fox was found, it was back to the diner for more coffee and to say goodbyes. As simple as that all sounds, I loved those hunts and everyone seemed to really enjoy it.

    While th hunts were actually borrowed from Hams who actually started those games, the Hams played differently and I think, had much more fun. They covered a much larger area and used radio direction finding equipment they'd designed and cobbled together themselves to find the fox - I love the technology component! I joined a fox hunt forum about 6 months ago and haven't participated yet because I don't have a 2m mobile and with Covid, haven't really met many other Hams except on line. Also, we've all been isolating and not joining other families in their vehicles. In addition, the foxes used today are all automatic and placed into the field by the builder who announces that "the foxes are on the loose" on the forum. They are all supposed to be within a 500 foot easy walk from a parking area. They can be in the forest, but must be by a trail. They're always hidden in difficult places and well camouflaged based on the reports I've read. Sometimes they're in a tree or a hollow in a tree. At other times, they're under some brush, but must be able to be seen from some angle a searcher can reach using a trail. The impression I get is that these foxes are not easy to find even when the builder follows all of these rules. I'm excited to try my hand at it and I'd like to go with another Ham to get a feeling for their technique, the RDF gear they're using, etc. It all sounds pretty sophisticated and fun.
    -mjk- likes this.
  20. skier

    skier Well-Known Member

    Joined:
    Jun 2016
    Messages:
    528
    Likes:
    476
    From:
    Connecticut, USA
    Gear:
    Tascam DM4800, PT 12
    @-mjk- in looking at the video URLs, they request images rather than videos.