Am I doin' it right?

Discussion in 'Becoming an Amateur Radio Operator/Upgrading Privi' started by KJ4RZZ, Feb 15, 2010.

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  1. K9ZMD

    K9ZMD Subscriber QRZ Page

    Your low inverted vee antenna will be detuned by proximity to the earth; the formula length may not be even close to resonance. Trouble is, without widely spaced SWR readings as a reference, you just don't know if your antenna is too long or too short. Granted, SWR apparently improved when you lopped 21 inches off; however, you still don't know if you should shorten, or lengthen the antenna to bring it to resonance. It is actually possible that you lopped off too much in the first place (overshooting resonance); if so, then further trimming will make it worse, not better.

    There is a way to get those reference points and, at the same time, square away the SWR function of your AT250. No calibration is needed as you change power (the AT250 manual sez) because it automatically calculates. I believe that :) , but also believe that any readings intended for comparison should all be taken at the same power level.

    BTW, just reminder that your antenna must be in its final intended position when you take the SWR readings (because changing its position relative to ground will change the SWR).

    Switch the tuner to OFF (which bypasses the tuning function), then manually select 28 MHz on the AT250 band switch and set the power meter to the 20 watt range. Dial in 28.005 at the low end of your CW authorization and LISTEN a while to be sure the frequency is not in use (BTW, doing all this at night all but eliminates the chance of interfering with someone else).

    With your transceiver in CW mode and the Power control at minimum, hold the key and adjust the Power control upward until the AT250 power meter reads 20 watts. Release the key. Switch your meter to SWR , then press the key again to read the SWR value. Write it down. Oh, oh - no key? Get a 1/4 inch phone plug, connect a short piece of lamp cord to it, and bare the wires at the other end of the lamp cord. Insert the plug into the key jack (back side of rig) and touch the bare wires together to simulate a key. You could, of course, connect a small on-off switch there instead just bare wires. Even a big switch would do.

    Next, dial up 28.250 in your CW authorization and repeat this process. I would expect the SWR reading to be different. Write it down.

    Now, dial in 28.495 and repeat this process. Write it down. You now have three widely-spaced readings that indicate how to bring your antenna to resonance on your desired frequency, 28.400 for example. Interpretation?

    (a) Do the SWR figures get progressively worse (larger ratio) as frequency increases? If so, your antenna is too long. Double back the wire at the end of each leg a little bit, say 4 inches. Wrap the doubled-back wire around the antenna wire. Take the SWR readings again.

    (b) Do the figures get progressively better (smaller ratio) as frequency increases? Then your antenna is too short. Just connect about 4 inches of wire onto the end of each leg (for simplicity, you can even let it just dangle beneath the insulator). Take the SWR readings again.

    (c) After making the length adjustment, retake your SWR readings. Repeat all of the above if needed. Once you see that your 28.250 SWR is the lowest of the 3 readings, it means that your antenna is now resonant within the band. You can take a few more SWR readings near (above and below) 28.250 to actually zero in on the lowest SWR. Once you find that frequency, adjust the length of your dipole legs just enough to shift resonance to 28.400. Or you can simply decide that anything less than 2:1 at 28.400 is good enough . . . and you would be right.

    If compulsive, however, you will keep adjusting until your lowest SWR reading is at 28.400. At that point, please stop fiddling with wires and begin operating. Because your antenna is now resonant (for all practical purposes) at your desired operating frequency, you can just leave the AT250 turned off.

    A word about identifying: Even though you are only putting an unmodulated carrier on the air to take your SWR readings, station identification is still required. Dilemma. You cannot transmit a voice ID in the CW portion of the band. Can you send your call sign in morse code by tapping those two bare wires together? Good enough. Identifying is easier when you're within your authorized SSB frequencies; just transmit the carrier to take your reading, then immediately switch to SSB and announce your call sign.

    I've given you the above ID procedure because it is what I would do if limited to technician class privileges. Someone else will likely chime in to say how wrong that is. Pay attention when they tell you the right way to do it, unless they tell you to just use AM mode to generate the carrier, then ID in AM voice. :eek: You and I both know that AM voice is not a technician class privilege anywhere on the 10 meter band.

    If someone should tell you that you (as a technician class licensee) cannot transmit an unmodulated carrier within your authorized SSB frequencies, then pay attention while they explain how you (or anyone else) could locate resonance without transmitting a carrier. They will, of course, offer to loan you their antenna analyzer so you can follow that procedure.

    Once you have that antenna analyzer, the whole job becomes incredibly easier for you (or anyone else) to accomplish. BTW, any chance you could buy or borrow one of those analyzers before you ever start taking all those SWR readings? :D 73

    Gary, K9ZMD/6
     
  2. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    K9ZMD, and and others, thanks for the help.

    I built a new antenna yesterday evening and I tuned it early this morning before the bands could open up. Yesterday I purchased probably the last remaining radio shack SWR meter in my area... it was to be sent back to radio shack as they are no longer going to carry them.

    I tested my antenna and the numbers confirmed what i see on my antenna tuner in bypass mode. The new antenna is all copper and marine grade pre-tinned RG8X (instead of thin aluminum wire and radio shack RG58) with an air choke of 8 turns on a 3" form. I admit, I just guessed at the choke size and turns.

    My SWR readings are 1.1:1 at 28.025 and 1.5:1 at 28.400. I could probably cut another 1/2" off of each end but I think I am close enough for now, I am not going to do any more tuning today as the band is opening up and I am listening. I will do final tuning tonight after the band closes up.

    I think the biggest problem I was having is just plain confusion about which mode to be in while tuning. Some told me to be in CW and key the mic, but this is an unmodulated carrier and nothing registers on my meters. I was not sure if I should key the mic or not. Thanks for the help. I have a home built key so keying my call sign was not an issue.

    Some pictures are below. Yes, the antenna is close to the house and some metal (the windows), but it's the best I can do for now. The white siding up on the top is not metal, it's plastic.

    [​IMG]

    [​IMG]

    [​IMG]

    73
     
  3. KE5FRF

    KE5FRF Ham Member QRZ Page

    "I think the biggest problem I was having is just plain confusion about which mode to be in while tuning. Some told me to be in CW and key the mic, but this is an unmodulated carrier and nothing registers on my meters. I was not sure if I should key the mic or not. Thanks for the help. I have a home built key so keying my call sign was not an issue."

    Unless your rig has a special function in the microphone, it will not key your rig in CW mode. You have to have a mono jack (or phono in the case of an electronic keyer) and a key or switch.

    But I do want to correct you on a small misconception.
    I highlighted in bold. Yes, CW (without being on/off keyed with a Morse character) IS in fact an unmodulated carrier...BUT THAT IS PRECISELY WHAT YOU WANT FOR AN ACCURATE FORWARD POWER AND SWR MEASUREMENT!

    For a SSB SWR measurement to be anywhere near accurate, you have to inject a steady tone of constant amplitude and duration into the AF stage of your rig. Yes, this will modulate the SSB transmitter, but it will simulate a CW signal by forcing the amplifier into continuous duty cycle, whereas the duty cycle of the amplifier in SSB with normal voice inflection is interrupted by the act of modulation.

    Often on 10 meters, you will hear spanish speaking stations in a monotone saying "HOOOOLA, HOOOOOOOOLA" as they tune up their rigs in SSB or AM. (Often they are CB (11 meter) pirates/freebanders encroaching on the CW portion of the band but thats another discussion) A steady voice works, and is typically what SSB ops do if they do not have CW capability or equipment...but it doesn't take the place of a pure, CW, unmodulated carrier.

    This might be a bit confusing, because it is easy to imagine that when you key up on SSB that you are transmitting a carrier...but that isn't the case. The carrier is suppressed and you are only transmitting a vestigal sideband.
     
  4. K0RGR

    K0RGR XML Subscriber QRZ Page

    You will also hear people whistle. Whenever I hear this, I have to ask if they have lost their dog.

    If you don't have a key, just wire a switch across a proper piug and put it in the key jack so you can generate CW. That rig has an AM function on it, too - that should give you enough carrier to check the antenna. Yes, as a Tech you can't transmit AM or FM, but you can transmit a carrier without any audio.
     
  5. K9ZMD

    K9ZMD Subscriber QRZ Page

    Tom,

    I like the way you work; it reminds me of K4GUN who asked a lot of good questions when he first got started only a few years ago. Now he is doing amazing stuff, and occasionally pops in here to visit. Wish it were more often, because he could give some good answers to the sort of questions he used to ask.
    Probably more like 1.3" off each end, but you can eliminate the "probably" with little math. That SWR reading of 1.1:1 at 28.025 MHz means your antenna is resonant about 1.32% low in frequency (if 28.400 MHz is, in fact, your target frequency). Measure the exact tip-to-tip length of wire in your dipole, expressed in inches. Multiply that figure by 0.0132 and the result will be exactly how many inches your dipole needs to be shortened to shift resonance up to 28.400 MHz. Wait though, because an SWR of 1.5:1 at 28.400 MHz is OK, especially since you've installed some lower-loss coax. However, if you want the learning experience, go ahead & trim half that calculated number of inches off each end of the dipole. Next, hoist the antenna back into position again, hold your breath, and retake the SWR readings. :p
    You do want to key the rig in CW, but with your key. Some rigs, but not all, can be programmed to send morse in CW mode by pressing certain mic buttons. Yours is apparently not programmed that way, so no carrier was transmitted at all when you keyed the mic. As Heath explained, you can only take a Power/SWR reading when a steady, unmodulated carrier is transmitted. Of course, it follows that simply keying the mic in SSB mode won't work for taking a Power/SWR reading either, because the carrier is suppressed.
    :) I love it. Folks, I think this fella is already behaving like a ham. 73

    Gary, K9ZMD/6

    Afterthought
    Tom, I belatedly :eek: got to thinking that maybe, just maybe, your 28.025 was a typo, and you really meant 28.250. If so, it just took me a little math to see that your "1/2" off of each end" was very accurate.
     
    Last edited: Feb 18, 2010
  6. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    Gary, there was a lot to quote in your reply so I am just going to leave it out, we all know how to scroll down :) First, thanks for the compliments, I appreciate it.

    Anyway, I figured out the issue with trying to tune with a CW carrier. My radio was set in SEMI mode, so even though the transmit light was on, it was not sending a carrier unless the key was pressed. The delay was also turned way down, so tapping the key would only send a carrier while the key was down. After a few moments of "duh" I flipped the CW mode switch to FULL, and now, when I press the mic or send button in CW mode, there is a carrier present and everything behaves as expected. When all else fails, read the cryptic poorly written manual a few more times with an open mind!

    Regarding the SWR, you gave me too much credit, I did not make a typo. Good thing, because I found your example very helpful.

    I never mind being wrong if I learn something from it :)


    Tom KJ4RZZ
     
  7. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    Good news :)

    Today I climbed about 30ft up and installed a new inverted V. I buried the coax so my wife wouldn't complain (the tree is in the middle of her turtle pen), and ran the coax into the shack. It was a bit noisy due to the proximity of the power lines, but the noise filter cleaned it up pretty well.

    I waited around for awhile, listening while doing some work, and then decided I would try a few calls before lunch. I picked a freq off of the main chatter, asked if it was in use (no answer) and started calling CQ... after about three calls, to my surprise I got a nice solid reply, AA6DD, and thus my first QSO! We chatted briefly and then moved off to another frequency with less noise and had a short chat about antennas, and I learned a bit about when 10 meter would start to improve, etc. Tested out both of my antennas, and tried transmitting with my tuner both on and off. The new antenna was just slightly better than the old one, tuner did not make much of a difference.

    Despite feeling a bit awkward, and forgetting to give my name, location, etc, until asked, this is an exciting moment for me because I have been trying almost every day to reach someone for the past two weeks. Fun!

    Below are a few pics of my new antenna placement.

    73
    KJ4RZZ

    [​IMG]

    [​IMG]

    [​IMG]
     
  8. KE5FRF

    KE5FRF Ham Member QRZ Page

    Wow! Good QSO for a first contact in the log. Doesn't get much better than California to Florida. Looks like today was an F2 opening, which means the MUF was high enough to support 28 MHz DX in certain parts of the world.

    Take a look at this map at this link (BTW!!! Bookmark DXSherlock, it is a GREAT tool for 10 meter and 6 meter enthusiasts) ;)

    http://www.vhfdx.net/spots/map.php?Lan=E&Frec=28&Map=W2L&mycall=&myloc=&freq=&prop=

    You see evidence here that there is NW to SE cross-equitorial opening. Probably some help for the F2 opening by some E layer propogation as well.

    Another map that indicates MUF

    http://www.windows.ucar.edu/spaceweather/quicklook7a.html

    Basically, you can imagine that probably starting around the Florida/California latitude, and you can kind of see it with the contour lines of the map, the F2 layer ionized densely enough today to reflect RF energy at and below 28 MHz. You may not typically see the MUF on these maps under current conditions get any higher than 21 MHz, and for a long time a 14 Mhz MUF was typical.

    Anywhere between the contours showing a 28, you should be able to work stations. In your case, the ionization was dense enough to support E-W propogation as well, probably single hop but possibly more.

    You should try to work DX. I understand that TX4T (French Polynesia DXpedition) has been spotted on 10 meters. From Florida, you have a lot of water between locations, but that might be a help!
     
  9. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    Great info, thanks this is the next part of my study and I am glad you brought it up. As for DX, I almost made a contact this morning with Argentina and yesterday Chile, seemed they could just barely hear me and not copy through the noise. Of course it may not have been me they heard either. I am happy with CA and a patient ham on the other end willing to chat for awhile. After all, it's just a wire in a tree and a small transceiver on my desk... fascinating really.

    I will have a good look at the site you linked!
     
    Last edited: Feb 19, 2010
  10. W4AIN

    W4AIN Ham Member QRZ Page

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    Last edited: Feb 19, 2010
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