Re: BL1 Balun
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Joe, AA4NN, posted:
"With K2/100 100w out after two QSOs on 40m overall about 40 minutes the BL1 balun is quite hot to the touch. This is the first time I have used the BL1 with a CF Zepp. Amazing SWR 1:1 80m-10m, works great. I'm thinking I might need to glue a heat sink on that toroid. Anybody done this or am I too much QRO and heat is normal. hi" I have used the BL-1 at both QRP and 100 watt levels on a couple of ladder-line fed doublets designed for multi-band operation. If you are using the ATU, the 1:1 SWR you are observing is what the K2 is "seeing" courtesy of the tuner. The actual SWR presented to the balun may be very high. The heat you observed from your balun is wasted RF. My BL-1 has quickly heated, then saturated, using 100 watts into both 265' and 176' doublets on 160, 80, and 40 meters. It is fascinating, although dismaying, to see the SWR LEDs on the ATU rise from green (low SWR) to red (high SWR) in a matter of seconds as saturation occurs. I'll continue to use the BL-1 at QRP levels but will "wind my own" more robust balun for QRO operation. 73 Todd N9NE _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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The losses may be no different at lower power levels. It's quite possible
that if you're throwing away 10 dB at 100 watts, you're throwing away 10 dB at 100 mw. It's just that the core doesn't heat enough to notice at lower power levels. The only way to be sure is to actually measure the losses under the conditions the balun is 'seeing' in that antenna setup and at that frequency. That's not easy to do. That's why it's so hard to evaluate the efficiency of systems using baluns. Ron AC7AC -----Original Message----- I have used the BL-1 at both QRP and 100 watt levels on a couple of ladder-line fed doublets designed for multi-band operation... My BL-1 has quickly heated, then saturated, using 100 watts into both 265' and 176' doublets on 160, 80, and 40 meters. It is fascinating, although dismaying, to see the SWR LEDs on the ATU rise from green (low SWR) to red (high SWR) in a matter of seconds as saturation occurs. I'll continue to use the BL-1 at QRP levels but will "wind my own" more robust balun for QRO operation. 73 Todd N9NE _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Todd Fonstad
Joe, Todd, Group,
It's time for me to get on my soap box again. The BL1 is a great balun, I haven't seen a better one on the market so the answer is not to find a better one, you can't. It should take 100 watts and not overheat, even when running into a SWR of 10:1, provided its load impedance is not too high. What is happening when the balun heats up is that you are did consider the impedance of its place in the feed line, and it is too high for the balun. Actually, the impedance on the open wire feed line varies from near zero to several thousand ohms in the distance of a 1/4 wave on the feed line. For example, take a full wave dipole on 40, 135' long, and feed it with open wire line. The impedance at 1/4 wavelength from the antenna is near zero. Go another 1/4 wavelength along the feed line, and it is several thousand ohms, an impossible situation for any balun. So you need to cut a length off the feed line, in this case on the order of 8', and your impedance will be somewhere in-between. A balun will work there but will not work when the impedance is several thousand ohms. Remember, the impedance of the feed line repeats itself every 180 degrees, or 1/2 wavelength. Just because you are using a 450 ohm line doesn't mean the impedance is 450 ohms, It depends upon the load at the antenna end and its length. 4:1 baluns will work into a SWR of up to 10:1, provided the impedance and voltage is not high. For that matter so will a 1:1 balun. Moving along the feed line changes the voltage and impedance, but does not change the SWR. How do you tell what the losses in a balun are? On the BL1, and other small balun kits, feel the wires after you have been operating a few minutes. If the balun feels hot or even warm to the touch, it is dissipating too much power, and you need to change the position in the feed line where you place it. A good balun will run about 94% efficient into a 7:1 SWR (my measurements) provided the impedance is not too high. Losses of 6% at 100 watts will not melt the balun. At a SWR of 1:1 the losses are half that, so a balun is not lossless, but manageable. How do you cut the feed line? There's a table on page 17 of Practical Wire Antennas, by John D Heys G3BDQ available from the ARRL, that shows lengths of 1/2 the antenna length plus feed line to avoid. My experience is that when you avoid these lengths, you can use a balun. It will amaze you :-) 73, Chas, W1CG At 02:20 PM 10/12/2004, Todd Fonstad wrote: >Joe, AA4NN, posted: > >"With K2/100 100w out after two QSOs on 40m overall about 40 minutes the >BL1 balun is quite hot to the touch. This is the first time I have used >the BL1 >with a CF Zepp. Amazing SWR 1:1 80m-10m, works great. I'm thinking I >might need to glue a heat sink on that toroid. Anybody done this or am I >too much >QRO and heat is normal. hi" > >I have used the BL-1 at both QRP and 100 watt levels on a couple >of ladder-line fed doublets designed for multi-band operation. If you are >using the ATU, the 1:1 SWR you are observing is what the K2 is "seeing" >courtesy of the tuner. The actual SWR presented to the balun may be very >high. The heat you observed from your balun is wasted RF. My BL-1 has >quickly heated, then saturated, using 100 watts into both 265' and 176' >doublets on 160, 80, and 40 meters. It is fascinating, although dismaying, >to see the SWR LEDs on the ATU rise from green (low SWR) to red (high SWR) >in a matter of seconds as saturation occurs. I'll continue to use the BL-1 >at QRP levels but will "wind my own" more robust balun for QRO operation. > >73 >Todd >N9NE >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): >http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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