Using K2 rant input
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I am experimenting with using the K2 rant input (that's receiver antenna, not
verbal outburst). I want to use my 20-meter quad as a receiving antenna when I am transmitting on 160 with an inverted L. It is a lot quieter. The L is right next to the quad, so a lot of voltage is induced in the quad when transmitting with high power. I tried putting a couple of back-to-back diodes and a 50-ohm resistor across the quad feedline. I put my scope across it and found that the signals from BC stations, etc. were well below the clipping level of the diodes, and received signals were plenty strong with the K2 preamp on. So far so good. Transmitting resulted in the clipping level being reached with about 100 watts output (I have an external amplifier capable of 1500 watts). All of a sudden, I realized that I have built a huge harmonic QRM generator! If I use this setup, as soon as the diodes clip they will generate harmonics all the way up into VHF, which will be re-radiated by the quad (it will do a real good job on the 4th harmonic, near 20 meters, too). Am I right? If so, this isn't a good way to do what I want. Does anyone know a) how much RF voltage can be safely applied to the K2 rant input when transmitting, or b) how to protect the input without making harmonics? I thought of using the diodes after a lowpass filter that cuts off around 2.5 MHz, but this is getting complicated. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ 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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Hi Vic,
Have you thought of just switching the rx antenna out of circuit whilst transmitting? Unless you are using fast break-in, a small externally switched relay should solve your problem. If you are feeling particularly paranoid:-), then use the same relay to earth the rx input via a 50 ohm resistor at the same time. gl, Trev G3ZYY In message <[hidden email]>, Vic Rosenthal <[hidden email]> writes >I am experimenting with using the K2 rant input (that's receiver >antenna, not verbal outburst). > >I want to use my 20-meter quad as a receiving antenna when I am >transmitting on 160 with an inverted L. It is a lot quieter. The L is >right next to the quad, so a lot of voltage is induced in the quad when >transmitting with high power. > >I tried putting a couple of back-to-back diodes and a 50-ohm resistor >across the quad feedline. I put my scope across it and found that the >signals from BC stations, etc. were well below the clipping level of >the diodes, and received signals were plenty strong with the K2 preamp >on. So far so good. > >Transmitting resulted in the clipping level being reached with about >100 watts output (I have an external amplifier capable of 1500 watts). > >All of a sudden, I realized that I have built a huge harmonic QRM >generator! If I use this setup, as soon as the diodes clip they will >generate harmonics all the way up into VHF, which will be re-radiated >by the quad (it will do a real good job on the 4th harmonic, near 20 >meters, too). > >Am I right? If so, this isn't a good way to do what I want. Does >anyone know a) how much RF voltage can be safely applied to the K2 rant >input when transmitting, or b) how to protect the input without making >harmonics? I thought of using the diodes after a lowpass filter that >cuts off around 2.5 MHz, but this is getting complicated. > -- Trevor Day UKSMG #217 www.uksmg.org _______________________________________________ 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 Vic K2VCO
Vic,
I don't have the full answer, but can offer this 'food for thought' -- The Rant input (when active) is connected to the output of the K2 T/R switch when in use, and when the Rant is not being used that point is subjected to the full output of the base K2 output collector RF voltage - so I would conclude that it should handle up to 15 watts of RF induced onto the Rant input jack, but OTOH, I have not tested it. 73, Don W3FPR > -----Original Message----- > > I am experimenting with using the K2 rant input (that's receiver > antenna, not > verbal outburst). > > ... > Am I right? If so, this isn't a good way to do what I want. > Does anyone know > a) how much RF voltage can be safely applied to the K2 rant input when > transmitting, or b) how to protect the input without making harmonics? I > thought of using the diodes after a lowpass filter that cuts off > around 2.5 MHz, > but this is getting complicated. > > -- > 73, > Vic, K2VCO > Fresno CA > http://www.qsl.net/k2vco > > _______________________________________________ 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 Vic K2VCO
On Feb 11, 2005, at 12:13 AM, Vic Rosenthal wrote: > I am experimenting with using the K2 rant input (that's receiver > antenna, not verbal outburst). > > I want to use my 20-meter quad as a receiving antenna when I am > transmitting on 160 with an inverted L. It is a lot quieter. The L > is right next to the quad, so a lot of voltage is induced in the quad > when transmitting with high power. Vic, I think you may be missing the point of using a separate receiving antenna on noisy bands like 160m. While the 20m quad may be quieter, that's likely due to the smaller size and gross impedance mis-match of the 20m antenna on 160m. The 20m quad is probably quieter for ALL signals and noise alike, which doesn't help. The key to using a separate receiving antenna on 160m is NOT just to have a quiet, lossy antenna -- but to have a quiet, lossy, DIRECTIONAL antenna. The idea is to improve the signal / noise ratio by limiting the noise intercepted at the antenna. Since noise is generally thought to come from all directions, using an directional antenna makes signals appear stronger. The Beverage antenna is probably the most popular receiving antenna in this service, but requires a lot of real estate. For 160m, a Beverage would be about 500 feet long. For those of us without room for such an antenna, the flag, pennant and K9AY loop are good substitutes. These antennas have a cardioid (heart-shaped) pattern, with a strong null in the opposite direction. Magnetic receiving loops area also useful, particularly for nulling out strong local noise sources. All of these receiving antennas should be mounted well away from the transmitting antenna, to avoid the type of coupling you're having trouble with now, as well as to avoid noise reception due to mutual coupling. Since these antennas are intentionally lossy, it usually doesn't take that much distance to avoid transmitter overload. Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email] Quote: "Not within a thousand years will man ever fly!" -- Wilbur Wright, 1901 _______________________________________________ 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 Don Wilhelm-3
W3FPR - Don Wilhelm wrote:
> I don't have the full answer, but can offer this 'food for thought' -- The > Rant input (when active) is connected to the output of the K2 T/R switch > when in use, and when the Rant is not being used that point is subjected to > the full output of the base K2 output collector RF voltage - so I would > conclude that it should handle up to 15 watts of RF induced onto the Rant > input jack, but OTOH, I have not tested it. I was just looking at the circuit and I think you're right. Let's see, 15 watts in 50 ohms comes out to about 27 volts. I can put a 47 ohm resistor across the antenna without significant signal loss, so the impedance cannot rise above that level under any circumstances. The t/r switch diodes will be cut off so there won't be harmonic generation from this source. Now I just need to measure the RF voltage with my scope and make sure that this level isn't exceeded (with plenty of safety factor!) -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ 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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