How Is Powering An LNA Best Accomplished?

[prcguy]

You might check Ebay every day for a surplus Katherin/Scala channel 2 through 6 TV log periodic. These are used for mostly cable TV head ends and they are very heavy duty and beautifully made. Look for a model CL-26/HCM (really big!) or a smaller ch 2 through 4 version, model CL-24. See pages 67 through 70 in this catalog. https://www.kathreinusa.com/wp-content/uploads/2016/02/Broadcast-Catalog-Scala-Gold-2016.pdf

I have their big 88-108 FM broadcast log periodic and its really nice.

I placed my order for this antenna last week, I got a notice that it finally shipped on Monday. Today I got an email saying that his stock was incorrect and he has no more of this antenna so that avenue is now closed. I never heard from that Italian company, I don't know whats going on over there. I will have to keep search for a suitable antenna.

 

[Merovingian]

Okay, thanks. eBay was my next stop, for what I didn't know but you gave me a place to start. Thanks.

You might check Ebay every day for a surplus Katherin/Scala channel 2 through 6 TV log periodic. These are used for mostly cable TV head ends and they are very heavy duty and beautifully made. Look for a model CL-26/HCM (really big!) or a smaller ch 2 through 4 version, model CL-24. See pages 67 through 70 in this catalog. https://www.kathreinusa.com/wp-content/uploads/2016/02/Broadcast-Catalog-Scala-Gold-2016.pdf

I have their big 88-108 FM broadcast log periodic and its really nice.

 

[Ubbe]

eBay was my next stop

Also try Amazon as sometimes they only sell thru them or they use both but at Amazon they have for some reason set a lower price and the shipping cost are often lower, at least for european business like antennas from Italy to other european countries. I have bought most of my antennas from Italy as it's lower prices than locally and the shipping cost turns out to be much lower shipping a 3000km distance instead of locally 200km.

/Ubbe

 

[Merovingian]

Okay, I will look there as well. Thanks

Also try Amazon as sometimes they only sell thru them or they use both but at Amazon they have for some reason set a lower price and the shipping cost are often lower, at least for european business like antennas from Italy to other european countries. I have bought most of my antennas from Italy as it's lower prices than locally and the shipping cost turns out to be much lower shipping a 3000km distance instead of locally 200km.

/Ubbe

 

[prcguy]

This antenna has been around a long time and works well, although the gain figures are probably inflated and it has more frequency coverage than you need. They are always available somewhere within the US and sometimes come up used for better pricing.

50-1300MHz Wideband Log Periodic Receive & Transmit Antenna Create CLP-5130-1N | eBay

Find many great new & used options and get the best deals for 50-1300MHz Wideband Log Periodic Receive & Transmit Antenna Create CLP-5130-1N at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[Merovingian]

Thanks! I'll look into it. I never realized finding a good antenna was so hard. At some point I may have to look into building my own or something. . .

This antenna has been around a long time and works well, although the gain figures are probably inflated and it has more frequency coverage than you need. They are always available somewhere within the US and sometimes come up used for better pricing.

50-1300MHz Wideband Log Periodic Receive & Transmit Antenna Create CLP-5130-1N | eBay

Find many great new & used options and get the best deals for 50-1300MHz Wideband Log Periodic Receive & Transmit Antenna Create CLP-5130-1N at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[Ubbe]

The CLP-5130 have a 7dBi gain. http://www.reeve.com/Documents/Articles Papers/Reeve_LogPeriodicAntennaModel.pdf
It's an expensive antenna and I would try to build my own from a $20 logperiodic TV antenna. Use an online calculator to get the kind of frequency range you want and the gain that will fit the boom lenght and rearrange the elements. The more gain the more narrow the loob will be with a higher directivity.

Some of the LP TV antennas are dual band, 175-220Mhz and 470-700Mhz. It's 1/2 wave dipoles with a reflector behind and one or two directors in front of it that resonates and have the proper lenghts from the antennas front. You measure a LP antenna from the front where the coax attaches. First calculate the highest frequency band and maybe use 1/3 of the boom lenght in the calculator. The gain are set by the number of elements and at lower frequencies it will need more space on the boom.

Calculate the lower band and adjust the calculators value for the highest frequency in that band so that the free positions on the 2/3 of the boom will start with the highest frequency 1/2 wavelenght dipole for the lower band + one or two director elements.

/Ubbe

 

[Merovingian]

Interesting paper, thanks for the link. I have been doing some reading a researching to try to determine whether or not I want to try to build my own antenna. I downloaded 4NEC2 because it supposedly has a CAD type interface to be able to draw the antenna elements but so far I have not been able to do that, I was hoping for a far more intuitive interface, I guess I don't understand the program yet. . .

I will look for a TV antenna but modifying one may be more trouble than it is worth for me. I only need a 2, 3 or 4 element antenna, I don't want a high gain with a narrow radiation pattern but at the same time that type of antenna won't offer the frequency range I also want.

The CLP-5130 have a 7dBi gain. http://www.reeve.com/Documents/Articles Papers/Reeve_LogPeriodicAntennaModel.pdf
It's an expensive antenna and I would try to build my own from a $20 logperiodic TV antenna. Use an online calculator to get the kind of frequency range you want and the gain that will fit the boom lenght and rearrange the elements. The more gain the more narrow the loob will be with a higher directivity.

Some of the LP TV antennas are dual band, 175-220Mhz and 470-700Mhz. It's 1/2 wave dipoles with a reflector behind and one or two directors in front of it that resonates and have the proper lenghts from the antennas front. You measure a LP antenna from the front where the coax attaches. First calculate the highest frequency band and maybe use 1/3 of the boom lenght in the calculator. The gain are set by the number of elements and at lower frequencies it will need more space on the boom.

Calculate the lower band and adjust the calculators value for the highest frequency in that band so that the free positions on the 2/3 of the boom will start with the highest frequency 1/2 wavelenght dipole for the lower band + one or two director elements.

/Ubbe

 

[Merovingian]

How about a common mode choke? If I were to use one at the receiver and another at the antenna would it matter where I put the choke? At the antenna I was thinking it would be better to insert the choke up the coax before the DC is extracted to power the preamp. Or is it better insert right at the antenna connection before the received signal goes through any filters and preamp?

Thanks

Always put the filter before the preamp, never put the preamp before the filter. The only exception to this is if you are not going to connect an atnena to the preamp and filter like on a test bench for sweeping or testing. Or you need to generate some IMD to play with.

The statements about not generating IMD unless you get to -20dBm are not true and a PGA103+ amplifier or most low level preamps with a bunch of signals off an antenna at a much lower level will generate lots of IMD that you will hear on your receiver. It might be distinct transmissions you will hear that don't belong on the frequency you hear them on or typically it will be a higher noise floor from hundreds or more frequencies mixing into a sea of low level IMD that looks like noise.

 

[prcguy]

There might be a few reasons to use a common mode choke or not depending on the antenna and your surroundings. One thing it can do is isolate the feedline from the coax and this can sometimes improve the radiation pattern of the antenna. It can also reduce noise from traveling on the coax shield from getting to the antenna and sometimes its better to have the choke near the radio end but after any cables or equipment that can induce noise onto the coax.

I've seen a big improvement in noise reduction on HF placing a choke near the antenna and a smaller improvement placing another one near the radio. I never measured just the one at the radio end without one at the antenna end, probably because I'm too lazy to remove the one up on the antenna.

How about a common mode choke? If I were to use one at the receiver and another at the antenna would it matter where I put the choke? At the antenna I was thinking it would be better to insert the choke up the coax before the DC is extracted to power the preamp. Or is it better insert right at the antenna connection before the received signal goes through any filters and preamp?

Thanks

 

[Merovingian]

Yes, my thinking was to reduce the noise traveling on the coax. I was planning to one at each end, I've seen YouTube videos where putting one at each end reduced any noise the most. With a bias tee at each end to power the pre amp I would put the choke after the output of the bias tee inside but does it matter where it is put at the antenna end? I was thinking just before the bias tee at the antenna end?

There might be a few reasons to use a common mode choke or not depending on the antenna and your surroundings. One thing it can do is isolate the feedline from the coax and this can sometimes improve the radiation pattern of the antenna. It can also reduce noise from traveling on the coax shield from getting to the antenna and sometimes its better to have the choke near the radio end but after any cables or equipment that can induce noise onto the coax.

I've seen a big improvement in noise reduction on HF placing a choke near the antenna and a smaller improvement placing another one near the radio. I never measured just the one at the radio end without one at the antenna end, probably because I'm too lazy to remove the one up on the antenna.

 

[Ubbe]

A ferrite choke works best where the interfering signals wavelenght are at a voltage maximum, at each 1/2 wave.

If you listen to a 430MHz frequency, the 70cm band, and you would like to choke out any interferencies riding on the coax, it will often be unpractical to install at choke directly at the antenna elements. You probably have a balun and no place to put a choke close enough. So then it should be a 1/2 wave, 35cm, from the antenna elements. The usual method are to use enough ferrite chokes so they will cover a 1/2 wavelenght from the antenna for most frequencies you are monitoring.

The antenna are open to all interferencies but the receiver are usually in a metalbox with shielding cans over the sensitive parts and putting chokes there on the coax have usually no effect.

/Ubbe

 

[Merovingian]

Okay, thanks!

A ferrite choke works best where the interfering signals wavelenght are at a voltage maximum, at each 1/2 wave.

If you listen to a 430MHz frequency, the 70cm band, and you would like to choke out any interferencies riding on the coax, it will often be unpractical to install at choke directly at the antenna elements. You probably have a balun and no place to put a choke close enough. So then it should be a 1/2 wave, 35cm, from the antenna elements. The usual method are to use enough ferrite chokes so they will cover a 1/2 wavelenght from the antenna for most frequencies you are monitoring.

The antenna are open to all interferencies but the receiver are usually in a metalbox with shielding cans over the sensitive parts and putting chokes there on the coax have usually no effect.

/Ubbe