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Coax Upgrade or LNA-5000 Preamp?

Aegir

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May 11, 2018
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Location
Eugene, Oregon
Hello Everyone!

I'm going to make an upgrade. I'm going to add about 6 feet of height to my discone by attaching 6 feet of fiberglass mast on top of my current mast. The feed point of the discone will then be at almost 30 feet above ground level. Since the antenna will be taken down, now will be a good time to consider either:

1.) Replacing the 50 ft of LMR-400 with higher grade Coax
Or
2.) Adding an LNA-5000 mast mounted preamp.

My Whistler TRX-2 shares an antenna (Diamond D-3000 N wideband discone) with my IC-8600 via a Stridesberg Multicoupler, and I'm using a Par FM trap which works great on eliminating the interned from some local FM broadcasters.

It's been about 8 months since I've purchased my Whistler TRX-2. I've enjoyed using it in the shack. I'm not new to the radio hobby, but I'm new to scanning. I'm an Amateur Extra (N7BB), and an avid SWL Utility Monitor and AM BCB Dxer.

Experience tells me that upgrading the coax would be a wise addition, especially at UHF frequencies. Adding a preamp may introduce more intermodulation, especially since I'm using a multicoupler. I considered upgrading to a Create Log Periodic antenna, but that's an entirely different project involving a rotator and additional cost.

So, if you were me, and you had abut $200-$300 to spend, would you add a preamp or just upgrade the LMR-400? If so, and since it's only 50 feet, what grade of coax would you get?

I realize I'm also adding a bit of height at the same time. It's always wise to do one upgrade at a time to really notice improvements. But, I don't want to add height only take down the whole assembly AGAIN to make another upgrade. Any input is appreciated.

Attached is a photo of my shack - the whistler is mounted just below the IT-100 antenna tuner.

73
Bryne

IMG_2975.jpg
 

w2lie

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If it was me, I would invest in LMR-400 and then see if you need the preamp.

Where I am, on Long Island, a preamp caused more harm than good with my setup. I am in a pretty dense RF environment.

73
 

Ubbe

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I got a LNA-2000 and it's nothing special besides the high cost. Instead of a LNA-5000 you can get better performance at a lower cost from Gpiolabs. Ultra LNA 2GHz Gain>20dB PGA103 ESD Gain Stabilization USB cable PGA-103 NF .5dB | eBay
If you really need a 5GHz range you could look at the other offerings they have. Low noise figure and high OIP3 together with linearity are important and you get better specs at 10 times lesser cost if you get a naked amplifier and put in a box yourself.

Stridsberg multicouplers doesn't like high signal levels so you have to use a variable attenuator just in front of it and increase attenuation until you notice no degradation or overload issues. An amplifier is the best purchase you can do if you only intend to receive. It will also keep the impedance constant to the coax regardless of the antenna mismatch.

/Ubbe
 

Aegir

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Joined
May 11, 2018
Messages
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Location
Eugene, Oregon
If it was me, I would invest in LMR-400 and then see if you need the preamp.

Where I am, on Long Island, a preamp caused more harm than good with my setup. I am in a pretty dense RF environment.

73
Thank you for that. I currently run LMR-400 and was weighing the advantages of upgrading to LMR-600 or Heliax. I wonder if the “bang for the buck” factor is there. Only about 50-60 feet is what I use, and I’ve noticed that most coax stats are measured in per 100 ft for loss figures in db.
 

Aegir

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May 11, 2018
Messages
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Location
Eugene, Oregon
I got a LNA-2000 and it's nothing special besides the high cost. Instead of a LNA-5000 you can get better performance at a lower cost from Gpiolabs. Ultra LNA 2GHz Gain>20dB PGA103 ESD Gain Stabilization USB cable PGA-103 NF .5dB | eBay
If you really need a 5GHz range you could look at the other offerings they have. Low noise figure and high OIP3 together with linearity are important and you get better specs at 10 times lesser cost if you get a naked amplifier and put in a box yourself.

Stridsberg multicouplers doesn't like high signal levels so you have to use a variable attenuator just in front of it and increase attenuation until you notice no degradation or overload issues. An amplifier is the best purchase you can do if you only intend to receive. It will also keep the impedance constant to the coax regardless of the antenna mismatch.

/Ubbe
Interesting. I do happen to have a Heathkit variable step attenuator. I use it with wideband FM on my Icom 8600.
I will look at this amplifier.
Thank you!
 

N4DJC

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Anderson SC
You already have such a nice station set up, a significant improvement in antenna would be my choice. So log periodic...$$$
 

Ubbe

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I do happen to have a Heathkit variable step attenuator. I use it with wideband FM on my Icom 8600.
Interesting. Do you get the 8600 overloaded just from the discone and the Stridsberg? It doesn't seem to handle strong signals very well then?
Do your other receivers work better with FM Broadcast?

/Ubbe
 

Aegir

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Eugene, Oregon
You already have such a nice station set up, a significant improvement in antenna would be my choice. So log periodic...$$$
A vote for the log periodic! I can see the advantages- the beam width is pretty wide- I can always add a rotor later. Thanks for this.
 

Aegir

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Eugene, Oregon
Interesting. Do you get the 8600 overloaded just from the discone and the Stridsberg? It doesn't seem to handle strong signals very well then?
Do your other receivers work better with FM Broadcast?

/Ubbe
Oh no- I use a home made Yagi for FM - it’s a 6 element on a 7 ft boom. The disconne doesn’t overload on WFM. With the yagi at only 20 feet I can get FM in Portland at over 200 miles away.
 

Ubbe

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4 directors, one dipole and one reflector element would need a 10 foot boom at 100MHz but you managed to shrink it to 7 foot. It would usually give a 9dBd gain. How much do you need to attenuate to make the 8600 well behaved? People say it can handle strong signals in the shortwave band really good but I guess it's not an equally strong performer at VHF/UHF?

/Ubbe
 

Aegir

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Messages
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Eugene, Oregon
It’s a fantastic performer! We have quite a few local broadcasters in Eugene. The signal path to Portland is due north from my qth. I just so happen to point directly at the local classical station’s transmitter at 91.5 fm. I can point the yagi 20 degrees to the east, but then the back of the beam is pointed directly at Blanton heights which houses several local fm transmitters. The digital attenuators work, however, I have better luck with an analog step attenuator for WFM with the 8600.
Information on the antenna I built can be found here:


K6JRF Home Pics
I
 

Aegir

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May 11, 2018
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Eugene, Oregon
Correction on the boom length- the details and pic are in the post. I combined two stellar lab yagi antennas together.
 

kb6hlm

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A vote for the log periodic! I can see the advantages- the beam width is pretty wide- I can always add a rotor later. Thanks for this.
That's the right choice !

Its always a good idea to have both if you can I have a log periodic beam using LMR-400 with N connectors and it works wonders to get rid adjacent signals and bring in the signals I'm interested in

A preamp would only be a downgrade to that type of antenna! unless of course your using it for satellite/moon bonce/SSB work or something of that nature ?

I use mine in a vertical position and have not tried it horizontal yet however I use other mono band beams for those bands and a preamp works fine for that however I would not recommend it on a log periodic

Remember Antenna first then coax and maybe a preamp but only if you intend to use it for special purposes otherwise it actually downgrades your antenna !

To give you a idea of how well a yagi can work even at something only 15 miles away I have a mono band 6db gain vertical up at 35ft for aircraft frequency's that works fine however there are some frequency's that don't even exist on the vertical mainly because of some local noise we have around here however when I turn the beam towards the station transmitting WOW SIG S-5 plus and a lot less noise ! you see this would absolutely be impossible with a discone and even worse with a preamp !

Most of the time I run a dual band receiver for aircraft that way I can use both antennas at the same time

Another thing to consider is the antenna gain remember only 3db gain is twice your power ! so you could use a splitter if you like to however you will lose about 3db (half the signal) or more depending on frequency and how many times you split it

Anyway just one example to consider :)

BTW Beautiful shack ! it would be a crime to hook up anything less then LMR-400 with N connectors on the icom 8600 and my god man please avoid using spliters on that thing !
 
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Ubbe

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3dB at receive are not much loss if you look at -110dBm which is 0.7uV and 3dB down to -113dBm are 0.5uV and consider that if you have a signal strenght meter graded in S units that 3dB are a half of a S unit.

But remember that most logperiodic antennas you can buy that covers something like 100MHz-1500MHz only have 3 elements more or less active at one given frequency and the rest of the non resonating elements are metal that are in the way of the radiosignals. It gives you a 6dB gain at most in the direction it points.

A preamp are always an improvement at weak signal monitoring, but you have to know how to use it and it's not just a matter of buying one and install it and be done with it, that will be a sure recipe for disaster. Not many receivers can handle the full gain from a preamp.

/Ubbe
 

Aegir

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Location
Eugene, Oregon
That's the right choice !

Its always a good idea to have both if you can I have a log periodic beam using LMR-400 with N connectors and it works wonders to get rid adjacent signals and bring in the signals I'm interested in

A preamp would only be a downgrade to that type of antenna! unless of course your using it for satellite/moon bonce/SSB work or something of that nature ?

I use mine in a vertical position and have not tried it horizontal yet however I use other mono band beams for those bands and a preamp works fine for that however I would not recommend it on a log periodic

Remember Antenna first then coax and maybe a preamp but only if you intend to use it for special purposes otherwise it actually downgrades your antenna !

To give you a idea of how well a yagi can work even at something only 15 miles away I have a mono band 6db gain vertical up at 35ft for aircraft frequency's that works fine however there are some frequency's that don't even exist on the vertical mainly because of some local noise we have around here however when I turn the beam towards the station transmitting WOW SIG S-5 plus and a lot less noise ! you see this would absolutely be impossible with a discone and even worse with a preamp !

Most of the time I run a dual band receiver for aircraft that way I can use both antennas at the same time

Another thing to consider is the antenna gain remember only 3db gain is twice your power ! so you could use a splitter if you like to however you will lose about 3db (half the signal) or more depending on frequency and how many times you split it

Anyway just one example to consider :)

BTW Beautiful shack ! it would be a crime to hook up anything less then LMR-400 with N connectors on the icom 8600 and my god man please avoid using spliters on that thing !
This is a good point to consider, especially since I already have the LMR 400. I can easily leave the discone as-is, and hook a log periodic up to the Icom. I could use a passive switch between both my whistler and Icom to swap antennas when necessary. I’m liking this idea. I could also use the log periodic for 2 meters transmit. I can hit many repeaters with my hustler vertical on 2 meters, but it would be great to have an extra 6db for some I can’t quite get in to from Eugene. I think this will be my next best upgrade, and then possibly a preamp next year. I’ll have to re-locate my AM BCB loop and take it off the rotor, but it’s usually pointed in the same direction most of the time anyway.
 

Ubbe

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FYI. A Hustler vertical 2m already has 3dBd gain, or so they advertise the G3 model anyway (or if it's a G6 or G7 it's 6 or 7dBd) so it will be a 3dB extra from an LP antenna but will also be more directional.

/Ubbe
 

kb6hlm

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3dB at receive are not much loss
You are joking right?

This is a tremendous amount of loss when you consider how much it takes to gain that much ! its night and day when it comes to weak signals at 3 db loss your signal is readable or not

Your comment about logperiodic antennas having 6db gain is irrelevant and not true at all to prove my point try using a discone the same height with the same coax and then point the logperiodic at the station transmitting and you will then see that the 6db your taking about has absolutely no relevance to anything

On your discone you may not even have a readable signal at all ! but with the beam you may have S-9 Plus !

you cant compare a Vertical to a beam the db gain on a Vertical has nothing to do with a db gain on a beam

I have worked all around the world with a three element beam that only had 3db gain and let me tell you something most of those signals did not even exsit on a Vertical and would have been impossible

Don't let those db gain specifications fool you its not fair to compare beam with a Vertical antenna of any sort just look at my example on my last post comparing a 6 db gain mono band Vertical to the logperiodic NOT EVEN CLOSE in fact it was a full 5 S units !!! so that would mean 30 db gain over a antenna that has 6db gain ??? see what i mean that makes no sense at all

Again dont compare antenna gain factors from verticals to yegis ! you can compare a vertical to a vertical or beam to beam but not to each other and even then the antenna manufacturers are taking about DBI (decibels relative to isotropic) this is foolish and its a way of making the antenna better then it is dont be fooled by this :)
 
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kb6hlm

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Just wanted to jump back in here

Here is a example of how hard it is to get 3 db gain you would need to add another logperiodic yep another $300 bucks just for 3db

Think you get my point :)
 
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