Yes again a returning question "preamp at the tower or near the shack"
I will have to do soon some maintenance work on my satellite antennas tower. I planned to use 2 heliax 1/78" 45' individual line. Each line will be terminated by high quality 2psp coaxial microwave switch feeding UHF and VHF antennas. I don't know if i can move my VHF and UHF preamp at the other end near the shack where each line will enter the house on short LMR 400 run 10 feet max?
I know the theory says the best place to put a preamp is at the antenna but with the very low loss on the Heliax coaxial line, is in the real world there will be any significant degradation in the noise figures who will be really noticeable?
Note: If the relays are introducing too much loss i can feed the antenna directly from them on the 8' run on LMR-400 directly on the female N type heliax connector.
P.S. One commercial microwave technician is telling me that i will be able to see difference only on labs spectrum/signal generator in short i will be unable to tell any difference due to the short length of my coaxial line. He told me he's playing with 300 to 600 feets of lines in his day to day work and 45 feet heliax run are nearly consider as jumper line in his world...
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Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe DSTAR urcall VE2DWE WAC BASIC CW PHONE SATELLITE
Hi Luc,
I am assuming you meant 7/8" Heliax.
45' of Heliax and a short LMR400 jumper will have around 0.6 dB of loss on 70cm so that just adds 0.6 dB to the noise figure of your preamp (i.e. ~1.0 dB to ~1.6 db.) With even a modest gain antenna, you probably will not be able to notice any difference on a satellite downlink.
On 2 meters, even less difference.
73, Tony AA2TX
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At 05:04 AM 1/24/2010, Luc Leblanc wrote:
Yes again a returning question "preamp at the tower or near the shack"
I will have to do soon some maintenance work on my satellite antennas tower. I planned to use 2 heliax 1/78" 45' individual line. Each line will be terminated by high quality 2psp coaxial microwave switch feeding UHF and VHF antennas. I don't know if i can move my VHF and UHF preamp at the other end near the shack where each line will enter the house on short LMR 400 run 10 feet max?
I know the theory says the best place to put a preamp is at the antenna but with the very low loss on the Heliax coaxial line, is in the real world there will be any significant degradation in the noise figures who will be really noticeable?
Note: If the relays are introducing too much loss i can feed the antenna directly from them on the 8' run on LMR-400 directly on the female N type heliax connector.
P.S. One commercial microwave technician is telling me that i will be able to see difference only on labs spectrum/signal generator in short i will be unable to tell any difference due to the short length of my coaxial line. He told me he's playing with 300 to 600 feets of lines in his day to day work and 45 feet heliax run are nearly consider as jumper line in his world...
"-"
Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe DSTAR urcall VE2DWE WAC BASIC CW PHONE SATELLITE
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
At 01:04 AM 1/24/2010, Luc Leblanc wrote:
Yes again a returning question "preamp at the tower or near the shack"
I will have to do soon some maintenance work on my satellite antennas tower. I planned to use 2 heliax 1/78" 45' individual line. Each line will be terminated by high quality 2psp coaxial microwave switch feeding UHF and VHF antennas. I don't know if i can move my VHF and UHF preamp at the other end near the shack where each line will enter the house on short LMR 400 run 10 feet max?
I know the theory says the best place to put a preamp is at the antenna but with the very low loss on the Heliax coaxial line, is in the real world there will be any significant degradation in the noise figures who will be really noticeable?
Note: If the relays are introducing too much loss i can feed the antenna directly from them on the 8' run on LMR-400 directly on the female N type heliax connector.
P.S. One commercial microwave technician is telling me that i will be able to see difference only on labs spectrum/signal generator in short i will be unable to tell any difference due to the short length of my coaxial line. He told me he's playing with 300 to 600 feets of lines in his day to day work and 45 feet heliax run are nearly consider as jumper line in his world...
"-"
Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe DSTAR urcall VE2DWE WAC BASIC CW PHONE SATELLITE
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
OK, Luc. To make this decision you need to do the math. But you can just try comparing performance by installing the preamps at the antenna and at the shack and make your own evaluation. I'm guessing that is not convenient as antennas are on a tower.
You mention running two coax lines "1/78". I do not know what that is but it sounds like ridiculously small stuff like RG-174. Or did you intend to say 7/8-inch? 7/8-inch Heliax is low loss (0.44 dB/100-ft and 0.83 dB/100-foot respectively) so that certainly helps when installing a preamp at the shack. But without numbers it is all hand waving and no decision is possible. How long is the Heliax? Also, not familiar with "psp" relays. What is their specification for insertion loss? If more than 0.2 dB they are not very good. I use relays rated at 0.05 dB loss.
What is the NF and gain of the preamps? What is the NF of the radios that will be fed? Get all that and coax loss figures and input them into my spreadsheet program to find out what the overall NF will be. http://www.kl7uw.com/emelink.xls
Add sky noise temp, Antenna noise temp, and radio bandwidth to determine minimum signal power that produces a zero SNR. Then you will have the figures to determine the effect.
My overall experience is you will not have the best receiving system unless the preamps are at the antennas. You may be "satisfied" with preamps in the shack if you never compare with having them at the antenna. That is sort of saying driving a Ford Pinto is "just as good" as driving a Ferrari. Both will get you to a destination, but the ride is definitely different ;-)
Regarding the opinion of the commercial mw engineer is not necessarily valid. Does he work with weak-signal detection? Probably not. My qualifications are ten years as mw engineer with NASA detecting spacecraft near the edge of the solar system. That is definitely "weak-signal". The typical receiving system at Goldstone had a noise temp of 16K at 2115 MHz and a minimum detectable sensitivity of -185 dBm (the best system had -198 dBm). You can achieve -152 dBm with amateur equipment at 432-MHz. Typical 70cm ham station is -122 dBm without low noise preamps.
73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com 500-KHz/CW, 144-MHz EME, 1296-MHz EME DUBUS Magazine USA Rep [email protected] ======================================
OK, Luc. To make this decision you need to do the math. But you can just try comparing performance by installing the preamps at the antenna and at the shack and make your own evaluation. I'm guessing that is not convenient as antennas are on a tower.
You mention running two coax lines "1/78". > 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com 500-KHz/CW, 144-MHz EME, 1296-MHz EME DUBUS Magazine USA Rep [email protected] ======================================
It is a Heliax 45' lenght of 7/8"... and here is the the relay info's i have:
http://www.recycledgoods.com/18955_RelComm%20Technologies_RDL-2N1D4%20SR006_... %20SR006_.html
There was some discussion about RelComm Technologies on the moon net in 2008: http://list-serv.davidv.net/pipermail/moon-net_list- serv.davidv.net/2008-November/014898.html
If their figures are reliable i will put them in your spread sheet with the preamps figures Icom AG-35 and AG-25 and the rig is the FT-847.
As i don't want to have an EME class station (Just working leo's) i will probably not be able to tell the difference even if there is one but as you said the only one way to be 100% sure is to tested it but this will have to wait until next summer If the antenna will survive our next 24hrs of predicted freezing rain...
Thank's for your help Ed
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Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe DSTAR urcall VE2DWE WAC BASIC CW PHONE SATELLITE
Have anyone compared the IC-821H with the IC-7000?
How is Satellite operation with the IC-7000 ?
participants (4)
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Anthony Monteiro -
Edward Cole -
Luc Leblanc -
Pat McGrath