CalebATC
Member
Ok, I didn't know you made that. Should it mess anything up too bad? I thought it may lower the frequency, but I wasn't sure. I found out as soon as I got home from buying the supplies.
MT magazine UHF Satcom antenna project
- Thread starter prcguy
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Ok, I didn't know you made that. Should it mess anything up too bad? I thought it may lower the frequency, but I wasn't sure. I found out as soon as I got home from buying the supplies.
prcguy
Member
Your thicker elements will lower the center frequency slightly and that can pull the phasing harness sweet spot around a bit but the antenna is fairly broad band and it may not be noticeable.
I tried zooming in on your pic and the lugs on the F connectors look larger than I used. The lugs and wires connecting to the elements are part of the elements and can add length to the elements if your not careful. Did you solder to the screws holding the elements in? I thought it would be easy to use two lugs back to back connecting the F connector ground to the respective element.
This antenna racked up many hours of computer design time (much done by a good friend) and many more hours of mechanical tweaking to get the performance to surpass the commercially made mil version. Then two prototypes were made to make sure the design is easily repeated.
During tweaking I found small mechanical changes to the elements have cascading effects on other aspects of the antenna so its best to use the recommended parts and do exactly what the instructions say, although the PVC pipe change should not cause any problem. If you pick up the pirates loud and clear on 255.55 then your on the right track.
prcguy
I tried zooming in on your pic and the lugs on the F connectors look larger than I used. The lugs and wires connecting to the elements are part of the elements and can add length to the elements if your not careful. Did you solder to the screws holding the elements in? I thought it would be easy to use two lugs back to back connecting the F connector ground to the respective element.
This antenna racked up many hours of computer design time (much done by a good friend) and many more hours of mechanical tweaking to get the performance to surpass the commercially made mil version. Then two prototypes were made to make sure the design is easily repeated.
During tweaking I found small mechanical changes to the elements have cascading effects on other aspects of the antenna so its best to use the recommended parts and do exactly what the instructions say, although the PVC pipe change should not cause any problem. If you pick up the pirates loud and clear on 255.55 then your on the right track.
prcguy
CalebATC
Member
Ok, thanks. I had a connector on the end of the big connector, but figured that might even lower the frequency even more. So, I just cut it off, and soldered it to the screw. Works fine, and it is a tight solder. Home Depot, or Radioshack did not have the connector with the skinny end. Also, they did not have the "T" connector, so I just found a splitter at home for temporary use. I am going to look online for a "T" tonight, and get that ordered.
You should do some plans to make a 2m uplink/downlink antenna, and since it has such a broad range, the weather guys would love the 137 MHz.
I'll let you know when I hear some pirates, but it will be a couple days.
techsender
Member
Just finished putting my antenna together. Will mount it up on the roof tomorrow and see what I can hear. I have the Yupiteru and the VX7 programmed up. No preamp or bandpass , I will see if I need them. Used BNC connectors since thats what I have plenty of and BNC T connecotrs are much easier to come by. I will let you know results after a few days of listening. Thanks for the easily repeatable antenna !
prcguy
Member
My VX7 was a bit numb in the UHF satcom band but my Yupiteru MVT-7100 is very hot there.
Going to BNC connectors may affect the critical lengths of the phasing harness and good way to see if its ok is to record some signal levels then swap the harness connectors at the feedpoint. This will change the antenna from RHCP to LHCP and the signals should disappear or degrade by 10dB or more.
If nothing changes the harness is way off and your not getting the most from the antenna. If it only changes a few dB your close but no cigar yet. The original dimensions should be very repeatable using common F components.
I used a vector network analyzer to determine the original harness lengths and fine tuned everything receiving several constant carriers while swapping cables and measuring signal strength with a spectrum analyzer.
prcguy
Going to BNC connectors may affect the critical lengths of the phasing harness and good way to see if its ok is to record some signal levels then swap the harness connectors at the feedpoint. This will change the antenna from RHCP to LHCP and the signals should disappear or degrade by 10dB or more.
If nothing changes the harness is way off and your not getting the most from the antenna. If it only changes a few dB your close but no cigar yet. The original dimensions should be very repeatable using common F components.
I used a vector network analyzer to determine the original harness lengths and fine tuned everything receiving several constant carriers while swapping cables and measuring signal strength with a spectrum analyzer.
prcguy
prcguy
Member
The antenna is designed to use 50ohm feedline and I would keep it less than 20ft for RG-58. RG-8 is better but keep it short like under 50ft. I used a Yupiteru MVT-7100 for testing the antenna and it worked great with a 25-30f of RG-58 but its a very hot receiver. I'm not familiar with the BCT15X.
The internal phasing harness must use RG-6 of the precise length mentioned in the article.
If you need to run a long feedline I would suggest a remote preamp at the antenna. A TV type preamp should work ok and there is plenty of room to hide it inside the support pipe for the dipoles.
prcguy
The internal phasing harness must use RG-6 of the precise length mentioned in the article.
If you need to run a long feedline I would suggest a remote preamp at the antenna. A TV type preamp should work ok and there is plenty of room to hide it inside the support pipe for the dipoles.
prcguy
CalebATC
Member
Out of curiosity, what is the best TV preamp for UHF Milair? I had a Sony that worked great, until it blew. Couldn't find it anywhere.
I use a Leviton 48210-VA, but it doesn't do really anything. I just keep it on their for public safety. It may add a couple db's, but not anything too noticeable.
prcguy
Member
I would try a small inline TV bullet amp similar to what Radio Shack used to sell but I don't see it on their website anymore.The antenna should not pick up very well outside the satcom band so the preamp will not be subjected to as many strong signals like using the preamp with a Discone, so it should not overload as easily.
The preamp in this case would be used to drive a long feedline and you want it right at the antenna, not at the radio end. Signals at the antenna will have the best signal to noise ratio and you want to preserve that on the way to your receiver as much as possible. A TV preamp may degrade the signal slightly due to its high noise figure and intermod contribution but in the end it will usually improve your reception with a long cable run.
If you want the best order an Angle Linear preamp tuned for the 245 to 270MHz range. Their basic model may not cover the entire range but the two high level versions will. You will pay dearly but you get what you pay for. See:Angle Linear Home Page
BTW, the Tee is free if you do your part and make the antenna to spec.
prcguy
The preamp in this case would be used to drive a long feedline and you want it right at the antenna, not at the radio end. Signals at the antenna will have the best signal to noise ratio and you want to preserve that on the way to your receiver as much as possible. A TV preamp may degrade the signal slightly due to its high noise figure and intermod contribution but in the end it will usually improve your reception with a long cable run.
If you want the best order an Angle Linear preamp tuned for the 245 to 270MHz range. Their basic model may not cover the entire range but the two high level versions will. You will pay dearly but you get what you pay for. See:Angle Linear Home Page
BTW, the Tee is free if you do your part and make the antenna to spec.
prcguy
CalebATC
Member
Ok, thanks alot!
I even painted the antenna military green, if that is to spec
After that, everything will be as you said.
A friend is giving me a tower, I should have pretty good results having it on it.
Angle Linear are a little preamps are a little too much for me, Christmas needs to come sooner!
I even painted the antenna military green, if that is to spec
After that, everything will be as you said. A friend is giving me a tower, I should have pretty good results having it on it.
Angle Linear are a little preamps are a little too much for me, Christmas needs to come sooner!
prcguy
Member
If the antenna can see the southern sky from your location in GA it can be on the ground, no tower is necessary. It will also be less susceptible to picking up unwanted stuff and overloading your scanner or preamp if its low to the ground.
prcguy
prcguy
Ok, thanks alot!
I even painted the antenna military green, if that is to spec
A friend is giving me a tower, I should have pretty good results having it on it.
Angle Linear are a little preamps are a little too much for me, Christmas needs to come sooner!
CalebATC
Member
Well, it somewhat can, but with tops of the trees in the way. But still get very good reception on the ground. About 2 bars on most comms.
The plastic isn't critical as long as it keeps all the other parts at the right position and spacing. I had to use a reducer as well and mine works fine.
prcguy
Member
That's why I originally used ABS, the caps seem to be more standardized than PVC across the country but mancow did made a nice looking version from PVC.
prcguy
prcguy
CalebATC
Member
I had to use a reducer also. Home Depot didn't have the flat cap, but ACE Hardware did. They had the reducer also.
My guess is that it does not matter if you use an adapter or not as long as the element spacing and hight above the reflector is correct. Did you have a chance to try yours out yet? Also ..not sure if you guys covered this yet but should the antenna be angled or pointed at the satellite? I live in RI and Im thinking the antenna should be pointed to the south east for Fltsatcom-8.
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prcguy
Member
Element spacing and height above reflector are the only concerns when choosing a support. If you change the dipole height the pattern and dipole impedance will change and the phasing harness will no longer be optimum for circular polarity. Everything interacts so follow the instructions closely.
The antenna reflector should sit flat and parallel to the ground with the antenna pointing straight up. It has a null straight up and the lobes are optimized for about 20 to 60deg above the horizon.
From RI the CONUS satellites are about 33deg elevation and the Atlantic sat is about 20deg elevation, both within the design limits of the antenna. Part 1 of the article explains all this.
prcguy
The antenna reflector should sit flat and parallel to the ground with the antenna pointing straight up. It has a null straight up and the lobes are optimized for about 20 to 60deg above the horizon.
From RI the CONUS satellites are about 33deg elevation and the Atlantic sat is about 20deg elevation, both within the design limits of the antenna. Part 1 of the article explains all this.
prcguy
CalebATC
Member
Mine works great with the modifications I had to do- I will hook it up to a friends antenna tuner sometime this weekend if I get a chance.
Mine is straight up, and shouldn't be angled as prc said. I did do some twisting to get some better reception. I did have to compensate some room for the cap being a different height, but other than that, all to spec.
Mine is straight up, and shouldn't be angled as prc said. I did do some twisting to get some better reception. I did have to compensate some room for the cap being a different height, but other than that, all to spec.
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