substitute for antenna 300 ohms to 75 connection.

[Frank55]

Hi guys; i'd like your opinion on this project i made for my roof top antenna,to substitute the matching transformer.
first my Antenna rotator broke so i took it down and fixed it,it had some bolts that fell off then i had to take out the antenna 300 ohms to 75 ohms matching transformer,which broke upon unbolting it, which was bad luck,now i have no matching balloon an the worst part nowhere to buy it ,use to get stuff near here from Radio Shack which closed ,
i have also installed a SVA15PRSM distribution Amp near the antenna and a 12v SVPI ,these items were installed before, but inside the house closer to the receiver.
now story short,since i did not have the matching transformer ,i did not want to go by without tv i made a straight connection with coaxial cable ,took out the F connector and striped the coaxial wire connected ground wire to one side and the middle wire to the other, and for my surprise i never had so many chan and so good reception,but someone suggested me, due to water getting inside the wires to get an outdoor matching transformer to connect to antenna.

well made this straight wire to connect from the antenna to the amp

as you see i cut 2 pieces of thin ground wire and connected and soldered an F type connector that i cut from type F cable connectors,
what you think about this? will it work?i know i should go up there and try! but up there are 50 feet high and no easy access and i'm not young anymore, so will this work at least same way i have now? thanks

http://postimg.org/image/d161lt343/ef75894e/

[Terryl]

No, you need to balance the antenna correctly it will work even better when this is done correctly, if you connect it the whay you are describing you will be grounding out 1/2 of the antenna.

A 300 ohm to 75 ohm baulin does this just fine.


One like this should work.

http://www.amazon.com/Steren-Outdoor-300-OHM-Matching-Transformer/dp/B000NQ9E4Y/ref=sr_1_3?ie=UTF8&qid=1435013747&sr=8-3&keywords=75+ohm+balun

[Terryl]

Most of these home built antennas are of a balanced modified log periodic/yagi design, they have dual radials,(several) one on each side, each side is of a 150 ohm inductance, combined equals a 300 ohm inductance, balanced system, putting one side to ground or using an unbalanced wave guide like 75 ohm coax effectively reduces your signal by 1/2.

A dipole antenna has a center radiator (usually a vertical radiator) with the ground tied to the radials (horizontal radials), a bipole antenna has a loading coil that is not electrically attached to the antenna it's self but through inductive coupling, you would wind a 75 ohm coil around the center coil of the bi-pole radiators, you can make this antenna as large as you want, this type of antenna (the bi-pole) was used in WW2 as a hidden antenna, as you could wind it around almost anything.

[Frank55]

Most of these home built antennas are of a balanced modified log periodic/yagi design, they have dual radials,(several) one on each side, each side is of a 150 ohm inductance, combined equals a 300 ohm inductance, balanced system, putting one side to ground or using an unbalanced wave guide like 75 ohm coax effectively reduces your signal by 1/2.

A dipole antenna has a center radiator (usually a vertical radiator) with the ground tied to the radials (horizontal radials), a bipole antenna has a loading coil that is not electrically attached to the antenna it's self but through inductive coupling, you would wind a 75 ohm coil around the center coil of the bi-pole radiators, you can make this antenna as large as you want, this type of antenna (the bi-pole) was used in WW2 as a hidden antenna, as you could wind it around almost anything.

thanks terryl for sharing your acknowledge,i 'm going to leave it with coaxial cable only between uhf/vhf antenna and the amp since i'm getting more chan and better signal this way,i've been with bad luck with matching transformers balloons,always end up braking,
i've just bought some silicon and i'm going to seal the endings that i striped that connect to the antenna to avoid humidity and water to get in the coaxial.

[jvvh5897]

Hum...have to think about that a little.....

Having the amp close to the antenna is good and likely why your antenna is working better. But running without a balun means high SWR, but does SWR really matter with antenna level signals?--where would the reflections go?--right back out the antenna I would think for most of it--most digital TV chips would just ignore any that got into the TV. I've had antenna is odd places where they likely were pulled way off the designed impedance and nothing really was horribly bad about the setup--maybe a little more touchy on some signals than others.

[Terryl]

You can do it anyway you want to, but your effectively only using 1/2 of the antenna, the other elements are grounded out.

The design used in these antennas is a modified log periodic/yagi design, this means that each element pair are resonating together in a balanced system, one side is at 1/4 or 1/2 wavelength of the total RF channel you are trying to recive, with one half the system missing the antenna is at one half it's effective design parameters.

And SWR is realy not that important on a recive only antenna, all it has to do is resonate on or close to the desired RF frequency, now if this was a transmit and receive antenna then we are on a whole different level.

If I were you I would add the baulin to the antenna, it will work a whole lot better, that is my professional opinion as RF broadcaster for over 60 years.

[Frank55]

Hum...have to think about that a little.....

Having the amp close to the antenna is good and likely why your antenna is working better. But running without a balun means high SWR, but does SWR really matter with antenna level signals?--where would the reflections go?--right back out the antenna I would think for most of it--most digital TV chips would just ignore any that got into the TV. I've had antenna is odd places where they likely were pulled way off the designed impedance and nothing really was horribly bad about the setup--maybe a little more touchy on some signals than others.

well i don't have any chan with any reflexions most chan coming from Boston 50 miles away come in with 90% strong now ,and you're right the SVA15PRSM distribution Amp that i put near the antenna brings in stronger signal and more channels.this is the way i made a small coaxial cable see pic, no more matching transf. balloons,no more worries.

[jvvh5897]

I did read in my ham manuals a little and if you have a 300 to 75 ohm change with no matching the SWR is 6 and if your cable looses 1 dB of signal normally the SWR would add almost another 0.8 dB loss. Now, your "cable" is very short, so losses would be very low---I'm thinking no issue.

[Terryl]

And he is still only working with half an antenna, one side is grounded out by the coax shield.

[Frank55]

And he is still only working with half an antenna, one side is grounded out by the coax shield.

What do you mean? i only have use of half of the signal,you mean if i put matching transf. balloon i get double signal then what i'm getting now?
how's that possible? i use to get 30 chan and now i get 60 with better signal strength,although i've moved the amp closed to the antenna.i think i'm pretty much satisfied with the way it is.I don't beleive if put in a matching balloon i'll get any better reception! or more chan,i think it's a waist of money.

[kutter]

What do you mean? i only have use of half of the signal,you mean if i put matching transf. balloon i get double signal then what i'm getting now?
how's that possible? i use to get 30 chan and now i get 60 with better signal strength,although i've moved the amp closed to the antenna.i think i'm pretty much satisfied with the way it is.I don't beleive if put in a matching balloon i'll get any better reception! or more chan,i think it's a waist of money.

just out of curiosity, how are you measuring this increased signal strength ?

obviously you don't understand antennas, so if your satisfied with how it works, then leave it like it is ...

I know that I would take Terryl's advice ... but if you're happy with half an antenna that's up to you ...

[Frank55]

just out of curiosity, how are you measuring this increased signal strength ?

obviously you don't understand antennas, so if your satisfied with how it works, then leave it like it is ...

I know that I would take Terryl's advice ... but if you're happy with half an antenna that's up to you ...

I measure on the receiver,it has strength signal meter with numbers.

if i have double chan, and double strength signal then before why should i change, give me a good reason?

i'm not a specialist in theory stuff but i'm a electronics hobbyist and i don't pay nobody to instal and repair all my electric and electronic stuff that's what matters to me,you think if a matching balloon would give me more chan or signal strength i would not have it installed by now,but it won't give me more,it gives me less.

[kutter]

I measure on the receiver,it has strength signal meter with numbers.

if i have double chan, and double strength signal then before why should i change, give me a good reason?

i'm not a specialist in theory stuff but i'm a electronics hobbyist and i don't pay nobody to instal and repair all my electric and electronic stuff that's what matters to me,you think if a matching balloon would give me more chan or signal strength i would not have it installed by now,but it won't give me more,it gives me less.

you moved the amp and cleaned up all the connections, that's the only logical explanation for your increase in channels and signal ... you're not getting more channels because you got rid of the balun

[Frank55]

you moved the amp and cleaned up all the connections, that's the only logical explanation for your increase in channels and signal ... you're not getting more channels because you got rid of the balun

but if you say that i'm getting only half of the antenna signal strength without the Matching balloon,since i moved the SVA15PRSM closer to the antenna,so I've got improved signal strength,but i'm not getting to much signal where it can overload on many chan.

so actually it's beneficial to have only half of the antenna in conjunction with the Amp,i have the right signal strength for my location and not overloaded by the amp.since on my location signal strength is fairly ok on most days without Amp.but it's unstable on some days on Winter special out of Boston 50 miles away,

once when i had the amp inside closer to the receiver, i swapped the SVA15PRSM 15DB amp for a 24 DB indoor amp with a control knob and on this weak Chan WSBK38 when i turned switch all the way up to the 24DB i would loose the Chan,even with the control knob all the way down to the minimum on some days i would loose Chan,
now i don't ever loose this Chan anymore and signal strength went from 34 max to 60 max.

[kutter]

but if you say that i'm getting only half of the antenna signal strength without the Matching balloon,since i moved the SVA15PRSM closer to the antenna,so I've got improved signal strength,but i'm not getting to much signal where it can overload on many chan.

so actually it's beneficial to have only half of the antenna in conjunction with the Amp,i have the right signal strength for my location and not overloaded by the amp.since on my location signal strength is fairly ok on most days without Amp.but it's unstable on some days on Winter special out of Boston 50 miles away,

once when i had the amp inside closer to the receiver, i swapped the SVA15PRSM 15DB amp for a 24 DB indoor amp with a control knob and on this weak Chan WSBK38 when i turned switch all the way up to the 24DB i would loose the Chan,even with the control knob all the way down to the minimum on some days i would loose Chan,
now i don't ever loose this Chan anymore and signal strength went from 34 max to 60 max.

all that tells me is that you probably don't need an amp ...

like I said before, if you're happy with it then leave it like it is ...

by the way, why did you ask for opinions (and on at least 3 different forums that I'm aware of) if you didn't want an honest answer ... most of us don't give a **** if you want to butcher your antenna, after all it is yours ... but don't try to bullsh*t us by suggesting that the antenna works better now than it did with the balun ... the fact that you are getting more channels and greater signal now has more to do with the positioning of the amp and the fact that you fixed the rotator