Dumb antenna question

[luRaichu]

What type of antenna is this?
Is it suitable for TX?
What's the expected frequency range? It has "1.8 GHz to 150-" written on it. The last bit is cut off so it could be 150 MHz or 150 kHz.
As you can see it has two separate sets of antennae on either side, One set is connected to center pin on the RF connector and the other set is connected to ground. Is that normal?

[old_tv_nut]

How wide are the widest and narrowest parts? That will determine the frequency range. Specifying the highest frequency first and the lowest second seems strange.
This is a highly directional antenna, so if you're looking to use it to transmit throughout your home, I'd guess maybe not the best.

Comments from those who do transmit locally, please?

[jr_tech]

Log-periodic antenna:

https://en.m.wikipedia.org/wiki/Log-periodic_antenna

https://hamwaves.com/lpda/en/index.html

jr

[luRaichu]

Originally Posted by old_tv_nut

Specifying the highest frequency first and the lowest second seems strange.

I got this from a local ham who'd died at 88, that's what he wrote on the antenna...

Thanks for the info guys.

[Dude111]

Originally Posted by luRaichu

I got this from a local ham who'd died at 88, that's what he wrote on the antenna...

Thanks for the info guys.

Your welcome bud........ No question is stupid remember that ok?

We are not all at the same level and thats ok!!

[Electronic M]

I prefer a tuned dipole for TV TX applications. This Shango video explains easily making them. https://m.youtube.com/watch?v=z4dhRt7tmd4
You don't need the fancy expensive SWR meter he uses. What he doesn't tell you is that the formulas he uses are for 50ohm impedance not 75ohm and that the trimming he does to retune its impedance scales linearly. Back in my college antennas elective I learned that the same percentage of length used to tune from 50 to 75 ohm will work on any frequency. So I calculate the percentage of length he cut off and apply that percentage to my antenna to tune it. Has worked great for me on CH2-13. UHF I tend to use factory made bowtie antennas, but I've only done ATSC UHF transmission seriously so far (I kinda want to get a permanent analogy TX going soon).

Phills old radios has a good write up on settings up a transmitter (good hardware to use, avoiding interfering with DTV stations, etc). https://www.antiqueradio.org/HomeTVTransmitter.htm

I've written this info here before probably more than 10x in several older threads....

[ChrisW6ATV]

As jr_tech said, it is a log-periodic antenna. Its practical range is more like 140 MHz to maybe the 33cm (902-928 MHz) ham band. A nice antenna!

[luRaichu]

Longest rod is 49cm. So that's VHF Channel 7 and above...
I could pick up FM broadcasts pretty good though! Even CB!! Despite the fact those bands are out of range for this antenna.

All in all I wouldn't use this one for television TX.
I have aluminum pipes from a Radio Shack antenna kit that're about 1.5cm in diameter. Are those OK for making a 50ohm dipole for Channel 3 TX? 50ohm because that's what my RF amplifier expects.

I use an RF amplifier because the signal from my agile modulator is too low. The amp generates awful harmonics. How do I filter it? Can't find appropriate RF filters from Digi-Key or Mini-Circuits for a reasonable price.

[Electronic M]

Pipe is fine...Maybe overkill (I use lamp cord for my dipoles), but there's no kill like overkill. Generally the thicker diameter the wire a dipole is made of the better bandwidth it can handle.

Is your modulators output 75 ohm or 50 ohm? If you're feeding a 50 ohm amp with a 75 ohm modulator you could be getting impedance mismatch reflections and confusing them for harmonics.

Any piece of wire is capable of being an antenna at any frequency, how good of an antenna it is depends on size shape, intended use and a LOT of fancy math . (When I was a teenager we had one of the last cellphones with an antenna and at the family cabin where I had setup a 100' long wire for shortwave the folks were able to clip the cell antenna to the longwire and get cell service there for the first time ever.)

[luRaichu]

My Olson Technology OTM-3000 should be 75ohm just like any other TV modulator. So I need a matching transformer now?

[Electronic M]

Originally Posted by luRaichu

My Olson Technology OTM-3000 should be 75ohm just like any other TV modulator. So I need a matching transformer now?

You should have something to do matching. I don't know if 75 to 50 ohm matching transformers are a thing. I know you can make resistor matching networks if it comes down to it.

[luRaichu]

As pictured, this person's UHF TX uses the same cheap chinesium RF amp as mine. At first I thought they had both lowpass+hipass filters attached (bandpass) on the RF input but they may be impedance matching devices?

Honestly I'm not sure if impedance matters on the RF amp input. The mentioned blog post on this amp only mentions output antenna impedance of being particularly important.

[old_tv_nut]

Originally Posted by luRaichu

As pictured, this person's UHF TX uses the same cheap chinesium RF amp as mine. At first I thought they had both lowpass+hipass filters attached (bandpass) on the RF input but they may be impedance matching devices?

Honestly I'm not sure if impedance matters on the RF amp input. The mentioned blog post on this amp only mentions output antenna impedance of being particularly important.

They could also be attenuators if the modulator output overdrives this amp.