digitalanalog
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Yeah, your right, guess that's out.
New Antenna Coming Soon based on Old Favorite.
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SW or HF bands are usually received at a distance after bouncing off the ionosphere, so the polarization you will receive is random. If you were close enough to a SW transmitter that used horizontal pol antennas then the signal strength would be so strong that polarization would not matter.
And that would bend the receiver's frontend for sure.
One should consider what they may want to RX nearby at 25 MHz and up that uses a vertically polarized antenna to TX.
I like that this thread made me re-deploy an ST2 and perform some testing. I'm going to use it for VHF and use the 1/2" Heliax for a UHF omni antenna to feed some radios.
Also, the ST2 w/RG-6 definitely outperformed a RS and Tram discone using LMR-400 except for one freq. at 273.6 MHz. My tests to get the numbers were done during the day and night because of the differences.
I like that this thread made me re-deploy an ST2 and perform some testing. I'm going to use it for VHF and use the 1/2" Heliax for a UHF omni antenna to feed some radios.
Also, the ST2 w/RG-6 definitely outperformed a RS and Tram discone using LMR-400 except for one freq. at 273.6 MHz. My tests to get the numbers were done during the day and night because of the differences.
digitalanalog
Active Member
here is a close up view and some information I shot prior to getting this ready to send off to the Tester.
Quality was Much better when I uploaded it compared to what it is now, but It's not to bad.
Get up and close to The Searcher I.
Quality was Much better when I uploaded it compared to what it is now, but It's not to bad.
Get up and close to The Searcher I.
Ubbe
Member
Capacity hat connected to the base of the antenna, and two of them, where it connects to the feedline?
A 1/2 wave dipole are approx 70 Ohm and a 1/4 wave approx 35 Ohm.
Those smaller V a bit up on the longest vertical element looks like 1/4 waves and then the distance down to the base are a 1/4 wave which makes them a 1/2 wave dipole, like most of the elments looks to be designed to work as and then everything is in parallell.
I agree that other elements in parallel will add capacitance and the elements lenght have been shortened to compensate for that.
The longest vertical element that are used for 35-50MHz have a physical lenght cut for 50MHz but the added elements for other bands will extend its electrical lengh and lower the resonance frequency, maybe 10% down to 45MHz.
/Ubbe
Ubbe
Member
That's because there's no antenna element designed to cover that frequency. It's a multiband antenna, several tuned elements, each cut for a specific frequency, that are connected in parallell. It's about a 10% bandwidth of an resonant element an none of the elements reach into the mil-air frequency band. It's enough metal in the air to receive any frequency but do not equal something designed for a specific frequency. I think that the ST-2 where advertised as covering these bands: 30-50, 108-174, 400-512, 800-950
/Ubbe
Since the ST2 has a 75 ohm to 300 ohm TV transformer at it feedpoint I don't think the elements would be 1/2 wavelength resonant. I don't think anyone knows for sure what the antenna is really doing except the original designers.
Ubbe
Member
In my mind I beleive that the original antenna designer just took a couple of dipoles for each frequency band and connected them in parallel. He then took a radio for each band programmed to different frequencies and used a SWR meter to cut the elements to best SWR and ended up with the final dimensions after trial and error. No sofisticated NEC calculations or expensive antenna analyzers where in use at that time period for the design of scanner antennas and the SWR appoach are probably the best way anyhow for this design.
/Ubbe
/Ubbe
digitalanalog
Active Member
I know from past use the ST2 did pickup MilAir and very well at that, This antenna Needs to have those capabilities as well, we will find out after testing if it's in that band and if not what ever we need to do to get it in that freq we will make the change.
Curious, why isn't the "Balun" set to produce 50 ohm at the scanner?
Also, weight on the original is 4 pounds....
Also, weight on the original is 4 pounds....
Antennacraft ST2 Scanner Antenna, Antenna Craft ST-2
www.universal-radio.com
The balun is probably close to a 4:1 ratio so if the antenna feedpoint is 300 ohms it would match to 75 ohms. If the antenna was around 200 ohms it should match to around 50 ohms and so on. I'm sure the designers optimized the antenna for whatever balun and coax the antenna was intended to use.
Based on my testing as well as just listening, I agree that a discone works better for Mil Air than the ST2. With my setup though, I have a purpose built Mil Air discone (AT-197A/GR) with a 225-400 MHz pass filter inline, so the ST2 would handle those frequencies you noted. While I wish the ST2 was not as directional, at its worse I think it is similar to my RS or Tram discone using LMR-400. I will eventually test the ST2 using 1/2" Heliax and LMR-400 just to know the results. Probably this week.
The antenna build of this thread looks robust compared to my ST2. I live in an area of California where it is all sunshine and fun. If I lived where snow, wind and or ice were a factor, I would order this antenna and or already have a Kreco to deal with the elements.
The antenna build of this thread looks robust compared to my ST2. I live in an area of California where it is all sunshine and fun. If I lived where snow, wind and or ice were a factor, I would order this antenna and or already have a Kreco to deal with the elements.
Ubbe
Member
MilAir is difficult to design an antenna for. The frequency from the lowest to the highest almost double, one octave. If you have almost all transmissions coming from the front of the antenna and none from the back, a logperiodic antenna built for 200-400MHz would be the best as it has gain.
But a standard discone can be used if all elements are cut to half lenghts to make it work best from 200MHz and up. It would make the wind load much less and weight would be reduced that would make even the cheapest $50 discone hold up much longer. It would receive fine between 200-900MHz but if it have to be combined with other antennas then filters needs to be used and MiniCircuits may have some suitable low cost ones.
/Ubbe
But a standard discone can be used if all elements are cut to half lenghts to make it work best from 200MHz and up. It would make the wind load much less and weight would be reduced that would make even the cheapest $50 discone hold up much longer. It would receive fine between 200-900MHz but if it have to be combined with other antennas then filters needs to be used and MiniCircuits may have some suitable low cost ones.
/Ubbe
digitalanalog
Active Member
The right size element cut to the right length and placed in the right location should be able to put this antenna in the milair band or at least close enough to work, the tester will more then likely help in this regard. I have faith it can be achieved. as mentioned before, the ST2 worked in the milair band and it was not designed to work in those freq's but it did. I guess we will wait and see.
Ubbe
Member
Let's keep the thread to the antenna and it's design. Arguing about shipping is non-contributory and not needed.
Rich C.
Forum Moderator.
Rich C.
Forum Moderator.
digitalanalog
Active Member
To be perfectly honest I am not sure at this point, there are some online calculators I could look at that should provide that information, but I am very confident that the tester will make that determination if it is possible to achieve the milair band with this antenna.
digitalanalog
Active Member
Antennas made it to the tester today, I guess the Special Handling stickers I put on the boxes din't help.
What a shame, that used to be a ST2 in that box.
What a shame, that used to be a ST2 in that box.
Wow, that is a real shame, stuff gets damaged so frequently any more. I hope you had it insured?
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