8 bay TV Antenna question

[gary350]

I built several of these 8 bay bow tie antennas in the past 15 years and made several improvements that increases antenna reception on TV field strength meter. Drawing shows 2 identical antennas only difference is the wires connecting each 4 bay to make 8 bay. Drawing #1 is what I have now, 2 baluns with 18" coax to T combiner. Drawing #2 the 4 bays are connected with wire using 1 balun to TV. Will wiring on antenna #2 be better than antenna #1 ?

I was going to build this today but decided before I do I should ask see if it will be an improvement ?

 

[Nigel Goodwin]

Short back fire arrays have low gain, but are good for their anti-ghosting properties - as all broadcasting now is digital, ghosting isn't a problem, so build a yagi with much more gain.

 

[gary350]

Short back fire arrays have low gain, but are good for their anti-ghosting properties - as all broadcasting now is digital, ghosting isn't a problem, so build a yagi with much more gain.

I had a yagi already & got rid of it. Yagi only picks up 5 degrees both sides of center that requires a rotor to watch all 53 channels between 229 to 325 degrees. I get 53 channels with no rotor using 8 bay antenna it picks up 12 degrees both sides of center. My antenna is only 7 ft high if I put it up 20 ft that will be better than an amplifier. I only want the 8 bay that I already have to work a little bit better if I can.

My Son gets 76 channels with same 8 bay antenna he is 7 miles farther away from stations his antenna is 20 ft high.

I am just experimenting having fun. No point in changing the antenna and making it worse. I don't think I can get this antenna up 20 ft at this new house. I'm not climbing up on the roof anymore roof is too steep.

 

[unclejed613]

it's a matter of finding things that cause losses.... the open wires in the second drawing likely cause a lot less loss than the combiner. the combiners used in CATV are resistive combiners, so you will have insertion loss. you also have insertion loss in the baluns (not as much as in the splitter). there'a also some loss in the cables and connectors, so the fewer lossy components you have the lower the loss. the second drawing is a better way of doing it. even better would be the use of twinlead all the way down to the TV room, and put the balun there.

 

[nsaspook]

Short back fire arrays have low gain, but are good for their anti-ghosting properties - as all broadcasting now is digital, ghosting isn't a problem, so build a yagi with much more gain.

That might be true with digital in the UK but it's not in the USA. ATSC has horrible multi-path tolerance vs COFDM. It causes total picture dropout for seconds at a time so anti-ghosting properties are a definite plus here.

 

[gary350]

it's a matter of finding things that cause losses.... the open wires in the second drawing likely cause a lot less loss than the combiner. the combiners used in CATV are resistive combiners, so you will have insertion loss. you also have insertion loss in the baluns (not as much as in the splitter). there'a also some loss in the cables and connectors, so the fewer lossy components you have the lower the loss. the second drawing is a better way of doing it. even better would be the use of twinlead all the way down to the TV room, and put the balun there.

Twin leads..... that is an idea I never thought of. 50 years ago everyone used twin lead I thought reason no one uses it anymore coax is better. I have not seen twin leads in 50 years does someone still sell that. Balun at TV...... I never thought of that either, I have rabbit ear balun for back of TV. I need twin leads to use it.

Years ago when my first factory cm4228 was crap the cm7777 amp never helped no increase on field strength meter. One day after taking antenna down then putting it up again and forgetting to put the cm7777 on the antenna so I connected it directly behind the TV and it worked great field strength meter showed a good signal increase.

If I was 50 years younger antenna would have been 20 ft up already. First things first, tomorrow I change antenna so it only has 1 balun then test it. Twin leads next if I can find it at Walmart.

 

[Tesla23]

If you double the number of elements and get everything right you may get 3dB extra gain less the loss in the extra combiner, whereas if you double the height you should get 6dB from increased field strength! (with a few caveats on local terrain.) Going up 40% should get you that 3dB.

Just read your post again - sorry - not trying to say you should go up - but at least think about a longer pole!

Also - I think that many of the modern CATV splitters/combiners are reactive - I have a spare here from my system and it shows on the label -3.5dB to each port. I'm sure there are cheap resistive ones out there, I'm not sure of the isolation between the split ports though.

 

[Nigel Goodwin]

That might be true with digital in the UK but it's not in the USA. ATSC has horrible multi-path tolerance vs COFDM. It causes total picture dropout for seconds at a time so anti-ghosting properties are a definite plus here.

As I understand it the UK system was specifically designed to prevent ghosting issues, with the ghosts actually increasing the signal levels - which is why terrestrial, satellite, and cable all use completely different systems, which each optimised for that use.

 

[nsaspook]

As I understand it the UK system was specifically designed to prevent ghosting issues, with the ghosts actually increasing the signal levels - which is why terrestrial, satellite, and cable all use completely different systems, which each optimised for that use.

The UK system was considered for US DTV but 8-VSB was the winner for ATSC 1.0 for some strange reason. The latest ATSC spin 3.0 is COFDM so we are finally moving back into the fold.

January 01, 2000
https://www.tvtechnology.com/opinions/comparing-8vsb-and-cofdm-for-dtv-terrestrial-broadcasting

 

[sagor1]

You may get an impedance mis-match. #1 has a balun from each to a "combiner". Assume antenna is 300 ohms. a 4:1 Balun changes it to 75 ohms, but via coax. Combiner is two 75 ohm inputs to one 75 ohm output. Now the antenna may be 75 ohms, and balun is a 1:1 design to keep it 75 ohms. Whatever, the following concept applies whether antenna is 300 or 75 ohms....
In #2, you are paralleling two 300 ohm antennas, making 150 ohms. Now you are trying to match that with a single 4:1 (300 to 75 ohm balun). That is a mismatch (SWR) of 2:1. A SWR of 2:1 is a loss of 11.1% of your signal, right at the start.
Now, in real life, you may not see the difference, but technically, you are losing signal with #2 design unless you can re-design each bowtie antenna to become 600 ohms at the start, or design the wire spreaders so it matches 300 ohms at the balun feedpoint.
Bottom line is you cannot just parallel two individual antennas with proper matching of the impedance. Your #1 design handles the two separate antennas by using the combiner.

 

[gary350]

Impedance for each 4 bay antenna with 4 bow ties is 300 ohms? Balun 4:1 on each 4 bay is 75 ohm to 75 ohm after T combiner perfect match for antenna. I don't understand how 1 bow tie is 50 ohms and 4 in parallel = 300 ohms ?

Two 4 bay antennas in parallel = 150 ohms. How can I make my own 150 to 75 ohm balun?

I have drawings to make a 4:1 balun but not a 2:1 balun. It requires a very small toroid.

The black plastic balun center of picture says 300 to 75.

The other black plastic balun says only UHF & VHF

I can not find the 2 baluns I want, 1 is for rabbit ears, 1 is for a folded dipole. They both look exactly identical. I don't remember if they are marked.
I found pictures of the baluns I have miss placed they are 300 to 75 ohm also.

Walmart has no twin lead wire. I have a 500 ft roll of 75 ohm coax.

Online search I only find 300 to 75 ohm TV baluns.

 

[Tesla23]

This splitter:

is a dead ringer for one I have (with different branding), but the fact it states 3.5dB insertion loss means it isn't resistive. Hopefully it is a reactive in-phase splitter (where if you use it as a combiner the two inputs are added in-phase), so I would try it first.

I'd be wary of twin-lead without any details on the UHF loss spec, I had a quick look and couldn't find any.

By all means experiment with the different ways of combining the two arrays, but if they are roughly 300 ohms, then I'd back the balun followed by a reactive combiner, as long as these are low loss. Every signal is going to have to go through a balun once.

I'm not sure if you are using an amplifier at the antenna, if not, how long is your lead-in? Check the specs on the coax you have, over here (Australia) they typically sell RG6 or RG59 (with variations on the level of shielding), but the 'specs' (if there are any) on some of the generic stuff can be lousy. At 500MHz the loss/100ft for a good coax can be below 5dB, but how important this is depends on the lead-in length.

 

[gary350]

At the moment my RG6 coax is 40 ft long. If I drill a hole in the house wall I can shorten coax to 17 ft. If I put another 10 ft on the tower coax will be 27 ft.

Tomorrow if I get time I will write down field strength readings on several channels then swap the combiner with the 1 above then check field strength readings again. I am not using an amplifier. I have an amp I have not used in 6 years, today I looked I found the amp but can not find power supply for amp.

 

[Tesla23]

I just roughly measured this splitter:

which looks identical to yours, and the transmission to the two ports are matched to around 0.2dB and less than a degree of phase difference. Also they have about 20dB of isolation. This would be good to combine your antennas, hopefully yours is similar.

The measurement was only rough as I have a 50 ohm analyser and I don't have F-type adaptors, but at 500MHz I should be pretty close. I measured about 4dB insertion loss in 50 ohms, but the cal was pretty rough, so the 3.5dB in 75 ohms is certainly believable.

The best RG6 is about 15dB/100m, so your 40ft would be about 1.8dB, more garden varieties about 18dB.100m which would be 2.2dB., so less of a worry - but it's still an easy dB if you halve the length (or 2dB if you add an amplifier).

 

[gary350]

Today when I did the tests I started about solar 12 noon. We are having high wind gusting to 25 mph. Temperature outside is 82 degree F.

First I located a channel with a weak signal it was in the range of 39 to 42 most of the time. I went outside to look at the T combiner that is on the antenna it says, ANTRONIX it is also -3.5 dB.

I replaced the ANTRONIX with the EXTREME signal is still in the 39 to 42 range most of the time.

Next I replaced the EXTREME with the ARCHER it has been modified inside all 3 terminals are connected no balun. Signal increased to 70 to 72 range.

Next I decided to test the EXTREME again to see if it still reads 39 to 42 the screw on connector to one of the 18" coax cables fell on into the grass and is lost. I looked for 10 minutes then checked to see if I have another connector but I don't. I checked field strength meter anyway with no screw connector signal is up in the 85 range.

I tried ANTRNIX, then ARCHER then EXTREME they are all reading 85 range with the coax screw on connector missing. I tested all channels they all work better with the coax cable connector gone. LOL. What ever works best is GOOD but not sure connector needs to stay gone? Maybe I cut off the shield wires on that coax then put on another connector. I can remove a connector from another coax.

I have been reading the number on the left side of field strength meter not the right number. Left number the one that is jumping around the other number was not changing very much.

I don't like clamp on connectors they damage the cables. Screw on connectors do not hold on tight but they can be reused of they don't get lost in the grass.

I have been watching the field strength meter for 45 minutes. Number on right side is max signal. When signal jumps round a lot left number shows signal change, right number show what signal was at the time it jumped to its strongest signal.

 

[Nigel Goodwin]

Looking at the last picture I'm not surprised you lose your F Connectors - over here we use Belling Lee coaxial plugs, and only use F Connectors for satellite connection - although an increasing number of splitter etc. are appearing with F connections, presumably American style imports?.

Anyway, don't you pull the screening back over the outer insulation, and then screw on top of that? - this makes a nice solid connection, and doesn't fall off. It's also VERY important that you get the exact right F-Connector for the cable you're using, as there are many different sizes.

 

[JimB]

I just love that impedance matching technique.

JimB

 

[Tesla23]

The fact that this combiner:

gave you a significant increase in signal strength means that your impedances are nothing like you expect.

But unless you have a network analyzer, or want to mess around with antenna modelling software, you really have no way to find out. If it interests you, impedance measurement seems to be more affordable these days: https://hackaday.com/2019/08/11/nanovna-is-a-50-vector-network-analyzer/ (I've not used one of these, I don't know if anyone else here has used one?). With a VNA you could measure the impedance at the output of the antenna and ensure that you match to it so that you combine it is such a way that all the power the antenna picks up is delivered to your receiver.

So by all means experiment with ways of combining the various bays and don't be afraid to simply parallel the bays (i.e. use the modified coupler in the pic above) if that works best for you.

 

[gary350]

Looking at the last picture I'm not surprised you lose your F Connectors - over here we use Belling Lee coaxial plugs, and only use F Connectors for satellite connection - although an increasing number of splitter etc. are appearing with F connections, presumably American style imports?.

Anyway, don't you pull the screening back over the outer insulation, and then screw on top of that? - this makes a nice solid connection, and doesn't fall off. It's also VERY important that you get the exact right F-Connector for the cable you're using, as there are many different sizes.

I knew steak on connectors are no good but I did't know certain ones work better. Which connector do I need to buy.

This is a 10 year old antenna it needs improvements and upgrades.

 

[Nigel Goodwin]

I knew steak on connectors are no good but I did't know certain ones work better. Which connector do I need to buy.

The right one for the cable you have, and then fit them properly.