The Big Swap: New Antennas for the attic

[N9JIG]

Antennas Compared:

I now have several scanner antennas in the attic:

• Omni-X
• ST-2 with new Channel Master Balun
• New Diamond D130NJ
• SkyBand Discone

All are connected to identical coax runs (50 foot Air10 LMR400-type ultra-low-loss with N-connectors at both ends) with an N to BNC 6-inch pigtail at the radio end. The Omni-X and D130NJ have the coax at that end connected directly to the antenna, the SkyBand has an N-PL259 adapter and the ST-2 has an N-F adapter connected to the new balun.

At first glance I did not notice any improvement with the Omni-X over my previous antennas (ST-2's with the original baluns connected to 50-foot RG6QS coax), in fact it might have been slightly worse.

Using a couple always-on data, NOAA, ATIS and AWOS stations and a couple regional trunking system control channels as beacons I compared each for indicated signal strength and apparent quality with an R8500. With what I have it is a pretty decent comparison of the antennas with each other.

My results show that the ST-2 and the SkyBand performed the best overall of the batch, with the D130NJ and the Omni-X performing worse. The SkyBand and ST-2 perform better than I was getting with my old antenna setup, the D130NJ and Omni-X slightly worse.

A good chunk of this can be attributed to location within the attic I think. There are quite a bit of AC ducting there as well as the airhandler/furnace itself. The ST-2 is in the same location as it was, just to the side of the airhandler and at about a 45 degree angle due to the slope of the roof. The D130 and SkyBand discones are in the clear to the side of the airhandler and the Omni-X is along the outside wall at the far end of the attic, in what I thought should be the best place.

I want to give them all a fair shake however so after a week or so of trial I will go up and reposition the antennas and swap some coaxes around to see if that changes things. I wonder too if the potential directionality of the Moni-X has anything to do with it, I might first just go up and try repositioning it so it faces a different direction.

As for the other antennas I have a couple ham dual banders and a UHF GMRS antenna. For grins and giggles I plan on trying them out when I get around to a more detailed analysis of the group. I suspect they would work pretty well on UHF and VHF stuff but poorly on 800.

 

[vagrant]

I have done a bit of testing. The antennas were a Radio Shack and Tram discone, as well as an ST2 antenna with each using the same mast location and height, and most of it on the same day. I used 50' of RG6, LMR-400, and LDF4-50A 1/2" Heliax. For 100~500 MHz testing, either discone using the LDF4-50A Heliax were the winners for a 360° pattern with LMR-400 next and RG6 close behind. The ST2 did show a few dB more of gain when aimed at the different transmitter sites. I should note that the ST2 was mounted at the top of a mast with the metal behind the lower end of it. I am unsure if it acted as a reflector in some way, as I did not perform A/B tests using a non metallic mast. Also, the LDF4-50A used a short patch cable indoors, due to its reduced bend radius.

There is a money jump from RG6, to LMR-400 to LDF4-50A coaxial cable. Also, LDF4-50A is heavy, stiff, costly and one will need a patch cable, or maybe two at the ends. It even bent/destroyed a piece of mast when lowering it down due to the weight, as it is meant for tower use. If one is monitoring strong, or nearby signals, RG6 works fine even if it is 75 ohm. LMR-400 or the Ultra Flex version I feel is a worth while upgrade when signals are at the fringe. LDF4-50A is a beast, but works fine on a tower. Many reading this are already aware of the coax differences, but I was observing numbers greater than a standard attenuation chart shows.

This thread had me reviewing my testing numbers again and it was overall worth the effort, but that's the fun part of the hobby for me. I may still try an Omni-X for testing later, but I am using LMR-400 and a discone now. I also use a diplexer and separate antenna to handle 770~940 MHz stuff. Most of the LDF4-50A is handling TX/RX radios and repeaters, but I would see a benefit for what I monitor and will probably add a run for the receivers/scanners next week. The design of the Omni-X seems like it would have some directivity/nulls, so a discone would be my preferred wide band antenna.

* Everyone's geographic/RF location is different. Add to that different receivers, coax, antennas, antenna height and mounting locations, etc. and it is a smorgasbord of results. Experimenting/upgrading is worth while if favorite signals are weak, but a discone and LMR-400 is a pretty safe bet for 118~470 MHz. I used an SDRPlay RSP2 to get some numbers.

 

[N9JIG]

In retrospect I think that using SuperFlex LMR400 might have been the better choice for me. The Air-10 coax has fantastically low loss but is extremely stiff and requires pigtails at the radios. I think overall the use of a pigtail and the stiffer coax still has less loss than a straight thru SuperFlex run of the same length but the difference is likely to be negligible in my situation.

The ease of use on the SuperFlex is readily apparent, I have one length of it and it is by far the easiest to use.

 

[NYAirOne]

In retrospect I think that using SuperFlex LMR400 might have been the better choice for me. The Air-10 coax has fantastically low loss but is extremely stiff and requires pigtails at the radios. I think overall the use of a pigtail and the stiffer coax still has less loss than a straight thru SuperFlex run of the same length but the difference is likely to be negligible in my situation.

The ease of use on the SuperFlex is readily apparent, I have one length of it and it is by far the easiest to use.

Rich
I use the Davis RF Bury-flex LMR400. Works great and you can make some pretty good bends to it feeding it places. I have a straight run from my discone to 8-port multicoupler and then use jumpers from multicoupler to radios. Just put all new jumpers on from USA coax. Got Times Microwave LMR-240. Real nice cables and they were made up and shipped quick.

 

[rbritton1201]

I put my Omni-X in a Christmas Tree Stand in the attic, works especially well for orienting the antenna in the most advantageous direction for signal reception, it is protected from the weather by being in the attic, and it performs extraordinarily well, much, much better than my former Discone. The feed line is about 60 feet long, uses RG213 coax, with a short (6') RG8X pigtail lead between the end of the RG213 in the shack and the SDS200, so that it takes some of the strain off the back of the SDS200 when connecting up the coax to the scanner.

Getting there:

All the antennas and coax have arrived. I might go up in the attic and do some preliminary work this weekend before the helper arrives.

View attachment 115319

 

[fireman_dude]

I am using an Archer (Radio Shack 20-176) antenna mounted to a roof rafter in my attic. I live in a bi-level on a hill in Southern New Jersey. Just to give an idea of how well it works, on a clear night I can receive all 5 Boros of New York City. NYC is about 88 miles from me by car.

 

[vagrant]

I am using an Archer (Radio Shack 20-176) antenna mounted to a roof rafter in my attic. I live in a bi-level on a hill in Southern New Jersey. Just to give an idea of how well it works, on a clear night I can receive all 5 Boros of New York City. NYC is about 88 miles from me by car.

If I was unable to fit an eight element discone, after removing the stop stinger due to the attic environment, I would begrudgingly use an RS 20-176. Please note that I am trying to receive distant 360° transmissions. My RS 20-176 does work with strong signals, but I avoid it due to my needs.