HF antenna quandary

[del1964]

I'm a broadcast feed provider for the VHF and 800Mhz SAFE-T system in Indiana using an ST-2 antennacraft scantenna mounted on top of my 2 story house on a mast secured to chimney. Works very very well.

Ok so now Since the advent of SDR and affordable rtl-sdr dongles and my awesome huge gaming laptop that I use for work programming CAD Catia V5 and 3D cutter paths for our laser cutting machine, I've delved into the 0-30Mhz band monitoring (would love to become a licensed HAM operator). And so I bought an end fed long wire antenna and have failed to get better reception than when I hook up to my ST-2 antenna. I ran the longwire through the inside peak of my attic and back down through a rear closet and hooked up to a coaxial cable hooked up to the box provided. Poor reception but maybe even more importantly is the huge amount of NOISE all across the bands. Whew. And getting up into the attic was no fun with the fiberglass insulation and low head room and taking careful steps across the framing of the ceiling. What am I doing wrong? Should I be getting like X times better reception with a long wire versus the low low noise and pretty darn good reception on that ST-2 antenna? Can anything be added to the ST-2 to improve HF reception? Are there vertical pole antennas that would work better mounting near the ST-2 antenna???

 

[del1964]

View of the ST-2 that seems to perform well on HF

 

[ka3jjz]

Hmm...the ST2 is really a bunch of dipoles with a common feed point. I can see where it would work fairly well on HF down to a certain point, then the response will probably fade off rather dramatically (likely below 10 Mhz or so...).

The antenna in your pic should work just fine in an attic, but as you found out, putting it indoors increases the chances of it picking up lots of noise from just about anything in the house. Anyway, the best place for this antenna is outside, as far away from the home as possible. Where did you get this antenna from?

I wouldn't put anything vertical near the ST2. In fact, some folks have done just that and found that it made the antenna somewhat directive (favors a certain direction), instead of roughly omni directional. Don't add anything to the ST2, as you'll likely interfere with how the dipoles interact with one another (although there is a mod to reinforce the long dipole element against high winds...).

It looks as though there is a ground lug on one end of the box of the antenna in the picture. If you were to mount the end with the box fairly low, ground the box and run the opposite end up into a tree or such, it should, in theory anyway, work pretty well as a sloper. Just get it away from the house as much as possible

It's almost impossible to quantify 'X times better reception' because HF doesn't work that way. You need to use the antenna for awhile, and learn how propagation and solar conditions will impact how you hear stuff on HF. Only doing an a-b comparison over time will tell you how well - or poorly - the wire antenna is working.

Mike

 

[ka3jjz]

Something that I didn't consider here - if a SDR is being overloaded, it will show up as an increased noise level. So when you had the antenna in the attic, and noticed the higher noise level, did you reduce your receive gain?

Having the antenna indoors would certainly increase the noise floor, but this is yet another aspect of these little SDR dongles that not many always consider...Mike

 

[majoco]

The OP hasn't said what he's using for an HF receiver? SDR with an Up-converter?

 

[ka3jjz]

Well he does mention having an interest in the rtl-sdr, and that he has a laptop. The assumption here is that he is indeed using a rtl-sdr with an up converter.

Besides from what I've been reading an increased noise floor can be caused by overdriving these little dongles. Much too easy to do, frankly. A little logic suggests he probably has the gain set kinda high to be able to hear HF on the ST2 with any decent signal levels - maybe too high for the wire antenna

Mike

 

[ridgescan]

Like ka3jjz pointed out, on that end fed antenna-did you connect a ground to the ground lug for counterpoise? It can be something nearest the feedpoint like the electrical service conduit of the home, a cold water pipe, etc.
I would give that a try before giving up on the wire.
Can you ID any ground sources close to that endfed transformer box (say within 10')
IMO a good RF ground would make a difference.

 

[del1964]

Thanks guys/gals? HaHa. (Never know)

Thanks for the input guys. Yes. RTL-SDR dongle with HAM IT UPCONVERTER.
I never even thought of overdriving the dongle. Need to re-do that test. But..............you're also correct. I did not ground the unit for the antenna. They suggest grounding for lower HF bands. So.......I'm going to try grounding either to cold water pipes through the wall is the upstairs bath. Or drill a hole through the outside wall which is right there. Haven't decided yet. Attached is a "sketch/drawing" from the antenna supplier. Sloping design and horizontal.

 

[del1964]

Sketch of optional antenna install

Second attachment

 

[del1964]

Floor...

Through the upstairs bedroom floor where I'm attempting this hookup, is the main electrical box for the house inside the garage. Straight down as a matter of fact. Forget the drill through outside wall idea. Whew. HaHa. So my install should closely represent the horizontal method with a slight downward "L" as it comes down from the pitch of the roof into the closet ceiling and down to the floor where I'll connect the transformer. Is a "tuner" recommended???

 

[ka3jjz]

Why the manufacturer (who distributes this antenna, del?) recommends one is not real clear, but you won't hurt a thing by not using one right now. These little dongles have so much gain on them that you probably wouldn't notice the difference.

Depending on your local environment you MAY need to add some front end filtering to keep any stray MW or FM signals out of the converter, but let's not borrow trouble just yet.

How much wire comes with that antenna? Mike

 

[del1964]

Why the manufacturer (who distributes this antenna, del?) recommends one is not real clear, but you won't hurt a thing by not using one right now. These little dongles have so much gain on them that you probably wouldn't notice the difference.

Depending on your local environment you MAY need to add some front end filtering to keep any stray MW or FM signals out of the converter, but let's not borrow trouble just yet.

How much wire comes with that antenna? Mike

It's 53 feet long #18 wire with 9:1 UNUN matching unit (whatever that is) Power handling 100W
6m-80m coverage according to item description. Item 191501224179 on Ebay $50

 

[cognetic]

Living in the midtown area of Indy (Broad Ripple), long wires have not been very successful for my environment. Add to that, most SDRs seem to get overloaded.. add the interference, overload... well... It just wasn't working. I've tried G%RVs, end fed Zepps, simple long-wires, etc.

I have had great luck with these antennas below (vertical and loop):

For Receiving (Loop):
Active Loop ALA1530S+ Imperium
Active Loop ALA1530S+ Imperium

For Transceiving or just receiving:
SIGMA EUROCOM SE-HF-360 FIBRE GLASS VERTICAL ANTENNA 80 TO 10 METRES
Sigma Eurocom SE HF 360 Fibre Glass Vertical Antenna 80 to 10 Metres | eBay

SIGMA EUROCOM SE HF X-80 & HF-360 PLUS KIT
Sigma Eurocom SE HF x 80 HF 360 Plus Kit | eBay


-cognetic

 

[ka3jjz]

I'm willing to bet that the tuner recommendation would apply if you were a ham trying to transmit on the 80 meter band - the wire is simply too short to be very effective. You're not transmitting, so I would ignore the tuner for now. Concentrate on getting a workable setup first

As is, the antenna should work pretty well until you get to about 5 Mhz or so. The 60m tropical band should be heard OK, but go lower than that, I would expect the response to drop off gradually. You'll hear stuff on 90 and 120m, to be sure, but not as well

At some point you might want to make that wire length longer, but proceed with caution. Too much antenna and you will run into overloading issues. We're not talking about using this antenna with a R75 here. There just isn't the robust front end filtering on these dongles that you get with a good receiver.

Mike

 

[del1964]

I'm going to experiment with the wire in the attic with grounding. Then I've got several longer lengths of wire I'm going to try and run up to a very high tree top outside the house and/or between two tree tops in the back yard....with grounding. Shooting for 3/4 wavelength for the 20M band and.....see what I can pull in. No tuner....not transmitting. At this point I basically want to beat the ST-2 antenna reception and noise rejection which I logically should be able to since it's not "designed" for under 30 Mhz.



Wish I could afford one of these as mentioned above:

For Transceiving or just receiving:
SIGMA EUROCOM SE-HF-360 FIBRE GLASS VERTICAL ANTENNA 80 TO 10 METRES
Sigma Eurocom SE HF 360 Fibre Glass Vertical Antenna 80 to 10 Metres | eBay

 

[majoco]

Unlike the PAR antennas, they haven't shown you how the Unun is wired internally. It may be that the support loop has to be grounded as it may be the other side of the primary of the transformer, or the loop may be just a physical support and the ground is through the coax cable outer. The UHF socket is connected to the secondary of the transformer.
The unun changes the nominal (very!) 450ohms of the antenna to the 50ohms of the coax and hopefully the radio - the tuner isn't doing anything although it may act as a bandpass filter - more than likely it will reduce the signal!
I have been using a 45ft. homebrew antenna just like this for years and it works very well.

 

[nanZor]

Del - I run a similar antenna myself for HF. When you can't obtain a GOOD rf-ground, such as in your case, or have the ability to run many radials out from the ground lug of the UNUN across the ground, you need to choke off the common mode current from the coaxial feeder. When there is an insufficient rf ground, the coax becomes a single "radial" so to speak.

All the UNUN does is provide an impedance transformation, but there is no choking of common-mode currents. (the "outside" skin of the coax braid if you will) This makes it very susceptible to becoming part of the antenna itself, and can easily transfer rf noise from your computer gear onto the braid of the coax, up to the unun, and then back down *inside* the coax in what is known as transmission-line mode. (normal operations)

Here, a 1:1 ferrite RF choke is handy. An inexpensive MFJ 915 (there are others) is an easy way to start, although there are a few options to place it for best effect:

https://www.youtube.com/watch?v=-7d1W24Ib_c

One place is right near the rig itself. Or you can place it with a small jumper right after the UNUN. Or perhaps near the ground, and then a coax run back into your shack. I would recommend either up near the unun, or near the ground when you have a "flying" coaxial lead up in the air.

Your antenna, even if well choked, may be so near rf noise sources, that this may not make a noticeable difference. Still, an RF choke for what is an inherently unbalanced antenna is solid engineering practice.

 

[del1964]

Got it grounded to main electrical box ground. Also play with gain settings and noise is virtually eliminated (compared to before ground and max gain). S0...the attic end fed long wire antenna works very well now. Also should mention that the large steel post with ring coming out the one end is NOT a ground....Only there for attaching a rope or whatever to hang the box. It's not connected to anything inside the box. I used one of the screws that holds the coax connector to afix the ground wire best I could.