Antenna for HF - RF Cafe Forums

 Post subject: Antenna for HF

Posted: Thu Jul 03, 2008 3:31 pm 

OK, I wasn't sure which forum this should go in (Antenna or Ham) but here goes.

I'm fairly new at Ham radio and I'd like to put up an antenna in my attic. I recently got a general license so I want to try HF (for once) and my living situation kinda hinders using an outside antenna (associations are prevalent here in So Cal). To get into the attic I first need to take the cable up through the ceiling (which is difficult). Therefore, I want to use some cable that I don't have to replace later for another application. It also needs to be good for frequencies from HF to, say, 440 band at least. I was thinking 9913 for it's low loss. This OK?

Also, what type of connectors are normally used? I think the radio has an N connector but in general what is best?

From there I'll just string up a dipole for now...

Thanks

jom

 Post subject:

Posted: Fri Jul 04, 2008 4:23 am 

Hi jom
You found the right forum.
If you want to cover all amateur HF bands, the choice depends mostly on the dimensions of the roof space. I am facing a similar decision process for a city center location for HG3OAD. I decided on a half size G5RV: a single coax feeder design that gives fairly low VSWR on all bands 40 thru 10m which I will feed from a Yaesu FC-707 tuner to iron out any remaining VSWR peaks. If you are only interested in 20-10m perhaps a Small Transmitting Loop with a remote-tuned vacuum variable capacitor might be better, because it keeps down the LF noise picked up by a long wire antenna in a roof space.
9913 feeder coax is OK. I will use something very similar: any large diameter Sat TV coax is good for HF. Most of them, however, are 75 ohms, which at HF is no problem, but at VHF/UHF the better choice would be LDF4-50 or similar foam coax.
73

 Post subject:

Posted: Fri Jul 04, 2008 4:33 am 

Jom
I also meant to advise on connectors.
If you plan HF thru UHF use on a single feeder, stick with N type.
Avoid PL259 like you would HIV. They are death at 432, even the ones that look like they have a teflon insulator. If N type are well put together they are good for a kW on a low VSWR system.
73

 Post subject:

Posted: Sun Jul 06, 2008 3:24 pm 

thanks for the replies!

A few things:

1) On the connector: My radio is an IC-7000 with, PL259 connectors on the back. So I guess I've already got HIV. Any solutions?

2) About the attic: It's above a two story home and is probably about 25 ft by 55 ft or so of space...roughly. It doesn't seem to me the 103 ft. GR5V is doable.

3) I also have a concern about fire in the attic. I read in QTS someone who used some load coils had some arcs that almost created a fire. Not good.

4) My roof is ceramic but I'm not sure what it was built with. Are these usually metal? If so, should I even be bothering with an antenna up there if it's nothing more than a Faraday cage?

5) I'd like to see if I can get as many bands as possible...even the lower ones.

6) I can't use some of that 450 ohm ladder line because I'd rather have something shielded running through the house. I could use some of it in the attic but I'd need a tuner. Are those passive or active? If active, how am I going to power it? There aren't many AC plugs up there.

Anyways, those are just some thoughts and concerns.

Again, thanks for the help.

jom

 Post subject:

Posted: Mon Jul 07, 2008 5:04 am 

Hi jom
Connectors:
The PL259 is only a menace on 70cm and 23cm. If you only have one in your system you would not notice on 2m, but with several the VSWR impact and the loss are bad.
"2) About the attic: It's above a two story home and is probably about 25 ft by 55 ft or so of space...roughly. It doesn't seem to me the 103 ft. GR5V is doable. "

No worries: the half-size G5RV will just fit in your 55ft roof space, with a mere foot or so bent down at each end so you can fit the insulators in. With this antenna the sacrifice is 80m.

3) I also have a concern about fire in the attic. I read in QTS someone who used some load coils had some arcs that almost created a fire. Not good.
The G5RV does not use loading or matching coils.

4) My roof is ceramic but I'm not sure what it was built with. Are these usually metal? If so, should I even be bothering with an antenna up there if it's nothing more than a Faraday cage?
Roof tiles/shingles are usually concrete based. The loss is minimal up to 70cm, so no problem for 3.5MHz-436MHz.

5) I'd like to see if I can get as many bands as possible...even the lower ones.
See above: with the G5RV half-sized with a 55ft top, you lose 80m.

6) I can't use some of that 450 ohm ladder line because I'd rather have something shielded running through the house. I could use some of it in the attic but I'd need a tuner. Are those passive or active? If active, how am I going to power it? There aren't many AC plugs up there.

The half-size 5RV uses a limited run of 300 ohm ribbon, then a 50 ohm balun. A tuner in the shack, ie remote from the balun, is useful because the G5RV does have peaks and troughs in the VSWR vs frequency curve. Whilst not serious, some solid state PAs might prefer to see them ironed out with a tuner. I intend to use an FC-707 with my FT-707 transceiver.
How does that sound?
73
G3OAD

 Post subject:

Posted: Mon Jul 07, 2008 12:24 pm 

Sorry for all of the questions but I've never used any of these things before.

On the remote tuner: How do these work exactly? The tuner would obviously be in the attic but how is it controlled and powered?

Any idea on how to get 80m or lower? Would some sort of large loop (seperate from the set up what we've already discussed) work?

On the connectors: If PL259 are a problem at 70 cm I now wonder why the IC-7000 uses them. There are actually two connectors on the 7000, one for HF and 6m and another for VHF/UHF and both use PL259. I guess I will just use a different connector at the other end of the VHF line. No sense in compounding the problem.

jom

 Post subject:

Posted: Tue Jul 08, 2008 11:02 am 

Hi jom,
No worries. The tuner sits next to the transceiver, because the VSWR on the 50 ohm coax feeder is quite low, but to ensure the transceiver sees a good 50 ohm match, the FC 707 (or similar) irons out the peaks of VSWR vs frequency. I think I am right in saying the half-size G5RV has a peak VSWR on 15 m, where it is about 2.5 to 1. Obviously there are high VSWR peaks, but G5RV designed it so these occur way outside the amateur band limits. I ought to look up the characteristics myself. Beware that some tuners, generally the lower cost ones, only have a limited range of Z adjustment and are only suitable for coax. Others have a very wide range of Z in to Zout ratio, withstand high power, and can drive a balanced line.
With the half-sized 5RV, a low cost limited range type like the FC-707 is fine. So the line-up is G5RV 55ft top, a balanced 300 ohm down-lead of limited length (much less than one leg of the dipole, but I forget how long. Look it up.) then any length of coax into the shack, then the tuner, then the transceiver. As the tuner is next to the rig, the adjustment is hand-u-matic, so no power is needed.

 Post subject:

Posted: Tue Jul 08, 2008 3:45 pm 

Thanks!

The 300 ohm down length is 30 ft I think (I looked up the G5 the other day). Do you know off hand if this 300 line has to come straight down from center of the dipole vertex? Or can it come off at an angle? For that matter does it have to be strung out tight or can it be just layed out? I'm not sure I can put 30 ft of it in the attic as I don't want any of that line in the house. Another words I want the connection from the 300 ohm to the coax to actually be IN the attic. I'm worried about the ladder line radiation if it has to come down into the house proper. There are people living there.

The ic-7000 has a companion matching device called an AT-7000 made by LDG or some such. I'll look it up to see how it compares to the one you use (FC707).

jom

 Post subject:

Posted: Wed Jul 09, 2008 3:53 am 

Hi jom
The half-size G5RV that covers 40, 20, 15 and 10m (and with some modification, 18 and 24MHz) needs only 15 feet of 300 ohm ribbon, and has a 51 foot top section, centre fed.
The 300 ohm feeder needs to hang down vertically for at least half its length, but can slope away from there. At the bottom of the 300 ohm section proximity to roof/floor is not so critical. At that point you need just a 1:1 balum into any length of coax. Thus most attics can accommodate a drop height of around 7 feet to the floor from the ridge timber. Run the 300 ohm ribbon along the floor (I presume this is timber) and into a 250W 1:1 balun. Any impedance change, due to the floor and any kink in the 300 ohm ribbon, can be ironed out by the AT7000 I imagine. Thus the 300 ohm ribbon is entirely in the roof space.
A number of companies produce the half-sized 5RV, but it is so easy to make, you can buy the bits and roll your own.

 Post subject:

Posted: Fri Jul 11, 2008 4:37 am 

Hi jom
Saw this on uk eBay today: gives you 80m with the half-size G5RV.
73 Trev

Hello and welcome to another m3zww / btb productions auction.


What we have on offer is a set of M3ZWW 80m inductors

If you are a bit tight for space this could be the answer.
Used to give you 80m from a half size G5RV.
I use these for /P work with a FT817 and have had fantastic reports, also used at home with FB reports
Just remove the insulators from the end of your g5rv crimp these on to both ends, and add another 6-8 feet for wire on the other side
(depending on what part of the band you want) re-attach the insulator.....job done!
You can even droop the ends down if needed!
Remember these are inductors and not lossy traps which will turn your rf to heat, (good for keeping the birds warm, not so good for radio work)

 Post subject:

Posted: Fri Jul 11, 2008 10:07 am 

I would like to suggest another antenna before you go to a lot of work on an in-attic antenna. Indoor antennas can work well, but they are a lot of work to get them to do so.

Here in southeast Florida, like California it is impossible to buy a house less than 20 years old that does not have a load of ridiculous deed restrictions. I know several hams that are happy with temporary antennas.

Buy a 20 or 30 foot telescoping pole (fishing pole). Cut off a piece of broom handle and sharpen one end. Go outside and stick this in the ground. Then slip the big end of the fish pole over the stake. Use the fishing pole to hold up your wire antenna. Use a 'antenna tuner' (matching network) and have fun on the air.

At least around here the deed restrictions cannot stop hams from doing this since it is not permanent. You take the antenna down when you are not using it.

 Post subject:

Posted: Mon Jul 14, 2008 4:59 am 

The last posting reminds me that many years ago there was a challenge mounted to a deed decision where an amateur had erected an aluminum pole that was an insulated vertical quarter wave with radials buried in his front lawn beneath it, and polypropylene guy ropes to support it. This ground plane idea was condemned and he was obliged under local statute to remove it, even though he pointed out that it served the dual purpose of a flagpole for the revered Stars and Stripes. He appealed and won, I think in the Supreme Court supported by the ARRL, because the judge deemed the removal order to be unconstitutional. So the amateur was able to operate on 20metres and fly the flag unrestrained.

 Post subject:

Posted: Mon Jul 14, 2008 8:25 pm 

Thanks for the help.

I bought a AT-7000 tuner and a G5RV that is supposed to work down to 80m (it has a pair of coils). It was literally hell putting the thing up in the dusty attic at an "elevated" temperature but I was able to finish. I still need to hook the ladder up to a coax line (which I don't have yet). These will have to be 259 as the G5RV already has a one of these connected to the ladder.

As to the vertical outside, that is a choice for my higher frequency stuff. I still need to drill thru the house to get outside (for the grounding of the radio) so I'll probably go that route with the VHF/UHF.

jom

 Post subject:

Posted: Tue Jul 15, 2008 3:32 am 

Hi jom
I had not realized it, but it seems I have led us both into shark-infested waters with this choice of antenna. On both qrz.com and eham.net it is clear the world population of amateurs is divided into those who love the 5RV and those who detest it. The half-sized one comes in for particular vitriolic comment from those who detest it.
Like you, I was busy with my 5RV build over the weekend. Preliminary results are baffling when measuring VSWR using an MFJ259B analyzer. The measured VSWR is greater than 10:1 over the entire spectrum from 7 MHz thru 30MHz.
People have analyzed the antenna (both versions) using EZNEC and such, and they report similar poor predicted performance, yet many others have worked around the world and comparison reports switching from 5RV to a tuned dipole report no difference.
One thing was very clear from all of that: you need a very good old-style antenna tuner that can drive parallel line open wire feeder and match a very wide range of impedances down to 50 ohms. These tuners do not come cheap, costing nearly as much as a second-user linear. The lower cost items almost certainly will not produce a low enough VSWR to satisfy a solid-state linear amp.
Depressing. If you want to get suicidal, google "half sized G5RV".

 Post subject:

Posted: Tue Jul 15, 2008 8:21 am 

Another thing, don't worry about the PL259/SO239 connectors until you start operation on 70cm and above. They are fine for HF and usable on VHF so long as there are only a couple of them.
Another nugget of wisdom from the eham.net reviews/experiences with the 5RV: the preferred position for the antenna tuner is right after the 450 ohm parallel line feeder section before the coax.
Not ideal I guess for your situation, but try it how we dicussed earlier. I certainly intend to do that and we can swap notes later.
73 G3OAD

 Post subject:

Posted: Mon Jul 28, 2008 9:21 pm 

OK, this is what I have so far:

1) I've got the antenna installed in the attic. The 450 ohm feedline I kept up in the attic. I meandered the feedline around so that it would stay in the attic proper. I brought the coax up into the attic and connected it up there. The "meandering" is not in a straight line by any stretch (literally). I sort of jigged it around the a-frame 2X4s and hung it over a few others.

2) The coax goes down into a room below. It is 50 ft long with UHF (PL259) on the end.

3) The radio is both the IC-7000 and its AT-7000 tuner hooked to the other end of the 50ft coax.

4) I have not got the radio in it's final location yet...therefore the radio wasn't properly grounded when I tried it. The room it's in now is on the 2nd floor so I can't get a ground line.

I tried the radio on all bands from 160m to 10m. The tuner was able to tune all bands except 160m (since the antenna isn't made for 160m that makes sense). This, of course, is AT THE TUNER. What is going on down the line is something I don't know. To check whether the matching was true I moved around each band a bit and re-tuned to see if it changed and it did. The radio has a function where it checks the SWR over a range (like a sweep). I redid this every time I retuned and it made sense as the tuning was only good over a short range of each band. I will check this more out when I receive an antenna/network analyzer I bought later in the week or next.

The part I'm disappointed about is my reception. There wasn't much I could pick up over most of the bands. I tried it both at night and morning and it didn't seem to make a difference. I caught a couple of conversations (one seemed only "one way" as I guess his partner was out of my pick up range). Mostly, I just got a bunch of noise and some tones.

This problem could be the grounding issue I mention, the antenna isn't too good or most likely the antenna location just sucks. I would hope it's the first problem but I'm guessing it's just the location. Ultimately, the antenna is, maybe, 30 ft up at best and my locale isn't great either.

Any thoughts?

Thanks

jom

 Post subject:

Posted: Tue Jul 29, 2008 4:57 am 

Hi jom
I was also busy with my half-sized G5RV over the weekend. I was only able to hoist it to 15 feet height outdoors. I have an Autek analyzer and an MFJ 259B. The antenna on its own, fed thru 450 open wire feeder 17 feet long gave high VSWR on 10 MHz, 18MHz, 21 MHz and 24 MHz.
I tried to broadband it, with great success. I took a roll of wide-mesh chicken wire 2 feet wide, cut it into 2 sections, and threaded each section over the two top wires of the 5RV. I replaced the 450 ohm open wire feeder with 100 ohm type (electrical twin flex), about 12 feet long. Then 50 ohm coax to the shack and the FC 707 tuner. It worked fine, and I had a number of contacts on 20m, 15m and 10m. Receives well on all bands 40m thru 10m. The analyzers show worst case VSWR 4.2:1 which is well within the range of the FC-707 tuner. This modification is easy to do, unobtrusive for neighbours if outdoors, and works well.
HF conditions last weekend were poor, but short skip sporadic-E was OK. The IOTA contest was running too, so activity was high, and you should have heard many signals during the day.

 Post subject:

Posted: Sun Aug 10, 2008 4:03 pm 

Hi jom,

I have the same situation in SoCal and about the same allowable area. I bought DX-CC antenna from HRO and installed it along the house wall right under the roof extension. Antenna almost invisible from the street and definitely does not impact the image of our community. Then I tuned it with MFJ-259 antenna analyzer and it works well. It is significantly outperform G5RV. Please let me know if you need any additional information about this issue.

73!

 Post subject:

Posted: Thu Aug 14, 2008 9:08 pm 

OM:

Which bands can you tune to? I'm trying to get everything from 80m-10m.

Thanks

jom

 Post subject:

Posted: Wed Aug 20, 2008 7:15 pm 

Another way of getting on HF with a "compromise" antenna:

Use a random-length dipole with a remote L-network, relay-switched autotuner mounted at the feedpoint; then run your coax from the tuner to your radio. A common-mode choke on the coax near the tuner may be needed to keep the RF out of the shack. There are a number of very efficient L-network, relay-switched autotuners available that can match a very wide range of antenna lengths all the way from 160 through 10 meters. Some also cover 6 meters.

If you're considering an amplifier, the high-power autotuner models tend to have narrower matching ranges and tend to be considerably more expensive than the 100-300W versions.

SGC, MFJ, and LDG each sell a variety of these. The important part here is to choose one that has low loss when matching a wide impedance range. Some models require control/DC power wires; others don't. Some have remote-control heads with manual tuning buttons & power/VSWR meters, others don't. Some will connect to a radio's CAT port, some don't. Most will tune with a just a low-power carrier (say, 5-10 watts). Usually, the circuitry measures your transmit frequency and automatically finds the most efficient match in a few seconds or so. The tuning solution is then stored in memory for nearly instant recall when you key up near the same frequency again. Some of these autotuners have thousands of memories. Many of them can efficiently couple power into a 40' dipole, or even a 23' ground-mounted vertical from 160-10 meters. For some of these, the only cable you need is the coax between the unit & your rig - the DC power is fed through the coax, using a device called a bias-T, and the tuning is done simply by briefly keying-up your radio at low power.

Attic-mounted, efficient antenna for 160-10 or 160-6 meters:

Build the longest dipole that will fit the attic, and mount one of these L-network autotuners directly at the feedpoint. Operate 160-10 or 160-6 meters on one antenna - with little loss from the tuner or feedline.

For horizontal antennas, antenna efficiency = radiation resistance/(ohmic resistance + parasitic losses). The key to efficiency with a short dipole is to use very low resistance wire for the radiators & use an efficient matching system. This is because a short antenna tends to have low radiation resistance. For a short vertical, a low-loss ground system is also very important, as the efficiency of a ground-mounted, Marconi-style vertical = radiation resistance/(ohmic resistance + ground system resistance + parasitic losses).

Since it's mounted indoors, the efficiency will likely be a bit worse than when mounted outdoors in the clear - due to parasitic losses such as metal conduit or wiring in the walls. A snow-covered roof can also reduce the performance of attic-mounted antennas.

In summary:

If your antenna is really short for the band you're tuning, its radiation resistance will likely be very low. In this case, a few ohms of wire resistance and/or 10-20 ohms of ground system resistance can cause much of your signal to be wasted in heating up the wires and/or heating the earthworms.

Concerning the "UHF" connector:

As others have said - the "UHF" connector is not an issue on HF or 6 meters, and is likely not an issue for casual operation on 2 meters, unless you're into weak-signal or EME.

Concerning Belden 9913:

Belden 9913 is a good choice for indoor use, however a number of people have had moisture problems with it when used outdoors. An alternative with similar performance is Belden 9913F7. The difference is that the 9913F7 uses a low-loss foam dielectric instead of air, like 9913 uses. This solves the moisture problem with little increase in the loss. At 150 MHz, a given length of 9913F7 has only slightly more loss than the same length of 9913 - not enough difference to notice at all at the receive end.

Another efficient "compromise" antenna (outdoor mounting only):

I'm very horizontal space-limited, plus - I'm renting the house. Fortunately - there are no antenna restrictions. Here's what I did to put out a decent signal at useful launch angles and in the most directions - on 160-10 meters - with only one antenna:

My lot is not large enough for long, high, horizontal antennas. I wanted to operate on 160-10 meters, and wanted to have a low angle of radiation on 160-20, so I could work some DX. I wanted as close to an omni-directional pattern as I could get on 160-20 meters, as well. I also wanted to rag-chew on 75 meters with the locals.

My solution was to build a 100' inverted-L - with the horizontal & vertical legs each 50' long; bury (33) 30-foot radials in the yard; and mount an SGC-230 L-network autotuner at the feedpoint. I hung the antenna from two trees - the vertical radiator just hangs down & is tied to the ground with a small bungee cord. From a distance, the antenna looks like a flat-top "T", except that one leg of the top of the "T" is rope. I operate this antenna from 160-10 meters.

Results:

I put it up last November, and have logged a fair number of DX contacts on 40 & 20 meters using SSB @ 100W - and I'm not a contester - just a casual operator. Plus, it plays very well on the low bands:

160 meters:

Although my radial field is quite small for 160 meters, it works surprisingly well down there. I can work a fair number of stations out to ~1000 miles or so on summer evenings, using SSB with 100W. In the winter, I can work most of the NA continent, but have yet to work any overseas stations.

75-20 meters:

On 75, 40, and 20 meters, most stateside & DX contacts are very surprised to learn that I'm running only 100W. Same thing on 75 meter local rag-chews - most think I'm running an amp. I enjoy some DX on 75-20 meters (mostly on 40 & up), and can sometimes bust pile-ups on 20 meters with my little 100W station. However, I have yet to work any DX on 75 SSB with it during the summer months. To date, my longest DX contacts on 40 & 20 meter SSB have been in the 5,000-6,000 mile range.

10 meters:

It has a number of high-angle lobes & deep nulls, however it also has some useful low-angle lobes with a lot of gain. In the favored directions, it performs very well, but the nulls are deep - I may work someone @ 20-over 9, but someone 20 degrees off the lobe may be in the noise.

Considering the poor band conditions over the past year, not too shabby for a "compromise" antenna, I think.

Conclusion: There are ways of getting on the air with a decent signal - even with short and/or "non-resonant" antennas. It's a matter of minimizing your losses.

On the other hand - I remember something an old ham once told me: Any antenna is better than no antenna!

Good luck & hope to work you on the bands!

_________________
73...

N0NCO

 Post subject:

Posted: Mon Oct 20, 2008 8:46 pm 

Well, I thought I'd give a quick update. After having some trouble with the G5RV lite antenna in the attic so I went and got this antenna called a "TAK-tenna". It is a spiral but it supposed to be a dipole (you can look it up on the web). It is small so I'm able to use it outside. The antenna only has a 30 inch boom and with it only about 6 feet off the ground I was able to tune it (1.3:1) on 40m. Not bad.

However, the reception isn't all that good. In fact, I'm beginning think it's simply may location...which would be a shame.

So, to summarize:

1) I've got a 50ft dipole G5RV (with coils half way down) up in the attic (ceramic tile roof) that I can get to tune (with tuner) on several bands (75m to 10m) and even had a contact on a 2m repeater. However, reception isn't all that great..a lot of noise.

2) This funky spiral antenna I can tune to several bands (40m 30m 20m) with a tuner. Same reception problem...lots of noise.

Overall, I think I need a better feedline or something as my tuner acts strange but more later...

jom