CAPACITY HATS FOR HF MOBILE ANTENNAS - testing the DX Engineering "Hot rodz"

What is a capacity hat?

Rather than explain it here, you can find a nice section dedicated to Capacity hats at K0BGs website


The goal of todays experiment: see how much a Cap Hat lowers frequency

(As usual, you can click on any of the photos to enlarge them)

I started with a quarter wave on 10m made up of two screw together sections plus the base of the hotrodz sytem :

 

As  you can see below, it was a bit long and resonated aroud 27 MHz, but since this is just for comparison, it doesnt really matter. 

I then added two 24" sections at the top to make a "T" shaped top loaded antenna.

 

As you can see, it brought the resonance down to 20.4 MHz, a 6.5 MHz drop in frequency.



I then took the bottom 4' section off, leaving the antenna at around 5' long

 

 

I ws unable to measure the resonant point since my analyser only goes up to 30 MHz but we can asume maybe 31 or 32 MHz.

The next step was to increase the capacity by installing another 4 24" rods

 

This brought the frequency down to around 25.6 MHz.

 

 

To see if I could raise the frequency I tried "shortening" the tips. After a few attempts using trial and error, I shortened each tip by approx 6 " (sorry, I didn't measure them) 

 

 And managed to get this final result



 

 



 

 

 

So, am I going to start using cap hats from now on to reduce the height of my antennas without losing much efficiency?

 

The answer in my case is no, and the reason is because of the weight/stability of the antenna system. The mast and hub is heavy duty and makes a pretty top heavy system for using with my puny ball mount on the roof. Not to mention that in my case where the antenna is always installed and taken off every time I park up, this is too long and unwieldy.a process.

 

Where I might use this information is if one of these days in the future I might decide to make a shortened 80m vertical on a spiderpole, for a contest or something. Or, to make vertical dipoles like the old Force 12 Sigma or XR series antennas for using in phased arrays or 4 squares on the dock, where I'd like to keep wire on the ground to a mínimum.

 

 

 

 

 

 

 

 

 

 

 

 

 



 

GROUND TUNING UNITS (GTU) IN A MOBILE

To GTU or not to GTU, that is the question.....

Something amiss in the new car?

Over the last couple of years, there have been a number of expeditions active which I needed for a"new entity", but was unable to work. In spite of doing my best to come on at the right time of day, and in spite of trying all the DXing tricks of the trade, I just wasn't making it through the pileup. Many of my local friends were making the contacts, so, I started thinking that maybe something was up with my station. I started suspecting that when I changed cars, something went amiss with the new antenna installation, or that there was maybe a problem with the antenna itself.

Parallel to this, I was reading a lot on the Real HF mobile yahoo group about how people were using GTUs (ground tuning units) to enhance their pedestrian mobile signals. Many of them were reporting good success, and I know that at least one station used a GTU on his car as well.

GTU theory
So, what is a GTU? Well, basically all it is is a device, similar to an Antenna Tuning Unit, which uses an inductor and a capacitor in series to maximise current flow in the radial system and therefore make the ground system less lossy and hence the whole antenna system (radiator+ground/radial) more efficient.

Attempt nº1
My first attempt at trying a GTU system was last year. I purchased an MFJ 931 artificial earth, which in theory does the job just fine. In order to isolate the antenna from the car body, I used a magmount on top of a plastic book binder. I connected the base of the magmount to one end of the the MFJ, and then the other end to one of the bolts on the antenna mount which is grounded to the car body. Result? Nowt. Zilch Nada. Couldn't get a current reading at all, anywhere, anyhow. Thought the MFJ was dud and even though I opened it up and couldn't find anything wrong with it.

Back to the drawing board

More DXpeditions came along and whilst some I was able to work, others continued to elude me. So, back to the drawing board it was.

I contacted GTU guru Dave G4AKC, who is a very well know signal on the bands, either pedestrian mobile or bicyle mobile. Dave wrote back to me to say:

Quote:

The first thing is to ensure the antenna is resonant against a resonant radial(s), this is best done using an antenna analyser and of course with the antenna off the car and the antenna length set to provide 50 ohms at resonance as you would expect. I usually resonate my vertical antennas at home on the top of my flat garage roof, so the radials are elevated and are located about a quarter mile from the sea, however I don't think it will make a lot of difference unless you are in the fresnel range of the sea where we get the enhancement to our signals.

 

The antenna is then refitted to the car and the antenna length is not changed, I know you are using the MFJ-1979 so I guess a mark to identify the length at resonance.

Its essential that the radio is isolated from the car body with regards to an RF path and so the radio needs to be physically kept off the car body and the DC negative line is taken via a simple toroid with several turns of this DC negative line wrapped around it and this is sufficient to prevent a direct RF path back to the chassis. As long as the toroid includes the negative return feed it shouldn't make any difference if you toroid both the + and the -ve lines, however you will need to get at least a couple of turns around the toroid for it to work effectively, so a large toroid will be required! You will have to toroid the amplifier negative line as well, but the clip on large toroids are fine as long as you can get a few turns around them to produce a high impedance path to the car body.

 

The braid of the coax feedline at the antenna end is routed via the GTU, if you are using a mag mount its easy to run a wire from the frame of the mag mount back to the GTU and then returned to the car body.

If you have a bonded mount then of course this needs to be insulated from the chassis of the car.

I usually tune with a low power carrier so as the ground current is at maximum, this current and tuning point alters depending upon location due to different ground conductance as you would expect and of course different settings for different bands, however generally once you have set the GTU for a particular static mobile location the setting will remain pretty much the same every time unless the location is very tidal.

 

You should be able to produce a considerable amount of ground current when near to the sea, I  can get as much as a couple of Amps of RF ground current at high tide with the bike running high power, so you will definitely know when its working properly, the key is to RF block any direct path to chassis other than the GTU path.

 

Unquote

 

Shopping!

 

I wanted to use the hustler mount on the car, so while checking out stuff on the web I came across these wonderful 45KW insulators by Breedlove antenna mounts. By the way these folks do an excellent line in all things antenna mounting.

 

I also thought it was high time to invest in a field strength meter so bought myself a cheap and cheerful MFJ 802 meter . I've read now in so many places that the best way to tell if antenna A or antenna B work better is simply by seeing if the near field is stronger or weaker. There is a great article by G3TSO where you can read all about this and other questions of resonating HF mobile antennas.

 

Attempt nº 2

 

So, once I got all the bits and pieces together, I went up to my house at La Eliana (where I can get peace and quiet, plus a soldering iron near the car if needed).

Before starting, and although most of the tests weren't using the car body, I followed Dave's suggestion about the toroids and snapped on a few to the rig's negative lead.

 

The first thing I did was try the MFJ 1979 in its usual position, using the untuned car body for earth. Here's how it looked on the analyser for SWR and resonance (reactance X = 0):

(remember you can click any of the images for larger size)

 

Ok so this looks pretty textbook and to be honest I don't remember that it looked like that last time I put the analyser on it.

The next step was to insulate the antenna from the car, and use a quarter wave radial cut to the exact same size as the radiator

This is what it looked like on the analyser:

OK, so it shifted down a bit in resonant frequency, and so obviously at the higher end we now see the L/C factor creeping into the total R. But still, not bad, and on the trusty FS meter (on a stepladder about 2m from the antenna), no noticeable change at all.

Then, the next logical step was to try tuning the radial with the GTU, so thats what I did:

And hey! The GTU Works! We got CURRENT FLOW!! :)

But you know what? Lower FS on the FS meter. Hmm..... What on earth (pardon the pun).

Here's how it looked on the analyser:

 

Again, an even lower resonant frequency and obvious departure from resonance (X = 0) the further away we get from the resonant frequeny.

Finally, I decided to tune up the coax that leads up the ball mount. This is what I was ulltimately aiming for, being able to tune either the cable or the body of the car for improved performance over the untuned car body. Well,. I was able to get decent amount of current to flow through the cable, but at the máximum current, the SWR was sky high on the radio's SWR meter. I didn't take any readings on the analyser for this. And also, the FS meter reading was a fair amount lower than for the previous configurations.

CONCLUSION

I am going to retest the "usual position" next to the water to see if it replicates the above readings.

If it does, the conclusión is that whilst GTUs are obviously good for improving performance of small counterpoise trolleys, bicycles, etc., for a larger metal object like a car, there is no advantage to be had. Unless of course Dave G4AKC can convince me otherwise!

 

 

 

 

NAVASSA - FEEDBACK AND LESSONS

I am a member of GMDX, the scottish DX group. Recently they held their annual meeting, where several DXpeditions gave presentations. One of them was the K1N expedition to Navassa Island. A transcript of the presentation was then published last week in the GMDX digest and I thought it would be of interest to copy the last part of the presentation, FEEDBACK AND LESSONS, food for thought for all of us:

 

 

"Feedback and Lessons

I learn a lot from every DXpedition I’ve ever been on. I’ve put together a summary of my two weeks of operation from Navassa. I’m sure all of my team mates will concur with what I’ve observed and learned.

European stations complained a lot for the “short time” we worked Europe. QUITE THE CONTRARY!!!!

This is a MOST interesting point of discussion! If you look at the times in our logs, we spent MORE

time working Europe than working North America. Our ClubLog statistics, however, show that North

America had 58% of the contacts, Europe 32% and Asia 6%. WHY, then, if MORE time was spent

working Europe, was Europe about half the number of North American contacts???

Simple answer: RATE. Period.

When you listened to us working North America, we could cruise right along at 300-350 Q’s/hour or

more! I have seen the “rate meter” hanging around 500-600 Q’s/hour for some times. (I heard that

someone on the team was clocked at 1200 Q/hour…..on 160M!!!!) When working Europe, we would be extremely lucky to see rates of 100 Q’s/hour. European signals are as strong, if not stronger than North American signals, in the Caribbean. The west coast U.S. is much harder to work than Europe. South American signals were among the strongest!

Here is a note I received after I returned home. It is from a well-known DXer in Europe:

“I listened to XXX working US pile-up on 80m. Fantastic, at least 10 QSO's minute and when he

turned to listen for Europe, the rate was only 10 % of that. Same on the other bands and modes.”

The problem is THROUGHPUT. Rate. Efficiency. Cooperation. Whatever you want to call it.

For the time we spent working Europe, we should have MORE contacts than with North America, but that did not happen. It COULD have happened!

No one more than me would like to have seen the European Q’s outnumber North American Q’s. For

the “next one” I have some helpful suggestions to help DXers, including myself, and particularly DXers in Europe, to be more successful.

Here is what I see are the issues:

1. Not listening to the DX operator

2. LISTEN to and LEARN the rate and rhythm of the operator

3. LISTEN to WHERE the operator is listening and his PATTERN of moving his VFO. You

MUST KNOW where he will listen next if you expect him to hear you! How simple is that? It

is part of the hunt…and the fun of DXing….and getting rewarded!

4. Learn to use your radio (split/simplex, etc)

5. Do NOT jump to and call on the frequency of the last station worked. The DX station will

NOT hear you because the din is total unintelligible chaos. Move UP or DOWN from that
frequency, as we on our end were continuously tuning up or down after each Q, so if one jumps
onto the last-worked frequency, we will not hear you, even if you were the only one there, as we
have already tuned off that frequency.

6. TURN OFF ALL SPEECH PROCESSORS AND COMPRESSION! Do NOT overdrive

ALC. There is a night and day difference in listening to NA/AS and EU pileups. The horrible
distortion makes it impossible to copy many, if not most European callsigns. I don’t know what
it is, but I would bet that mike gain and compression controls are “firewall forward,” all the way
clockwise. There were MANY loud stations that we did not work, COULD NOT WORK, simply
because we could NOT understand their terribly distorted callsign. Have you ever listened to
yourself in a pileup? We gave many stations a “19” signal report. Very loud, but extremely
unintelligible! You want to have INTELLIGABILITY, not distortion!

7. Give your callsign ONCE and ONLY ONCE! DO NOT KEEP CALLING! Call. Listen.

Call again if needed. Listen. Listen. We would tune on by those who did not stop calling.

We are looking for RATE and getting stations into the log. You should be, too!!!

8. If the DX station comes back with your callsign, DO NOT REPEAT YOUR CALLSIGN, AS

WE ALREADY KNOW IT or we would not have answered you. Many stations (in all modes)
would repeat their callsign two, three and even four times or more! This was so frustrating at
times that we would just move on to the next station. We ONLY want to hear “5NN” or “59”
from you. Anything else is a total waste of time. Let me repeat, if we come back with YOUR
callsign, DO NOT REPEAT it back to us! (Did I repeat myself?.....forgive me!) It CHEATS
others out of a chance to get into the log. Only repeat your callsign if it needs correction, and
then let us know it is a correction. Anything else is cheating others out of a contact. Others are
cheating YOU out of a contact! Our propagation windows and time on the island are limited
and we need to maximize the opportunity for everyone. SPEED and EFFICIENCY ARE OF
UTMOST IMPORTANCE!

9. LISTEN to the DX station come back to someone. IF THERE IS NOTHING CLOSE TO OR

RESEMBLING YOUR CALLSIGN……SHUT UP! SHUT UP!!!!! This needless interference
slows things up and lessens YOUR chance of getting into the log! We are focused on the
callsign we heard and do not hear you, only your QRM’

10. Take some time to listen to the next DXpedition working North America and listen to the rate

and rhythm of the operator. It is fast, quick and efficient, and more people get into the log!
Then listen to him work Europe. The wise operator will catch on quickly to what it takes to get
into the log!

11. SPREAD OUT! Our highest rates (for any continent) were working the center and far edges

of the pileup where there was less QRM. Weak stations were much easier to work than loud
stations in the middle of the pileup. If we say, “Listening 200 – 210,” 70% of the pileup sits
exactly on 200 in an unintelligible din, 25% of the pileup sits on 210 and is almost as bad. 5% of
the pileup will be spread out somewhere between 201 and 209, making them very quickly put
into the log. S P R E A D O U T ! ! ! ! Dare to be different! Dare to be heard!

12. LOUD is NOT better! MORE AUDIO/COMPRESSION is NOT better! Finding the spot to

be HEARD is the MOST important thing you can do to get into the log. My biggest thrill (and
I’m sure on both ends) is finding the lone weak station and getting him into the log quickly.

13. LISTEN to the DX operator INSTRUCTIONS! As we would constantly tune our VFO, if
we find a clear spot, we would often say, “33” (meaning for YOU to transmit on 14033, 28433,
etc). A few would listen and get into the log very quickly. You cannot hear these hints if you
keep calling calling calling calling……… Many times I would say, “listening 200-210” and
after a while would say, “listening 240-250”. Often 30-45 minutes, even and HOUR later, I
would find MANY still calling on the original “200-210”…..of course, they would never show up
in our log, as I was not listening there. LISTEN, LISTEN, LISTEN and LISTEN SOME MORE.
The less you transmit, the better chance you have of getting into the log. You must know where
I am listening if you really want to get into the log.

14. LISTEN to the “good” guys to make it into the log. Study how they do it! It is not easy to

find the “good” guys, as they are quick and efficient and are in the log and gone, long before
anyone can find them. They don’t transmit much. They are listening.

15. LISTEN to the “bad” guys. It won’t take you long to find them. They keep calling and

calling. They aren’t listening to find out where to transmit or they wouldn’t be calling. How
simple is that? Being LOUD helps, but not if the DX is not hearing you!

16. If you don’t want to get into the DX log, just ignore the above suggestions, and keep calling,

calling, calling….. I wish you the best of luck. You’ll need it."

PLEASE RESPECT MY CQ DX CALL

I never thought I'd need to post this but in view of what I'm hearing on the air these days, perhaps it's not a bad idea.

What is DX?
As far anyone can tell, the terms means "distance X", and in modern day English has the equivalent of "LONG DISTANCE". Now, its clear that this term is subjective and not the same for everybody. Long distance on uhf is not the same as on HF, for example, nor is it the same for someone running qrp and simple antennas as someone using a more sophisticated setup.

In order to qualify what DX means, it was established in times well before I was licenced that DX on HF is a station on another continent. This was, and is, the definition I and millions of other hams understand and accept.

However, in view of the fact that it seems a large number of hams might never have had this fact clarified, I think it's time to set the record straight, even if it is only on a little-read and uninfluential blog.

IF YOU HEAR ME CALLING CQ DX, I AM LOOKING FOR CONTACTS ON ANOTHER CONTINENT. PLEASE RESPECT ME.

Now, it may well be that you are in Europe and want to give me a call for some reason. You might want a qsl from my province, you might want a rig check, or you might be a friend wanting to say hello. Does this mean you shouldn't call me? No. What it means is the following:

Please listen.

If you hear me working another station, please don't call.

If you hear me call DX but don't hear anyone come back to me, please don't call. There may be a weak DX station calling me that you can't hear. If you call at the same time, I will need to ask the other guy for a repeat.

If you hear me call more than once with no apparent reply, give me your call. If I don't reply, please don't insist.

If when giving your call you say something like "not dx but would like a short qso/antenna check /etc" there's a good chance I will reply.

If I do reply to your call, please keep it short.

I'm sure that at this point a number of readers will be indignant at my attitude. Please take into consideration the following:

My operating times are usually short. I am a busy man with a demanding job and with family commitments. I do not have all day to chat on the radio (I wish I did).

I live in a country that is the fifth least wanted on the dxcc list. In the event that you do need Spain confirmed let me know and I'll be happy to send you a card.

I do not always call dx. There are times when I am looking for a chat with anyone anywhere.

I don't always operate from a dx capable station and know what its like to be qrp or antenna limited and the only guy you can hear on the band is looking for dx. As you can read above, respect my call, if no one comes back after a couple of times then go ahead. I am sensitive to things like qrp, portable, and novice licence holders.

To recap:
For those who are unaware of what dx is, on HF it's contacts on another continent.
For those who think their need for a qso is more important than what I want, time to revise your operating. I am not a bad operator for not answering you. You are a bad operator for calling when you shouldn't.

Please feel free to comment if you I'm wrong!

MFJ 1979 telescopic whip

This entry is an update to the info already published about MFJ telescopic whips at this link

Basically, the MFJ 1979 is the logical extension of the MFJ 1977: the same improved quality and design of the 1977, but in a 5 metre (17ft) long version. This way, in one simple whip which you can put in the back of your car, you have an antenna that will work all bands from 20m to 6m, when telescoped out to the appropriate length.

Any comments to make regarding this new version? Well, I've had mine for about 18 months, average use several times a week so you can calculate its been telescoped up and down some 300 to 400 times. A couple of weeks ago on 20m I noticed that SWR had jumped up slightly, and after a bit of head scratching, I noticed that one of the sections had loosened up a bit and had slipped down into the one below. After a note on the "REAL HF MOBILE" yahoo group, it seems like many users of this antenna have had the same problem. The quick fix is a bit of insulating tape on the offending joint, the more permanent fix is apply some pressure with pipe tools or similar to make the joint stiffer again. Like the 1954 and 1956 models, life expectancy is not great, but at around 70 euros, I think its probably still worth it.

Performance wise this is like the other whips, it works very well and I have been able to net lots of good DX worldwide, including a couple of New Ones.

I bought mine at WIMO but they are also available now in Spain at ASTRO RADIO.

Happy mobiling!

A couple of strays

A wee rhyme I read on LA1BNA's QSL card (tnx Svein):

"The QSL, the holy grail,
The DX'ers joy that comes in the mail,
And though we prize these souvenirs,
It sure takes long - it seems like years!"


And now, check out the reason for KH6CB selling his radio!:

RADIOHF - FOR SALE; Kenwood TS-590S

Purchased from AES on 2-20-2013. Factory upgrades already done. Serial #B3100061. Bought this rig as back-up to my IC-7600. My amp blew-up when without knowing a 4 inch lizard got inside my amp and was laying on a RF coil. when I turned power ON, sparks, flame and smoke erupted from amp. Not only was lizard cooked but his intestines was splattered around the coil. Therefore - - I need cash to buy a new amp. $1300 + shipping (from Hawaii). Postal Money Order only. Thanks for looking SONNY KH6CB P.S. Absolutly NO issues with this rig. Still new condition. Approximate air time 20 hours.