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Author Topic: Can I improve my single band HF mobile system?  (Read 5160 times)
HS0ZIB
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« on: December 10, 2011, 06:38:54 AM »

I only operate mobile on 20 meters, (due to the lack of availability of mobile rigs in Thailand).  I have an MFJ SSB rig feeding a 200 watt amp and use a Hustler resonator (and stinger) on a DX Engineering 24 inch mast, center-mounted on my car roof with a Breedlove mount.

This system works well, with daily contacts at dusk up 5,000 km, both mobile and parked.  But during daylight hours and after dark the 20 meter band seems dead.

At dusk, I can hear stations up to 10,000 km away, but they cannot hear me. (That's not really surprising considering my short, omni-directional antenna...)

What could I do (if anything), to improve my mobile station?

Would there be a benefit to using a longer antenna, (eg 2 x 24 inch mast sections), but mounted on my rear bumper, so as not to exceed the height of my current, roof-mounted antenna?

I realise that this is a trade-off between longer antenna and optimum antenna mounting location on a car.

Any advice is much appreciated.  I'd love to be able to have mobile QSOs during all daylight hours.  I suspect part of the problem is simply the lack of HF amateur stations within my immediate  region.

Simon
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W8JX
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« Reply #1 on: December 10, 2011, 08:05:57 AM »

I would try a different antenna altogether. I tried those antennas in 80's mobile and did not like them. I went to single band ham stick style ones and they worked well for me. Some like screw driver type antennas but Ham Stick clones are cheap and work well on 20. You have to change antenna to change bands but they can be had here for less than 20 buck US.
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AC4RD
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« Reply #2 on: December 10, 2011, 08:21:38 AM »

Would there be a benefit to using a longer antenna, (eg 2 x 24 inch mast sections), but mounted on my rear bumper, so as not to exceed the height of my current, roof-mounted antenna?

Simon, I spent a few months experimenting with this sort of thing, this spring and summer.  For years I used Hamsticks on a trunk mount, and I've played with the 1-meter short HF antennas at roof level, but I'm now using the Hustler/DXE system on a bumper mount.  (pictures at http://www.duke.edu/~kuzen001/ac4rdmobile.htm)

I suspect that for any given person, what works best has a LOT of variables, and there's no one best system that works for everybody.  One thing I like about the Hustler/DXE system is that it's easy and inexpensive to change things and experiment.  And I'd suggest you might TRY the bumper mount and see if it works better for you.

My current setup is the best I've had so far, for mobile.  I've got a mast long enough that the resonator is well clear of the roof of my box-shaped car.   K0BG says I might do better with a shorter mast and a longer whip/cap-hat setup, and I'm planning to give that a try one day soon.

For the record, the way I evaluate these mobile antennas is this:  How strong does someone need to be for me to have a good shot at working him?   With my current system, if I have someone at S3, I've got a decent chance of working him.  That's the best I've found so far.

So I'd suggest, if you have time, that you try that bumper-level mount and see if it works for you.  It does for me, but as I said, I think there are a lot of variables, and what works best for me might not work best for YOU.

HTH!  73!   --ken ac4rd

I've also
« Last Edit: December 11, 2011, 06:04:21 AM by AC4RD » Logged
K0BG
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« Reply #3 on: December 10, 2011, 10:05:42 AM »

The biggest drawback to Hustler coils is their large end caps, especially the high power ones. In fact, the bigger coils are actually lossier than the smaller ones as a result.

One of the problems nowadays, almost no one is making monoband coils, except Hustler. There is some company in the SE making some huge monoband coils, but the whips (if you can call them that) are only a foot or so long.

The issue here is simply this. One of the factors for determining the optimal position of the loading coil, is ground loss. However, doing all math, and the point is never higher than 60% (worse case), and is usually closer to 40%.

Cap hats help too, but they must be kept away from body work, and at the top of the antenna. In other words, not next to the coil where most folks put them. Ugh!
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WX7G
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« Reply #4 on: December 10, 2011, 02:16:19 PM »

Roof mounting is the best you can do. Bumper mounting would not work as well.

By reciprocity your signal will be as strong at the other station's receiver as his signal is at your receiver if both you and he are running the same transmitter power. You are running 200 watts and should actually be 3 dB stronger at the receiver of a 100 watt station than he is at your receiver.

The stations that you hear, but cannot hear you, are either running much more power and/or they are in noisier locations.
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HS0ZIB
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« Reply #5 on: December 10, 2011, 04:18:28 PM »

Thanks for the good advice.  The Hustler resonators that I'm using are not the 'Super' type - I bought a job lot of old resonators for various bands and the stinger is retained by screwing down a lock nut, not by the small hex screws.  This seems a sturdy method and better than the modern Hustler resonators.

I've found that I can only work stations which are very strong - S9, typically Indian stations on the other side of the Indian Ocean which I'm adjacent to, or over the western Pacific to Guam.  My QTH in Phuket means that there is ocean in most directions. I'm testing whilst my car is parked in a quiet location with no power lines nearby, and a few km from the sea.

I do have the DX Engineering Hot Rodz top cap, but I'm not using it right now, (so I'm using an RM-15 resonator on 20 metres).  The large top cap quite frankly looks pretty stupid as I'm driving along - vanity is an over-riding factor - and I do want to be able to make mobile contacts - as opposed to only static-mobile

Perhaps I'll try a small top cap and experiment using a longer mast and the bumper mount - these tests will not involve much cost.

Simon
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K5LXP
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« Reply #6 on: December 11, 2011, 07:59:49 AM »

Another simple test you could do is compare your mobile antenna to a reference antenna like a dipole (while parked).  This way the results aren't quite so subjective.   

Mark K5LXP
Albuquerque, NM
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ONAIR
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« Reply #7 on: December 11, 2011, 09:14:57 AM »

I only operate mobile on 20 meters, (due to the lack of availability of mobile rigs in Thailand).  I have an MFJ SSB rig feeding a 200 watt amp and use a Hustler resonator (and stinger) on a DX Engineering 24 inch mast, center-mounted on my car roof with a Breedlove mount.

This system works well, with daily contacts at dusk up 5,000 km, both mobile and parked.  But during daylight hours and after dark the 20 meter band seems dead.

At dusk, I can hear stations up to 10,000 km away, but they cannot hear me. (That's not really surprising considering my short, omni-directional antenna...)

What could I do (if anything), to improve my mobile station?

Would there be a benefit to using a longer antenna, (eg 2 x 24 inch mast sections), but mounted on my rear bumper, so as not to exceed the height of my current, roof-mounted antenna?

I realise that this is a trade-off between longer antenna and optimum antenna mounting location on a car.

Any advice is much appreciated.  I'd love to be able to have mobile QSOs during all daylight hours.  I suspect part of the problem is simply the lack of HF amateur stations within my immediate  region.

Simon
  Why don't you pick up a used HTX-100 and a 9 foot whip?  For a little over $100 dollars US, you should have no problem working the world from your mobile, especially now that 10 Meters is open.  I recently heard a few hams from your region using similar set ups.
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W8JX
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« Reply #8 on: December 11, 2011, 10:35:11 AM »

Why don't you pick up a used HTX-100 and a 9 foot whip?  For a little over $100 dollars US, you should have no problem working the world from your mobile, especially now that 10 Meters is open.  I recently heard a few hams from your region using similar set ups.

But maybe he does not want to work 10?  10m is a lot more limited in openings and flexibility than 20m. One reason 20 is so darn popular.
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K0BG
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« Reply #9 on: December 11, 2011, 01:11:51 PM »

There's a problem with one of the references here. While it is true that the reciprocity of receive gain to transmit gain (or lack of it in the case of a mobile antenna) is the same, the on-air performance may not be.

Two (of many) things we have no control over is the incoming angle of radiation, and its polarity. These variables make enough of a difference, that sometimes you can hear without being heard, and sometimes visa versa.

It is also important to remember, that it is much easier to make up for poor antenna performance with enough receive gain, but it is a lot harder to (and costlier) to ante up the ERP!
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HS0ZIB
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Posts: 424




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« Reply #10 on: December 11, 2011, 05:04:27 PM »

Quote
Why don't you pick up a used HTX-100 and a 9 foot whip

I live in Thailand.  Importation of the vast majority of ham transceivers is illegal, and those on the 'very short' legal list have to be submitted to the authorities for testing and certification.

QRP and 'homebrew' equipments seem to fall into a gray area, but the bottom line is that trying to import any rig runs the risk of having it either confiscated or stolen by customs or the postal service, if they are not damaged during transit.

There is nothing that can be done if this occurs except to try again to import a rig.

I managed to import an MFJ 20 meter rig, but in the same timeframe I 'lost' my ATS-4 all-band QRP rig, another QRP rig was damaged beyond repair, and a small PA was dead on arrival

I'm happy that I managed to receive the 20 mb MFJ rig without issue - so that is what I'm working with.

I would certainly like to do 10 mb, but after losing the other rigs, I am somewhat short of cash to try another rig import....

Simon
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ONAIR
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« Reply #11 on: December 12, 2011, 11:22:11 AM »

Quote
Why don't you pick up a used HTX-100 and a 9 foot whip

I live in Thailand.  Importation of the vast majority of ham transceivers is illegal, and those on the 'very short' legal list have to be submitted to the authorities for testing and certification.

QRP and 'homebrew' equipments seem to fall into a gray area, but the bottom line is that trying to import any rig runs the risk of having it either confiscated or stolen by customs or the postal service, if they are not damaged during transit.

There is nothing that can be done if this occurs except to try again to import a rig.

I managed to import an MFJ 20 meter rig, but in the same timeframe I 'lost' my ATS-4 all-band QRP rig, another QRP rig was damaged beyond repair, and a small PA was dead on arrival

I'm happy that I managed to receive the 20 mb MFJ rig without issue - so that is what I'm working with.

I would certainly like to do 10 mb, but after losing the other rigs, I am somewhat short of cash to try another rig import....

Simon
    I understand.  Would they interfere with insured FedEx or DHL deliveries as well? 
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HS0ZIB
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« Reply #12 on: December 12, 2011, 04:58:37 PM »

Quote
I understand.  Would they interfere with insured FedEx or DHL deliveries as well?

In fact, courier companies are the worst for failure to deliver or for applying high and unjustified custom taxes.  I just take my chances with orders and it's a bonus if they actually arrive safely Smiley

Simon

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N2RRA
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« Reply #13 on: December 13, 2011, 06:15:14 AM »

While all these mobile ideas are great let's really solve this problem. I for one am no stranger to "go big or go home". It takes a little work but I'm no stranger to work either. If your mobile in transit is one thing but I know that you have to park some where when you have time ,or just can't operate from home to enjoy working that propagation. So here's this suggestion.

When I was just mobile operation, or wanted to work from a different location mobile I mounted a tow hitch to the car and constructed an aparatus that allowed me to install a 1/2 wave mono band vertical to the hitch. Either that or a full size dipole of sorts and even a yagi. Yes, it took getting out the car and about 5-15 minutes of installation time dependent on the antenna but a few minutes resulted in hours of fun well worth it. Constructing a mast setup is easy. Again depending on antenna even a fiberglass mast with wire attached is even easier. So you can't purchase one of particular type and have it shipped then improvise.

I still do it today and have probably more fun operating mobile/portable than I ever did operating from home QRO at 1Kw. Even if you parked by the beach or a park where you can set up a tripod and full size light weight vertical, dipole or yagi you will love it. Find a spot with a tree and send up an end fed full size mono band dipole and your good to go.

All this takes just a few minutes and antenna ERP problem solved. Only thing that will stop you is you and maybe some real bad luck. LOL!

Hope to work you sometime and 73!
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N2RRA
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« Reply #14 on: December 13, 2011, 06:24:08 AM »

By the way try a 102" steel whip a AT-180 tuner and you like it. Modify it with a home brew coil made of 3/8" or 1/2" O.D. Copper or aluminum tubing for band of choice or large enough to use a tap and have fun.

There's just so many things you can do than having to purchase an antenna. DIY homebrew is a lot more fun than buying one and better because it's made to your specs.

73!
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