10m mobile antenna ideas?

[VK5IR]

G'day

Anyone thing this is weird, just a bad batch or something else?

I went to the AHARS buy and sell today and impulse got the best of me and I bought a Diamond HF10FX 10m mobile vertical from Slim.

Driving home we just couldn't get it to tune. Got home, put it on the analyser (through the car's coax and mount) and I couldn't get it to dip lower than 29 MHz (this antenna is made for 28 MHz).

Raced back to the buy and sell, told Slim so he came out to the car to have a look - same result. So he goes inside and gets another one - same again! So he gave me my money back and we parted our ways both feeling confused.

Yes, my grounding is fine and I currently own the HF40FXW and HF20FX which both work flawlessly on the same setup.
Pretty disappointed because I really wanted a mobile whip for 10m and I've had a good run with the two Diamonds I already have.

So, does anyone have any ideas for a 10m mobile antenna? Ideally it needs to be no longer that about 1.4 meters and needs to look half decent.

[VK3DXE]

Why not run a Mobile One CB helical? I've got a couple I've scored for nix along the way and they work fantastically. Obviously the bigger, the better. They're quite cheap and work nicely.

I've worked all continents except Antarctica in a day with my HTX-100 running 25w whilst running around doing Saturday chores. That antenna is about 1.7m though.

[VK5PJ]

Theo,
have you run into the awkward feed line length problem? In a previous life I did a lot of commercial HF work in VK8 and got quite good at it but when putting whips on my own car ran into problems in the higher bands (especially 10 metres) where a feed line can easily be quite close to being a 1/4 wave long in a vehicle.

I know you do not have that whip any longer but for the next whip you chose (the heavy duty mobile One whips are good) keep that in mind before you go snipping it too short while looking for a dip.

Regards,
Peter (also at the AHRS buy and sell)

P.S A big thanks to Slim for a great deal on a Diamond vertical for UHF.

[VK5IR]

Theo,
have you run into the awkward feed line length problem? In a previous life I did a lot of commercial HF work in VK8 and got quite good at it but when putting whips on my own car ran into problems in the higher bands (especially 10 metres) where a feed line can easily be quite close to being a 1/4 wave long in a vehicle.

This could be a possibility, I'm not 100% sure how long my coax run is, but its just a little Ford Laser so perhaps that is the problem... I dunno. The problem is that its crimped onto the connector at the boot so changing that is going to be a pain in the bum.

Would be nice if I knew someone in Adelaide that had one they kew was tuned and working on 10m that I could test with.

[VK3DXE]

[quote="VK5MTMThis could be a possibility, I'm not 100% sure how long my coax run is, but its just a little Ford Laser so perhaps that is the problem... I dunno. The problem is that its crimped onto the connector at the boot so changing that is going to be a pain in the bum.[/quote]

Not at all. Simply lengthen it with an adapter and another piece of coax.

[VK7HH]

Hi Theo,
As Alan described, a 27MHz helical slightly cut to 29MHz works well.... you can get these from Jaycar too.

I have the exact Diamond HF10FX antenna you described. Put it on the base, adjusted the length and that was all there was too it.
Mine is on the front right bonnet.

Regards
Hayden VK7HH

[VK3RX]

I had the same tuning strife with a 6m whip on the boot.

I'd read that with some modern vehicles the boot "skin" was not always grounded to the mounting arms due to paint and rust prevention material, and in particular the whole thing was not necessarily electrically grounded to the body of the car for the same reasons.

I then fitted braid from the antenna base to the boot, and another length from the boot to the body of the car and problem solved.

Edit: and after watching your video I see you've done the same thing

Yep, 27MHz helicals cut down fine for 10m.

[VK5IR]

I had the same tuning strife with a 6m whip on the boot.

I'd read that with some modern vehicles the boot "skin" was not always grounded to the mounting arms due to paint and rust prevention material, and in particular the whole thing was not necessarily electrically grounded to the body of the car for the same reasons.

I then fitted braid from the antenna base to the boot, and another length from the boot to the body of the car and problem solved.

Yep, 27MHz helicals cut down fine for 10m.

That's exactly what I did. See my video a few posts up.

Sent from my SM-N910G using Tapatalk

[VK6ZFG]

I alway include bonding straps across the hood and boot hinges - primarily as part of my standard electrical noise suppression process. Depending on where the antenna is located this may also help with the antenna matching

However besides the items breviously covered there is another complication that can be encountered that needs to be considered.

If the antenna base is raised from the car body like on an extension of the tow bar to say make the base of the antenna level with the top of the boot you will experience problems in achieving a match on the higher frequencies where the support constitutes a significant length on that frequency. Such an arrangement will be difficult to match on say a 6M quarter wave whip as a low earth impedance is required. A half wave on 6M will however match as it does not require a low earth impedance. Roo bars can introduce similar complications. Unfortunately there appears to be no simple solution to this.


Someone once said life was not meant to be easy - then made sure it wasn't.

[ZL3MF]

Ok had very similar issues when I owned a Peugeot 308 none of the 1/4w antenna's would resonate (6m or 10m) tried the braid thing still with poor results. Discovered the Peugeot's don't have much metalwork and most of the body and side panels are fibreglass (I previously owned a Honda and both antenna's worked a treat) Have since sold the Peugeot and now own a Ford Territory antenna's work flawlessly. Have now got a IC-7000 run that into a AH-4 antenna tuner to a 2.5m vertical element on the back of the car...the best setup I have ever had 40-6m works a treat

Mike ZL3MF

[ZL3PX]

Looking at the picture of the car and where the antennas are mounted that's the best insulated spot you can mount them . Modern paints are very good insulators hence no car earthing for the antennas, you say you put an ant analyser on it did you have a 50omh dummy load at the other end to see whether the coax was resonating? instead of the antenna, try adding an extra length of coax coiled up in the boot.
Earth bonding is a must braid everywhere scrape the paint heavens above bare metal is required, hinges not exempt either

Geoff ZL3PX

[VK5IR]

Looking at the picture of the car and where the antennas are mounted that's the best insulated spot you can mount them . Modern paints are very good insulators hence no car earthing for the antennas,
Earth bonding is a must braid everywhere scrape the paint heavens above bare metal is required, hinges not exempt either

Geoff ZL3PX

I think I have sufficient grounding and my log backs that up. Did you watch my video?

I'll try a cheap 27 MHz antenna trimmed down. If I get similar results I'll try adding some coax as I'm guessing I may have close to a 1/4 wavelength of feedline going to the antenna. Any ideas how much I should add?

[VK7HH]

I'll try a cheap 27 MHz antenna trimmed down. If I get similar results I'll try adding some coax as I'm guessing I may have close to a 1/4 wavelength of feedline going to the antenna. Any ideas how much I should add?

What is a 1/4 wavelength at 10 metres? What coax are you using to account for velocity factor?

If you have access to an MFJ analyser or something you can measure your coax. Remove the antenna and measure with an open end. X should not equal 0 near the frequency of operation.

[VK5IR]

I'll try a cheap 27 MHz antenna trimmed down. If I get similar results I'll try adding some coax as I'm guessing I may have close to a 1/4 wavelength of feedline going to the antenna. Any ideas how much I should add?

What is a 1/4 wavelength at 10 metres? What coax are you using to account for velocity factor?

If you have access to an MFJ analyser or something you can measure your coax. Remove the antenna and measure with an open end. X should not equal 0 near the frequency of operation.

Sorry, no MFJ analyser. I only have my Chinese KVE-60C which won't measure coax length.

Coax being used is RG58.

Sent from my SM-N910G using Tapatalk

[VK7HH]

Hi again Theo,
I am not familar with the Chinese model. Does it have a reactance readout, or just a SWR meter? What is the rough length of the coax? Is it a pre-made assembly and base? Usually these come in standard lengths of 5 metres long.

300/28.5(MHz) = 10.53m divided by 4 = 2.63m. If we then multiply that by the VF (assuming 0.66) then it turns out to be 1.737m long is a electrical 1/4 length at that frequency using RG-58 of VF 0.66.

If we times that by three (3/4 wavelength) we get a result of 5.21m. Perhaps this may be closer to your actual coax length?

[VK5IR]

This is the analyser I have - http://www.409shop.com/409shop_product.php?id=122114

It does measure reactance, so I will try to take a measurement with no antenna connected and will report my results once I'm home from work tonight.

When I said 1/4 wavelength of coax, I was simply referring to it actual length being (ROUGHLY and at a guess) at around 2.5 meters.

The coax came pre-crimped with a SO-239 base end.

[VK4TIM]

I was wondering if there's possibly an issue with coax length, as other have suggested.

From memory, and a few 26/27MHz installations I have donein years gone by, when the coax length was a multiple of half electrical wavelength (300/f x vf) everything was happy.
I recall problems when we had a cable that approached an odd multiple of 1/4 electrical wave.

For RG58, the ideal length should be 300/28.5 = 10.53m, Electrical wavelength will be 0.67 x 10.53 = 7.055m, and 1/2 electrical wavelength is 7.055/2 = 3.53m give or take rounding.
26/27 MHz CB antennas used to come with a pre-terminated coax that was 3.6m long.

Cable lengths only seem to be a problem in vehicle installations at high HF such as 15 to 10m, and 6m, not as much of a problem at 2m and above from my experience.
As others have suggested, ensure the antenna base is well grounded.

I have CR8900 quad band antenna (10, 6, 2 and 70) on the left guard of my work ute, and that seems to work well enough on 10m to work into VK1, 2, 3, 5 and 7 almost daily at this time of year, I hear plenty of squigglies, JAs and Asian FM as I drive around all over 10m. The return loss on mine at 28.5 is about 16dB, not perfect but the radio doesn't complain.

[VK3ZAZ]

Too many variables
Having trouble with a cb whip is weird it probably the most known and use mobile antenna by far.
Mounting place on car for one, mudguard boot lid gutter all change
Snipping down with swr bridge works.
Base loaded vertical works well on tow bar.
So do US made centre loaded whips.
if its spring loaded make sure the braid in the spring is good.
Helicals work fine all varieties thick and thin.
Hundreds to choose from.
Use of an analyser best way to go if not swr and snip from long to short in centre of 10M band
helical may tune cw and phone end might make 28.0 to 29.0 between 3db corner points
Length of cable if earthed at far point should not line tune a 1/4 unless its not resonant and way of frequency.

2 cents

[VK6APK]

2 questions.

1. Are you not able to adjust the frequency by lengthening the adjustable tip, as described by VK7HAY in the eham review of that antenna?

2. There may be a 28MHz and a 29MHz version. What is printed on your packaging? Is it like this picture?
https://www.google.com.au/search?q=Diam ... OMsDjHM%3A

73, Alek
VK6APK

[VK7HH]

1. Are you not able to adjust the frequency by lengthening the adjustable tip, as described by VK7HAY in the eham review of that antenna?

Haha... my review from ages ago...