Are these any good?

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bigbassman
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Are these any good?

Post by bigbassman »

Can anybody put me right?Are these things any good? Is there any point to them? I'll be using it with a 40' random wire into an ATU,and then into my FRG 100.Is it likely to improve the massive QRM that I have at the moment,do you think? Thanx.
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MrWeetabix
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Re: Are these any good?

Post by MrWeetabix »

I'd be interesting to know how they justify the claim of an extra 3 s-points..... its all relative.
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Alan Pilot
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Re: Are these any good?

Post by Alan Pilot »

I use a 9.1 unun with a 10 meter length of wire with a MFJ993B tuner and get very little qrm.
The one thing i did change was the lighting in my shack to 12v led and that dropped the last bit of qrm i had down to less than 1 s point.
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Mikel
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Re: Are these any good?

Post by Mikel »

I would probably go for the 9.1 unun as well. There are loads around if you don't want to make you're own but I noticed this one which looks reasonable:

https://www.ebay.co.uk/itm/Ham-Radio-Sp ... SwpqJfzgBP

The idea is to present a better impedance match to the receiver input, and certainly should increase signal strength on some frequencies but weather it will reduce your local interference levels is dependent on what is causing it.
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bigbassman
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Re: Are these any good?

Post by bigbassman »

Wish I had seen this before I got the other one.Seems well made,and reasonably priced.I only do SWL by the way but that red one doesnt seem to help much.As the guy says,when you can see whats actually inside,you can make a better judgement.Thanx Mike.
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Mikel
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Re: Are these any good?

Post by Mikel »

Yes definitely better to see know what's inside, saying that I have never had a problem with anything I have bought from Rocket Radio in the past.
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MrWeetabix
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Re: Are these any good?

Post by MrWeetabix »

Rocket Radio used to post on here. Lost of people have dealt with him and no hassles no worries 👍
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Alan Pilot
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Re: Are these any good?

Post by Alan Pilot »

The one i have (9.1) was a gift last christmas and it sat in the shack until May when i got round to putting it up.
I didn't think much of it so didn't get used and around October i took the unun off and had a look inside.
Was moonraker branded but looking at it inside it didn't look to be wound right to me so i cut all the wire off and re made it myself.
What a difference wow it works fantastic now the only problem i have now is i wand to make the wire longer as it is only 10 meters and i want it 20.
Got into north and south America on Friday on it with 10w.
The one linked above does look ok to me and would buy if i needed one.
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Mikel
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Re: Are these any good?

Post by Mikel »

First of all well done on getting the callsign Alan as it is obviously new. :thumbup:

As far as antennas and matching devices go, it is as you know a very big subject and I would not in any way claim to be an expert and I am certainly happy to be corrected. :)

As far as I understand it the choice and ratio of unun/balun will be dependent on a number of factors, such as wire length and configuration and for a 9:1 unun, that is doing a conversion of impedance from about 450-700 ohms down to 50 ohms.

You don't want the length to be an actual 1/4 wave on any amateur band if using a 9:1 or the impedance will be very high and you may have trouble tuning it and lose efficiency.

My research leads me to believe that the magic lengths to use with an end-Fed longwire and a 9:1 unun for amateur band coverage are around 9, 10.6, 12.5, 17.7, 21.6 and 25.6 meters.

Would these lengths seem about right to your understanding?

You don't say what band you got into north and south America on but you know the old saying 'If it aint broke, don't fix it'.

Of course experimenting with different antennas is half the fun of it, so if your anything like me you will probably change it for a different length at some point. :)
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Alan Pilot
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Re: Are these any good?

Post by Alan Pilot »

Hi Mikel
Thanks for that info i have many different lengths written down so not sure but a lot sell a 9.1 unun with 20 meters of wire.
I have ordered a book so waiting to have a good read of it when it comes.
Also the north and south last week where on the 20m band.
Must admit playing making aerials does put a smile on your face when they work made a 2m then a 2m/70cm both worked well but easy to do.
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Mikel
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Re: Are these any good?

Post by Mikel »

Someone who knows a lot more than me about antennas has said:

'For a 9.1 unun, about 26m wire will work well between 7MHz and 18MHz, and up to 50MHz and down to 1.8MHz with less efficiency, and only using an internal tuner, doubling the length improves the efficiency down to 3.5MHz

49:1 with approx 40m wire will resonate on 8 bands from 3.5 to 28'

But of course it all depends what works at your particular QTH - nothing works here because the noise levels are usually very high unfortunately.
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scan125
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Re: Are these any good?

Post by scan125 »

I'm a bit late to this but just my thoughts.

I used to run a long wire with receive only balun (make & ratio forgotten). This was fine.

Then I got an MFJ-956 ATU and found that the ATU had more control without the balun. I was able to more easily and effecticiely "tune out" unwanted reception.

I now run both the MFJ-956 and and MFJ-959C without a long wire balun.

I think my observation is that a long wire balun (9:1 ?) is a must. However if you have a "receiver only" ATU then the effectiveness of the ATU will be reduced. This is not to say that the two are detrimental to each other. More a case of "no problem" but the ATU may be more effective without an inline balun.
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