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Old 19th Mar 2020, 11:06 am   #1
jsbhavsar
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Default MLA-30 Active loop antenna for valve radios

Anyone here who has bought MLA-30 active loop antenna to use on a valve radio set from 1950's and 1960's?
Where especially, the radio has "Aerial" and "Earth" sockets on the rear?
And where radio sets typically look for high impedance at the Aerial socket?

If yes, please post some pictures how you connected MLA-30?

If you did some modifications to the MLA-30, what were the mods and any pictures?

And whether anyone noticed great improvement using MLA-30 loop as compared to a very long wire connected on aerial?

Thanks,

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Old 19th Mar 2020, 12:25 pm   #2
Herald1360
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Default Re: MLA-30 Active loop antenna for valve radios

Can't help with any hands on experience but general perceived wisdom seems to be that a suitable wideband step up transformer between the 50R downlead from the loop box and the Aerial and Earth inputs to the set works as well as anything.



https://vk6ysf.com/unun_9-1_v2.htm


Shows how to make yourself a 9:1 wideband transformer. In the article it's used to step down a high impedance antenna to a 50R radio but you will need to use it the other way round with the 50R output from the MLA-30 downlead into the 50R port of the transformer and the 450R port from the transformer into the Ae and E points of the radio.


Hope this helps.....
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Old 19th Mar 2020, 12:28 pm   #3
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Default Re: MLA-30 Active loop antenna for valve radios

The MLA-30 is very poor as an antenna, I bought one for experiment it is now in the bin. If I want to use one of my valve sets I simply connect my Wellbrook loop directly to the aerial and earth terminals. OK it's not matched and doesn't matter much (that is down 100 feet of co-ax), there is more than enough signal to get noise free reception.
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Old 19th Mar 2020, 12:35 pm   #4
jsbhavsar
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Default Re: MLA-30 Active loop antenna for valve radios

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Originally Posted by merlinmaxwell View Post
The MLA-30 is very poor as an antenna, I bought one for experiment it is now in the bin. If I want to use one of my valve sets I simply connect my Wellbrook loop directly to the aerial and earth terminals. OK it's not matched and doesn't matter much (that is down 100 feet of co-ax), there is more than enough signal to get noise free reception.
Ok, does it mean in MLA-30 parlance, that using company provided RG174 cable (removing the SMA connector) and directly connecting the RG174 center wire to Aerial of radio and Braid to the Earth socket can work?

And we would not need the 9:1 or 1:9 in between?
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Old 19th Mar 2020, 12:55 pm   #5
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Default Re: MLA-30 Active loop antenna for valve radios

Quote:
and directly connecting the RG174 center wire to Aerial of radio and Braid to the Earth socket can work?
Yes it will, to the limits of the MLA-30, your results may be better than mine, I hope so. Domestic valve radios where designed for any old bit of wire for an aerial, they work fine with a low impedance source too as long as there is enough signal.
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Old 19th Mar 2020, 2:17 pm   #6
jsbhavsar
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Default Re: MLA-30 Active loop antenna for valve radios

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Originally Posted by merlinmaxwell View Post
Domestic valve radios where designed for any old bit of wire for an aerial
Those days there were no thoughts for RF noise, no creation of coaxial cable those days.
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Old 19th Mar 2020, 8:21 pm   #7
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Default Re: MLA-30 Active loop antenna for valve radios

Didn't know what we were talking about so I took a look on eBay, seems an attractive unit for non-critical MW use. All the listings simply quote the manufacturer's Chinglish nonsense so you have to look for reviews to learn anything more. All reviews are American and all are using some SDR kit so a) they don't mention LW, and b) they all power it from the SDR over USB which may be injecting a load of digital qrn.

Obviously, don't expect the gain and dynamic range of a Wellbrook loop, but I'd like to know how it performs from a battery supply, feeding into a battery portable, and whether the response goes sensibly down to LW as per the specs. I expect it would do well with a vintage valve set if you take the trouble to wind a little transformer, maybe 3:10 turns of fine wire on one of those Dual Aperture Ferrite Cores like from RS
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Old 20th Mar 2020, 3:04 am   #8
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Default Re: MLA-30 Active loop antenna for valve radios

I did wind up a 1:9 balun for this few days ago, even though I still do not own a MLA-30. However, further work is pending on this toroid part as I dont know which connector(s) to fit in on the box. And getting those connectors matching MLA-30 is a big challenge.

I also asked copper tube technicians to bend a 12mm soft copper tube to a round loop. (Indians hardly like to do anything on their own by the way, and I am being very frank here.). I am even looking for a readymade 1:9 balun if available. Mumbai market has none. They have nothing for RF hobbies, nothing on RF, no baluns, no Pots, no connectors to radio sets. All they now have is latest stuff HD Video, CCTV stuff.

Couple of reviews on MLA 30 experimenters group on FB indicate that their MW was reception was boosted on their tube sets when using this loop.
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Old 20th Mar 2020, 12:01 pm   #9
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Default Re: MLA-30 Active loop antenna for valve radios

Well done, very neat work on both items.
You can now connect the three windings in series, with taps at 3 and 9 turns.
I wouldn't bother with using SMA connectors at MF and HF: if you clip off the plug and carefully strip off an inch of the outer sheath, you can work the inner insulated conductor out through the screening and fit inner and outer with whatever connector suits you
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Old 20th Mar 2020, 12:22 pm   #10
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Default Re: MLA-30 Active loop antenna for valve radios

Or just solder or even use a little twin screwed connector block to connect the inner and outer of the coax to the appropriate wires of the transformer, no need for any connector.



Depending on the enamel insulation on the transformer wires you may need to scrape the wires clean before soldering and you will definitely need to do so with a terminal block connection.
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Old 21st Mar 2020, 12:28 am   #11
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Default Re: MLA-30 Active loop antenna for valve radios

Thanks, and this means, for valve sets it still can work with RG174 cable that comes with the MLA-30. Just cutting off the SMA Male and stripping away the insulation a little would be enough.

I can then choose to connect it directly or use 1:9 balun (reverse way to connect.

I agree most who have bought the MLA-30 are using it for SDR or better Rigs like ICOM or some other high grade receivers.
I just wanted to know how it would benefit any valve sets as compared to a simple long wire which is prone to RF interference noise.
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Old 21st Mar 2020, 10:57 am   #12
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Default Re: MLA-30 Active loop antenna for valve radios

hello all,, I have a mla/30. but its on a battery 3 valve trf so local
stations only ?. the long wire is about 60ft, top floor down and along
8ft high fence ,the mla hangs on the curtain rail in the spare room it works
as well as the long wire (poss pulls in 1 more station) BUT the lack of
injected noise is very impressive !!(my RF earth is a radiator pipe) I had
it on a 5 volt phone charger, TO much noise on the bench so I've found
a 5 volt regulator board 9volt battery silence !! I cut the end off the coax
centre the aerial braid to earth, is very sensitive to direction but again not
really a good test as I have to walk and turn it on the curtain rail, im quite pleased with it. but I have not got a better radio for further testing
I will be interested to see how you get on with your improvements

dave
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Old 21st Mar 2020, 11:55 am   #13
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Default Re: MLA-30 Active loop antenna for valve radios

I recently used the tuned circuit of my Roberts R200 as a tuned antenna (connecting to the input to the mixer with the radio OFF) the results were very good. You have the benefits of the selectivity and directionality of the ferrite rod and it's tuned circuit. Of course you have to tune both radios. I didn't disconnect the mixer stage which theoretically I suppose one should do but it works well. I used a single external transistor stage between the two radios to provide suitable matching and gain.

Chris
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Old 13th Apr 2020, 8:32 pm   #14
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Default Re: MLA-30 Active loop antenna for valve radios

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Originally Posted by Julesomega View Post
You can now connect the three windings in series, with taps at 3 and 9 turns
My mistake, should have said "at 10 and 20 turns"

I had to try one so I bought from a UK seller and it arrived quickly. The original 66cm loop is 1.1mm dia stainless and the sensitivity was poor though it shows sharp nulls. I increased the loop to 1m dia using 6mm thick wire, like CT100 outer, and the sensitivity increased disproportionately. Now even the local noise background is S9 on MW and I'm hearing audio or carriers on most of the UK channels. The main limitation may be the internal noise (noise factor) but it is extremely good for local signals including anything you can hear weakly on a transistor portable. I was expecting signs of intermod everywhere but I can find none, even around local powerhouse Moorside Edge (400+50+50kW).
The sensitivity remains good at HF, though I've not done any critical tests above 5MHz. The most wonderful feature is that it has fabulous immunity to local mains noise. The loop and amplifier are balanced with a transformer output to feed the receiver via 10m of co-ax. Reception is unaffected by appliances in the house with the loop 10m from the house. This without any chokes or braid breaks on the cable. Hooray!
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Old 13th Apr 2020, 11:22 pm   #15
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Default Re: MLA-30 Active loop antenna for valve radios

Chinglish sales guff states "Stainless steel vibrator"... Hope they don't put that on the box if I happen to order one of these antennae!
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Old 14th Apr 2020, 6:51 am   #16
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Default Re: MLA-30 Active loop antenna for valve radios

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Originally Posted by ekjdm14 View Post
Chinglish sales guff states "Stainless steel vibrator"... Hope they don't put that on the box if I happen to order one of these antennae!
Tell them you're listening to Steely Dan!
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Old 14th Apr 2020, 9:16 am   #17
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Default Re: MLA-30 Active loop antenna for valve radios

Silicon chips mag did a home brew jan 2009 and a Distribution amp
neither off which I have had time to build
I should not upload scans here as they are hot on there copyright
if you want to experiment
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