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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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14th Aug 2018, 12:24 am | #1 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,061
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Good MW reception conditions
Over the years I have always associated the winter months with the best MW DXing. However, recent experiments with a DIY amplifier loop antenna in the loft has brought me in some low power catches I had never heard in the summer till now. The first one is Vahon Hindustani radio on 1566 kHz from a 1 kHz transmitter in Holland. The second one is Radio Panj from Coventry with a listed power of only 0.04 KW. Both were heard around midnight tonight. I am using a Sangean ATS 909X for my DXing. Maybe the recent closure of some BBC LPTs has helped or maybe we are heading towards a solar cycle trough
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14th Aug 2018, 7:23 am | #2 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,061
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Re: Good MW reception conditions
Apologies for the typo..I meant 1 KW, not kHz.
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14th Aug 2018, 9:07 am | #3 |
Nonode
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
Posts: 2,965
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Re: Good MW reception conditions
Hi, MW reception depends on your location including the local noise levels. Your DIY amplified loop is obviously working very well. I have found that the local noise levels from late evenings onwards can drop significantly allowing for some very conditions. I think its down to nosy plasma TV's, LED and CFL lamps being switched off.
Are you able to rotate your loop aerial whilst you are listening?
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Simon BVWS member |
14th Aug 2018, 12:38 pm | #4 |
Octode
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,323
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Re: Good MW reception conditions
Medium wave is also slowly clearing of stations across Europe, leaving gaps though which DX stations can now be heard. But your loop antenna certainly helps!
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14th Aug 2018, 1:35 pm | #5 | |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,061
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Re: Good MW reception conditions
Quote:
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14th Aug 2018, 2:09 pm | #6 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Good MW reception conditions
Were there RF chokes fitted with the DC up the coax and motor?
Lawrence. |
14th Aug 2018, 2:53 pm | #7 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,061
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Re: Good MW reception conditions
No, I haven't fitted any RF chokes.
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14th Aug 2018, 3:43 pm | #8 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Good MW reception conditions
Connecting a DC power supply across the coax will present a low impedance to the signal, ditto for a motor, hence the need for RF chokes (as well as a DC isolating capacitor for the loop antenna and also one for the receiver if needed) A problem might be the frequencies you're interested in, lower frequencies would need a higher inductance choke, that in turn might mean power dissipation or voltage drop problems for the DC circuit depending on the motors current draw.
Lawrence. |
15th Aug 2018, 9:11 am | #9 |
Rest in Peace
Join Date: Sep 2010
Location: Ripley, Derbyshire, UK.
Posts: 785
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Re: Good MW reception conditions
I think ms660 has a circuit something like the attached in mind.
The main problem I came across when I constructed such an arrangement was motor noise on the signal when turning the loop. This was eventually resolved with lots of suppression at the motor end of the co-ax, on the motor supply. A D.C. motor was used, and reversed by reversing the polarity of the supply. Voltage drop in the R.F. chokes is easily dealt with by increasing the motor circuit D.C. supply voltage. Tony |
15th Aug 2018, 9:15 am | #10 | |
Nonode
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
Posts: 2,965
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Re: Good MW reception conditions
Quote:
Nowadays I find the best AM aerial to use is the radios built in rod aerial with its directional properties to null out local electrical interference as much as possible.
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Simon BVWS member |
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15th Aug 2018, 10:51 am | #11 |
Dekatron
Join Date: Jan 2006
Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex.
Posts: 5,817
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Re: Good MW reception conditions
I'm not sure if this relates to the issues discussed here or should be on a "Pirate" Thread. My friend Pat [ex Electronics Tech and Street "Furniture" ie Lighting etc supremo] has returned to Bury from Leeds. Last Saturday he heard Radio Caroline North on 1368k Broadcasting from the Ross Revenge parked in Ramsey Bay. He says he listened for a long time and it was 1964 all over again!
Apologies if this is already known to retro Medium Wavers Dave W There is a list of outings on http://www.offshoreradiomuseum.co.uk/page1022.html |
15th Aug 2018, 5:42 pm | #12 | |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,061
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Re: Good MW reception conditions
Quote:
Thanks for the above and the diagram. I hadn't considered suppressing motor noise on the RF signal till now, so I will bear that in mind. Here is an example of motor noise suppression using a 473Z capacitor across the motor leads with one lead also connected to the motor case. This is a surplus motor I bought recently, so I might steal the cap for my loop antenna motor |
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15th Aug 2018, 6:52 pm | #13 |
Rest in Peace
Join Date: Sep 2010
Location: Ripley, Derbyshire, UK.
Posts: 785
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Re: Good MW reception conditions
Looks the right style of cap for the job.
You will need, I think, at least one across the motor terminals (Assuming its a similar type of construction to the one you show), then a small ferrite choke in each lead, followed by another cap of the same type across the leads on the other side of the chokes, and good motor terminal screening, connected to the braid of the co-ax cable, too. The caps should be at least 100nf in value. Tony. |
15th Aug 2018, 10:07 pm | #14 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,061
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Re: Good MW reception conditions
I finally solved the problem of isolating the loop from the motor by connecting a 474K cap from one end of the loop to the central conductor of the downlead. I found out by trial and error that this value does not cause any attenuation of MW signals in my amplifier circuit before they reach my radio. Here are some photos of the loop and the controller unit, which I purchased from eBay. My next steps will be to try and fit both controller unit and amplifier in one box. I am able to control both the geared motor speed and direction.
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17th Aug 2018, 1:58 am | #15 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,061
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Re: Good MW reception conditions
Here is a fresh DX catch from tonight using my loop antenna without any signal amplification. Betar Bangla on 1503 kHz from London was heard with fair to good signals for around 5 mins around 0145 BST in Southampton. Normally this channel is almost always occupied by BBC Radio Stoke or a Spanish station. I heard this station only once before on a 10m longwire antenna for a few seconds. The transmitter is only 100 W.
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18th Aug 2018, 12:20 am | #16 | |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,061
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Re: Good MW reception conditions
Quote:
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18th Aug 2018, 9:04 am | #17 |
Rest in Peace
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
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Re: Good MW reception conditions
Jolly 7, you are correct. Manx Radio turns it's 1368kHz transmitter over to R. Caroline, I think, every four weeks at weekends. The programs are broadcast from the Ross Revenge, presumably via either an internet or satellite link. Schedules and other info. should be on both the R. Caroline and Manx Radio websites (I haven't checked recently, or yet been able to receive Manx R. here in N. Oxfordshire.)
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18th Aug 2018, 8:11 pm | #18 |
Nonode
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
Posts: 2,350
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Re: Good MW reception conditions
Over the next two weeks, Manx Radio's MW transmission prioritises the "Festival of Motorcycling", a mix of the traditional Manx Gran Prix and a Classic TT. Practice was on from shortly after 5:00pm, but appears to have finished early tonight (Mist on mountain probably)
Definitely better listening! Les (who may be a wee bit biassed) Last edited by MotorBikeLes; 18th Aug 2018 at 8:13 pm. Reason: Changed "is" to prioritised. |
23rd Aug 2018, 9:22 am | #19 |
Nonode
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
Posts: 2,965
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Re: Good MW reception conditions
Here is an interesting one for you to try during the daytime. BBC Radio Hereford and Worcester is transmitted from the Worcester transmitter on 738Khz but it only uses a power of 37w. It comes in well here near Bath and I wonder if it makes it to Southampton.
I am just amazed at its coverage for such little power, it must be a good transmitter aerial and/or site.
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Simon BVWS member |
23rd Aug 2018, 3:30 pm | #20 |
Octode
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 1,219
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Re: Good MW reception conditions
That quoted figure of 37W is going to be the ERP (or EMRP), i.e. the radiated power after feeder losses and aerial efficiency have been taken into account. The actual transmitter will be producing more power, probably a few hundred watts. But yes, it's surprising how little radiated power is required for a radio signal to provide good coverage.
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