UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Amateur and Military Radio

Notices

Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

Reply
 
Thread Tools
Old 20th Apr 2021, 4:09 pm   #1
ORAWA01
Hexode
 
Join Date: Apr 2011
Location: Stirlingshire, UK.
Posts: 407
Default Spectrum Comms. Active Antenna problem

Hi All

This active antenna has been set up in the garden the other day. When it is all connected and powered up, the reception on my radio is full of MW overloading everywhere. From MW to SW, it is just full of MW overloading.

When power is off, it goes quiet, which means the RF amp is working?

I have another active antenna PA0RDT copy from China, and that one works perfect. No problems.

This spectrum comms active antenna had been also marketed as NASA or Gareth before, I think. I took it apart the element, and it has a PCB with conventional parts, 2x transistors, capacitors and resistors all pretty well accessible.

But without any documentation or circuit diagram, I am not sure where to start trouble shooting the problem. I got it months ago used one from eBay, and left it in the cupboard for months without even checking it worked. It obviously is faulty somewhere, looks like.

But from the symptoms = power on and immediate overloading with MW signals every where? What could it be?

I was going to power on again, and measure voltages on the transistors, 2 of them, if they have any voltages?

Any ideas? Thanks 73s
__________________
ORAWA = Old Radios And Wire Antennas
ORAWA01 is offline   Reply With Quote
Old 20th Apr 2021, 10:19 pm   #2
space charge
Tetrode
 
space charge's Avatar
 
Join Date: May 2013
Location: Enniscorthy, County Wexford, Ireland.
Posts: 71
Default Re: Spectrum Comms. Active Antenna problem

oscillating maybe , is it transmitting as well ?
EI7KA
space charge is offline   Reply With Quote
Old 20th Apr 2021, 11:02 pm   #3
majoconz
Hexode
 
majoconz's Avatar
 
Join Date: Jan 2008
Location: Palmerston North, New Zealand
Posts: 321
Default Re: Spectrum Comms. Active Antenna problem

Does it look like any components have been taken out or maybe a section shorted out? I'm thinking that there should be a high pass HF filter in there to stop the MW getting through. Have you got an MW transmitter near you?
__________________
Cheers - Martin ZL2MC
majoconz is offline   Reply With Quote
Old 20th Apr 2021, 11:10 pm   #4
Julesomega
Octode
 
Julesomega's Avatar
 
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 1,289
Default Re: Spectrum Comms. Active Antenna problem

Quote:
Originally Posted by majoconz View Post
Have you got an MW transmitter near you?
..like on 198, 810, 909, 1089 and 1215kHz?
__________________
- Julian

It's good here

Last edited by Cobaltblue; 21st Apr 2021 at 6:22 am. Reason: fixed quote
Julesomega is offline   Reply With Quote
Old 20th Apr 2021, 11:46 pm   #5
Andrew2
Octode
 
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 1,765
Default Re: Spectrum Comms. Active Antenna problem

Some of these active antennas have too much gain and will put (almost) volts into your receiver if there are strong broadcast stations around. Is there a gain adjustment in there somewhere, or maybe your radio has an attenuator?
__________________
Andy G1HBE.
Andrew2 is offline   Reply With Quote
Old 21st Apr 2021, 7:43 am   #6
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 4,428
Default Re: Spectrum Comms. Active Antenna problem

Spectrum Communications is run by Tony Nailer, assisted by his wife Jean.

He's been in business since 1981 serving the amateur radio/CB/SWL community.

He became a long-standing and respected author with PW in 2004, developing new projects which featured in the excellent 'Doing It By Design' series. He authored another PW series in 2005 entitled 'Technical For The Terrified' and parted company with PW in 2017 following the change of ownership of PW. He's still very much in business selling kits, ready made equipment, aerials, aerial traps, and components, (including those for the Mini-Mod project).

Long standing amateurs may recall G2DYM Aerials, run by Richard Benham-Holman G2DYM, which Tony purchased in 2006. Also, in 2011 Tony purchased Garex Electronics, run by Peter Longhurst G3ZVI. He's still very much in business so you might wish to contact him.

His website is here: http://www.spectrumcomms.co.uk/

You can email him directly with technical queries at: g4cfy@talktalk.net

Hope that might help.

(I'm not his PR manager by the way - I just think he's one of the few remaining proprietors of small firms who isn't just a 'box shifter' but has a genuine interest in serving and keeping alive the remnants of what was once a technical, experimental and constructional hobby).
__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is offline   Reply With Quote
Old 21st Apr 2021, 11:25 am   #7
ORAWA01
Hexode
 
Join Date: Apr 2011
Location: Stirlingshire, UK.
Posts: 407
Default Re: Spectrum Comms. Active Antenna problem

We have an AM transmitter about 5 miles from us (Westergren, https://en.wikipedia.org/wiki/Wester...itting_station), but it does not cause too much problems on HF RXing unless directional antennas are pointed at it.

As I have said, I have another active antenna (copy of PA0RDT), and it works OK without overloading problem.

I will try to get a photo of the PCB inside the element, and upload here.
Looking at closely, the PCB does not have anything for RF gain control. It just have 2x transistors, capacitors and many resistors on the PCB.

To test the Bias-T, it was paired with the other active antenna, and it works OK.
But the element with the PCB, is clearly something not right.

Thanks for the contact info on Spectrum communication. I will try to troubleshoot as much as I can, but if fail to repair it or sort it, will contact them for the last resort

Thank you.
__________________
ORAWA = Old Radios And Wire Antennas
ORAWA01 is offline   Reply With Quote
Old 21st Apr 2021, 5:06 pm   #8
Skywave
Dekatron
 
Skywave's Avatar
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,112
Arrow Re: Spectrum Comms. Active Antenna problem

The classic method to determine the cause of the problem - considering that you have two active antennas - is to devise a method of comparing the gain of the two active antennas. There are many ways of doing that, generally determined by what test equipment you have available.

Ideally, you need to set up both antennas in the garden, pointing in the same direction, each fed with coax cable of the same type and length, fed into your workshop / listening room. At that point, you need the instrumentation to discover the signal levels arriving at the end of each cable - terminated in the appropriate load resistance - probably 75 or 50 ohms. A spectrum analyzer would be ideal for that comparative measurement.

Having said all that, my suspicion is that the offending antenna simply has excessive gain for the radio you are connecting it to and the 'front end' of that radio is simply becoming overloaded. A series of measurements with a switched, variable attenuator, alternatively connected to each antenna, should confirm - or otherwise - that suspicion.

Al.
__________________
Chard, Somerset - The birthplace of powered flight and prosthetic limbs.
Skywave is offline   Reply With Quote
Old 21st Apr 2021, 5:56 pm   #9
Julesomega
Octode
 
Julesomega's Avatar
 
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 1,289
Default Re: Spectrum Comms. Active Antenna problem

The Stirlingshire AM transmitting station runs a lot of power on all those five frequencies
See MWLIST

Quote:
Originally Posted by Skywave View Post
A series of measurements with a switched, variable attenuator, alternatively connected to each antenna, should confirm - or otherwise - that suspicion
For a quick test, just use a 100Ω pot like a volume control at the input to your receiver
__________________
- Julian

It's good here
Julesomega is offline   Reply With Quote
Old 21st Apr 2021, 10:25 pm   #10
ORAWA01
Hexode
 
Join Date: Apr 2011
Location: Stirlingshire, UK.
Posts: 407
Default Re: Spectrum Comms. Active Antenna problem

Sure. Great points and advice. Thank you.

I have 2-3 GC radios (IC-R75 and NRD 525 and SDRPlay RSPdx ..etc), and they all work well, has good front ends I believe. They all work well with the other active antennas (PA0RDT and MLA30 and Wellbrook 1530 no problems).

I wanted to connect this spectrum active antenna to see how it will compare with the other ones. It just blasts out with MW signals from LW to MW and HF and everywhere, as soon as power on.

As I said the power unit (Bias-T) works ok with the other active antennas. But the element does exact samething with whatever power unit is paired to it.
No control for RF gain adjustment noticed in the pcb or anywhere. So guessed it has faults of some sort.

But will try with 100 ohms pot and even with the attenuator in the ATU, and will update with the results here.
Thanks.
__________________
ORAWA = Old Radios And Wire Antennas
ORAWA01 is offline   Reply With Quote
Old 22nd Apr 2021, 7:43 pm   #11
cruisinradio
Tetrode
 
Join Date: Jul 2018
Location: London, UK
Posts: 83
Default Re: Spectrum Comms. Active Antenna problem

I have had similar problems twice.

Once it was caused by a poor ground connection on the coax/braid to a pcb, and the other was due to water ingress where corrosion had built up on the cct board and the formed green and yellow/brown crystalline structure was acting like a diode and it literally looked like a comb generator when looked at on an analyser.
cruisinradio is offline   Reply With Quote
Old 22nd Apr 2021, 10:52 pm   #12
majoconz
Hexode
 
majoconz's Avatar
 
Join Date: Jan 2008
Location: Palmerston North, New Zealand
Posts: 321
Default Re: Spectrum Comms. Active Antenna problem

What radio are you connecting to the Spectrum Loop antenna? If other radios work well with other loops, why not try one of those radios with the Spectrum? If you still get the overloading/cross modulation then the loop amplifier is the problem - no amount of filtering or radio gain reduction will get rid of that - but reducing the gain of the loop amplifier will - unless of course there is a fault with the amplifier itself. At a pinch you could try Julesomega's idea of the 100 ohm pot, but put it across the loop with the wiper to the amplifier input.
__________________
Cheers - Martin ZL2MC
majoconz is offline   Reply With Quote
Old 23rd Apr 2021, 4:23 pm   #13
ORAWA01
Hexode
 
Join Date: Apr 2011
Location: Stirlingshire, UK.
Posts: 407
Default Re: Spectrum Comms. Active Antenna problem

The Spectrum antenna has been connected to every different radios here for testing. But they all were the same = overloading, and the MW signals appearing all over, as soon as power is on the antenna.

It was connected to the ATU and Attenuator, 10dB, 20dB, 30dB and 40dB. It just got quiet, but the overloading signals are still there, not going away.

When the Spectrum antenna was powered on, I got the DMM, and read voltage on the transistors and diodes. They all seem alive with the live DC voltages present on the legs.

Good point on the poor connection from the coax braid and the pcb. I will check it. Looking at it very closely, the PCB is clean and all the parts seem physically OK. Will upload the photo. I got it in the iPad, but now seems having problems with the internet, which makes uploading problematic.
__________________
ORAWA = Old Radios And Wire Antennas

Last edited by ORAWA01; 23rd Apr 2021 at 4:37 pm.
ORAWA01 is offline   Reply With Quote
Old 24th Apr 2021, 11:47 pm   #14
majoconz
Hexode
 
majoconz's Avatar
 
Join Date: Jan 2008
Location: Palmerston North, New Zealand
Posts: 321
Default Re: Spectrum Comms. Active Antenna problem

Quote:
If you still get the overloading/cross modulation then the loop amplifier is the problem - no amount of filtering or radio gain reduction will get rid of it.
As I said, if the cross-modulation is taking place in the loop amplifier, no amount of attenuation subsequent is going to get rid of it.

Quote:
It was connected to the ATU and Attenuator, 10dB, 20dB, 30dB and 40dB. It just got quiet, but the overloading signals are still there, not going away.
__________________
Cheers - Martin ZL2MC
majoconz is offline   Reply With Quote
Old 25th Apr 2021, 9:33 am   #15
murphyv310
Dekatron
 
murphyv310's Avatar
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 4,428
Default Re: Spectrum Comms. Active Antenna problem

If its getting overloaded try two 1N4148 diodes back to back directly across the loop connections to the amplifier pcb.
__________________
Cheers,
Trevor.
2M0GZQ BVWS, GQRP KLARC. Member
murphyv310 is offline   Reply With Quote
Old 25th Apr 2021, 9:44 am   #16
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 17,951
Default Re: Spectrum Comms. Active Antenna problem

Quote:
Originally Posted by ORAWA01 View Post
I have 2-3 GC radios (IC-R75 and NRD 525 and SDRPlay RSPdx ..etc), and they all work well, has good front ends I believe. They all work well with the other active antennas (PA0RDT and MLA30 and Wellbrook 1530 no problems)
The JRC NRD525 is a triple conversion set. It'd take a very strong MW signal to break through on SW. Perhaps the antenna is generating harmonics?
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 25th Apr 2021, 10:07 am   #17
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 17,328
Default Re: Spectrum Comms. Active Antenna problem

If something is getting overloaded, protecting its input with back-to-back diodes will protect it from damage, but the clamping effect of the diodes will generate terrific amounts of harmonic and intermod distortion, crossmodulation and also blocking.

If you still want to use the signals afterwards, then there are some other routes to go down.

An attenuator between the antenna and the amplifier will reduce the amount of the big signal hitting the amplifier. It will also reduce your wanted signal. This might still be a good deal. It will also reduce local environmental noise picked up by the antenna, so you may have more sensitivity which you can use from your receiver. However, doing an attenuator in the lead of an antenna of awkward impedance can be a challenge.

A preselector filter between the antenna and the amplifier can do a bit better if the strong and wanted signals are spaced enough for it to pull the big one down more than the small one. This is heading towards mechanical variable capacitors remotely operated by a servo or stepper motor. Varactor diodes distort quite a lot. For the full HF range, you're also into relay switched coils.

Finally, you can womph up the active antenna amplifier to something more linear through being substantially more powerful than you'd think the signal levels need. All amplifiers are non-linear to an extent. As your signals, even the big one, now use a smaller part of the amplifier's swing capability, they see less curvature of its characteristic, and so less distortion. This will run warm and take a fair amount of quiescent current, but it is broadband. One disadvantage is that the full dynamic range of all the signals hitting your antenna gets passed straight on to your receiver.

The NRD525 was one of the better amateur receivers of its day in terms of large signal handling, but it was not as much better as legend has it.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now   Reply With Quote
Old 25th Apr 2021, 2:45 pm   #18
merlinmaxwell
Dekatron
 
merlinmaxwell's Avatar
 
Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 10,591
Default Re: Spectrum Comms. Active Antenna problem

Small wideband amplified aerials are at best a compromise, at worst bloomin' awful (as you, the OP, have found). At HF at the atmospheric noise is quite high so anything with noise lower than that will work well. But you need quite a large signal handling capability, this can be noisy. Luckily for HF this more than cancels out. These days one of the better off the shelf opamps makes a good HF wideband (kHz to 10's of MHz) amplifier. We are blessed with people amplifying weeny signals from CMOS video chips cheaply for example.

Quote:
The NRD525 was one of the better amateur receivers of its day in terms of large signal handling, but it was not as much better as legend has it.
The AOR 7030 was very good in that respect.
__________________
Cats have staff, it's dogs that have owners.
merlinmaxwell is offline   Reply With Quote
Old 25th Apr 2021, 5:44 pm   #19
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 17,328
Default Re: Spectrum Comms. Active Antenna problem

The AOR7030 was John Thorpe at work, designed in the UK by the people behind the old Lowe's receivers. It's based around the H-Mode mixer that was publicised by Colin Horrabin via Pat Hawker's column. A good receiver and a bit ahead of the pack.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now   Reply With Quote
Old 25th Apr 2021, 7:50 pm   #20
merlinmaxwell
Dekatron
 
merlinmaxwell's Avatar
 
Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 10,591
Default Re: Spectrum Comms. Active Antenna problem

The AOR7030 looked good too, mine was my (via headphones to not annoy the missus) bedside radio for years. The much maligned button/menu system was brilliant to use by touch alone. Back on topic, I think it's the OPs aerial that is the problem.
__________________
Cats have staff, it's dogs that have owners.
merlinmaxwell is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 4:36 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.