Date   

Re: Common mode chokes on receiving loops

Tom Crosbie G6PZZ
 

Thanks very much Chris.

I’m sure the others will also appreciate the effort.

 

I’ve got a few Chinese clip on ferrites left. Might it be worth fitting them to each end of the mains input lead?
I’ve also got some IEC panel fitting sockets with built-in filtering. I’ve connected these to a short lead with an IEC plug to make a filtered extension. Would that help improve the performance of your PSU?

I trust you and your family are keeping well during these uncertain times.

 

Best wishes and 73

Tom G6PZZ

 

From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Chris Moulding
Sent: 04 October 2020 19:14
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Common mode chokes on receiving loops

 

OK I'll build another batch of the Mains Filter next week.

I stopped making quite a few products due to the Covid-19 lockdown as at the time it was uncertain if I could travel to the workshop.

I'll add a post to the forum when they are ready.

Regards,

Chris


Re: Common mode chokes on receiving loops

Chris Moulding
 

OK I'll build another batch of the Mains Filter next week.

I stopped making quite a few products due to the Covid-19 lockdown as at the time it was uncertain if I could travel to the workshop.

I'll add a post to the forum when they are ready.

Regards,

Chris


Re: Common mode chokes on receiving loops

Tom Crosbie G6PZZ
 

Count me in too.

Tom G6PZZ

-----Original Message-----
From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Bob G3REP via groups.io
Sent: 04 October 2020 16:07
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Common mode chokes on receiving loops

Me too,
useful to have in the arsenal ;-)
Bob
G3REP


Re: Common mode chokes on receiving loops

Tom Crosbie G6PZZ
 

I made some CMC’s as described by Everett Sharpe, N4CY, using Fair-Rite and TKD ferrites purchased via mouser.co.uk. They came direct from the USA at a fraction of the price of UK suppliers. Buy £30.00 or more and get free carriage – Three days via courier.  If you build GM3SEK’s mains filter, you won’t have a problem getting to £30.00!!

 

Tom G6PZZ

 

From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Chris Moulding
Sent: 03 October 2020 16:42
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Common mode chokes on receiving loops

 

Very interesting Ray.

Up until the Covid-19 lockdown we used to manufacture a Mains Filter that combined an IEC mains filter with a ferrite toroid to provide very high suppression of conducted HF RF interference on the electricity supply.

The web page showing the details and spec of our filter is: http://www.crosscountrywireless.net/mains_filter.htm

The GM3SEK pages are interesting but he follows the conventional radio amateur practice of only using Fair-Rite or Amidon toroids. This is fine in the US but the prices when imported into Europe are high after tax and shipping is included. We now use Ferroxcube ferrite toroids from Poland which to us in the UK are around 1/4 the price of Fair-Rite or Amidon. It's also a higher spec product with a greater range of ferrite materials and often with epoxy coating of the toroid for extra electrical safety.

On the PA0NHC web page the description of how a common mode choke works with coax is incorrect. If it worked how he describes it then RF wouldn't flow through the coax in differential mode when a toroid is used on the outside of the coax.

Now that I feel like I've marked your homework if you are a RSGB member you might be interested in the article I've written in RSGB RadCom this month. Using loop counterpoises and an isolation transformer I've described a vertical antenna that is resistant to local RF noise.

I've got the agreement of the Technical Editor of RadCom to share the article next month when the next issue comes out.

I know from the emails I'm receiving that a lot of RSGB members are trying out the design with some success. The Ferroxcube distributor Arrow Electronics has now run out of the toroid I specified in the article and I'm now suggesting the next size down. They have 800 in stock so they should last a while.

Regards,

Chris


Re: Common mode chokes on receiving loops

PA3BCB
 

Hi all,

Being a radio amateur for more than fifty years I was aware of the existence of Aero NDB’s, having heard some local ones in the course of time.

And of course I read about NDB hunting an dx-ing.

A few months ago I started serious NDB listening, first with an SDRPlay RSP2 and a multi-turn, manually tuneable indoor frame loop antenna that I made many years ago.

Then I coincidentally discovered that my Airspy Discovery was very sensitive in the NDB band using my 2 x 21 meter ( 2 x 70 ft) low doublet antenna, using different ratio rf transfomers.

In the next step I ordered the VLF version of the CCW loop antenna and used a 4.5 m (15 ft) circumference loop in the shape of an inverted delta on an long bamboo pole that was washed ashore locally.

I used this wire instead of the 3 meters (10 ft) of wire supplied by Chris for the only reason that its diameter was slightly larger and the length was available.

I like to use what is lying around here.

Noise is not a great problem here, I live in a rather RF quiet rural location in the North of the Netherlands although on some days I have an unidentified strong rattling interference.

My own switch-mode telephone wall chargers produce interference on some days, on most other days they strangely do not.

The CCW loop works great and I can testify it has sharp nulls and pickup by the coax feeder is unnoticeable.  Cannot notice any excess noise or imd.

My reference NDB for antenna comparison  is a local low power beacon on 330 kHz, situated 25 km (14 nm) from here and I can completely null it out with the CCW loop.

In two months’ time I logged almost 100 different NDB’s, largest dx being FarOer and Iceland in the North to Belarus in the East and Romania to the Southeast. Many from Scandinavia and my surrounding countries but none from the UK  except Norwich.

My main listening period is around 21:00 UTC which is probably too early for the UK. Of course I take the loop orientation into account. Main receivers are Airspy Discovery SDR with SDR Console and an old Lowe HF-225. I use a CCW RF protection and isolation unit as well.

 

Ferrocube is a former Dutch Philips company where many ferrites were developed. Before the wide-spread use of Amidon or Fair-rite ferrite cores, our national radio society supplied Philips ferrite toroids, the larger purple-finished 4C6 and green 3E1 ones being intended mainly for antenna baluns and RFI suppression at the neighbours’, the smaller 4C6 toroids were used in broadband RF transformers. Chris, I hope you will not run into supply-, tax- and import duties problems after the UK’s Brexit from the EU.

 

Two days ago I put up a vertical antenna, using a CCW High-Z amplifier. The vertical 5 meter (16 ft) antenna wire is supported by a 6 meter (20 ft) high multi-section guyed GRP pole, resting against a 1.5 m ( 5 ft) aluminium fence post driven halfway into the ground. At first I used the 10 meter (33 ft) counterpoise wire kindly supplied by Chris as a temporary crisis solution but I noticed much noise. The signal to noise ratio improved dramatically when instead of the counterpoise wire I connected the ground connection of the amplifier to the aluminium ground post. This ground post was intended initially solely for mechanical support only because it will ultimately be covered with aluminium oxide which is a bad conductor. The intention was to drive a copper tube into the ground as an electrical earth ground. BBC4 on 198 kHz comes booming in, as well as several MW broadcast stations in the late afternoon. Several LW broadcast stations heard but I am not very interested in broadcast dx.

The counterpoise wire picked up a lot of noise, not present on the ground post connection while signal strengths were unchanged. The insulated counterpoise wire relies on its capacitance to ground and although aluminium is not the best choice for grounding, I think the capacitance to ground of the fence post, which because of its H-shape has a relatively large area, is sufficient as an earth connection without picking up noise. Perhaps I will skip the copper tube earth completely.

I already received a few “new” NDB’s with this antenna. On 80 meters the locals were much weaker on the vertical than on my NVIS doublet as was to be expected. UK amateurs on 80 meters were rather strong but I have to get more listening experience for further conclusions.

Thanks Chris for the fun I have with the CCW products mentioned.

 

I look forward to Chris sharing his article on loop counterpoises and isolation transformers in the RSGB RadCom issue because I am not an RSGB member anymore.

 

Regards,

 

Gerard PA3BCB


Re: Common mode chokes on receiving loops

Bob G3REP
 

Me too,
useful to have in the arsenal ;-)
Bob
G3REP


Re: Common mode chokes on receiving loops

Stephen Farthing
 

I would also buy one

On Sun, 4 Oct 2020 at 15:41, Ray G3NKL <ray@...> wrote:
Hi Chris,

It's a pity you don't still manufacture the mains filter, I would be at the front of the queue to buy one!

I read your article the same day as Radcom dropped through my letter box. I was quite surprised at the reduction in noise that you obtained.  I have always suggested that it is unsatisfactory and potentially unsafe to connect the mains supply earth to a local earth such as is commonly used with long wire or vertical antennas. Under some conditions, high currents could flow through the house wiring between these two earth systems. Your isolator overcomes this in a very elegant manner and even if there was no improvement in noise performance, there are very good reasons for using one.

Ray
G3NKL

On Sun, 4 Oct 2020 at 15:01, Ray G3NKL via groups.io <ray=rayjones.me.uk@groups.io> wrote:
Hi Chris,

It's a pity you don't still manufacture the mains filter, I would be at the front of the queue to buy one!

I read your article the same day as Radcom dropped through my letter box. I was quite surprised at the reduction in noise that you obtained. However, there is one other great advantage of your isolator that you don't mention. I have always suggested that it is unsatisfactory and potentially unsafe to connect the mains supply earth to a local earth such as is commonly used with long wire or vertical antennas. Under some conditions, high currents could flow between these two earth systems. Your isolator overcomes this in a very elegant manner and even if there was no improvement in noise performance, there are very good reasons for using one.

Ray
G3NKL


On Sat, 3 Oct 2020 at 16:42, Chris Moulding <chrism@...> wrote:
Very interesting Ray.

Up until the Covid-19 lockdown we used to manufacture a Mains Filter that combined an IEC mains filter with a ferrite toroid to provide very high suppression of conducted HF RF interference on the electricity supply.

The web page showing the details and spec of our filter is: http://www.crosscountrywireless.net/mains_filter.htm

The GM3SEK pages are interesting but he follows the conventional radio amateur practice of only using Fair-Rite or Amidon toroids. This is fine in the US but the prices when imported into Europe are high after tax and shipping is included. We now use Ferroxcube ferrite toroids from Poland which to us in the UK are around 1/4 the price of Fair-Rite or Amidon. It's also a higher spec product with a greater range of ferrite materials and often with epoxy coating of the toroid for extra electrical safety.

On the PA0NHC web page the description of how a common mode choke works with coax is incorrect. If it worked how he describes it then RF wouldn't flow through the coax in differential mode when a toroid is used on the outside of the coax.

Now that I feel like I've marked your homework if you are a RSGB member you might be interested in the article I've written in RSGB RadCom this month. Using loop counterpoises and an isolation transformer I've described a vertical antenna that is resistant to local RF noise.

I've got the agreement of the Technical Editor of RadCom to share the article next month when the next issue comes out.

I know from the emails I'm receiving that a lot of RSGB members are trying out the design with some success. The Ferroxcube distributor Arrow Electronics has now run out of the toroid I specified in the article and I'm now suggesting the next size down. They have 800 in stock so they should last a while.

Regards,

Chris






























Re: Common mode chokes on receiving loops

Ray G3NKL
 

Hi Chris,

It's a pity you don't still manufacture the mains filter, I would be at the front of the queue to buy one!

I read your article the same day as Radcom dropped through my letter box. I was quite surprised at the reduction in noise that you obtained.  I have always suggested that it is unsatisfactory and potentially unsafe to connect the mains supply earth to a local earth such as is commonly used with long wire or vertical antennas. Under some conditions, high currents could flow through the house wiring between these two earth systems. Your isolator overcomes this in a very elegant manner and even if there was no improvement in noise performance, there are very good reasons for using one.

Ray
G3NKL

On Sun, 4 Oct 2020 at 15:01, Ray G3NKL via groups.io <ray=rayjones.me.uk@groups.io> wrote:
Hi Chris,

It's a pity you don't still manufacture the mains filter, I would be at the front of the queue to buy one!

I read your article the same day as Radcom dropped through my letter box. I was quite surprised at the reduction in noise that you obtained. However, there is one other great advantage of your isolator that you don't mention. I have always suggested that it is unsatisfactory and potentially unsafe to connect the mains supply earth to a local earth such as is commonly used with long wire or vertical antennas. Under some conditions, high currents could flow between these two earth systems. Your isolator overcomes this in a very elegant manner and even if there was no improvement in noise performance, there are very good reasons for using one.

Ray
G3NKL


On Sat, 3 Oct 2020 at 16:42, Chris Moulding <chrism@...> wrote:
Very interesting Ray.

Up until the Covid-19 lockdown we used to manufacture a Mains Filter that combined an IEC mains filter with a ferrite toroid to provide very high suppression of conducted HF RF interference on the electricity supply.

The web page showing the details and spec of our filter is: http://www.crosscountrywireless.net/mains_filter.htm

The GM3SEK pages are interesting but he follows the conventional radio amateur practice of only using Fair-Rite or Amidon toroids. This is fine in the US but the prices when imported into Europe are high after tax and shipping is included. We now use Ferroxcube ferrite toroids from Poland which to us in the UK are around 1/4 the price of Fair-Rite or Amidon. It's also a higher spec product with a greater range of ferrite materials and often with epoxy coating of the toroid for extra electrical safety.

On the PA0NHC web page the description of how a common mode choke works with coax is incorrect. If it worked how he describes it then RF wouldn't flow through the coax in differential mode when a toroid is used on the outside of the coax.

Now that I feel like I've marked your homework if you are a RSGB member you might be interested in the article I've written in RSGB RadCom this month. Using loop counterpoises and an isolation transformer I've described a vertical antenna that is resistant to local RF noise.

I've got the agreement of the Technical Editor of RadCom to share the article next month when the next issue comes out.

I know from the emails I'm receiving that a lot of RSGB members are trying out the design with some success. The Ferroxcube distributor Arrow Electronics has now run out of the toroid I specified in the article and I'm now suggesting the next size down. They have 800 in stock so they should last a while.

Regards,

Chris


Re: Common mode chokes on receiving loops

Chris Moulding
 

Very interesting Ray.

Up until the Covid-19 lockdown we used to manufacture a Mains Filter that combined an IEC mains filter with a ferrite toroid to provide very high suppression of conducted HF RF interference on the electricity supply.

The web page showing the details and spec of our filter is: http://www.crosscountrywireless.net/mains_filter.htm

The GM3SEK pages are interesting but he follows the conventional radio amateur practice of only using Fair-Rite or Amidon toroids. This is fine in the US but the prices when imported into Europe are high after tax and shipping is included. We now use Ferroxcube ferrite toroids from Poland which to us in the UK are around 1/4 the price of Fair-Rite or Amidon. It's also a higher spec product with a greater range of ferrite materials and often with epoxy coating of the toroid for extra electrical safety.

On the PA0NHC web page the description of how a common mode choke works with coax is incorrect. If it worked how he describes it then RF wouldn't flow through the coax in differential mode when a toroid is used on the outside of the coax.

Now that I feel like I've marked your homework if you are a RSGB member you might be interested in the article I've written in RSGB RadCom this month. Using loop counterpoises and an isolation transformer I've described a vertical antenna that is resistant to local RF noise.

I've got the agreement of the Technical Editor of RadCom to share the article next month when the next issue comes out.

I know from the emails I'm receiving that a lot of RSGB members are trying out the design with some success. The Ferroxcube distributor Arrow Electronics has now run out of the toroid I specified in the article and I'm now suggesting the next size down. They have 800 in stock so they should last a while.

Regards,

Chris


Re: Common mode chokes on receiving loops

Ray G3NKL
 

I returned to listening on the bands below 30 MHz after an absence of many years. (I spent many years on VHF, UHF and microwaves). I was appalled at the amount of noise I was receiving over much of the spectrum. Things had changed dramatically since the advent of the digital era. A bit of googling opened my eyes (or should that be ears?) to the problem and possible cures.

Conventional long wire antennas which I was brought up on were out due to the noise picked up on them. There is noise on every bit of wire out there, including the mains wiring. I now have common mode chokes on my mains supply and the antenna feeders where they enter my shack. One of my loops is strategically orientated to null out a particularly strong noise source received on 80 metres.

These references may be useful:
http://www.m0nwk.co.uk/mains-electricity-filter-for-emc-noise-reduction/
http://www.ifwtech.co.uk/g3sek/in-prac/
And a bit more in depth;
https://www.pa0nhc.nl/CommonModeChokes/indexE.htm

Ray
G3NKL


Re: Common mode chokes on receiving loops

Paul Newland
 

However you did it Chris it certainly works a treat!
It's an absolute "killer" on NDB's for instance. from Puerto Rico in the West, to near Lake Bajkal in the East.
And I've only just started "looking" in those directions.
Best Wishes
Paul




On Sat, 3 Oct 2020 at 08:58, Chris Moulding <chrism@...> wrote:
Built into the Loop Antenna Amplifier + is a common mode choke on the co-ax output to isolate the amplifier and loop from any RF picked up by the coax shield or noise coming from the receiver ground.

There is also an isolation transformer on the input to prevent the loop acting as an electric field antenna.

Extra common mode chokes are unlikely to have much effect.

The reason that loop antennas made with the Loop Antenna Amplifier + have such deep nulls is that the loop is working correctly as a loop and the nulls are not being filled in by RF reception in other loop modes or from the coax feeder.

Regards,

Chris


Re: Common mode chokes on receiving loops

Chris Moulding
 

Built into the Loop Antenna Amplifier + is a common mode choke on the co-ax output to isolate the amplifier and loop from any RF picked up by the coax shield or noise coming from the receiver ground.

There is also an isolation transformer on the input to prevent the loop acting as an electric field antenna.

Extra common mode chokes are unlikely to have much effect.

The reason that loop antennas made with the Loop Antenna Amplifier + have such deep nulls is that the loop is working correctly as a loop and the nulls are not being filled in by RF reception in other loop modes or from the coax feeder.

Regards,

Chris


Common mode chokes on receiving loops

Stephen Farthing
 

Good morning, 

I’ve just watched a couple of YouTube videos by Paul W1VLF on using common mode chokes to reduce interference on receiving loops. They seem to be quite effective. 

Stay safe, 

Steve G0XAR


Re: Revised version of the HF Antenna isolator

david
 

Hi Chris,

Thanks for the feedback. I managed to run the cores to ground on Arrow's
web-site, but they are listed as not available for order at present.
However, I have lots of ferrite left over from a noise-reduction campaign in
the shack and on the house's mains supply. If 4A11 is a suitable mix, I have
some equivalents. I might go for something a little 'stronger' to give me
better coverage of the lower bands. It _IS_ about experimentation, after
all.

Thanks for sharing your experiences.
Best Wishes
David, GM8XBZ

-----Original Message-----
From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On
Behalf Of Chris Moulding
Sent: 28 September 2020 15:02
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Revised version of the HF Antenna
isolator

Hi David,

I've tested the 1:1 transformer on the 160m band (1.810 - 2000 kHz) with
barely measureable loss.

I agree that the toroid will have too low a u for the 2200 and 430m bands.

The toroid is in stock at Arrow Electronics but from many emails I'm
receiving quite a few people are having difficulty finding the toroid
ontheir web site.

We do have a small stock here so if anyone is having difficulty sourcing one
contact me by private email.

Regards,

Chris


Re: Revised version of the HF Antenna isolator

Chris Moulding
 

Hi David,

I've tested the 1:1 transformer on the 160m band (1.810 - 2000 kHz) with barely measureable loss.

I agree that the toroid will have too low a u for the 2200 and 430m bands.

The toroid is in stock at Arrow Electronics but from many emails I'm receiving quite a few people are having difficulty finding the toroid ontheir web site.

We do have a small stock here so if anyone is having difficulty sourcing one contact me by private email.

Regards,

Chris

On 28 Sep 2020, at 13:58, david via groups.io <zinc65=btinternet.com@groups.io> wrote:

Chris,

I have been following the discussions on the Antenna Isolator, following on from your article in RadCom on Loop Counterpoises, with extreme interest.
I am concerned at your (strong) recommendation of a Ferroxcube core with a 4A11 mix for the transformer. The part is identified in both the text and in the schematic, so I am sure it isn't a mis-print.
It is hard to source in the UK, anyway, but it seems to have a very low u' for LF work. Ferroxcube's data sheet suggests it has a u' of only 850. They rate the material for transformers from 10 - 1000MHz. For LF bands, I was expecting something around 3000 for u'. Can you put me right, here?

Best Wishes
David, GM8XBZ




Re: Revised version of the HF Antenna isolator

david
 

Chris,

I have been following the discussions on the Antenna Isolator, following on from your article in RadCom on Loop Counterpoises, with extreme interest.
I am concerned at your (strong) recommendation of a Ferroxcube core with a 4A11 mix for the transformer. The part is identified in both the text and in the schematic, so I am sure it isn't a mis-print.
It is hard to source in the UK, anyway, but it seems to have a very low u' for LF work. Ferroxcube's data sheet suggests it has a u' of only 850. They rate the material for transformers from 10 - 1000MHz. For LF bands, I was expecting something around 3000 for u'. Can you put me right, here?

Best Wishes
David, GM8XBZ

-----Original Message-----
From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Chris Moulding
Sent: 25 September 2020 19:57
To: CrossCountryWireless@groups.io
Subject: [CrossCountryWireless] Revised version of the HF Antenna isolator

Following the publication of my recent article on loop counterpoises for low noise vertical antennas in the RSGB RadCom magazine, I've had a lot of feedback from RSGB members trying the design.

One question that came up a few times was could it be used with the non-resonant HF verticals such as the popular 43 foot vertical?

To work with those antennas the HF Antenna Isolator would need a 200 ohm output so I've re-designed it to have both 50 and 200 ohm outputs along with the 1 M ohm resistor and 20 kA gas discharge tube to provide protection from static electricity on the antenna.

It's now available.

The web page is:

http://www.crosscountrywireless.net/hf_antenna_isolator.htm

Regards,

Chris


Re: Variable gain preamp anyone?

Tom Crosbie G6PZZ
 

FWIW, my interests are in broadcast DXing. MW, HF, VHF, DAB and TV in that order. Not much going on with the last three due to lack of antennas and in about a year or so I'm going to be in a position where I'm going to be forced to relocate. So I need to rethink my interests. I'm looking for compact antennas that I can use indoors hence the renewed interest in loops.
I can't see a loop/amp combo working from 80-900MHz.
But thanks to everyone for the advice and input.
Always appreciated!

Tom G6PZZ

-----Original Message-----
From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Simon
Sent: 26 September 2020 18:21
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Variable gain preamp anyone?

Or even better still, depending upon frequency of use..( and in conjunction with reducing gain on rx.)

This will not work if you want dc-light but say just want 10-30mhz..make loop small.
Want dc-2mhz..make loop bigger.
Reduces gain where not needed..

Etc..

To remove nasty imd’s from strong mw stations add a notch filter inline with coax.

But yes Chris, I run my loop amps at 12v..(13.8v.) Fully agree with your post.

Simon


Re: Variable gain preamp anyone?

Tom Crosbie G6PZZ
 

I’m doing that already Chris with my current amp. Not one of yours, just some cheap Chinese lump hooked up to a longwire.

My attenuator is quite a lump and I was hoping to replace it with something that takes up less shelf space.

Hopefully I’ll be ordering a CCW unit quite soon and start experimenting with loops.

I’ve also got some material that’s just slightly weirder than a bicycle wheel to use as a loop that I don’t think that has been used before.

Three decades ago, after solving an engineering problem, a G4 told me I was a first class bodger and it pleases me to be still living up to that reputation after all this time!

 

 

From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Chris Moulding
Sent: 26 September 2020 17:11
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Variable gain preamp anyone?

 

I just want to raise a point about using the Loop Antenna Amplifier + with a variable supply.

It will be possible to reduce the gain by reducing the voltage applied to the amplifier.

The reduction in gain below 5 V is caused by the bias voltage dropping to a barely workable level.

The amplifier would be prone to generating cross-modulation and intermodulation at that point and I wouldn't recommend it.

For the best RFperformance run the amplifier with a bias-tee at 12 V and add an external attenuator between the amplifier and the receiver if you want to reduce the overall gain.

Regards,

Chris


Re: Variable gain preamp anyone?

Simon
 

Or even better still, depending upon frequency of use..( and in conjunction with reducing gain on rx.)

This will not work if you want dc-light but say just want 10-30mhz..make loop small.
Want dc-2mhz..make loop bigger.
Reduces gain where not needed..

Etc..

To remove nasty imd’s from strong mw stations add a notch filter inline with coax.

But yes Chris, I run my loop amps at 12v..(13.8v.) Fully agree with your post.

Simon


Re: Variable gain preamp anyone?

Chris Moulding
 

I just want to raise a point about using the Loop Antenna Amplifier + with a variable supply.

It will be possible to reduce the gain by reducing the voltage applied to the amplifier.

The reduction in gain below 5 V is caused by the bias voltage dropping to a barely workable level.

The amplifier would be prone to generating cross-modulation and intermodulation at that point and I wouldn't recommend it.

For the best RFperformance run the amplifier with a bias-tee at 12 V and add an external attenuator between the amplifier and the receiver if you want to reduce the overall gain.

Regards,

Chris

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