Date   

Re: Gain of a Vivaldi Horn

KENT BRITAIN
 

Hi Andy

I remember working with you on the Vivaldi article for "Microwave Know How".

The ridges in the Ridged Horn takes the horn to a lower frequency range than a basic horn.
So it you have a 8-12 GHz horn.  Adding the ridges can make it a 5-12 GHz horn.
Upper frequency can be extended, but you have to go to coax.  I have a 1-18 GHz version I use on the antenna range.    

There are some vintage DOS programs that will calculate the gain of a horn from it's dimensions.  These programs work quite well with the Waveguide versions of the ridged horns, until they think you have waveguide cutoff at the low frequency range of the horns.

After years of unsuccessful experiments I think I have a way to make cross polarized Vivaldi's.
Getting all those bits to slide together is more complex that I first though.   And by using commerical 90 deg broad band splitters, we can make them CP over a very wide range of frequencies. 

Cheers   Kent WA5VJB/2E0VAA/G8EMY

On Tuesday, August 3, 2021, 08:17:47 AM CDT, Andy G4JNT <andy.g4jnt@...> wrote:


I have a commercial Vivaldi horn, with mouth dimensions 105 x 70mm
 
In calculating it's gain, is it reasonable to use the area and then assume, say, 70% efficiency?   Or is there something about Vivaldis that inherently lowers the gain?

If the former case, then at 2.4GHz I reckon it works out at 6.2dBi


Re: 10GHz Activity from Brittany

Neil Smith G4DBN
 

Thaks Barry, I reckon I could be in with a chance from up here in IO93 if conditions are right, depending on their locations.  If they are west of Lannion, perhaps at Pleumeur-Bodou, I might get lucky with RS or AS or tropo west of my tree line. I'll email J-M direct and share any sked info.

Pity about the group being on Facebook, I'm amazed that people really still use that dreadful cesspit of harassment, abuse and cyber-trolling.  Ho hum.

Neil G4DBN

On 03/08/2021 15:01, Barry Lewis via groups.io wrote:
Folks,
I've just received the following through the RSGB Microwave Manager contact point:

Message: Dear Barry, I am located north of Brittany, in France. Just in border of the sea coast. With some other OM's we are doing some 10GHz experiences. I wonder if some guys, south of England, are interested to make contact with us. By mail first to engage the relation and by radio, with planed qso. We use DB6NT systems and home made equipments. We have some high points (max 302m asl). Our group has started a facebook group to feed it with the news from here. https://www.facebook.com/groups/bzh10ghz ok this is in french, but google translate can assist. Thank you for reading my mail, best 73's Jean Marie 

I have replied asked for dates as I'm sure this will be your first question.

The email address is contact@...

Best 73
Barry G4SJH


Re: Gain of a Vivaldi Horn

Marcus Walden
 

Hi Andy

From your description of the aperture, it sounds like you have a double- or dual-ridged horn antenna.

Some freely available papers describing dual-ridged horn antennas that have similar dimensions to yours. It would appear that your lower limit is about 2 GHz.



The term 'Vivaldi antenna' was coined for a PCB design.

Don't shoot the messenger but R. C. Hansen describes the term 'Vivaldi antenna' as whimsical and its use should be deprecated because the name converys no meaning. He prefers TEM horn.

The gain will also depend on the length and shape of the flare. At what point along the flare is the design radiating at 2.4 GHz? One of the free papers achieves 3-4 dBi at the bottom end of its range, while a Steatite horn antenna gets around 5-6 dBi.

73 Marcus G0IJZ

On Tue, 3 Aug 2021 at 14:17, Andy G4JNT <andy.g4jnt@...> wrote:
I have a commercial Vivaldi horn, with mouth dimensions 105 x 70mm
 
In calculating it's gain, is it reasonable to use the area and then assume, say, 70% efficiency?   Or is there something about Vivaldis that inherently lowers the gain?

If the former case, then at 2.4GHz I reckon it works out at 6.2dBi


10GHz Activity from Brittany

Barry Lewis
 

Folks,
I've just received the following through the RSGB Microwave Manager contact point:

Message: Dear Barry, I am located north of Brittany, in France. Just in border of the sea coast. With some other OM's we are doing some 10GHz experiences. I wonder if some guys, south of England, are interested to make contact with us. By mail first to engage the relation and by radio, with planed qso. We use DB6NT systems and home made equipments. We have some high points (max 302m asl). Our group has started a facebook group to feed it with the news from here. https://www.facebook.com/groups/bzh10ghz ok this is in french, but google translate can assist. Thank you for reading my mail, best 73's Jean Marie 

I have replied asked for dates as I'm sure this will be your first question.

The email address is contact@...

Best 73
Barry G4SJH


Gain of a Vivaldi Horn

Andy G4JNT
 

I have a commercial Vivaldi horn, with mouth dimensions 105 x 70mm
 
In calculating it's gain, is it reasonable to use the area and then assume, say, 70% efficiency?   Or is there something about Vivaldis that inherently lowers the gain?

If the former case, then at 2.4GHz I reckon it works out at 6.2dBi


GB3ZME beacons power-cuts

Martyn G3UKV
 

GE beacon followers:
The GB3ZME microwave beacons at Little Wenlock in Shropshire are likely to suffer some off-air periods due to a new heating system being installed at the village hall site (IO82RP78). The contractors have warned that mains power may be interrupted during this installation process this week for a week or two.
The beacons operate on the 13, 9, 6 and 1.2 cm bands (see beaconspot for details).
73
Martyn G3UKV (NoV holder for GB3ZME)

Virus-free. www.avg.com


Re: News items and Pictures for DUBUS

Ralph
 

Good morning John,

 

Hope all is well.

 

Sorry but nothing to report again, but just to let you know .

 

73 Ralph G4ALY

 

Sent from Mail for Windows 10

 

From: John Quarmby via groups.io
Sent: 01 August 2021 21:53
To: UKMicrowaves@groups.io
Subject: [UKMicrowaves] News items and Pictures for DUBUS

 

I would be grateful to receive your news items and pictures for the

forthcoming European Microwaves column in DUBUS 3/21. Operating news,

interesting construction topics, and propagation notes, all are welcome.

My deadline is next weekend so please send items during this week.

 

73

 

John G3XDY

 

 

--

This email has been checked for viruses by Avast antivirus software.

https://www.avast.com/antivirus

 

 

 

 

 

 


News items and Pictures for DUBUS

John Quarmby
 

I would be grateful to receive your news items and pictures for the forthcoming European Microwaves column in DUBUS 3/21. Operating news, interesting construction topics, and propagation notes, all are welcome. My deadline is next weekend so please send items during this week.

73

John G3XDY


--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Re: Spurious box modes

Ian White
 

On Fri, Jul 30, 2021 at 09:29 AM, Andy G4JNT wrote:
Signals at frequencies above cut off, where the width of the box is a half wave, will propagate down the box with virtually no attenuation.   So if you have plenty of gain in there at a frequency above cut off, it only needs a small amount of coupling to promote oscillation. 
This problem goes back to the early days of radar, where extremely high-gain IF strips were required, typically around 30MHz. Despite a straight-line layout with careful shielding underneath each individual valve base, the whole thing oscillated at the IF. Remove the top cover, and the oscillation stopped. 

The notion that the "shielding cover" was actually creating the feedback was clearly ridiculous. The idea of a "waveguide beyond cutoff" at 30MHz, coupling the output signal back to the input, was literally beyond belief. At least, it was until someone did the calculation.

73 from Ian GM3SEK


New 30THz video

Barry Chambers
 

Hi Folks

the latest 30THz video is now on YouTube, thanks to Peter, G3PHO. It shows some mirror tests that Bob and I did a few weeks ago at the Finningley club site. Development of the system is ongoing and we hope to do some more tests when the Sun returns to the UK!

https://youtu.be/mfNiEaK5HDg <https://youtu.be/mfNiEaK5HDg>

73 Barry, G8AGN


Re: DStar on 10 GHz

Mark GM4ISM
 

Hi all

Some rambling thoughts on DStar and DV modes...

The modulation of DStar Vs FreeDV appears to be quite different ( ignoring the Codecs)

DStar uses GMSK   (Gaussian Minimum Shift Keying) where a 4800bpS data stream  frequency shifts  the carrier  (but not by a constant dF)

FreeDV uses 14 individual DQPSK carriers spaced 75Hz apart with an additional DBPSK carrier in the middle. It signals at only 50 symbols per sec ( x 15 of course)

These modulation schemes will behave differently depending on propagation. I would expect DStar to perform worse with severe multipath if delays become long (actually unlikely).  Under heavy spreading, FreeDV may fall apart earlier.  FreeDV however seems to include a very reliable weak signal mode (albeit lowish audio  quality).   At low signal strength, 700D is decoded maybe better than most people can read weak SSB and of course once error rates drop enough, the  quality  is as good as it gets. It may be better than distorted SSB    (I would just stick the the key of course)

Setting up  FreeDV would be easy. Its certainly worth trying although I have no way to compare to DStar.  My gut feeling is the DStar may win with rain scatter because of the difference in modulation and the width of scattered signals. It rather depends on the DSP decoders though. Scattered signals wider that the carrier spacing are likely to break things and 200Hz spread is not uncommon at 10GHz

Given FreeDV is open source, it may be possible to  increase the  carrier separation (and of course the bandwidth) but if it can still fit in the SSB channel and pass through the SSB modulator, it is very likely that wider spaced carriers would  be more tolerant of the Doppler  spreading, in much the same way as the wider spaced JT4 tones help.

All very interesting.


Mark GM4ISM




On 31/07/2021 13:34, Dave_G0WBX via groups.io wrote:

From: Murray Niman
Date: Fri, 30 Jul 2021 07:46:50 PDT

Hi
Most intriguing...
The other promising candidate would be to try Yaesu C4FM  as its modulation concept should be fairly robust  aamd if it does get thru  has a better quality voice  codec

And if you have SSB , try FreeDV... 

73

 Murray


Hi.

Not equipped for 10GHz.   I'm not 100% sure of the finer details, but I think D*, YSF DMR etc, use very similar on-air signals, RF wise.  But the underlying protocols and encoding are different.

Maybe some of the faster (and wider) MFSK data modes (using a SSB radio and Fldigi or MultiPSK etc) might work over rain scatter?   They are remarkably robust in the face of QRM and rampant selective fading on HF.  Though I appreciate the mechanisms are very different.  The Faster/wider Olivia modes give you some FEC error mitigation too.

In truth, just guessing, but would be interested to know the results of any such tests, not that I can partake in any way.

73.

Dave G8KBV.




-- 
Created on and sent from a Unix like PC running and using free and open source software:

Virus-free. www.avg.com


Re: DStar on 10 GHz

Dave_G0WBX
 

From: Murray Niman
Date: Fri, 30 Jul 2021 07:46:50 PDT

Hi
Most intriguing...
The other promising candidate would be to try Yaesu C4FM  as its modulation concept should be fairly robust  aamd if it does get thru  has a better quality voice  codec

And if you have SSB , try FreeDV... 

73

 Murray


Hi.

Not equipped for 10GHz.   I'm not 100% sure of the finer details, but I think D*, YSF DMR etc, use very similar on-air signals, RF wise.  But the underlying protocols and encoding are different.

Maybe some of the faster (and wider) MFSK data modes (using a SSB radio and Fldigi or MultiPSK etc) might work over rain scatter?   They are remarkably robust in the face of QRM and rampant selective fading on HF.  Though I appreciate the mechanisms are very different.  The Faster/wider Olivia modes give you some FEC error mitigation too.

In truth, just guessing, but would be interested to know the results of any such tests, not that I can partake in any way.

73.

Dave G8KBV.




-- 
Created on and sent from a Unix like PC running and using free and open source software:


Re: Spurious box modes

DougF VK4OE
 

Hello Greg and other readers.

Given the excellent input already posted, I'd like to add a couple of practical observations from years (decades) of making such things.

There are fundamentally two practical ways of quelling spurious oscillations of microwave-capable electronics contained between waveguide-like RF-reflective walls.  They are (a) use of RF-absorptive ferrite-containing pieces (flexible or solid), or (b) fitting RF-grounded metal fences and/or covers around one or more amplifying stages such that desired fields are kept where we would want them to stay and not radiated so much around the interior of the offending enclosure.

One should be aware that not all ferrite RF-absorptive materials have the same characteristics, meaning that one that works well in the 1-4 GHz range will almost certainly not be useful much above 10 GHz.  (I have sheets of that sort of material - ask!)  And there are some types which are very useful in the 20-30 GHz range which are worth 'recovering' from K or Ka band surplus items if they happen to come your way.  The RF-absorptiveness of these HF materials may still be happening at lower frequencies to some extent, it's just that the lower mass/volume of typical pieces you'll have in hand is significantly less than materials designed for lower frequencies - undesired fields only partially attenuated.  The typical K or Ka band absorptive pieces have to be able to fit into smaller spaces, thus there is usually not so much absorptive material present.  But the products designed for the higher bands really 'shine' at the higher frequencies.

Now one personal observation is that the two approaches to stray field attenuation which I have described don't necessarily deliver identical results.  By way of example, if the apparently easier approach of applying many different types of ferrite absorptive material at different experimental locations seems not to be taming the amplifier chain, I have often found that fitting a carefully cut fence (or fences!) to the full internal height and width of the interior of the box, with numerous points of attachment to the PCB ground whilst allowing a small cut-away for each of the RF and DC tracks which pass by on that side of the board (you have to be creative sometimes!) will get the job done. And sometimes a complete cover just above the amplifier components (which still looks like a type of waveguide but one that only propagates a much higher frequency) may be the only working solution.  (Both approaches are often seen in commercially designed/built microwave equipment.)

When you're experimenting in these ways, it helps to be imagining the various possible RF fields (both desired and undesired) which could be bouncing around inside a given box.  There is significant satisfaction available to those who persevere and are successful!

Very best 73,

--Doug Friend, VK4OE.

On 30/07/2021 4:37 pm, Greg - ZL3IX wrote:
Can someone please tell me a bit more about spurious modes in equipment mounted in metal boxes, or at least point me to a reference that I can read for myself. In particular, I'd like to know how much of a wanted TEM wave propagating along a microstrip track 1.5 mm wide on a 0.8 mm FR4 substrate at 10 GHz, can be siphoned off into unwanted TExx/TMxx modes. I've heard of moding problems, but assumed that they were only applicable to troubles with filter stop band attenuation.

I think I may have such a problem with my new transverter. I find that if I put the lid on, or even bring the lid close, I lose a varying amount of gain, up to 4 dB or so, and the noise floor also rises 5 dB or so. Can this be caused by moding, or is there something else at play? I don't think anything is oscillating. If it is moding, can it be prevented by the use of absorber material on the lid and sides of the box? I must say that I'm really surprised at how bad the effect seems to be.

73, Greg, ZL3IX


#WSPR on QO-100 #wspr

Andy G4JNT
 

Bit of a pointless exercise really, but just to prove it could be done and tick the box.   Here's WSPR transmitted via QO-100

Its a bit boring transmitting to myself, even if both callsigns are used :-)

image.png


PD85004 device for the G4BAO 23 and 70cm driver kits

John Worsnop
 

I've just looked again at the shipping date on these devices, and my order on RS has now been pushed out to January 2022.

No other distributors have stock or are showing an availability date. The manufacturer's website shows no stock at any distributor in the World

If you're waiting to place an order for for a kit, don't hold your breath!

Out of my control, sorry.

73
John


Hello from across the pond

Gedas
 

Greetings from a 10 GHz terrestrial op from Indiana, USA. Thank you for allowing me to join up. 73

-- 
Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.


Re: DStar on 10 GHz

Andy G4JNT
 

QO-100 is so stable, WSPR would work
Wonder if anyone  has tried it



On Fri, 30 Jul 2021 at 16:18, Murray Niman <g6jyb@...> wrote:
BTW - FreeDV has already been used on QO-100 so long microwave DX (without scatter )

73

Murray


Re: LMR-LW-400

alwyn.seeds1
 

Dear Colin,

It’s aluminium tape, covered by aluminium braid.

Centre conductor, non-stranded copper clad aluminium.

This is not a cable intended for repeated flexing.

As well as the solid inner conductor, I am not keen on long term use of aluminium braided cables outdoors or indeed at all, unless weight is critical. 

Braid screening becomes poor unless there is negligible resistance between overlapping strands. Aluminium is not a good choice for this, especially as moisture is absorbed.

Suggest you use LMR-400-UF or even better, one of the braided only cables, such as Times Microwave TCOM400 & 600  “Flexstrand” “DB”; these are ideal for rotator loops, but not cheap.

Regards,

Alwyn 
_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________


Re: DStar on 10 GHz

Murray Niman
 

BTW - FreeDV has already been used on QO-100 so long microwave DX (without scatter )

73

Murray


Re: DStar on 10 GHz

Andy G4JNT
 

Free DV, if it uses an SSB bandwidth, will have a slower symbol rate , making it more susceptible to the scatter.
C4FM and 9600 GMSK are nice and wide compared wiith the scatter BW.



On Fri, 30 Jul 2021 at 15:46, Murray Niman <g6jyb@...> wrote:
Hi
Most intriguing...
The other promising candidate would be to try Yaesu C4FM  as its modulation concept should be fairly robust  aamd if it does get thru  has a better quality voice  codec

And if you have SSB , try FreeDV... 

73

 Murray

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