Date   

Re: Smith Chart

Mark GM4ISM
 

I agree Brian,
the graphical rotating around real impedances away from the normalised value works well only for a limited  range of transformations.  It is particularly useful for determining the intermediate impedance for a single or double quaterwave transformer.
 
This was taught  on BBC Shortwave stations as a quick and easy way of matching  antennas  in the days before computers and vector network analysers became  everyday objects.  Even then the graphical method was frowned upon when it came to formal training on Smith Charts at the BBC.
 
The technique of shifting the iconocentre, if I recall came into its own when the iconocentre about which it was necessary to rotate was complex itself.  This makes normalising ‘difficult’ and the mathematics of correcting for  a rotation about a complex impedance became less difficult, relatively.
I don’t remember much about it  but the case that always came up in the exam ( this was taught at University) was for a coax to waveguide transition.
It made my brain hurt then and it has never been needed in anger in my 30+ years as a professional antenna engineer, which is why I have all but forgotten it.
 
Regards
Mark GM4ISM
 

Sent: Saturday, July 09, 2016 12:54 PM
Subject: [ukmicrowaves] Re: Smith Chart
 
 

Hi Andy, Barry and Mark,

I can see Mark's suggestion will be good enough for most practical
cases, but as I teach
this stuff I have to show the students how to do it "properly", ;-) . By
the time the correction
is done it sounds simpler to normalise!

73s
Brian GM8BJF.

No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.7640 / Virus Database: 4613/12584 - Release Date: 07/09/16


Transverter Interface

Andy G4JNT
 

Well, I must really be losing it in old age here...

A slightly earlier version of this FT817 (and similar) transverter  interface without the DC switching  was  written up and published in RadCom Dec 2013, page 60.

Which I'd completely forgotten about until now!     So perhaps just as well I didn't get round to writing-up the whole thing all over again!

Found the text for that and incorporated it into a new version, to be found at 

Andy  G4JNT


On 29 June 2016 at 08:42, Andy Talbot <andy.g4jnt@...> wrote:
Is it worth writing this up, or are there already commercial designs that people just plug-n-play with?

A single board transverter interface that connects low power transceivers such as FT817 (or that olde favourite. the IC202) with low power mixers.  Single bi-directional mixers or separate Tx/Rx are catered for.    It extracts the PTT signal superimposed on the transceiver RF, generates +VTx and +VRx voltages at a couple of amps switching capability, and uses PIN diodes to switch RF through an attenuator on Tx and straight though on Rx.   A PIN diode on the Tx path allows varying the Tx drive level with a  DC  control signal.  Not a relay in sight

All components available via the catalogue suppliers or Chipbank if you're prepared to substitute and experiment a bit.


Re: Smith Chart

Brian Flynn GM8BJF
 

Hi Andy, Barry and Mark,

I can see Mark's suggestion will be good enough for most practical cases, but as I teach
this stuff I have to show the students how to do it "properly", ;-) . By the time the correction
is done it sounds simpler to normalise!

73s
Brian GM8BJF.


Andrews TNC Connectors needed.

Christopher Bartram <cbartram@...>
 

I have a very good coax relay for the lower frequency bands, ie. 1.3 - 3.4GHz, and I want to use it in a new preamp for small antenna EME on 23. The snag is that it uses TNC connectors.

Now, I could use adaptors to type-N, but in a situation where, particularly on receive, I'll be scrabbling for every last 0.05dB of loss in this unit, the use of adaptors is not a good idea!

I'm looking for two connectors: TNC(m) to FSJ4-50. I'm quite happy to pay for these, so if you have some in your junk-box (I don''t mind at all if they've been used, providing they are complete) please get in touch!

Vy 73

Chris
GW4DGU


Re: Smith Chart

Barry Chambers
 

Brian

Yes, I would second your suggestion about renormalisation.

73

Barry, G8AGN
On 08/07/2016 11:52, 'brian.flynn@...' brian.flynn@... [ukmicrowaves] wrote:

 

Hi Andy,

I get involved in this a bit. I have always read off the
impedance/admittance and re-normalised. I have never come across the
procedure you suggest. I do this fairly regularly to design quarter wave
matching sections when the the impedances are not real.

73s

Brian, GM8BJF.
--



Re: Smith Chart

Andy G4JNT
 

The  reply below from Mark was sent direct  :

Which is, more-or-less, what I can now recall being shown all those years ago.   It works for quarter wave transformers
Honour is satisfied and it appears that route was only ever a quick approximation for an impedance that had a mostly real component.

So there isn't an exact way of doing it - I felt all along it wasn't possible as a 'correct' Smith chart procedure!  At least without renormalising.
Much prefer calculation and software for microwave design than the manual Smith chart of old.

Andy  G4JNT

>Andy
>sorry I cant reply to the list, I am away from home and don't have the correct email account set up
>In answer to the question, a slightly reserved yes
> simply place the rotation point  on the real axis   at the 50 ohm normalised value ( eg. rotate round 1.5 for 75 ohm >system on a 50 ohm chart)
> for  rotations that don't result in a large reactive transformed impedance this is really quite accurate (ie.1/4 wave >rotations and multiples of this)
>
>there is an increased error in both the displayed real and imaginary components with rotations further from the >centre and with those that result in points away from the real axis.
> there is a mathematical correction that can be applied, but that last time i looked at that was 35 years ago
> look up shifting the iconocentre
>
>hope that helps 
>Mark
 



On 8 July 2016 at 11:52, 'brian.flynn@...' brian.flynn@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

Hi Andy,

I get involved in this a bit. I have always read off the
impedance/admittance and re-normalised. I have never come across the
procedure you suggest. I do this fairly regularly to design quarter wave
matching sections when the the impedances are not real.

73s

Brian, GM8BJF.
--



Re: Smith Chart

Brian Flynn GM8BJF
 

Hi Andy,

I get involved in this a bit. I have always read off the impedance/admittance and re-normalised. I have never come across the procedure you suggest. I do this fairly regularly to design quarter wave matching sections when the the impedances are not real.

73s

Brian, GM8BJF.
--


Crawley microwave round table

Chris G0FDZ
 

Hi folks

Another reminder that the Crawley microwave round table takes place on Sunday September the 18th at the usual venue. Since Derek G3GRO's passing, the Crawley club have said that they are happy to continue hosting the event as long as there is a demand for it. Unfortunately at this time I still have no definite talks confirmed, and the future of this event lies entirely in the users hands. It would be great shame to have to abandon the event in the future due to lack of support, so please do offer to help out in this area not leave it to others. You do not have to be an 'expert' to give a talk. I feel very reluctant to ask yet again those who have helped me in the past by giving talks on a regular basis. Please contact me direct if you are able to help or require any information.

Thanks and regards

Chris G0FDZ


Re: Locking a 20-26GHz YIG oscillator

Andy G4JNT
 

continued...

There are usually two tuning coils on a YIG.   One main tuning coil has high inductance and wide tuning range.  Its high inductance limits tuning speed and loop bandwidth to a very low value if that were used inside the PLL. A few tens of Hz bandwidth and even that would require a high voltage and current coil driver stage.   Another small tuning coil allows fast modulation to be superimposed.

The usual way to use a YIG within a PLL is to pretune using the main coil via a manually adjusted pot type control or, more scientifically,  via  lookup table and D/A converter within the controller. Aim toi tune open-loop to withn a couple of MHz of the target.  Certainly well within the pulling range of the fast modulation coil.   The PLL works on the fast tuning coil which is typically a few 100uH inductance and can manage loop bandwidths in kHz region.

YIGs have inherently good far out phase noise, so you can get away with PLL loop bandwidths lower than you would for a traditional  VCO, as a start, try going for a couple of kHz, just to get outside audible effects listening to  a narrow tone.

If you can get hold of the May 2009  RadCom, I wrote about driving YIGs as part of PLLs in that issue.  See pages 41-42

Andy  G4JNT


On 8 July 2016 at 07:35, Andy Talbot <andy.g4jnt@...> wrote:
Try this, a new take on the old mixer-synth design :

Use one synth, perhaps an integer N design,  to make a locked source that simply  multiplies the reference to a frequency not too far from your wanted output.    Mix that with the YIG output to give an IF of say a few hundred MHz, even up to a couple of GHz.   Use this synth-mixer combination as a single entity, forming the VCO for a second synthesizer, driving the YIG control.

Either synth could be fract-N to give you your fine tuning; only one needs to be fixed frequency.

Andy  G4JNT



On 7 July 2016 at 23:29, Neil Smith G4DBN neil@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

I am playing with a 20-26.5GHz YIG oscillator. What is the received wisdom on the best way to use one of these as the VCO in a synth locked to a 10MHz standard?

I am building some LMX2582-based LO boards but I’d like to find a way to use the YIG for a source/LO on the mm bands.

Neil G4DBN




Re: Locking a 20-26GHz YIG oscillator

Andy G4JNT
 

Try this, a new take on the old mixer-synth design :

Use one synth, perhaps an integer N design,  to make a locked source that simply  multiplies the reference to a frequency not too far from your wanted output.    Mix that with the YIG output to give an IF of say a few hundred MHz, even up to a couple of GHz.   Use this synth-mixer combination as a single entity, forming the VCO for a second synthesizer, driving the YIG control.

Either synth could be fract-N to give you your fine tuning; only one needs to be fixed frequency.

Andy  G4JNT



On 7 July 2016 at 23:29, Neil Smith G4DBN neil@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

I am playing with a 20-26.5GHz YIG oscillator. What is the received wisdom on the best way to use one of these as the VCO in a synth locked to a 10MHz standard?

I am building some LMX2582-based LO boards but I’d like to find a way to use the YIG for a source/LO on the mm bands.

Neil G4DBN



Locking a 20-26GHz YIG oscillator

Neil Smith G4DBN
 

I am playing with a 20-26.5GHz YIG oscillator. What is the received wisdom on the best way to use one of these as the VCO in a synth locked to a 10MHz standard?

I am building some LMX2582-based LO boards but I’d like to find a way to use the YIG for a source/LO on the mm bands.

Neil G4DBN


Smith Chart

Andy G4JNT
 

Can anyone remember :

On a smith chart normalised to Zo, is it possible to move along a transmission line with a different characteristic impedance using a single (paper / pen / dividers compass) action?

And if so, what's the procedure?   I very vaguely recall someone doing it, but not too sure when / who / why / how

Or does the Smith chart have to be renormalised to the new Zo with the impedance recalculated and replotted?  

Andy  G4JNT


SG Labs 23cm Transverter

ian hope (2E0IJH)
 

Hi all
Before I start Re-inventing the wheel, anyone sucessfuly Mast head mounted a Sg Labs 23cm Transverter, getting all the bits together to mount transverter, power amp and pre amp in one box, and just bring a 144mhz into the shack.
I'd like to bring the Monitoring LEDS in the transverter down to Shack Level
 
Ian
2E0IJH
 
Reply via web post Reply to sender Reply to group Start a New Topic Messages in this topic (1)

Have you tried the highest rated email app?
With 4.5 stars in iTunes, the Yahoo Mail app is the highest rated email app on the market. What are you waiting for? Now you can access all your inboxes (Gmail, Outlook, AOL and more) in one place. Never delete an email again with 1000GB of free cloud storage.

 
.


APC 3.5 lead

Paul G8KFW
 

Hi all

I am looking for an APC 3.5  lead  and  mail to mail  connector at the right price  

Any surjection’s welcome

Paul B



Finningley - Rigs for Sale

dave powis <g4hup@...>
 

Good afternoon folks,

I've decided to rationalise the number of rigs that I have, so I've come to the conclusion that my FT847 and IC706Mk2 will be the ones going.  I will have both of them with me at Finningley on Saturday (please note that I can only be there on Sat this year).

Both rigs were purchased from new - the IC706 in about 1996/7 and the FT847 in 1999.

IC706 is complete with mic, powerlead and manual.  It has been modified to stabilise the drift but running the fan at low speed during Rx, and it also has the mod on it for 10MHz locking.  It does not come with a DFS30, but I can supply one, ready built if necessary.  It also has a PAT board fitted as an IF tap for running an SDR in parallel.   The 13 pin Accessory lead is present too, terminated in a DB15 way plug.

The FT847 is also with power lead, and mic.  It too has a PAT board fitted for an external SDR.  It has also had the Tx and Rx separated on both 144MHz and 432MHz, so that it can be integrated into a system with external PA's and masthead preamps, minimising the relay losses.   These connections are accessible on the rear panel.  It has NOT had the 4m mods done to it.

I'm open to sensible offers on either rig - have a look at what they go for on eBay.

I will of course, have the range of hupRF products with me on Saturday as well!

Best 73,
Dave G4HUP

twitter @hupRF


Re: External Reference for the Octagon LNB

Andy G4JNT
 

There are a lot of papers and descriptions around of waveguides, but few of them treat circular waveguide simply - probably because, other than the two trivial TE01 waves, all the truly circular ones involve Bessel functions and squiggly maths.

About half way though it specifically calls up the TE11 mode - the true first order circular waveguide mode and gives the equation for cutoff as:

  Fo (circ)  = 1.841.c / (2.pi.R)  

Agglomerating constants and using D[iamter]  = 2.R[adius] 
 Fo(circ) = 175.6 / D.   (using GHz and mm)  

So a diameter of 20mm has a TE11 mode cutoff of 8.78GHz, compared with a TE01 mode cutoff of 7.5GHz for the same diameter

( I thought I remembered it being lower than teh TE01 cutoff frequency, seems not... ?

Andy  G4JNT

On 6 July 2016 at 12:18, kenneth@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

Confusion here?

It is the waveguide that is circular, not the polarization.

CP is only superposition of two linear polarization waves at right angles in time and space so the cut off frequency of the waveguide is the same for CP or  linear.

Ken




---In ukmicrowaves@..., <andy.g4jnt@...> wrote :

Furthermore:
If two orthogonal and isolated TE01 modes could not be supported in circular guide, then dual mode cavity filters could not be possible.  Yet they are, and work extremely well with tuning screws at right angles, and coupling screws at 45 degrees.   Witness the one designed by GW4DGU for his 10GHz transverter system.

I suppose they could be forced to work if two orthogonal (LHCP and RHCP) TE11 modes were launched, but I hate to think how they could be tuned or the coupling adjusted.

Andy G4JNT



Re: External Reference for the Octagon LNB

Andy G4JNT
 

There IS a circular propagation more in circular waveguide, and it does indeed have a lower cutoff that the two orthogonal TE01 linear ones.   But it has to be specifically excited or converted from linear using various odd shaped bits of metal inside the WG.

In fact, it is circular waveguide propagation that sets the upper frequency limit for microwave connectors; 18GHz for SMA and 26.5GHz for 3.5mm (like SMA but without the dielectric.    It is the presence of the PTFE that lowers the maximum working frequency of SMA connectors)

Andy  G4JNT


On 6 July 2016 at 12:18, kenneth@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

Confusion here?

It is the waveguide that is circular, not the polarization.

CP is only superposition of two linear polarization waves at right angles in time and space so the cut off frequency of the waveguide is the same for CP or  linear.

Ken




---In ukmicrowaves@..., wrote :

Furthermore:
If two orthogonal and isolated TE01 modes could not be supported in circular guide, then dual mode cavity filters could not be possible.  Yet they are, and work extremely well with tuning screws at right angles, and coupling screws at 45 degrees.   Witness the one designed by GW4DGU for his 10GHz transverter system.

I suppose they could be forced to work if two orthogonal (LHCP and RHCP) TE11 modes were launched, but I hate to think how they could be tuned or the coupling adjusted.

Andy G4JNT



Re: External Reference for the Octagon LNB

F6DRO
 

yes  the two probes are not used simultaneously but chosen depending on which polarisation (V or H) the sattelite is transmitting

73
Dom

Le 06/07/2016 13:18, kenneth@... [ukmicrowaves] a écrit :
 

Confusion here?

It is the waveguide that is circular, not the polarization.

CP is only superposition of two linear polarization waves at right angles in time and space so the cut off frequency of the waveguide is the same for CP or  linear.

Ken




---In ukmicrowaves@..., wrote :

Furthermore:
If two orthogonal and isolated TE01 modes could not be supported in circular guide, then dual mode cavity filters could not be possible.  Yet they are, and work extremely well with tuning screws at right angles, and coupling screws at 45 degrees.   Witness the one designed by GW4DGU for his 10GHz transverter system.

I suppose they could be forced to work if two orthogonal (LHCP and RHCP) TE11 modes were launched, but I hate to think how they could be tuned or the co upling adjusted.

Andy G4JNT



Re: External Reference for the Octagon LNB

 

Confusion here?

It is the waveguide that is circular, not the polarization.

CP is only superposition of two linear polarization waves at right angles in time and space so the cut off frequency of the waveguide is the same for CP or  linear.

Ken




---In ukmicrowaves@..., <andy.g4jnt@...> wrote :

Furthermore:
If two orthogonal and isolated TE01 modes could not be supported in circular guide, then dual mode cavity filters could not be possible.  Yet they are, and work extremely well with tuning screws at right angles, and coupling screws at 45 degrees.   Witness the one designed by GW4DGU for his 10GHz transverter system.

I suppose they could be forced to work if two orthogonal (LHCP and RHCP) TE11 modes were launched, but I hate to think how they could be tuned or the coupling adjusted.

Andy G4JNT


Re: External Reference for the Octagon LNB

Andy G4JNT
 

Furthermore:
If two orthogonal and isolated TE01 modes could not be supported in circular guide, then dual mode cavity filters could not be possible.  Yet they are, and work extremely well with tuning screws at right angles, and coupling screws at 45 degrees.   Witness the one designed by GW4DGU for his 10GHz transverter system.

I suppose they could be forced to work if two orthogonal (LHCP and RHCP) TE11 modes were launched, but I hate to think how they could be tuned or the coupling adjusted.

Andy G4JNT

On 6 July 2016 at 11:58, Andy Talbot <andy.g4jnt@...> wrote:
Dom

I cannot accept that for linearly polarised signals, into two probes 90 degrees apart, the propagation in the waveguide of teh LNB  throat is anything other than TE01; with V and H  orthogonal in the two planes.

Circular waveguide may well support several circular modes with different cutoff frequencies, but that is not is what is happening here.   Circular waveguide is used in LNBs simply because it is easier to manufacture than square waveguide in a mass-produced low cost assembly.   And cutoff frequency of TE01 mode is at a half wavelength across the reference axis of the guide, whatever its cross section.

If polarisation of the satellite signals were RHCP / LHCP instead of linear, then I could happily accept circular propagation modes in the Waveguide, except that there would then have to be properly designed probes to just intercept to two polarisations.

Just because a WG will accept one propagation type, doesn't mean it is actually doing so - it all depends on the launch method.

Andy  G4JNT

On 6 July 2016 at 11:43, 'dominique.dehays' Dominique.DEHAYS@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

For linear TE01 propagation, the cutoff will therefore be 299.8/(2. *
18mm) = 8.3GHz

no for circular waveguide , the propagation mode we use is TE11, the
cutoff is 1.706*D= 1.706*18= 30.7mm and then 299.8/0.0307=9.7Ghz

if fact the waveguide is a little bit bigger than the normalized C120 n
, which is 0.688*25.4=17.47mm and found in all catalogs as showng a
10.0Ghz cutoff
for exemple:
http://www.alpharep.de/downloads/ATWALL%20Hohlleiter%20www.Alpharep.de.pdf
page 9

73
Dom