[Moon-Net] Prime-focus vs. Offset-dish

dl7yc at snafu.de dl7yc at snafu.de
Tue Nov 22 20:57:58 CET 2016


Just another comment regarding the discussion offset dish vs. prime focus 
dish:


Both "sides" claim better results, but reality shows the truth, hi.

If you calculate the "shadow" of the feed-system (in my perspective 
including the WG-switch, preamp, transverter AND TWT with power supply for 
10 GHz OR 24GHz) its 1-2% of the whole surface only !! (based on my 2.4 m 
precision prime focus dish)

The results for such a setup showing moon- and sunnoise results very close 
as predicted in VK3UM`s programs. Compared with other well equiped stations 
nothing is worse, therefore the effiency should be as high as caculated. 
And...... the feed design and focal point adjustment / calculation is VERY 
easy.

Looking to my friends having offset dishes the same size, its all a bit 
motre complicated. I know all the recommendations from Hannes well and they 
where all very helpful. Even the "trick" with the waterhose, I think Dick, 
PA2DW told this,  is very nice and helps a lot....

But the offset feed design and adjustment to its phase center is much, much 
more complicated than it looks. I personally know some very wellknown 
Microwave EME friends, struggeling many times to "optimize" their dish 
performance.

If one loose 5% effiency due to a "bad" phase center, not perfect adapted 
feed in respect to the dish`s f/D (i.e. wrong feed system selection) and 
therefore spillover results in AZ or EL orientation due to "breaking" 
the -10dB rule in one direction at least, this all together is MORE worse, 
than a 2% "feedbox"-shadow of a prime focus RX/TX setup with no extra line 
losses !! Its true ... , especially for the more rectangular beam of the 
Super-VE4MA-Feed (Kumar feed / see W1GHZ handbook).

Therefore, it could be allready an open question!!  If one have a PERFECT 
offeset dish setup, this might be 2% better compared to the same prime focus 
dish setup ?? But if NOT, hmm....

My reccommendation:

Try to put the equipment you need for the given band straight inline with 
the prime focus feedhorn and beat your neighbour with more moonnoise 
performance, hi. Forget struggeling and time consuming processes to optimize 
overall performance of microwave EME dishes.
But, .... you really will loose the possibility to SIT on the ground for 
adjustment of your offset feed, because NO adjustment is neccessary 
anymore!! And the focalpoint of an 2.4m prime focus dish is 1.2 m far from 
the surface only (plus some extra cm) Feed change is not a dangerous thing !

I NEVER re-adjusted  the feedsystems in its focal point after a perfect 
calculation and mechanical measurement by a laser distance meter from a 
hardware shop.

BUT at the end: its much more important to be QRV than to grab the last 
tenth of a dB !!!!!!!!!!!!!!!

Vy 73 Manfred, DL7YC


2.4m precision prime focus dish (Areal OY Finnland), f/D 0.4 used for 10 GHz 
and 24 GHz
VE4MA "Super feeds" for both QRG`s
0.6dB NF (10GHz) 1.3dB NF (24 GHz)
DB6NT transverter with 10 MHz time base connection (GPS)
modified RW1127 TWTA`s with RWN 320 PSU`s
Output: > 90 watts (10GHz) 40 watts (24 GHz)
Autotracking NITEC rotator


-----Ursprüngliche Nachricht----- 
From: moon-net-request at mailman.pe1itr.com
Sent: Tuesday, November 22, 2016 8:37 AM
To: moon-net at mailman.pe1itr.com
Subject: Moon-net Digest, Vol 289, Issue 16

Send Moon-net mailing list submissions to
moon-net at mailman.pe1itr.com

To subscribe or unsubscribe via the World Wide Web, visit
http://mailman.pe1itr.com/mailman/listinfo/moon-net
or, via email, send a message with subject or body 'help' to
moon-net-request at mailman.pe1itr.com

You can reach the person managing the list at
moon-net-owner at mailman.pe1itr.com

When replying, please edit your Subject line so it is more specific
than "Re: Contents of Moon-net digest..."


Today's Topics:

   1. Icom 9100 and RigBlaster Advantage (Richard Lawn)
   2. Re: FLEX 1500 & MAP65 (Edward R Cole)
   3. Re: 2.4M PRIME FOCUS / 2.4M OFFSET/ ALSO SEPTUM FOR 1296
      (Edward R Cole)
   4. Re: 3cx1500 or 3cpx1500 (Mark)
   5. Re: 2.4M PRIME FOCUS / 2.4M OFFSET/ ALSO SEPTUM FOR 1296
      (Hansen Peter)


----------------------------------------------------------------------

Message: 1
Date: Mon, 21 Nov 2016 18:24:12 -0500
From: Richard Lawn <rjlawn at gmail.com>
Subject: [Moon-Net] Icom 9100 and RigBlaster Advantage
To: moon-net at mailman.pe1itr.com
Message-ID:
<CADQmrTGeLWopjcimwxCyaPX7fvKXcT5BchQc=_LnuQ-nZCjf_w at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

I took someone's advice and added the RigBlaster Advantage to my new EME
station. Now I'm getting sufficient audio in to WSJT and beginning to
decode some signals. Next step is activating PTT to the DEMI sequencer
which works great and PTT on the radio seems to work but I'm not getting
any audio in to the radio. I've fiddled and fiddled with the Icom menu but
to no avail. Someone out there must be using the 9100 with an external
sound card and I'd love to hear from you.

73
Rick, W2JAZ
-------------- next part --------------
An HTML attachment was scrubbed...
URL: 
http://mailman.pe1itr.com/pipermail/moon-net/attachments/20161121/12998028/attachment-0001.html

------------------------------

Message: 2
Date: Mon, 21 Nov 2016 14:28:05 -0900
From: Edward R Cole <kl7uw at acsalaska.net>
Subject: Re: [Moon-Net] FLEX 1500 & MAP65
To: Cowles Andrus III K4EME <candrus at mgwnet.com>, Moon-net
<moon-net at mailman.pe1itr.com>
Message-ID: <201611212327.uALNRoje010308 at mail42c28.carrierzone.com>
Content-Type: text/plain; charset="us-ascii"

Cowles,

I didn't reply on the Flex-1500 but have heard that quite a few who
bought them for eme or mw IF use with transverters had sold the Flex
citing freq instability and interfacing issues.

I waited several years, using a FT-847 on 2m and on 1296 with144/1296
transverter.  But having heard such glowing  comments on the K3 for
CW use, I decided using transverters with top-end HF radio made for a
superior eme and VHF-mw operation.  I bought my K3 in 2010 and
commissioned DEMI to build a custom dual-Rx transverter to use with
MAP65 for adaptive-pol receiving (IQ+ was not available at that time).

Since have acquired the 220, 432, 1296 transverters using 28-MHz as
std IF.  I am not upgrading to the K3S as most of the upgraded boards
are available to install in my K3 (I bought the new synth boards
which I have not yet installed).  I decided to buy the K3/10 which
does not have the 100w HF amp inside the radio.  I also have a KX3 so
bought the separate KXPA-100 for use on HF/6m by either radio.  Cost
is about the same.

The K3S is expensive but ranks at the top of the list compared with
other HF radios and very popular with dxpeditions due to
size/weight.  I think their transverter I/F is superb in comparison
with other makers.  No computer I/F is required -
plug-n-play.  Transverter output is 0.1-1.5mw so take that into
consideration for obtaining compatible transverters.  Rx and Tx
separate connectors std.  And great Tx-inhibit function makes
sequencing fool-proof.

Guess you would say I like my K3.

But saying that the KX3 is pretty nice and is usable with
transverters with a little more work in doing the I/F.

73, Ed - KL7UW

At 09:35 AM 11/21/2016, Cowles Andrus III K4EME wrote:

>I want to thank VE4MA, W2HRO, KC4SW and everyone else who responded
>to my email about using the FLEX 1500 with MAP 65.
>
>It appears at this time no one has been able to get theses two to
>play together, so I don't plan to buy the FLEX 1500.
>
>Some have recommended the Elecraft K3S!
>
>The K3S would cost considerable more than the FLEX 1500, so I may
>put the K3S on my wish list!
>
>Thank you & 73!
>
>Cowles K4EME
>Home page: <http://cowlesradio.webs.com/>http://cowlesradio.webs.com/
>_______________________________________________
>Moon-Net posting and subscription instructions are at
>http://www.nlsa.com/nets/moon-net-help.html

73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag Business e-mail:
     dubususa at gmail.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: 
http://mailman.pe1itr.com/pipermail/moon-net/attachments/20161121/d5b0fc96/attachment-0001.html

------------------------------

Message: 3
Date: Mon, 21 Nov 2016 14:54:38 -0900
From: Edward R Cole <kl7uw at acsalaska.net>
Subject: Re: [Moon-Net] 2.4M PRIME FOCUS / 2.4M OFFSET/ ALSO SEPTUM
FOR 1296
To: serge <ve1kg at eastlink.ca>, moon-net at mailman.pe1itr.com
Message-ID: <201611212356.uALNuGoa023083 at mail40c28.carrierzone.com>
Content-Type: text/plain; charset="us-ascii"

Serge,

Just my opinion but if you can acquire an offset feed dish I suggest
its slightly better:
1.  Feed does not block part of the dish surface (no apparent shadow)
2.  It requires a narrower beamwidth feed that may improve rejection
of ground noise pickup (lower sidelobes; better G/T)
3.  You can mount all the electronics at the feed eliminating
feedline losses (max bang for the buck)
4.  Often these dish surface are rated to 10-12 GHz so multi-band use
is greater.

The feed support would need to be robust to handle the higher weight
at the feed.
Dish may be fiberglass vs mesh so heavier weight.
Cost may be higher

Az-El requirements are the same.

Offset dish needs a feed designed for a F/d of 0.6-0.7 (W2IMU would
work).  Ordinary septum would not be good.
I believe VE4MA is using one on 24/47 GHz so ask him about feedhorns.

I have a idle 1.8m offset feed dish I am considering for 10-GHz
use.  It used to be our satellite-TV dish until recently switching to
Direct-TV (which included free dish and HD receiver).  Recently
occurred to me that 6-foot (1.8m) makes it a candidate for portable
use with our RV trailer.
http://www.kl7uw.com/1.8m_dish.jpg

73, Ed - KL7UW

At 12:00 PM 11/21/2016, serge wrote:
>Which is best a 2.4M prime focus dish or a 2.4M offset dish? & WHY?
>What kind of septum would you use on both dishes for 1296???
>Thank you
>Serge, VE1KG
>_______________________________________________
>Moon-Net posting and subscription instructions are at
>http://www.nlsa.com/nets/moon-net-help.html

73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag Business e-mail:
     dubususa at gmail.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: 
http://mailman.pe1itr.com/pipermail/moon-net/attachments/20161121/22463f92/attachment-0001.html

------------------------------

Message: 4
Date: Tue, 22 Nov 2016 00:23:04 +0000
From: Mark <EA8FF at yahoo.com>
Subject: Re: [Moon-Net] 3cx1500 or 3cpx1500
To: moon-net at mailman.pe1itr.com
Message-ID: <3e5c9c39-211b-84e7-d078-7d83d4999470 at yahoo.com>
Content-Type: text/plain; charset=utf-8; format=flowed

Hi,

3cx1500 and 3cpx1500 are the same tubes, they were probably selected
after production on flashover voltage and stamped differently. the
3cpx1500 were more expensive than the 3cx1500. Nowadays new design uses
LDMOS and most people think the 3cpx1500 is only for pulse, thats why
there less expensive. Same thing with 3cx800 and 3cpx800.

73, Mark EA8FF



------------------------------

Message: 5
Date: Tue, 22 Nov 2016 07:36:40 +0000
From: Hansen Peter <peter.hansen at dk.saabgroup.com>
Subject: Re: [Moon-Net] 2.4M PRIME FOCUS / 2.4M OFFSET/ ALSO SEPTUM
FOR 1296
To: Edward R Cole <kl7uw at acsalaska.net>, serge <ve1kg at eastlink.ca>,
"moon-net at mailman.pe1itr.com" <moon-net at mailman.pe1itr.com>
Message-ID:
<8d659953b4264132b3a5212f53301d4f at corpappl841.corp.saab.se>
Content-Type: text/plain; charset="iso-8859-1"

Hi All I am an extensive user of a Offset dishes.
I started out with a 1.8meter offset dish (6foot) with 35W in the feed. I 
worked easily 35initials on CW and it would have been going on. But 1? year 
ago I changed to a 2.4meter Offset dish and this really opened the world. I 
use the dish on 3 and 6cm currently but will do 24Ghz also. My dish is 
channel master/Andrew dish. The mesh is small enough for use on 24Ghz.
I can confirm most of the things KL7UW states. The dish is easy to feed 
linear on 3cm as there are waveguide feeds used originally that works great. 
On 6cm where I am circular I designed my own feed type as I find W2IMU feed 
little off peak being used for my dish. I had 0.2dB too little Moonnoise on 
6cm. I know I could have tried with larger W2IMU feeds but I went another 
way.
Efficiency is much better on the Offset dish due to low blockage and higher 
efficiency in the Feed to illuminate a higher F/d.

What can be worked on a 2.4meter ??
3CM
I worked a 90cm that was using 12W in JT4F EME
I worked a 90cm that was using 25W in CW

6CM
I worked a 1meter and 10W in CW

Many qso is possible just try it out.

All forgot one VERY NICE feature on Offset dish. When I work on my Feeds, 
Change system etc I simply sit on the ground and have the feed just in front 
of me. Or I can tilt the dish and work on it standing up.


73 Peter OZ1LPR

From: moon-net-bounces at mailman.pe1itr.com 
[mailto:moon-net-bounces at mailman.pe1itr.com] On Behalf Of Edward R Cole
Sent: 22. november 2016 00:55
To: serge; moon-net at mailman.pe1itr.com
Subject: Re: [Moon-Net] 2.4M PRIME FOCUS / 2.4M OFFSET/ ALSO SEPTUM FOR 1296

Serge,

Just my opinion but if you can acquire an offset feed dish I suggest its 
slightly better:
1.  Feed does not block part of the dish surface (no apparent shadow)
2.  It requires a narrower beamwidth feed that may improve rejection of 
ground noise pickup (lower sidelobes; better G/T)
3.  You can mount all the electronics at the feed eliminating feedline 
losses (max bang for the buck)
4.  Often these dish surface are rated to 10-12 GHz so multi-band use is 
greater.

The feed support would need to be robust to handle the higher weight at the 
feed.
Dish may be fiberglass vs mesh so heavier weight.
Cost may be higher

Az-El requirements are the same.

Offset dish needs a feed designed for a F/d of 0.6-0.7 (W2IMU would work). 
Ordinary septum would not be good.
I believe VE4MA is using one on 24/47 GHz so ask him about feedhorns.

I have a idle 1.8m offset feed dish I am considering for 10-GHz use.  It 
used to be our satellite-TV dish until recently switching to Direct-TV 
(which included free dish and HD receiver).  Recently occurred to me that 
6-foot (1.8m) makes it a candidate for portable use with our RV trailer.
http://www.kl7uw.com/1.8m_dish.jpg

73, Ed - KL7UW

At 12:00 PM 11/21/2016, serge wrote:

Which is best a 2.4M prime focus dish or a 2.4M offset dish? & WHY? What 
kind of septum would you use on both dishes for 1296???
Thank you
Serge, VE1KG
_______________________________________________
Moon-Net posting and subscription instructions are at 
http://www.nlsa.com/nets/moon-net-help.html

73, Ed - KL7UW
http://www.kl7uw.com
<http://www.kl7uw.com/>    "Kits made by KL7UW"
Dubus Mag Business e-mail:
    dubususa at gmail.com<mailto:dubususa at gmail.com>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: 
http://mailman.pe1itr.com/pipermail/moon-net/attachments/20161122/e8850b4a/attachment.html

------------------------------

_______________________________________________
Moon-Net posting and subscription instructions are at 
http://www.nlsa.com/nets/moon-net-help.html

End of Moon-net Digest, Vol 289, Issue 16
***************************************** 



More information about the Moon-net mailing list