You have a good memory, Steve. There have been several articles in
RADCOM (RSGB - Radio Communications) highlighting the need for a square
wave LO input to a double balanced mixer. But the mixers used have been
a tad more exotic than anything in my OMNI-V. The latest is some kind
of Fairchild high speed bus driver chip that costs almost zilch, but
gives astonishing IMD performance when driven by a square wave LO.
Fitting that into my OMNI-V would be a real challenge !! I believe
G3SBI is one of the experts, altho there are also several US hams
involved in pushing this RX frontier to new limits.
I hope someone at TT is following these developments, which promise
seriously better receiver performance, without using exotic hardware.
I should mention that to make use of what can be achieved, the
following IF strip and AGC system need to be good, and perhaps those
ten pole INRAD filters would come in handy. But all the bits are readily
available, unlike the Crystalonics power FETS Bill mentioned.
No, I have made no measurements. My 17 dBm LO guesstimate was based on
the OMNI-V manual, plus published specs for mixers and on a few magazine
articles on the subject. And my OMNI-V still works very well, altho it
would be fun to compare it in a 40m European pile-up against a
heavyweight commercial RX. During the recent 3C0R operation, I had to
switch in 20 dB of attenuation and I still had overload problems on 40m.
How the guys on Annobon handled the wall of noise from 7050 to 7100 I do
not know.
If I had $10k plus to spare, I might be tempted to buy a receiver to
make the comparison. A local firm sells late model, ex-military Racal
receivers, at that kind of price ...... but who fixes them when they go
wrong ?? At least if I open up my OMNI-V I can recognise the parts
inside it. And someone at Sevierville can tell me how to fix it. That
has to be good.
73 John G3JAG
On 27-Sep-99 Steve Baron wrote:
> Well - did u see the e-mail that I got from Synergy ? They gave the
> new
> model number which is not on their site! The CMP mixers are 13 and
> 17
> dbm...the mini-circuits 17 dbm mixers are a lot more expensive than
> the 13
> dbmone.
>
> So, why do you think it is 17 ? Did you measure the level gg into it
> ?
>
> BTW, noe that the LO goes thru a filter on its way to the mixer.
> Seems to
> me that some one in G land wrote at least one article (Quarterly
> COmmunications ?) that said that a square wave was best for feeding
> the
> mixer ! Really want it to behave like a chopper.
>
>
> -----Original Message-----
> From: John - G3JAG <patents@dx0man.prestel.co.uk>
> To: Steve Baron <SteveBaron@StarLinX.com>
To: <tentec@contesting.com>
> Date: September 27, 1999 11:01 PM
> Subject: Re: [TenTec] OMNI VI mixer
>
>
>>I guess from the circuitry in the Omni-V manual, plus the spec sheet
>>for the Synergy CPM 212 that its below 17dBM, but not too far below,
>>or
>>the radio would not handle strong signals as well as it does ..
>>John
>>
>>On 26-Sep-99 Steve Baron wrote:
>>> ANy idea what the actual LO level is in the OMNI V and VI ?
>>>
>>> -----Original Message-----
>>> From: John - G3JAG <patents@dx0man.prestel.co.uk>
>>> To: Alfred Lorona <alforo@mail.megsinet.net>
>>> Cc: Ten-Tec EMAIL Reflector <TenTec@contesting.com>
To: <tentec@contesting.com>
>>> Date: September 26, 1999 6:29 PM
>>> Subject: RE: [TenTec] OMNI VI mixer
>>>
>>>
>>>>
>>>>I just downloaded a couple of the Synergy spec sheets, out of
>>>>curiosity. They give enough info for me to stick my neck out and
>>>>pontificate, although I do not have an Omni-VI. My Omni-V appears
>>>>to
>>>>use exactly the same mixer -- unless someone out there knows
>>>>better.
>>>>
>>>>There should be no problem - the Synergy CMP 212 is probably a safe
>>>>bet.
>>>>It appears to have all the right characteristics. I cannot believe
>>>>that
>>>>they made a version of it with a special pin-out, just for TT -
>>>>these
>>>>packaged mixers all have the same pin-out almost regardless of
>>>>manufacturer. Ham Radio even published a generic PC board layout
>>>>based on this common pin-out.
>>>>
>>>>Unless the TT mixer really is unique, the Mini Circuits RAY-3 is a
>>>>very
>>>>safe bet. I found one for a few bucks at Dayton (its a $50+ piece
>>>>here
>>>>in UK) and I'd have no hesitation in dropping it into my Omni-V if
>>>>I
>>>>thought the mixer had gone out. The SRA1-H may be another option.
>>>>The
>>>>key figures to look for are the local oscillator level (17 dBM or
>>>>higher) and the frequency range, which needs to go low enough,
>>>>like
>>>>down to 0.025MHz (most go high enough). The regular SBL-1 type of
>>>>device simply does not have the local oscillator signal handling
>>>>capability.
>>>>
>>>>But given that manufacturers often have a minimum order size/cost,
>>>>why
>>>>not get a new from TT ??
>>>>
>>>>If that is not your choice, I guess its worth looking at
>>>>www.surplussales.com; they did have the RAY-3 listed. There may be
>>>>other
>>>>sources.
>>>>
>>>>73 John G3JAG
>>>>On 25-Sep-99 Alfred Lorona wrote:
>>>>> Does anybody have specs on the OMNI VI PLUS first mixer? It is a
>>>>> synergy CMP-A12. Synergy will not release this information nor
>>>>> will
>>>>> they recommend a replacement from their standard catalog.
>>>>>
>>>>> 73, AL, w6wqc
>>>>
>>>>----------------------------------
>>>>E-Mail: John - G3JAG <patents@dx0man.prestel.co.uk>
To: <tentec@contesting.com>
>>>>Date: 26-Sep-99
>>>>Time: 12:13:18
>>>>
>>>>This message was sent by XFMail
>>>>----------------------------------
>>>>
>>>>--
>>>>FAQ on WWW: http://www.contesting.com/tentecfaq.htm
>>>>Submissions: tentec@contesting.com
>>>>Administrative requests: tentec-REQUEST@contesting.com
>>>>Problems: owner-tentec@contesting.com
>>>>Search: http://www.contesting.com/km9p/search.htm
>>>>
>>
>>----------------------------------
>>E-Mail: John - G3JAG <patents@dx0man.prestel.co.uk>
To: <tentec@contesting.com>
>>Date: 27-Sep-99
>>Time: 00:08:20
>>
>>This message was sent by XFMail
>>----------------------------------
----------------------------------
E-Mail: John - G3JAG <patents@dx0man.prestel.co.uk>
To: <tentec@contesting.com>
Date: 28-Sep-99
Time: 00:21:38
This message was sent by XFMail
----------------------------------
--
FAQ on WWW: http://www.contesting.com/tentecfaq.htm
Submissions: tentec@contesting.com
Administrative requests: tentec-REQUEST@contesting.com
Problems: owner-tentec@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|