[CQ-Contest] CQ-Contest Digest, Vol 180, Issue 31

[Holger Hannemann]

Hi
I wonder what the question is tasking here. My feeling is, that the
challenge of using SS amps is bigger in a M/2 environment than it is for a
M/M station. 

We have two main problems here. ONE is harmonics and interference audible on
the other radio(s) and TWO is the triggering of protections on the SS amp
(typically SWR) by another station.

Problem one is manageable by filtering. Plus you can do a lot here at low
power level.

Problem two is what we had most trouble with here. Part of that may be that
we use multiband antennas via triplexer (& filters of course). But there are
always combinations where one amp would kick out the other one. 

Both problems are more tricky to solve in a M/2 environment. Due to the more
complex station automation you have to deal with about twenty more
combinations, than in a M/M set-up, especially the "competitive" ones where
you typically find monobander antennas.

We wish you all a Happy New Year!

73 Holger, ZL3IO/ZM4T

Date: Wed, 27 Dec 2017 03:07:45 +0000
From: Ria Jairam <rjairam at gmail.com>
To: Tom Georgens <tomgeorgens15 at gmail.com>
Cc: Jeffrey Maass <jmaass at k8nd.com>, cq-contest at contesting.com
Subject: Re: [CQ-Contest] Solid State Amps in Multi-Multi Stations?
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I?ve used three models of SS amps here.

The dirtiest of them all is the Tokyo HyPower 2.5. Next up is the SPE 1.3K,
which uses a single LDMOS. Cleanest is the Power Genius XL (2 LDMOS) which
is under beta test here.

I think the concern about SWR and ruggedness is based on outdated info. The
latest LDMOS devices by design can tolerate high SWR, up to 66:1. With
de-rating the devices can handle around 3:1 SWR continuous at reduced power.
The limitation is in the output filter which are limited by saturation of
toroidal inductors. The newest amps are also microprocessor controlled and
protected to the hilt. I am more concerned I will blow up a tube amp than I
will a modern solid state.

IMD is less of a concern with two devices as there is plenty of headroom and
again - microprocessor control of biasing and other parameters such as is
done with MEffA in the PGXL produces a very clean signal, even without
adaptive predistortion.

I do agree that in a K3LR type of environment there is little benefit to
change out all of those existing, working tube amps for SS ones. That is,
other than as a trial run, or experiment to see how well they can do.
However if designing from scratch or expanding, amps can be shared between
run and mult stations in M/S or M/2. Even in M/M it provides some
redundancy.

Ria
N2RJ

On Mon, Dec 25, 2017 at 9:07 PM Tom Georgens <tomgeorgens15 at gmail.com>
wrote:

> I have been  using home brew SS amps at my 8P5A station exclusively 
> for the last two years.  The flexibility and increased operator 
> efficiency  are a big advantage.  As such, I am a true believer for this
use case.
>
> However, I am not sure that they are a better solution than single 
> band amps for the pure Multi Multi.  With the operating efficiency of 
> instant band change largely moot, there is less to offset the down 
> sides.  With potentially 6 full power signals at once, and in band 
> receivers, signal cleanliness is a key factor.  The LDMOS parts simply 
> do not have the IMD specs of tubes.  K3LR has supreme engineering 
> skill and may be able to design around some of these limitations on a 
> per band basis.  Plus, the predistortion techniques are very exciting, 
> but not limited to SS amps.
> Overall, if it can be done, K3LR will find a way, but I would not be 
> sure that current off the shelf solutions would be the cleanest for M-M.
>
> Overall, I think creative engineering can help with IMD, but it is not 
> standard today. Also, the parts have come a long way, but the LDMOS
> transistors are not as rugged as tubes in most fault situations.   If kept
> cool, reliability will be fine with well matched antennas, but will 
> not be as tolerant of antenna system faults.  Without the need of the 
> flexibility of instant band switching,  I am not certain that SS amps 
> are a better option than single band tube amps for the dedicated M-M
station.
> Situations other than M-M can be good matches for SS Amps, but the 
> need for a well controlled environment and well matched antennas is still
there.
>
>  Just to be clear, I am not claiming to have solved any of these 
> problems, just that I feel the advantages outweigh the risks in my 
> case.  YMMV
>
>
> 73, Tom W2SC 8P5A
>
>
>
> -----Original Message-----
> From: CQ-Contest [mailto:cq-contest-bounces at contesting.com] On Behalf 
> Of Jeffrey Maass
> Sent: Friday, December 22, 2017 10:13 AM
> To: cq-contest at contesting.com
> Subject: [CQ-Contest] Solid State Amps in Multi-Multi Stations?
>
> Is anyone using solid-state amps at a competitive multi-multi station?
>
>
>
> Which? Any problems?
>
>
>
> 73,  Jeff  K8ND