RAM Official Position RE: Intermod
The RAM 2 meter repeater was built and tested in September and
October 2007, and put on the air October 10. It was done on a
standard, 2-meter repeater channel, duly coordinated with the
FCC, and thoroughly tested via software and actual on-the-air
tests prior to inaugurating it. No issues were apparent then.
However, once the repeater was in use, it turned out that SPARC's 2-meter downtown receiver on 146.34 would wipe itself out when SPARC people were transmitting. With no one from SPARC transmitting, no signal from RAM got into their system.
After some more experiments and analysis, it was discovered that the SPARC system is apparently deficient: it does not keep its own transmitter out of its own receiver. The sum of all the signals add up to an intermod for them. As a matter of fact, even if RAM changed to another repeater channel, the SPARC configuration is such that it would wipe itself out.
The Technical Discussion on Intermod explains this fully.
At the time this ocurred, SPARC's president, Colby Carter was out of town on vacation. Testing was done with Nate Perkins KL3NP on SPARC's side. The situation was verified by Nate, and it appeared that the matter was going to be resolved on a technical basis. However, upon Mr. Carter's return, SPARC's official position was that they have long been on the .94/.34 pair and that they are going to do nothing. That it is up to RAM to change.
This mischaracterizes the situation. RAM has suggested that a "quick fix" for SPARC would be to change splits, but indeed SPARC's repeater can easily continue to operate on .34/.94 provided they take steps to fix their problem. Indeed, all ham repeaters in the lower 48 face this issue, and they take care of it. SPARC appears to want to fix it by improperly blaming RAM.
The following email was received Tuesday, November 20, 2007 by Ramon Gandia, but intended for RAM, Inc:
Note, email addresses have been munged to prevent spambots from picking them up. You may contact RAM privately if you need this information.
Date: Tue, 20 Nov 2007 22:37:15 -0900
From: Perkins Family {perkins@xxxxxx.xxx}
Subject: Intermod resolution proposal
To: Ramon Gandia {ramon@xxxxxx.xxx}
Mr Gandia,
On behalf of SPARC, I have been authorized to offer a resolution to the
intermod problems associated between RAM and SPARC.
SPARC's belief is that we would very much like to continue with the VHF
146.94/.34 split on it's downtown repeater, which SPARC has been using
for many years. Since SPARC's user group is large and the members are
content with the frequency with which they have become accustomed to,
SPARC feels it would bring hardship and confusion if we were to
implement a different frequency pair.
As a solution, SPARC offers to RAM to monetarily compensate for the
re-crystalling of RAM's downtown repeater receiver and transmitter, as
well as the retuning of RAM's duplexer to a frequency pair of a
different configuration than what RAM is currently using.
Of course SPARC cannot recommend a frequency without prior testing,
however we feel that with the proper use of available intermodulation
software, a pair can be easily found, with a split other than .6, so as
not to create a similar incompatibility that the two clubs currently have.
Please let me know if the RAM organization finds this offer of
resolution in the best interest of both clubs.
Thank You,
Nate Perkins, KL3NP
Public Relations Officer
SPARC
The Alaska Frequency Coordinator, Jerry Curry, KL7EDK, has been kept appraised of the situation, including the information on the Intermod Page and he was contacted and asked for advice: should RAM change its split?
This was his answer:
Date: Fri, 23 Nov 2007 19:05:24 -0900
From: Jerry Curry {jecurry@xxxxxx.xxx}
To: Ramon Gandia {ramon@xxxxxxx.xxx}
Subject: Re: Some Advice
Ramon,
I can certainly understand some of the logic behind both options you
discussed however I think BOTH organizations need to keep some important
points in mind.
1) Poor design and planning by any one agency should not be a burden on
OTHER users. By other users I don't just mean existing organizations in
place. You could move frequencies as they suggest and in 5 months have
the new Anvil Mtn. Radio Group put in a repeater and be faced with the
same problems as what RAM is currently seeing. My question is would
they be willing to pay to move THAT group and would that group even be
willing to move. It could even be a single ham who might be in conflict
just using his radio on a simplex frequency. Frequency coordinators
don't do intermod studies...we are only tasked with trying NOT to assign
the same frequency to 2 groups. We try to put some spacing in so as to
make it easy for adjacent channel spacing to work better but we expect
some technical expertise in the design and construction of the repeater
being turned up.
2) There are clubs which work in environments much more congested than
what you have up there and have far less interference problems. Poor
engineering practices could very well make it so only 1 repeater with a
600Khz split can be used in that entire area. That is certainly not the
intent of the ARRL or the FCC.
3) The use of wide band front end radios, lack of duplexers, lack of
pre-selector filters if needed, and other poor design and engineering
practices do not constitute legitimacy for the existence of a 2 meter
repeater or cross band operation.
My recommendations would be as follows:
1) Review each repeater- both organizations. Those without
duplexers...add them. Those with radios having DC to Light front
ends...replace them. Use receivers with helical coils in the front end
to improve selectivity if needed. Use PL tones if required. After
all...money does not seem to be an object especially if one group is
willing to fund all the fixes to the other groups equipment which may
not be at fault.
2) If one organization is lacking the technical folks to fix their
problems maybe they would be willing to PAY the group with the 'know
how" to help fix it. I know this sounds easy to do but can be very
hard to do if personalities come into play. Some people may have to
swallow their pride for the betterment of the groups and OUR hobby.
3) The whole RF spectrum would be better off if both groups addressed
the problems with their own systems. The first complaints from
commercial or government users to the FCC could very well result in
detailed investigation that probably no one up there wants or needs.
I'm sure if good design and engineering is used the intermod problems
will go away by themselves.
Not sure if this really helps or not. If it was my system that was
lacking in technical design or equipment problems...I would want to fix
it myself and take pride in a well engineered repeater operation.
Defending a well designed system is a lot easier than trying to defend a
linear transponder.
Jerry
KL7EDK
Northern and Interior Alaska Frequency Coordinator
RAM Conclusion, Position & Recomendation
We view Nate's proposal as sincere, but it lacks technical merit and is in the long run contrary to SPARC's best interests.
Instead, Jerry's response is to the point. However, it is based only on information that RAM supplied, and we invite SPARC to contact him if they have anything contrary to offer.
RAM believes that subject to any subsequent testing, that the matter is laid to rest. SPARC is jamming themselves. Their Nome system lacks the sophistication to enable it to operate in a typical Amateur Radio environment. SPARC Needs To Fix Its System.
Essentially, RAM feels, and has Resolved, that RAM's communications and its members are of no lesser importance or precedence and that only a technical solution is acceptable.
In particular, the SPARC system would prevent any present or future repeater to operate on the U.S. Standard 0.6 mHz split without wiping themselves out.
A technical solution along the lines suggested by Jerry is optimal, and technically correct. We urge SPARC to implement those steps. Doing so would mean they can continue to use their existing 146.94/.34 frequency pair "to which they have become accustomed to."
RAM will extend all possible assistance with test transmissions, roaming mobiles, planning, thinking and coordinating, as needed, but short of becoming a contractor to fix their hardware. There are commercial contractors, such as the one that did the Police Radios here in Nome, that have the expertise, equipment and wherewithal to do so should SPARC be lacking in that ability.
If SPARC feels that the outlined course of action is improper, and that they have a vested right in their present operation, and that RAM should change their parameters to suit them, we urge them to contact the Alaska Frequency Coordinator or escalate to the F.C.C.
The RAM Board of Directors.
Copyright © 2007, RAM, Inc.
All rights reserved.